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Little Albert Experiment (Watson & Rayner)

Saul Mcleod, PhD

Editor-in-Chief for Simply Psychology

BSc (Hons) Psychology, MRes, PhD, University of Manchester

Saul Mcleod, PhD., is a qualified psychology teacher with over 18 years of experience in further and higher education. He has been published in peer-reviewed journals, including the Journal of Clinical Psychology.

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Olivia Guy-Evans, MSc

Associate Editor for Simply Psychology

BSc (Hons) Psychology, MSc Psychology of Education

Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

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Watson and Rayner (1920) conducted the Little Albert Experiment to answer 3 questions:

Can an infant be conditioned to fear an animal that appears simultaneously with a loud, fear-arousing sound?

Would such fear transfer to other animals or inanimate objects?

How long would such fears persist?

Little Albert Experiment

Ivan Pavlov showed that classical conditioning applied to animals. Did it also apply to humans? In a famous (though ethically dubious) experiment, John Watson and Rosalie Rayner showed it did.

Conducted at Johns Hopkins University between 1919 and 1920, the Little Albert experiment aimed to provide experimental evidence for classical conditioning of emotional responses in infants

At the study’s outset, Watson and Rayner encountered a nine-month-old boy named “Little Albert” (his real name was Albert Barger) – a remarkably fearless child, scared only by loud noises.

After gaining permission from Albert’s mother, the researchers decided to test the process of classical conditioning on a human subject – by inducing a further phobia in the child.

The baseline session occurred when Albert was approximately nine months old to test his reactions to neutral stimuli.

Albert was reportedly unafraid of any of the stimuli he was shown, which consisted of “a white rat, a rabbit, a dog, a monkey, with [sic] masks with and without hair, cotton wool, burning newspapers, etc.” (Watson & Rayner, 1920, p. 2).

Approximately two months after the baseline session, Albert was subjected during two conditioning sessions spaced one week apart to a total of seven pairings of a white rat followed by the startling sound of a steel bar being struck with a hammer.

When Little Albert was just over 11 months old, the white rat was presented, and seconds later, the hammer was struck against the steel bar.

After seven pairings of the rat and noise (in two sessions, one week apart), Albert reacted with crying and avoidance when the rat was presented without the loud noise.

By the end of the second conditioning session, when Albert was shown the rat, he reportedly cried and “began to crawl away so rapidly that he was caught with difficulty before reaching the edge of the table” (p. 5). Watson and Rayner interpreted these reactions as evidence of fear conditioning.

By now, little Albert only had to see the rat and immediately showed every sign of fear. He would cry (whether or not the hammer was hit against the steel bar), and he would attempt to crawl away.

The two conditioning sessions were followed by three transfer sessions. During the first transfer session, Albert was shown the rat to assess maintained fear, as well as other furry objects to test generalization.

Complicating the experiment, however, the second transfer session also included two additional conditioning trials with the rat to “freshen up the reaction” (Watson & Rayner, 1920, p. 9), as well as conditioning trials in which a dog and a rabbit were, for the first time, also paired with the loud noise.

This fear began to fade as time went on, however, the association could be renewed by repeating the original procedure a few times.

Unlike prior weekly sessions, the final transfer session occurred after a month to test maintained fear. Immediately following the session, Albert and his mother left the hospital, preventing Watson and Rayner from carrying out their original intention of deconditioning the fear they have classically conditioned.

Experimental Procedure

Session	Age	Stimuli Shown
	8 months & 26 days	Included tests with rat, rabbit, dog, monkey, masks with and without hair, cotton wool, and burning newspapers (no fear).
	11 months & 3 days	Rat paired with loud noise (two pairings).
	11 months & 10 days	Test with rat alone (elicited mild fear). Rat paired with loud noise (5 pairings). Test with rat alone (elicited strong fear).
	11 months & 15 days	Tests with rat, rabbit, dog, fur coat, cotton wool, Watson’s hair, 2 observers’ hair, and Santa Claus mask.
	11 months & 20 days	In original testing room: tests with rat, rabbit, and dog; an extra conditioning trial with rat; and conditioning trials with rabbit and dog (1 pairing each). In a new room: tests with rat, rabbit, and dog; extra conditioning trial with rat; plus barking incident with dog. Included comment that all previous tests had been conducted on a table.
	12 months, 21 days	Tests with Santa Claus mask, fur coat, rat, rabbit, and dog. Albert was also discharged from the hospital on this day.

Classical Conditioning

Neutral Stimulus (NS): This is a stimulus that, before conditioning, does not naturally bring about the response of interest. In this case, the Neutral Stimulus was the white laboratory rat. Initially, Little Albert had no fear of the rat, he was interested in the rat and wanted to play with it.
Unconditioned Stimulus (US): This is a stimulus that naturally and automatically triggers a response without any learning. In the experiment, the unconditioned stimulus was the loud, frightening noise. This noise was produced by Watson and Rayner striking a steel bar with a hammer behind Albert’s back.
Unconditioned Response (UR): This is the natural response that occurs when the Unconditioned Stimulus is presented. It is unlearned and occurs without previous conditioning. In this case, the Unconditioned Response was Albert’s fear response to the loud noise – crying and showing distress.
Conditioning Process: Watson and Rayner then began the conditioning process. They presented the rat (NS) to Albert, and then, while he was interacting with the rat, they made a loud noise (US). This was done repeatedly, pairing the sight of the rat with the frightening noise. As a result, Albert started associating the rat with the fear he experienced due to the loud noise.
Conditioned Stimulus (CS): After several pairings, the previously Neutral Stimulus (the rat) becomes the conditioned stimulus , as it now elicits the fear response even without the presence of the loud noise.
Conditioned Response (CR): This is the learned response to the previously neutral stimulus, which is now the Conditioned Stimulus. In this case, the Conditioned Response was Albert’s fear of the rat. Even without the loud noise, he became upset and showed signs of fear whenever he saw the rat.

In this experiment, a previously unafraid baby was conditioned to become afraid of a rat. It also demonstrates two additional concepts, originally outlined by Pavlov .

Extinction : Although a conditioned association can be incredibly strong initially, it begins to fade if not reinforced – until is disappears completely.
Generalization : Conditioned associations can often widen beyond the specific stimuli presented. For instance, if a child develops a negative association with one teacher, this association might also be made with others.

Over the next few weeks and months, Little Albert was observed and ten days after conditioning his fear of the rat was much less marked. This dying out of a learned response is called extinction.

However, even after a full month, it was still evident, and the association could be renewed by repeating the original procedure a few times.

Unfortunately, Albert’s mother withdrew him from the experiment the day the last tests were made, and Watson and Rayner were unable to conduct further experiments to reverse the condition response.

The Little Albert experiment was a controversial psychology experiment by John B. Watson and his graduate student, Rosalie Rayner, at Johns Hopkins University.
The experiment was performed in 1920 and was a case study aimed at testing the principles of classical conditioning.
Watson and Raynor presented Little Albert (a nine-month-old boy) with a white rat, and he showed no fear. Watson then presented the rat with a loud bang that startled Little Albert and made him cry.
After the continuous association of the white rat and loud noise, Little Albert was classically conditioned to experience fear at the sight of the rat.
Albert’s fear generalized to other stimuli that were similar to the rat, including a fur coat, some cotton wool, and a Santa mask.

Critical Evaluation

Methodological limitations.

The study is often cited as evidence that phobias can develop through classical conditioning. However, critics have questioned whether conditioning actually occurred due to methodological flaws (Powell & Schmaltz, 2022).

The study didn’t control for pseudoconditioning – the loud noise may have simply sensitized Albert to be fearful of any novel stimulus.
It didn’t control for maturation – Albert was 11 months old initially, but the final test was at 12 months. Fears emerge naturally over time in infants, so maturation could account for Albert’s reactions.
Albert’s reactions were inconsistent and the conditioned fear weak – he showed little distress to the rat in later tests, suggesting the conditioning was not very effective or durable.

Other methodological criticisms include:

The researchers confounded their own experiment by conditioning Little Albert using the same neutral stimuli as the generalized stimuli (rabbit and dog).
Some doubts exist as to whether or not this fear response was actually a phobia. When Albert was allowed to suck his thumb he showed no response whatsoever. This stimulus made him forget about the loud sound. It took more than 30 times for Watson to finally take Albert’s thumb out to observe a fear response.
Other limitations included no control subject and no objective measurement of the fear response in Little Albert (e.g., the dependent variable was not operationalized).
As this was an experiment of one individual, the findings cannot be generalized to others (e.g., low external validity). Albert had been reared in a hospital environment from birth and he was unusual as he had never been seen to show fear or rage by staff. Therefore, Little Albert may have responded differently in this experiment to how other young children may have, these findings will therefore be unique to him.

Theoretical Limitations

The cognitive approach criticizes the behavioral model as it does not take mental processes into account. They argue that the thinking processes that occur between a stimulus and a response are responsible for the feeling component of the response.

Ignoring the role of cognition is problematic, as irrational thinking appears to be a key feature of phobias.

Tomarken et al. (1989) presented a series of slides of snakes and neutral images (e.g., trees) to phobic and non-phobic participants. The phobics tended to overestimate the number of snake images presented.

The Little Albert Film

Powell and Schmaltz (2022) examined film footage of the study for evidence of conditioning. Clips showed Albert’s reactions during baseline and final transfer tests but not the conditioning trials. Analysis of his reactions did not provide strong evidence of conditioning:

With the rat, Albert was initially indifferent and tried to crawl over it. He only cried when the rat was placed on his hand, likely just startled.
With the rabbit, dog, fur coat, and mask, his reactions could be explained by being startled, innate wariness of looming objects, and other factors. Reactions were inconsistent and mild.

Overall, Albert’s reactions seem well within the normal range for an infant and can be readily explained without conditioning. The footage provides little evidence he acquired conditioned fear.

The belief the film shows conditioning may stem from:

Viewer expectation – titles state conditioning occurred and viewers expect to see it.
A tendency to perceive stronger evidence of conditioning than actually exists.
An ongoing perception of behaviorism as manipulative, making Watson’s conditioning of a “helpless” infant seem plausible.

Rather than an accurate depiction, the film may have been a promotional device for Watson’s research. He hoped to use it to attract funding for a facility to closely study child development.

This could explain anomalies like the lack of conditioning trials and rearrangement of test clips.

Ethical Issues

The Little Albert Experiment was conducted in 1920 before ethical guidelines were established for human experiments in psychology. When judged by today’s standards, the study has several concerning ethical issues:

There was no informed consent obtained from Albert’s parents. They were misled about the true aims of the research and did not know their child would be intentionally frightened. This represents a lack of transparency and a violation of personal autonomy.
Intentionally inducing a fear response in an infant is concerning from a nonmaleficence perspective, as it involved deliberate psychological harm. The distress exhibited by Albert suggests the conditioning procedure was unethical by today’s standards.
Watson and Rayner did not attempt to decondition or desensitize Albert to the fear response before the study ended abruptly. This meant they did not remove the psychological trauma they had induced, violating the principle of beneficence. Albert was left in a state of fear, which could have long-lasting developmental effects. Watson also published no follow-up data on Albert’s later emotional development.

Learning Check

Summarise the process of classical conditioning in Watson and Raynor’s study.
Explain how Watson and Raynor’s methodology is an improvement on Pavlov’s.
What happened during the transfer sessions? What did this demonstrate?
Why is Albert’s reaction to similar furry objects important for the interpretation of the study?
Comment on the ethics of Watson and Raynor’s study.
Support the claim that in ignoring the internal processes of the human mind, behaviorism reduces people to mindless automata (robots).

Beck, H. P., Levinson, S., & Irons, G. (2009). Finding Little Albert: A journey to John B. Watson’s infant laboratory. American Psychologist, 64 , 605–614.

Digdon, N., Powell, R. A., & Harris, B. (2014). Little Albert’s alleged neurological persist impairment: Watson, Rayner, and historical revision. History of Psychology , 17 , 312–324.

Fridlund, A. J., Beck, H. P., Goldie, W. D., & Irons, G. (2012). Little Albert: A neurologically impaired child. History of Psychology , 15, 1–34.

Griggs, R. A. (2015). Psychology’s lost boy: Will the real Little Albert please stand up? Teaching of Psychology, 4 2, 14–18.

Harris, B. (1979). Whatever happened to little Alb ert? . American Psychologist, 34 (2), 151.

Harris, B. (2011). Letting go of Little Albert: Disciplinary memory, history, and the uses of myth. Journal of the History of the Behavioral Sciences, 47 , 1–17.

Harris, B. (2020). Journals, referees and gatekeepers in the dispute over Little Albert, 2009–2014. History of Psychology, 23 , 103–121.

Powell, R. A., Digdon, N., Harris, B., & Smithson, C. (2014). Correcting the record on Watson, Rayner, and Little Albert: Albert Barger as “psychology’s lost boy.” American Psychologist, 69 , 600–611.

Powell, R. A., & Schmaltz, R. M. (2021). Did Little Albert actually acquire a conditioned fear of furry animals? What the film evidence tells us. History of Psychology , 24 (2), 164.

Todd, J. T. (1994). What psychology has to say about John B. Watson: Classical behaviorism in psychology textbooks. In J. T. Todd & E. K. Morris (Eds.), Modern perspectives on John B. Watson and classical behaviorism (pp. 74–107). Westport, CT: Greenwood Press.

Tomarken, A. J., Mineka, S., & Cook, M. (1989). Fear-relevant selective associations and covariation bias. Journal of Abnormal Psychology, 98 (4), 381.

Watson, J.B. (1913). Psychology as the behaviorist Views It. Psychological Review, 20 , 158-177.

Watson, J. B., & Rayner, R. (1920). Conditioned emotional reactions . Journal of Experimental Psychology, 3 (1), 1.

Watson, J. B., & Watson, R. R. (1928). Psychological care of infant and child . New York, NY: Norton.

Further Information

Finding Little Albert
Mystery solved: We now know what happened to Little Albert
Psychology’s lost boy: Will the real Little Albert please stand up?
Journals, referees, and gatekeepers in the dispute over Little Albert, 2009-2014
Griggs, R. A. (2014). The continuing saga of Little Albert in introductory psychology textbooks. Teaching of Psychology, 41(4), 309-317.

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The Little Albert Experiment

The Little Albert Experiment is a world-famous study in the worlds of both behaviorism and general psychology. Its fame doesn’t just come from astounding findings. The story of the Little Albert experiment is mysterious, dramatic, dark, and controversial.

The Little Albert Experiment was a study conducted by John B. Watson and Rosalie Rayner in 1920, where they conditioned a 9-month-old infant named "Albert" to fear a white rat by pairing it with a loud noise. Albert later showed fear responses to the rat and other similar stimuli.

The Little Albert Experiment is one of the most well-known and controversial psychological experiments of the 20th century. In 1920, American psychologist John B. Watson and his graduate student, Rosalie Rayner, carried out a study. Their goal was to explore the concept of classical conditioning. This theory proposes that individuals can learn to link an emotionless stimulus with an emotional reaction through repeated pairings.

For their experiment, Watson and Rayner selected a 9-month-old infant named "Albert" and exposed him to a series of stimuli, including a white rat, a rabbit, a dog, and various masks. Initially, Albert showed no fear of any of these objects. However, when the researchers presented the rat to him and simultaneously struck a steel bar with a hammer behind his head, Albert began to cry and show signs of fear. After several repetitions of this procedure, Albert began to show a fear response to the rat alone, even when the loud noise was not present.

The experiment was controversial because of its unethical nature. Albert could not provide informed consent, and his fear response was deliberately induced and not treated. Additionally, the experiment lacked scientific rigor regarding experimental design, sample size, and ethical considerations. Despite these criticisms, the Little Albert Experiment has had a significant impact on the field of psychology, particularly in the areas of behaviorism and classical conditioning. It has also raised important questions about the ethics of research involving human subjects and the need for informed consent and ethical guidelines in scientific studies.

Let's learn who was behind this experiment...

Who Was John B. Watson?

John B. Watson is pivotal in psychology's annals, marked by acclaim and controversy. Often hailed as the "Father of Behaviorism," his contributions extend beyond the well-known Little Albert study. At Johns Hopkins University, where much of his groundbreaking work was conducted, he delivered the seminal lecture "Psychology as the Behaviorist Views It."

This speech laid the foundation for behaviorism, emphasizing observable and measurable behavior over introspective methods, a paradigm shift in how psychological studies were approached. Watson's insistence on studying only observable behaviors positioned psychology more closely with the natural sciences, reshaping the discipline. Although he achieved significant milestones at Johns Hopkins, Watson's tenure there ended in 1920 under controversial circumstances, a story we'll delve into shortly.

Classical Conditioning

John B. Watson was certainly influential in classical conditioning, but many credit the genesis of this field to another notable psychologist: Ivan Pavlov. Pavlov's groundbreaking work with dogs laid the foundation for understanding classical conditioning, cementing his reputation in the annals of psychological research.

Classical conditioning is the process wherein an organism learns to associate one stimulus with another, leading to a specific response. Pavlov's experiment is a quintessential example of this. Initially, Pavlov observed that dogs would naturally salivate in response to food. During his experiment, he introduced a neutral stimulus, a bell, which did not produce any specific response from the dogs.

However, Pavlov began to ring the bell just before presenting the dogs with food. After several repetitions, the dogs began to associate the sound of the bell with the forthcoming food. Remarkably, even without food, ringing the bell alone led the dogs to salivate in anticipation. This involuntary response was not a behavior the dogs were intentionally trained to perform; instead, it was a reflexive reaction resulting from the association they had formed between the bell and the food.

Pavlov's research was not just about dogs and bells; its significance lies in the broader implications for understanding how associative learning works, influencing various fields from psychology to education and even marketing.

Who Was Little Albert?

John B. Watson took an idea from this theory. What if...

...all of our behaviors were the result of classical conditioning?
...we salivated only after connecting certain events with getting food?
...we only became afraid of touching a stove after we first put our hand on a hot stove and felt pain?
...fear was something we learned?

These are the questions that Watson attempted to answer with Little Albert.

Little Albert was a nine-month-old baby. His mother was a nurse at Johns Hopkins University, where the experiment was conducted. The baby’s name wasn’t really Albert - it was just a pseudonym that Watson used for the study. Due to the baby’s young age, Watson thought it would be a good idea to use him to test his hypothesis about developing fear.

Here’s how he conducted his experiment, now known as the “Little Albert Experiment.”

Watson exposed Little Albert to a handful of different stimuli. The stimuli included a white rat, a monkey, a hairy mask, a dog, and a seal-skin coat. When Watson first observed Little Albert, he did not fear any stimuli, including the white rat.

Then, Watson began the conditioning.

He would introduce the white rat back to Albert. Whenever Little Albert touched the rat, Watson would smash a hammer against a steel bar behind Albert’s head. Naturally, this stimulus scared Albert, and he would begin to cry. This was the “bell” of Pavlov’s experiment, but you can already see that this experiment is far more cruel.

Like Pavlov’s dogs, Little Albert became conditioned. Whenever he saw the rat, he would cry and try to move away from the rat. Throughout the study, he exhibited the same behaviors when exposed to “hairy” stimuli. This process is called stimulus generalization.

What Happened to Little Albert?

The Little Albert study was conducted in 1920. Shortly after the findings were published in the Journal of Experimental Psychology, Johns Hopkins gave Watson a 50% raise . However, the rise (and Watson’s position at the University) did not last long. At the end of 1920, Watson was fired.

Why? At first, the University claimed it was due to an affair. Watson conducted the Little Albert experiment with his graduate student, Rosalie Rayner. They fell in love, despite Watson’s marriage to Mary Ickes. Ickes was a member of a prominent family in the area, upon the discovery of the affair, Watson and Rayner’s love letters were published in a newspaper. John Hopkins claimed to fire Watson for “indecency.”

Years later, rumors emerged that Watson wasn’t fired simply for his divorce. Watson and Rayner were allegedly conducting behaviorist experiments concerning sex. Those rumors included claims that Watson, a movie star handsome then, had even hooked devices up to him and Rayner while they engaged in intercourse. These claims seem false, but they appeared in psychology textbooks for years.

There is so much to this story that is wild and unusual! Upon hearing this story, one of the biggest questions people ask is, “What happened to Little Albert?”

The True Story of the Little Albert Experiment

Well, this element of the story isn’t without uncertainty and rumor. In 2012, researchers claimed to uncover the true story of Little Albert. The boy’s real name was apparently Douglas Merritte, who died at the age of seven. Merritt had a serious condition of built-up fluid in the brain. This story element was significant - Watson claimed Little Albert was a healthy and normal child. If Merritte were Little Albert, then Watson’s lies about the child’s health would ruin his legacy.

And it did until questions about Merritte began to arise. Further research puts another candidate into the ring: William Albert Barger. Barger was born on the same day in the same hospital as Merritte. His mother was a wet nurse in the same hospital where Watson worked. Barger’s story is much more hopeful than Merritte’s - he died at 87. Researchers met with his niece, who claimed that her uncle was particularly loving toward dogs but showed no evidence of fear that would have been developed through the famous study.

The mystery lives on.

Criticisms of the Little Albert Experiment

This story is fascinating, but psychologists note it is not the most ethical study.

The claims about Douglas Merritte are just one example of how the study could (and definitely did) cross the lines of ethics. If Little Albert was not the healthy boy that Watson claimed - well, there’s not much to say about the findings. Plus, the experiment was only conducted on one child. Follow-up research about the child and his conditioning never occurred (but this is partially due to the scandalous life of Watson and Rayner.)

Behaviorism, the school of psychology founded partly by this study, is not as “hot” as it was in the 1920s. But no one can deny the power and legacy of the Little Albert study. It is certainly one of the more important studies to know in psychology, both for its scandal and its place in studying learned behaviors.

Other Controversial Studies in Psychology

The Little Albert Experiment is one of the most notorious experiments in the history of psychology, but it's not the only one. Psychologists throughout the past few decades have used many unethical or questionable means to test out (or prove) their hypotheses. If you haven't heard about the following experiments, you can read about them on my page!

The Robbers Cave Experiment

Have you ever read Lord of the Flies? The book details the shocking and deadly story of boys stranded on a desert island. When the boys try to govern themselves, lines are drawn in the sand, and chaos ensues. Would that actually happen in real life?

Muzafer Sherif wanted to find out the answer. He put together the Robbers Cave Experiment, which is now one of the most controversial experiments in psychology history. The experiment involved putting together two teams of young men at a summer camp. Teams were put through trials to see how they would handle conflict within their groups and with "opposing" groups. The experiment's results led to the creation of the Realistic Conflict Theory.

The experiment did not turn out like Lord of the Flies, but the results are no longer valid. Why? Sherif highly manipulated the experiment. Gina Perry's The Lost Boys: Inside Muzafer Sherif's Robbers Cave Experiment details where Sherif went wrong and how the legacy of this experiment doesn't reflect what actually happened.

Read more about the Robber's Cave Experiment .

The Stanford Prison Experiment

The Stanford Prison Experiment looked similar to the Robbers Cave Experiment. Psychologist Phillip Zimbardo brought together groups of young men to see how they would interact with each other. These participants, however, weren't at summer camp. Zimbardo asked his participants to either be a "prison guard" or "prisoner." He intended to observe the groups for seven days, but the experiment was cut short.

Why? Violence ensued. The experiment got so out of hand that Zimbardo ended it early for the safety of the participants. Years later, sources question whether his involvement in the experiment encouraged some violence between prison guards and prisoners. You can learn more about the Stanford Prison Experiment on Netflix or by reading our article.

The Milgram Experiment

Why do people do terrible things? Are they evil people, or do they just do as they are told? Stanley Milgram wanted to answer these questions and created the Milgram experiment . In this experiment, he asked participants to "shock" another participant (who was really just an actor receiving no shocks at all.) The shocks ranged in intensity, with some said to be hurtful or even fatal to the actor.

The results were shocking - no pun intended! However, the experiment remains controversial due to the lasting impacts it could have had on the participants. Gina Perry also wrote a book about this experiment - Behind the Shock Machine: The Untold Story of the Notorious Milgram Psychology Experiments.

The Monster Study

In the 1930s, Dr. Wendell Johnson was keen on exploring the origins and potential treatments for stuttering in children. To this end, he turned to orphans in Iowa, unknowingly involving them in his experiment. Not all the participating children had a stutter. Those without speech impediments were treated and criticized as if they did have one, while some with actual stuttering were either praised or criticized. Johnson's aim was to observe if these varied treatments would either alleviate or induce stuttering based on the feedback given.

Unfortunately, the experiment's outcomes painted a bleak picture. Not only did the genuine stutterers fail to overcome their speech issues, but some of the previously fluent-speaking orphans began to stutter after experiencing the negative treatment. Even by the standards of the 1930s, before the world was fully aware of the inhumane experiments conducted by groups like the Nazis, Johnson's methods were deemed excessively harsh and unethical.

Read more about the Monster Study here .

How Do Psychologists Conduct Ethical Experiments?

To ensure participants' well-being and prevent causing trauma, the field of psychology has undergone a significant evolution in its approach to research ethics. Historically, some early psychological experiments lacked adequate consideration for participants' rights or well-being, leading to trauma and ethical dilemmas. Notable events, such as the revelations of the Milgram obedience experiments and the Stanford prison experiment, brought to light the pressing need for ethical guidelines in research.

As a result, strict rules and guidelines for ethical experimentation were established. One fundamental principle is informed consent: participants must know that they are part of an experiment and should understand its nature. This means they must be informed about the procedures, potential risks, and their rights to withdraw without penalty. Participants consent to participate only after this detailed disclosure, which must be documented.

Moreover, creating ethics review boards became commonplace in research institutions, ensuring research proposals uphold ethical standards and protect participants' rights. If you are ever invited to participate in a research study, it's crucial to thoroughly understand its scope, ask questions, and ensure your rights are protected before giving consent. The journey to establish these ethical norms reflects the discipline's commitment to balancing scientific advancement with the dignity and well-being of its study subjects.

John B. Watson (Psychologist Biography)
The Psychology of Long Distance Relationships
Behavioral Psychology
Beck’s Depression Inventory (BDI Test)
Operant Conditioning (Examples + Research)

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Operant Conditioning

Observational Learning

Latent Learning

Experiential Learning

The Little Albert Study

Bobo Doll Experiment

Spacing Effect

Von Restorff Effect

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The Little Albert Experiment

A Closer Look at the Famous Case of Little Albert

Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

Amy Morin, LCSW, is a psychotherapist and international bestselling author. Her books, including "13 Things Mentally Strong People Don't Do," have been translated into more than 40 languages. Her TEDx talk, "The Secret of Becoming Mentally Strong," is one of the most viewed talks of all time.

A Closer Look

Classical conditioning, stimulus generalization, criticism and ethical issues, what happened to little albert.

The Little Albert experiment was a famous psychology experiment conducted by behaviorist John B. Watson and graduate student Rosalie Rayner. Previously, Russian physiologist Ivan Pavlov had conducted experiments demonstrating the conditioning process in dogs . Watson took Pavlov's research a step further by showing that emotional reactions could be classically conditioned in people.

Verywell / Jessica Olah

The participant in the experiment was a child that Watson and Rayner called "Albert B." but is known popularly today as Little Albert. When Little Albert was 9 months old, Watson and Rayner exposed him to a series of stimuli including a white rat, a rabbit, a monkey, masks, and burning newspapers and observed the boy's reactions.

The boy initially showed no fear of any of the objects he was shown.

The next time Albert was exposed to the rat, Watson made a loud noise by hitting a metal pipe with a hammer. Naturally, the child began to cry after hearing the loud noise. After repeatedly pairing the white rat with the loud noise, Albert began to expect a frightening noise whenever he saw the white rate. Soon, Albert began to cry simply after seeing the rat.

Watson and Rayner wrote: "The instant the rat was shown, the baby began to cry. Almost instantly he turned sharply to the left, fell over on [his] left side, raised himself on all fours and began to crawl away so rapidly that he was caught with difficulty before reaching the edge of the table."

The Little Albert experiment presents an example of how classical conditioning can be used to condition an emotional response.

Neutral Stimulus : A stimulus that does not initially elicit a response (the white rat).
Unconditioned Stimulus : A stimulus that elicits a reflexive response (the loud noise).
Unconditioned Response : A natural reaction to a given stimulus (fear).
Conditioned Stimulus : A stimulus that elicits a response after repeatedly being paired with an unconditioned stimulus (the white rat).
Conditioned Response : The response caused by the conditioned stimulus (fear).

In addition to demonstrating that emotional responses could be conditioned in humans, Watson and Rayner also observed that stimulus generalization had occurred. After conditioning, Albert feared not just the white rat, but a wide variety of similar white objects as well. His fear included other furry objects including Raynor's fur coat and Watson wearing a Santa Claus beard.

While the experiment is one of psychology's most famous and is included in nearly every introductory psychology course , it is widely criticized for several reasons. First, the experimental design and process were not carefully constructed. Watson and Rayner did not develop an objective means to evaluate Albert's reactions, instead of relying on their own subjective interpretations.

The experiment also raises many ethical concerns. Little Albert was harmed during this experiment—he left the experiment with a previously nonexistent fear. By today's standards, the Little Albert experiment would not be allowed.

The question of what happened to Little Albert has long been one of psychology's mysteries. Before Watson and Rayner could attempt to "cure" Little Albert, he and his mother moved away. Some envisioned the boy growing into a man with a strange phobia of white, furry objects.

Recently, the true identity and fate of the boy known as Little Albert was discovered. As reported in American Psychologist , a seven-year search led by psychologist Hall P. Beck led to the discovery. After tracking down and locating the original experiments and the real identity of the boy's mother, it was suggested that Little Albert was actually a boy named Douglas Merritte.

The story does not have a happy ending, however. Douglas died at the age of six on May 10, 1925, of hydrocephalus (a build-up of fluid in his brain), which he had suffered from since birth. "Our search of seven years was longer than the little boy’s life," Beck wrote of the discovery.

In 2012, Beck and Alan J. Fridlund reported that Douglas was not the healthy, normal child Watson described in his 1920 experiment. They presented convincing evidence that Watson knew about and deliberately concealed the boy's neurological condition. These findings not only cast a shadow over Watson's legacy, but they also deepened the ethical and moral issues of this well-known experiment.

In 2014, doubt was cast over Beck and Fridlund's findings when researchers presented evidence that a boy by the name of William Barger was the real Little Albert. Barger was born on the same day as Merritte to a wet-nurse who worked at the same hospital as Merritte's mother. While his first name was William, he was known his entire life by his middle name, Albert.

While experts continue to debate the true identity of the boy at the center of Watson's experiment, there is little doubt that Little Albert left a lasting impression on the field of psychology.

Beck HP, Levinson S, Irons G. Finding Little Albert: a journey to John B. Watson's infant laboratory . Am Psychol. 2009;64(7):605-14. doi:10.1037/a0017234

Van Meurs B. Maladaptive Behavioral Consequences of Conditioned Fear-Generalization: A Pronounced, Yet Sparsely Studied, Feature of Anxiety Pathology . Behav Res Ther. 2014;57:29–37.

Fridlund AJ, Beck HP, Goldie WD, Irons G. Little Albert: A neurologically impaired child . Hist Psychol. 2012;15(4):302-27. doi:10.1037/a0026720

Powell RA. Correcting the record on Watson, Rayner, and Little Albert: Albert Barger as "psychology's lost boy" . Am Psychol. 2014;69(6):600-11.

Beck, H. P., Levinson, S., & Irons, G. (2009). Finding little Albert: A journey to John B. Watson’s infant laboratory. American Psychologist, 2009;64(7): 605-614.
Fridlund, A. J., Beck, H. P., Goldie, W. D., & Irons, G. Little Albert: A neurologically impaired child. History of Psychology. doi: 10.1037/a0026720; 2012.
Watson, John B. & Rayner, Rosalie. (1920). Conditioned emotional reactions. Journal of Experimental Psychology, 3 , 1-14.

By Kendra Cherry, MSEd Kendra Cherry, MS, is a psychosocial rehabilitation specialist, psychology educator, and author of the "Everything Psychology Book."

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Little Albert Experiment

Classical conditioning plays a central role in the development of fears and associations. Some phobias may be due at least in part to classical conditioning. For example, a person who associates leaving the home with being abused by their parents might develop agoraphobia .

Who Conducted the Little Albert Experiment?

Psychologist John Watson conducted the Little Albert experiment. Watson is known for his seminal research on behaviorism, or the idea that behavior occurs primarily in the context of conditioning. He was a professor of psychology at Johns Hopkins University, and much of his research revolved around animal behavior. Some sources report that Watson implicated his children in some of his studies, creating tension in his family. After a scandal that resulted in his resignation from John Hopkins, Watson worked in advertising until his retirement.

How Did the Experiment Work?

Albert was a 9-month-old baby who had not previously demonstrated any fear of rats. In the beginning of the experiment, when Albert was 11 months old, John Watson placed a rat (in addition to some other animals and objects with fur) on the table in front of Albert, who reacted with curiosity and no sign of fear.

He then began making a loud noise behind the baby by pounding on a steel bar with a hammer on several separate occasions while showing Albert the rat. Albert cried in reaction to the noise and, after a period of conditioning, cried in response to the rat even without the loud noise. When presented with the other animals, he also responded with varying degrees of fear despite not ever hearing the loud noise when presented with those animals.

This experiment is prototypical example of classical conditioning. One conclusion Watson drew from the experiment was that fear may have a critical impact on personality development.

The Little Albert Experiment: Ethical Issues and Criticism

Watson had originally planned to decondition Albert to the stimulus, demonstrating that conditioned fears could be eliminated. However, Albert was removed from the experiment before this could happen, and thus Watson created a child with a previously nonexistent fear. This research practice would be widely considered unethical today; standards outlined by the American Psychological Association and the British Psychological Society would also deem the study unethical.

Watson rationalized his treatment of Little Albert by stating that even if they did not conduct the experiment on the child, he would experience similar conditioning as he grew older. “At first there was considerable hesitation upon our part in making the attempt to set up fear reactions experimentally,” Watson wrote. “We decided finally to make the attempt, comforting ourselves … that such attachments would arise anyway as soon as the child left the sheltered environment of the nursery for the rough and tumble of the home.”

Although the experiment is remembered as a case for classical conditioning, some critics point out that the study was done without any type of control. However, adding a control element to psychological research was not common at this time.

What Happened to Little Albert?

“Little Albert” was the son of a wet nurse by the name Arvilla Merritte who worked at the Harriet Lane Home for Invalid Children. Because of this, much of Albert’s infancy was spent in Johns Hopkins Hospital with his mother. Arvilla received $1 for her son’s part in the experiment, which would be equivalent to around $13 today.

Most sources agree that Albert’s real name was Douglas Merritte. Nobody knows whether his fear of rats persisted into adulthood, as he died at six years of age from hydrocephalus.

Classical Conditioning in Popular Culture

Several pieces of literature have addressed classical conditioning in children, including Thomas Pynchon’s Gravity’s Rainbow and Aldous Huxley’s Brave New World . In Brave New World , poor children were conditioned to dislike or fear books. Thus their lower status was maintained as they avoided learning from books. This page contains at least one affiliate link for the Amazon Services LLC Associates Program, which means GoodTherapy.org receives financial compensation if you make a purchase using an Amazon link.

References:

American Psychological Association. APA concise dictionary of psychology . Washington, DC: American Psychological Association, 2009. Print.
Augustyn, A. (n.d.). John B. Watson. Encyclopedia Britannica . Retrieved from https://www.britannica.com/biography/John-B-Watson
Burgemeester, A. (n.d.). The Little Albert experiment. Retrieved from https://www.psychologized.org/the-little-albert-experiment
Cherry, K. (2019, July 3). The Little Albert experiment: A closer look at the famous case of Little Albert. Retrieved from https://www.verywellmind.com/the-little-albert-experiment-2794994
DeAngelis, T. (2010). ‘Little Albert’ regains his identity. Monitor on Psychology, 41 (1), 10. Retrieved from https://www.apa.org/monitor/2010/01/little-albert
Inflation calculator. (n.d.). Retrieved from http://www.in2013dollars.com/us/inflation/1920?amount=1
Watson, J. B., & Rayner, R. (1920). Conditioned emotional reactions. Journal of Experimental Psychology, 3 (1), 1-14. Retrieved from https://psychclassics.yorku.ca/Watson/emotion.htm

Last Updated: 07-30-2019

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18 comments

wow little albert had a hard life

He did. Unfortunately he died at the age of 6 after contracting hydrocephalus.

The only problem I have with this is that it says about if they had permission from Little Albert’s mother for the experiment, Yet to my knowledge Little Albert was an orphan

therefore how do we know she wouldnt have given permission?

Little Albert was in a special needs hospital for the first year of his life. His mother was a nurse there. The experiments were done without her presence. There were not any research regulations at the time saying that the parent or participant needed to be fully informed of the experiment.

His mother was actually present everyday for the experiments. She gave permission to Watson to do these experiments because Watson was giving her 1 dollar (which was a lot back then) after each of the experiments, and she needed that money to survive and help feedL’little Albert’

Which behaviourist theory is being discussed in the little albert story

I think we need more of this kind of experimentation, too bad he died before he was permanently scared. Woulda been cool to see his life deteriorate naturally instead of some freak accident medical phenomena.

TheFastAndTheCurious

I think Albert was a troubled child with bad parents

but why was he removed from the experiment?

He was orphaned out to a family.

Can someone please maybe tell me who wrote it and the date, i want to reference this site for an assignment.

We are happy to hear you’re finding our site to be a helpful resource! There is no named author — the author of this page is simply “GoodTherapy.” I would recommend asking your professor or faculty how they would like you to cite a website with no named author.

We hope this is helpful! Please let us know if you have further questions!

Great article. thanks

bro he should have been put down this poor child was abused by his own (illegitimate) father#Maury#unfortunate#thatstuff

Poor little Albert :( . Bless his soul may he RIP. Great article (;.

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Classical Conditioning
John Watson

Notice to users

Inside The Horrifying Little Albert Experiment That Terrified An Infant To The Point Of Tears

In 1920, the two psychologists behind the little albert experiment performed a study on a nine-month-old baby to determine if classical conditioning worked on humans — and made him terrified of harmless objects in the process..

In 1920, psychologists John Watson and Rosalie Rayner performed what’s known today as the Little Albert Experiment. In an attempt to prove that classical conditioning worked on humans as well as animals, they trained an infant to show fear toward completely harmless objects, a concept that goes against all modern ethical guidelines.

YouTube The nine-month-old subject of the Little Albert Experiment.

Twenty years earlier, Ivan Pavlov had conditioned dogs to drool upon hearing the sound of a dinner bell, even when no food was presented to them. Watson and Rayner wanted to similarly condition a human to react to a stimulus, but their idea quickly went wrong.

The Johns Hopkins University psychologists were able to train Little Albert to react negatively to objects like a white rat, a Santa Claus mask, and even his own family pets. However, the boy’s mother pulled him out of the study before Watson and Rayner could try to reverse the conditioning, leaving parts of their hypothesis unproven.

What’s more, critics were quick to point out that the Little Albert Experiment had several flaws that may have made it scientifically unsound. Today, it’s remembered as a profoundly unethical study that may have traumatized an innocent child for life — all in the name of science.

What Was The Little Albert Experiment?

Even people who aren’t in the psychology field know about “classical conditioning” thanks to the infamous experiment conducted by Russian scientist Ivan Pavlov. The psychologist proved that it was possible to teach animals to react to a neutral stimulus (that is, a stimulus that produced no natural effect) by conditioning them.

According to Verywell Mind , Pavlov made a metronome tick every time he fed his canine test subjects. The dogs soon associated the sound of the metronome (the neutral stimulus) with food.

Soon, Pavlov could make the dogs salivate in expectation of food simply by producing the ticking sound, even when he didn’t actually feed the dogs. Thus, they were conditioned to associate the sound of the metronome with food.

YouTube Little Albert showed no fear toward the white rat at the beginning of the experiment.

Watson and Rayner wanted to try to reproduce Pavlov’s study in humans, and the Little Albert Experiment was born. The researchers presented a nine-month-old boy they called “Albert” with fluffy animals like a monkey, a rabbit, and a white rat. Albert had no negative reaction to them, and he even tried to pet them.

Next, the psychologists struck a hammer against a steel pipe every time they presented Albert with the creatures. The sudden, loud noise made the baby cry.

Soon, Albert was conditioned to associate the loud noise with the fuzzy animals, and he began crying in fear whenever he saw the creatures — even when Watson and Rayner didn’t strike the pipe.

Albert became terrified of not only the monkey, rabbit, and rat, but also anything furry that looked like them. He cried when he saw a Santa Claus mask with a white beard and grew scared of his own family’s dogs.

Watson Scaring Little Albert With A Mask

YouTube Throughout the course of the study, Little Albert became frightened of a Santa Claus mask.

Watson and Rayner intended to attempt to reverse the conditioning performed on Little Albert, but his mother pulled him from the study before they had the chance. Thus, there is a chance the poor child remained scared of furry objects for life — which raises countless questions related to ethics.

The Controversy Surrounding The Little Albert Experiment

Many of the ethical debates regarding the Little Albert Experiment involved not only the methods that Watson and Rayner deployed to “condition” the infant but also the way in which the psychologists conducted the study. For one, the experiment had only a single subject.

What’s more, according to Simply Psychology , creating a fear response is an example of psychological harm that’s not permitted in modern psychological experiments. While the study was conducted before modern ethical guidelines were implemented, criticism of how Watson and Rayner executed the experiment was raised even at the time.

Wikimedia Commons John Watson, the psychologist behind the Little Albert Experiment.

Then there was the issue of the scientists’ failure to deprogram the child after the experiment was over. They initially intended to attempt to “uncondition” Little Albert, or remove the irrational fear from the poor child’s mind. However, since his mother withdrew him from the experiment, Watson and Rayner were unable to do so.

As such, the fear was potentially firmly embedded in the child’s brain — a fear that was previously nonexistent. Because of this, both the American Psychological Association and the British Psychological Society would ultimately deem this experiment unethical.

The Unknown Fate Of Little Albert

After criticism arose, Watson tried to explain his behavior, claiming that Little Albert would have been exposed to the frightening stimuli later in life anyway. “At first there was considerable hesitation upon our part in making the attempt to set up fear reactions experimentally,” he said, according to GoodTherapy .

Watson continued, “We decided finally to make the attempt, comforting ourselves… that such attachments would arise anyway as soon as the child left the sheltered environment of the nursery for the rough and tumble of the home.”

The true fate of Albert remained unknown for decades, however, and experts still aren’t positive about his actual identity.

YouTube Little Albert was conditioned to become frightened of furry creatures.

One study, as reported by the American Psychological Association , posited that Little Albert was a pseudonym for Douglas Merritte, the son of a nurse at Johns Hopkins named Arvilla Merritte. Arvilla was reportedly paid one dollar for her son’s participation in the study.

Sadly, young Douglas died of complications from hydrocephalus when he was just six years old. If he was indeed the true Little Albert, his medical condition adds another layer of questionability to the experiment. If he was born with hydrocephalus, he may have reacted to the stimulus differently than a typical baby would have.

Other research, however, suggests the true Albert was a little boy named William Albert Barger. Per New Scientist , Barger lived a long, happy life and died in 2007. However, his relatives report that he had an aversion to animals — and they even had to put the family dogs away when he came to visit.

If the Little Albert Experiment has taught scientists nothing else, it’s this: While it’s important to make discoveries in order to understand the human condition better, it’s vital to remember that the test subjects are human beings who may carry the impacts with them for the rest of their lives.

Now that you’ve read all about the Little Albert Experiment, go inside the Milgram experiment , which proved that everyday people are capable of monstrous acts. Then, discover the tragedy of David Reimer , the boy who was forced to live as a girl for a doctor’s experiment.

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SCIENTIST AT WORK: Joseph LeDoux

Using Rats to Trace Anatomy of Fear, Biology of Emotion

By Sandra Blakeslee

Nov. 5, 1996

THE realm of emotion and feeling is a treacherous one for science. Rage, lust, envy and shame churn in the human psyche. Yearning, disappointment and fear mingle with conscious thought, sway decisions and then recede like phantoms.

Writers, psychoanalysts and psychologists may try to sort out the interplay of cognition and desire, of thought and compulsion. But understanding the origin and architecture of human emotions in the brain is another matter altogether. What is the key to linking emotions to activity in the cells of the brain?

Rats -- better yet, frightened rats -- are the key, says Dr. Joseph LeDoux, a 46-year-old neuroscientist at New York University who pioneered the study of emotions as biological phenomena.

''You start with something you can study,'' Dr. LeDoux said in a recent interview. Like most animals, rats exhibit fear, an emotion that may help creatures escape from predators. In experiments over the last 15 years, Dr. LeDoux has traced fear inside the rat's brain -- from the first sounds of danger detected by the outer ear to inner brain circuits that cause the animal either to freeze or to run for its life.

Using this strategy, Dr. LeDoux has given researchers the first real glimpse into the neuroanatomy of an emotion. And though the work has been done in rats, Dr. Ledoux says the findings also apply to humans, providing insights into why it is so difficult to control emotions with rational, conscious thought.

One of the biggest surprises from Dr. LeDoux's work is that there may be no such thing as the limbic system -- a brain structure that has been supposed to underlie emotion and motivation. All students are taught about the limbic system, Dr. LeDoux said, ''but in my opinion, it's no longer a valid concept.''

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Fear or No Fear – The Little Albert Experiment

Objective of the experiment, the experiment, what the results mean, leave a reply cancel reply.

December 1, 2013

Fearful Memories Passed Down to Mouse Descendants

Genetic imprint from traumatic experiences carries through at least two generations

By Ewen Callaway & Nature magazine

From Nature magazine

Certain fears can be inherited through the generations, a provocative study of mice reports. The authors suggest that a similar phenomenon could influence anxiety and addiction in humans. But some researchers are sceptical of the findings because a biological mechanism that explains the phenomenon has not been identified.

According to convention, the genetic sequences contained in DNA are the only way to transmit biological information across generations. Random DNA mutations, when beneficial, enable organisms to adapt to changing conditions, but this process typically occurs slowly over many generations.

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Yet some studies have hinted that environmental factors can influence biology more rapidly through 'epigenetic' modifications, which alter the expression of genes, but not their actual nucleotide sequence. For instance, children who were conceived during a harsh wartime famine in the Netherlands in the 1940s are at increased risk of diabetes, heart disease and other conditions — possibly because of epigenetic alterations to genes involved in these diseases. Yet although epigenetic modifications are known to be important for processes such as development and the inactivation of one copy of the X-chromsome in females, their role in the inheritance of behaviour is still controversial.

Kerry Ressler, a neurobiologist and psychiatrist at Emory University in Atlanta, Georgia, and a co-author of the latest study, became interested in epigenetic inheritance after working with poor people living in inner cities, where cycles of drug addiction, neuropsychiatric illness and other problems often seem to recur in parents and their children. “There are a lot of anecdotes to suggest that there’s intergenerational transfer of risk, and that it’s hard to break that cycle,” he says.

Heritable traits

Studying the biological basis for those effects in humans would be difficult. So Ressler and his colleague Brian Dias opted to study epigenetic inheritance in laboratory mice trained to fear the smell of acetophenone, a chemical the scent of which has been compared to those of cherries and almonds. He and Dias wafted the scent around a small chamber, while giving small electric shocks to male mice. The animals eventually learned to associate the scent with pain, shuddering in the presence of acetophenone even without a shock.

This reaction was passed on to their pups, Dias and Ressler report today in Nature Neuroscience 1. Despite never having encountered acetophenone in their lives, the offspring exhibited increased sensitivity when introduced to its smell, shuddering more markedly in its presence compared with the descendants of mice that had been conditioned to be startled by a different smell or that had gone through no such conditioning. A third generation of mice — the 'grandchildren' — also inherited this reaction, as did mice conceived through in vitro fertilization with sperm from males sensitized to acetophenone. Similar experiments showed that the response can also be transmitted down from the mother.

These responses were paired with changes to the brain structures that process odours. The mice sensitized to acetophenone, as well as their descendants, had more neurons that produce a receptor protein known to detect the odour compared with control mice and their progeny. Structures that receive signals from the acetophenone-detecting neurons and send smell signals to other parts of the brain (such as those involved in processing fear) were also bigger.

The researchers propose that DNA methylation — a reversible chemical modification to DNA that typically blocks transcription of a gene without altering its sequence — explains the inherited effect. In the fearful mice, the acetophenone-sensing gene of sperm cells had fewer methylation marks, which could have led to greater expression of the odorant-receptor gene during development.

But how the association of smell with pain influences sperm remains a mystery. Ressler notes that sperm cells themselves express odorant receptor proteins, and that some odorants find their way into the bloodstream, offering a potential mechanism, as do small, blood-borne fragments of RNA known as microRNAs, that control gene expression.

Contentious findings

Predictably, the study has divided researchers. “The overwhelming response has been 'Wow! But how the hell is it happening?'" says Dias. David Sweatt, a neurobiologist at the University of Alabama at Birmingham who was not involved in the work, calls it “the most rigorous and convincing set of studies published to date demonstrating acquired transgenerational epigenetic effects in a laboratory model".

However, Timothy Bestor, a molecular biologist at Columbia University in New York who studies epigenetic modifications, is incredulous. DNA methylation is unlikely to influence the production of the protein that detects acetophenone, he says. Most genes known to be controlled by methylation have these modifications in a region called the promoter, which precedes the gene in the DNA sequence. But the acetophenone-detecting gene does not contain nucleotides in this region that can be methylated, Bestor says. "The claims they make are so extreme they kind of violate the principle that extraordinary claims require extraordinary proof,” he adds.

Tracy Bale, a neuroscientist at the University of Pennsylvania in Philadelphia, says that researchers need to “determine the piece that links Dad's experience with specific signals capable of producing changes in epigenetic marks in the germ cell, and how these are maintained”.

“It's pretty unnerving to think that our germ cells could be so plastic and dynamic in response to changes in the environment,” she says.

Humans inherit epigenetic alterations that influence behaviour, too, Ressler suspects. A parent’s anxiety, he speculates, could influence later generations through epigenetic modifications to receptors for stress hormones. But Ressler and Dias are not sure how to prove the case, and they plan to focus on lab animals for the time being.

The researchers now want to determine for how many generations the sensitivity to acetophenone lasts, and whether that response can be eliminated. Scepticism that the inheritance mechanism is real will likely persist, Ressler says, “until someone can really explain it in a molecular way”, says Ressler. “Unfortunately, it’s probably going to be complicated and it’s probably going to take a while.”

This article is reprinted with permission from Nature magazine. It was first published on December 1, 2013.

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Observational Fear Learning in Rats: Role of Trait Anxiety and Ultrasonic Vocalization

Affiliations.

1 Institute for Pharmacology and Toxicology, Medical Faculty, Otto-von-Guericke University Magdeburg, 39120 Magdeburg, Germany.
2 Center for Behavioral Brain Sciences, Otto-von-Guericke University Magdeburg, 39120 Magdeburg, Germany.
3 Integrative Neuroscience Program, Otto-von-Guericke University Magdeburg, 39120 Magdeburg, Germany.
PMID: 33810488
PMCID: PMC8066558
DOI: 10.3390/brainsci11040423

Rats can acquire fear by observing conspecifics that express fear in the presence of conditioned fear stimuli. This process is called observational fear learning and is based on the social transmission of the demonstrator rat's emotion and the induction of an empathy-like or anxiety state in the observer. The aim of the present study was to investigate the role of trait anxiety and ultrasonic vocalization in observational fear learning. Two experiments with male Wistar rats were performed. In the first experiment, trait anxiety was assessed in a light-dark box test before the rats were submitted to the observational fear learning procedure. In the second experiment, ultrasonic vocalization was recorded throughout the whole observational fear learning procedure, and 22 kHz and 50 kHz calls were analyzed. The results of our study show that trait anxiety differently affects direct fear learning and observational fear learning. Direct fear learning was more pronounced with higher trait anxiety, while observational fear learning was the best with a medium-level of trait anxiety. There were no indications in the present study that ultrasonic vocalization, especially emission of 22 kHz calls, but also 50 kHz calls, are critical for observational fear learning.

Keywords: anxiety; observational fear learning; rat; ultrasonic vocalization.

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Conflict of interest statement

The authors declare no conflict of interest.

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Role of trait anxiety in observational fear learning. ( a ) Behavioral protocol…

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( a ) Behavioral protocol of experiment 2 was identical to experiment 1,…

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Curt Richter's rat hope experiment: Why did the first nine rats survive for days?

I can understand the part that the experimenter saved the rat just before it was about to die and then the rat lasted longer for the next drowning. But I do not understand what it means that before such intervention, when he first tried drowning, first 3 rats died in 2 minutes but the remaining 9 rats survived for days.Was it just a random chance that the first 3 rats happened to have little hope and the remaining 9 rats had naturally more hopes?

The first rat, Richter noted, swam around excitedly on the surface for a very short time, then dove to the bottom, where it began to swim around, nosing its way along the glass wall. It died two minutes later. Two more of the 12 domesticated rats died in much the same way. But, interestingly, the nine remaining rats did not succumb nearly so readily; they swam for days before they eventually gave up and died. ..... Richter then tweaked the experiment: He took other, similar rats and put them in the jar. Just before they were expected to die, however, he picked them up

https://www.psychologytoday.com/gb/blog/kidding-ourselves/201405/the-remarkable-power-hope

experimental-psychology
animal-cognition

$\begingroup$ The first experiment used domesticated rats so they were used to having someone take care of them. The ones that survived so long probably had more confidence that someone would come. $\endgroup$ – Just Weighinin Commented Mar 29 at 12:09

2 Answers 2

For more information on the experiment, there is Swamy (2020) :

The conclusion drawn was that since the rats BELIEVED that they would eventually be rescued, they could push their bodies way past what they previously thought impossible.

and the source ( Richter, 1957 ) can be downloaded in PDF

I had to re-read the Richter paper a couple of times to digest it, and from my understanding, the differences in swimming time was in the same (first) experiment. The tweak to the experiment was where, instead of using domesticated rats, they used hybrid rats ("crosses between domesticated and wild rats").

Richter, C. P. (1957). On the phenomenon of sudden death in animals and man. Psychosomatic Medicine, 19 , 191–198. https://doi.org/10.1097/00006842-195705000-00004

Swamy, S. (2020). The Power of Hope: A Rat Experiment by Dr Curt Richter. LinkedIn https://www.linkedin.com/pulse/power-hope-rat-experiment-dr-curt-richter-santosh-swamy

3 $\begingroup$ But the time that the experimenter introduced "hope" by rescuing rats was AFTER the first batch of 12 rats had died, wasn't it? I mean, the liked article says "Richter then tweaked the experiment". Did I misunderstand it and the experimenter introduced "hope" between the third and fourth rat? $\endgroup$ – Damn Vegetables Commented Feb 12, 2022 at 15:29

It's not clear what caused this. This variation in swimming times is in fact what motivates Richter to continue tweaking his experiment:

The significance of this average curve was greatly reduced by the marked variations in individual swimming times. At all temperatures, a small number of rats died within 5 - 10 minutes after immersion, while in some instances others apparently no more healthy, swam as long as 81 hours. The elimination of these large variations presented a real problem, which for some time we could not solve. Then the solution came from an unexpected source - the finding of the phenomenon of sudden death, which constitutes the main topic of this communication.

The numbers you cite regarding the 3 versus 9 rats comes from his second run of the experiment where he tests whether trimming the whiskers in the rats would result in different times.

The first rat swam around excitedly on the surface for a very short time, then dove to the bottom, where it began to swim around nosing its way along the glass wall. Without coming to the surface a single time, it died 2 minutes after entering the tank. Two more of the twelve domesticated rats tested died in much the same way; however, the remaining 9 swam 40 to 60 hours.

It seems that it was just caused by random luck.

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Observational fear learning in rats: role of trait anxiety and ultrasonic vocalization.

1. Introduction

2. materials and methods, 2.1. animals and housing, 2.2. apparatus, 2.3. behavioral procedure, 2.3.1. experiment 1: role of trait anxiety, 2.3.2. experiment 2: role of ultrasonic vocalization, 2.4. offline analyses of behavior and ultrasonic vocalization, 2.5. descriptive and analytical statistics, 3.1. experiment 1: role of trait anxiety, 3.2. experiment 2: role of ultrasonic vocalization, 4. discussion, 5. conclusions, author contributions, institutional review board statement, informed consent statement, data availability statement, acknowledgments, conflicts of interest.

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Fendt, M.; Gonzalez-Guerrero, C.P.; Kahl, E. Observational Fear Learning in Rats: Role of Trait Anxiety and Ultrasonic Vocalization. Brain Sci. 2021 , 11 , 423. https://doi.org/10.3390/brainsci11040423

Fendt M, Gonzalez-Guerrero CP, Kahl E. Observational Fear Learning in Rats: Role of Trait Anxiety and Ultrasonic Vocalization. Brain Sciences . 2021; 11(4):423. https://doi.org/10.3390/brainsci11040423

Fendt, Markus, Claudia Paulina Gonzalez-Guerrero, and Evelyn Kahl. 2021. "Observational Fear Learning in Rats: Role of Trait Anxiety and Ultrasonic Vocalization" Brain Sciences 11, no. 4: 423. https://doi.org/10.3390/brainsci11040423

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Baby Mice Can Inherit Fear of Certain Smells From Their Parents

But researchers are far from pinning down the mechanism by which this may be possible, or what specific roles epigenetics plays in human disease

Rachel Nuwer

Epigenetics has become something of a buzzword these days. Researchers have long studied how changes in an organism's DNA sequence affect how genes behave, but epigenetics looks at how environmental factors, like diet or lifestyle, can change gene activity in a way that passes from generation to generation. There's interest in how epigenetics might be connected to conditions ranging from cancer to kidney disease to autism . Yet scientists struggle to pin down the specifics of this phenomenon. As the New Scientist explains :

Previous studies have hinted that stressful events can affect the emotional behaviour or metabolism of future generations, possibly through chemical changes to the DNA that can turn genes off and on – a mechanism known as epigenetic inheritance. However, although epigenetic changes have been observed, identifying which ones are relevant is a bit like searching for a needle in a haystack. That's because many genes control behaviours or metabolic diseases like obesity.

Now, a new study published in Nature Neuroscience provides "some of the best evidence yet" that behaviors can indeed be passed from one generation to another, the New Scientist says.

In an experiment reminiscent of A Clockwork Orange , researchers trained male mice to fear a cherry blossom-like scent called acetophenone by inducing slight electric shocks every time the smell wafted into the animals' cages. After ten days of this treatment, whenever cherry blossoms were in the air, they report, the mice trained to fear it went on edge. The researchers found that those mice developed more smell receptors associated with that particular scent, which allowed them to detect it at lower concentrations. Additionally, when researchers examined those males' sperm they found that the gene responsible for acetophenone detection was packaged differently compared to the same gene in control mice.

After imprinting those males with a fear of acetophenone, the researchers inseminated females with the scared mice's sperm. The baby mice never met their father, but those sired by a blossom-hating dad had more acetophenone smell receptors. Compared to pups born of other dads, most were also agitated when acetophenone filled the air. This same finding held true for those original males' grandpups.

Information transfer from one generation to another, outside experts told the New Scientist , may play a role in human diseases such as obesity, diabetes and psychiatric disorders. But researchers are far from pinning down the mechanism by which this may be possible, how long these sensitivities may last or whether these seemingly inherited behaviors affect anything more than smell in mice.

In other words, epigenetics is a field still largely obscured by unanswered questions. As Virginia Hughes summarizes at National Geographic , about all we can know for certain is this: "Our bodies are constantly adapting to a changing world. We have many ways of helping our children make that unpredictable world slightly more predictable, and some of those ways seem to be hidden in our genome."

A fear conditioned cue orchestrates a suite of behaviors in rats

Nicholas T Gordon
Aleah M DuBois
Christa B Michel
Katherine E Hanrahan
David C Williams
Stefano Anzellotti
Boston College, United States ;
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Michael A McDannald
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Pavlovian fear conditioning has been extensively used to study the behavioral and neural basis of defensive systems. In a typical procedure, a cue is paired with foot shock, and subsequent cue presentation elicits freezing, a behavior theoretically linked to predator detection. Studies have since shown a fear conditioned cue can elicit locomotion, a behavior that - in addition to jumping, and rearing - is theoretically linked to imminent or occurring predation. A criticism of studies observing fear conditioned cue-elicited locomotion is that responding is non-associative. We gave rats Pavlovian fear discrimination over a baseline of reward seeking. TTL-triggered cameras captured 5 behavior frames/s around cue presentation. Experiment 1 examined the emergence of danger-specific behaviors over fear acquisition. Experiment 2 examined the expression of danger-specific behaviors in fear extinction. In total, we scored 112,000 frames for nine discrete behavior categories. Temporal ethograms show that during acquisition, a fear conditioned cue suppresses reward seeking and elicits freezing, but also elicits locomotion, jumping, and rearing - all of which are maximal when foot shock is imminent. During extinction, a fear conditioned cue most prominently suppresses reward seeking, and elicits locomotion that is timed to shock delivery. The independent expression of these behaviors in both experiments reveal a fear conditioned cue to orchestrate a temporally organized suite of behaviors.

Raw images and observer judgments are freely available: https://doi.org/10.7910/DVN/HKMUUN

Hanrahan KE
Williams DC
McDannald MA

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For correspondence, competing interests.

National Institutes of Health (MH117791)

The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.

Reviewing Editor

Matthew N Hill, University of Calgary, Canada

Animal experimentation: All protocols were approved by the Boston College Animal Care and Use Committee and all experiments were carried out in accordance with the NIH guidelines regarding the care and use of rats for experimental procedures. The Boston College experimental protocol supporting these procedures is 2024-001.

Version history

Received: August 6, 2022
Accepted: May 16, 2024
Accepted Manuscript published: May 21, 2024 (version 1)

This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.

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Cite this article (links to download the citations from this article in formats compatible with various reference manager tools), categories and tags, research organism, further reading, spatial and temporal pattern of structure–function coupling of human brain connectome with development.

Brain structural circuitry shapes a richly patterned functional synchronization, supporting for complex cognitive and behavioural abilities. However, how coupling of structural connectome (SC) and functional connectome (FC) develops and its relationships with cognitive functions and transcriptomic architecture remain unclear. We used multimodal magnetic resonance imaging data from 439 participants aged 5.7–21.9 years to predict functional connectivity by incorporating intracortical and extracortical structural connectivity, characterizing SC–FC coupling. Our findings revealed that SC–FC coupling was strongest in the visual and somatomotor networks, consistent with evolutionary expansion, myelin content, and functional principal gradient. As development progressed, SC–FC coupling exhibited heterogeneous alterations dominated by an increase in cortical regions, broadly distributed across the somatomotor, frontoparietal, dorsal attention, and default mode networks. Moreover, we discovered that SC–FC coupling significantly predicted individual variability in general intelligence, mainly influencing frontoparietal and default mode networks. Finally, our results demonstrated that the heterogeneous development of SC–FC coupling is positively associated with genes in oligodendrocyte-related pathways and negatively associated with astrocyte-related genes. This study offers insight into the maturational principles of SC–FC coupling in typical development.

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Spontaneous human CD8 T cell and autoimmune encephalomyelitis-induced CD4/CD8 T cell lesions in the brain and spinal cord of HLA-DRB1*15-positive multiple sclerosis humanized immune system mice

Autoimmune diseases of the central nervous system (CNS) such as multiple sclerosis (MS) are only partially represented in current experimental models and the development of humanized immune mice is crucial for better understanding of immunopathogenesis and testing of therapeutics. We describe a humanized mouse model with several key features of MS. Severely immunodeficient B2m-NOG mice were transplanted with peripheral blood mononuclear cells (PBMCs) from HLA-DRB1-typed MS and healthy (HI) donors and showed rapid engraftment by human T and B lymphocytes. Mice receiving cells from MS patients with recent/ongoing Epstein–Barr virus reactivation showed high B cell engraftment capacity. Both HLA-DRB1*15 (DR15) MS and DR15 HI mice, not HLA-DRB1*13 MS mice, developed human T cell infiltration of CNS borders and parenchyma. DR15 MS mice uniquely developed inflammatory lesions in brain and spinal cord gray matter, with spontaneous, hCD8 T cell lesions, and mixed hCD8/hCD4 T cell lesions in EAE immunized mice, with variation in localization and severity between different patient donors. Main limitations of this model for further development are poor monocyte engraftment and lack of demyelination, lymph node organization, and IgG responses. These results show that PBMC humanized mice represent promising research tools for investigating MS immunopathology in a patient-specific approach.

Stochastic characterization of navigation strategies in an automated variant of the Barnes maze

Animals can use a repertoire of strategies to navigate in an environment, and it remains an intriguing question how these strategies are selected based on the nature and familiarity of environments. To investigate this question, we developed a fully automated variant of the Barnes maze, characterized by 24 vestibules distributed along the periphery of a circular arena, and monitored the trajectories of mice over 15 days as they learned to navigate towards a goal vestibule from a random start vestibule. We show that the patterns of vestibule visits can be reproduced by the combination of three stochastic processes reminiscent of random, serial, and spatial strategies. The processes randomly selected vestibules based on either uniform (random) or biased (serial and spatial) probability distributions. They closely matched experimental data across a range of statistical distributions characterizing the length, distribution, step size, direction, and stereotypy of vestibule sequences, revealing a shift from random to spatial and serial strategies over time, with a strategy switch occurring approximately every six vestibule visits. Our study provides a novel apparatus and analysis toolset for tracking the repertoire of navigation strategies and demonstrates that a set of stochastic processes can largely account for exploration patterns in the Barnes maze.

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Published: 30 November 2021

Stressed rats fail to exhibit avoidance reactions to innately aversive social calls

Ashutosh Shukla 1 &
Sumantra Chattarji 1 , 2

Neuropsychopharmacology volume 47 , pages 1145–1155 ( 2022 ) Cite this article

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Neuroscience

Disruptions in amygdalar function, a brain area involved in encoding emotionally salient information, has been implicated in stress-related affective disorders. Earlier animal studies on the behavioral consequences of stress-induced abnormalities in the amygdala focused on learned behaviors using fear conditioning paradigms. If and how stress affects unconditioned, innate fear responses to ethologically natural aversive stimuli remains unexplored. Hence, we subjected rats to aversive ultrasonic vocalization calls emitted on one end of a linear track. Unstressed control rats exhibited a robust avoidance response by spending more time away from the source of the playback calls. Unexpectedly, prior exposure to chronic immobilization stress prevented this avoidance reaction, rather than enhancing it. Further, this stress-induced impairment extended to other innately aversive stimuli, such as white noise and electric shock in an inhibitory avoidance task. However, conditioned fear responses were enhanced by the same stress. Inactivation of the basolateral amygdala (BLA) in control rats prevented this avoidance reaction evoked by the playback. Consistent with this, analysis of the immediate early gene cFos revealed higher activity in the BLA of control, but not stressed rats, after exposure to the playback. Further, in vivo recordings in freely behaving control rats exposed to playback showed enhanced theta activity in the BLA, which also was absent in stressed rats. These findings offer a new framework for studying stress-induced alterations in amygdala-dependent maladaptive responses to more naturally threatening and emotionally relevant social stimuli. The divergent impact of stress on defensive responses––impaired avoidance responses together with increased conditioned fear––also has important implications for models of learned helplessness and depression.

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Introduction.

Stress-related psychiatric disorders are associated with a range of debilitating emotional symptoms, as well as structural and functional alterations in the amygdala [ 1 , 2 ]. Rodent models have offered insights into how stress affects the amygdala across multiple levels of neural organization, including behavioral analyses of fear memories using Pavlovian conditioning [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. As useful as these behavioral studies have been in exploring the functional consequences of stress-induced plasticity in the amygdala, they relied largely on stimuli that were not ethologically natural, e.g. exposure to foot shocks. Little is known about the impact of stress on unconditioned fear reactions to innately aversive stimuli that are ethologically relevant to rodents.

Accumulating evidence from studies of social interactions in rodents offer a useful framework for addressing this gap in knowledge [ 14 ]. For instance, rodents communicate their affective states through ultrasonic vocalizations (USVs), which constitute a key component of their social interactions [ 15 , 16 , 17 , 18 ]. Broadly, rats emit two distinct types of USV calls – 22-kHz alarm calls conveying negative emotional states triggered by aversive experiences or threats such as predators and painful stimuli, and 50-kHz appetitive calls elicited during mating, play behavior, direct social contact etc. [ 19 , 20 ]. However, previous studies of defensive responses triggered by playback of aversive social calls, and other innately aversive auditory stimuli, yielded mixed results. While a few studies observed stimulus-induced defensive responses, others did not [ 21 , 22 ]. Moreover, earlier analyses of playback-induced defensive responses focused on hypermotility as a primary behavioral readout, without taking the animals’ direction of motion into consideration. Further, experience and environment also influence whether mice preferentially exhibit flight or freezing responses [ 23 , 24 , 25 , 26 ]. What kind of defensive reactions would playback of innately aversive 22-kHz alarm calls evoke in rats? Would prior exposure to chronic stress affect these defensive responses? Would stressed rats exhibit higher fear by responding with enhanced flight or avoidance reactions? Previous studies reported that chronic or repeated stress enhanced the recall of conditioned fear in rodents, manifested as higher levels of freezing to an auditory tone used as the conditioned stimulus [ 11 , 27 ]. Neurons in the basolateral amygdala (BLA) are essential for the acquisition of the tone-shock association in auditory fear conditioning [ 10 ]. Would responses to innately aversive USV calls also depend on neural activity in the BLA? If so, how would stress affect this? Here we combine behavioral, pharmacological, immunohistochemical and in vivo electrophysiological analyses to address these questions using a well-established rat model of chronic immobilization stress [ 28 , 29 ].

Materials and methods

Details are provided in Supplementary information

Animal experiments were approved by the CPCSEA (Committee for the Purpose of Control and Supervision of Experiments on Animals), and Institutional Animal Ethics Committee (IAEC) of NCBS, Bangalore.

Experimental procedures

Supplemental information contains all protocols for behavioral experiments, BLA inactivation, cFos immunohistochemistry and in vivo recordings.

Statistical analyses

All values are expressed as mean ± s.e.m., unless stated otherwise. GraphPad Prism (La Jolla, CA) was used for statistical tests; specific details are described in figure legends.

Playback of 22-kHz ultrasonic vocalizations elicits avoidance behavior in control rats

First, we set out to characterize innate behavioral responses of adult male rats to the playback of aversive 22-kHz vocalization (USV) calls. To this end, rats were habituated to a linear track (Supplementary Fig. 1A ) for 5 minutes without any playback, during which control rats spent comparable durations of time in the proximal and distal halves of the track, exhibiting no preference for one or the other half (Fig. 1 A, 1B–D , left ). Following habituation, the rats were subjected to two 3-minute episodes of playback of 22-kHz USV calls, 5 minutes apart, on the same track. These USV calls caused them to spend significantly more time in the distal half of the track, away from the source of the playback calls (Fig. 1B right, 1D, left). This avoidance response is not habituated in these rats even after exposure to a prolonged aversive call playback episode (Supplementary Fig. 8 ). Next, a separate group of rats were subjected to a well-characterized model chronic immobilization stress (2 h/day for 10 days), the efficacy of which was verified using two separate measures. First, this chronic stress paradigm caused a significant increase in anxiety-like behavior in the open-field test (Supplementary Fig. 1B–G ) [ 30 ]. Second, this chronic stress also led to a significant reduction in body weight gain [ 31 ]. Stressed rats were subjected to the same sequence of habituation followed by USV playback. Stressed rats also spent comparable amounts of time in the two halves of the track during habituation, similar to control rats (Fig. 1C right, 1E, left). Surprisingly, stressed rats continued to exhibit this lack of preference even when the aversive USV was played back. The aversive USV failed to elicit avoidance reactions in stressed rats as they spent similar amounts of time in either halves of the track (Fig. 1C right, 1E, left). The distance traveled by both control and stressed rats, in response to the aversive call playback, was also higher relative to habituation (Fig. 1 D, 1E , right).

A Experimental design. B , C Time spent by a representative control ( B ) and stressed ( C ) rat along the track during habituation (left) and playback (right ) . D , E Time spent in proximal and distal halves and distance traveled. D Control: Left: Two-way RM ANOVA, Sidak’s multiple comparisons test, location: F 1, 19 = 5.03, p < 0.05, playback: F 1, 19 = 1.00, p > 0.05, location X playback: F 1, 19 = 9.28, p < 0.01, N = 20. Right: Paired t-test, t 19 = 12.58, p < 0.0001. E Stress: Left: Two-way RM ANOVA, Sidak’s multiple comparisons test, location: F 1, 17 = 0.02, p > 0.05, playback: F 1, 17 = 1.00, p > 0.05, location X playback: F 1, 17 = 1.97, p > 0.05, N = 18. Right: Paired t-test, t 17 = 3.36, p < 0.01.

To ensure that the avoidance behavior and its impairment seen in control and stressed rats is specific to aversive calls, and not a generic response to auditory stimuli or USV calls, we subjected a separate group of rats to USV calls conveying a positive emotional valence [ 17 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. To this end, control and stressed rats were exposed to a playback of 50-kHz appetitive USV calls using the same protocol as the aversive calls (Supplementary Fig. 2A ). During habituation, control rats spent equal time in the proximal and distal halves of the track. Control rats showed approach behavior during the 1st minute of the 1st playback episode of the appetitive call as they spent significantly more time in the proximal half of the track (Supplementary Fig. 2B , middle, 2D, left). Stressed rats also exhibited approach behavior (Supplementary Fig. 2C , middle, 2D, left) during 1st minute of the 1st playback. In striking contrast to control rats, however, stressed rats also showed avoidance behavior in response to the 2nd playback of the appetitive calls (Supplementary Fig. 2C , 2E , right), suggesting a switch in the perception of the emotional valence of the call from positive to negative. This suggests that social call playback-induced behavioral differences are not limited to aversive call playbacks but extend to appetitive call playback as well. Thus, the behavioral responses were specific and distinct between the appetitive and aversive call playback in the stressed animals.

Having established that control rats exhibit avoidance behavior that is specific to the 22-kHz USV playback, we focused on the paradoxical finding that prior exposure to stress impairs, rather than enhance, the avoidance reaction to aversive calls. We tested if this stress-induced impairment generalizes to other forms of aversive auditory stimuli. Playback of auditory white noise has been reported to be an innately aversive stimulus that elicits avoidance/flight responses in rodents [ 24 , 25 , 26 , 48 ]. In fact, it is aversive enough to be used as an unconditioned stimulus in Pavlovian fear conditioning paradigms [ 49 ]. Thus, a different group of control and stressed rats were presented with the same sequence of habituation and playback of white noise in the linear track (Supplementary Fig. 3A ). Playback of white noise also elicited a robust avoidance reaction in control (Supplementary Fig. 3B , 3D ), but not stressed rats (Supplementary Fig. 3C , 3E ). Together, these results demonstrate that playback of aversive calls and white noise both elicited a robust avoidance behavior in control rats. However, this was absent in stressed rats, which explored the half of the track that was closer to the source of the aversive auditory stimuli to the same extent as the safer distal half that was preferred by the control rats.

Stress impairs inhibitory avoidance behavior

In an effort to further examine the robustness of these paradoxical findings, we adapted the inhibitory avoidance paradigm to our experimental design. The linear track was modified to include a small shock-grid at one end of the linear track (Supplementary Fig. 4 , Supplementary Materials and Methods ). Thus, in this experiment, one end of the track still contained an aversive stimulus (i.e. the “proximal” half), but now the USV call or white noise was replaced by a strong noxious stimulus in the form of a foot shock. First, control rats were habituated to the track for 10 minutes (habituation, Supplementary Fig. 4A ), wherein they spent equal time in both halves (Supplementary Fig. 4B , 4D , left). Next, the shock-grid was turned on for 90 s such that rats received a DC foot-shock (0.4 mA) whenever they visited the end of the track containing the shock-grid (shock, Supplementary Fig. 4A ). Once the shock-grid was turned off, the rat’s behavior was monitored for another 10 minutes (post-shock, Supplementary Fig. 4A ). Control rats spent significantly more time in the distal half of the track, away from the shock-zone (Supplementary Fig. 4B , 4D , right). Thus, exposure to the shock enhanced avoidance behavior in control rats. In contrast, stressed rats spent comparable time in both halves of the track despite exposure to the shock, similar to that exhibited during habituation in the absence of shock (Supplementary Fig. 4C , 4E ). Further, while control rats avoided the shock zone following the cessation of shock, the stressed rats did not.

Despite the overall similarity in the findings on stress-induced suppression of avoidance behavior, the actual nature of the aversive stimuli across these paradigms were quite different. The playback of USV calls and white noise, although emanating from one end of the track, spread across the entire track. But, the shock grid was spatially restricted to a specific location on the track. This raises the possibility that despite spending comparable amounts of time post-shock in both halves overall, the stressed rats may still have successfully avoided the shock-zone itself. To test this, we first analyzed the time spent by control and stressed rats in the shock-zone. After receiving the shock, control rats showed a significant reduction in time spent in the shock-zone compared to habituation. However, stressed rats spent equal time in the shock-zone both during habituation and post-shock exploration (Supplementary Fig. 4F ). The impairment of avoidance behavior in stressed rats may also arise due to control and stressed rats receiving different extents of foot shocks during the shock period. We quantified the time spent on, and visits to, the shock-grid during the shock period. This analysis revealed no difference in these two measures between control and stressed rats (Supplementary Fig. 4G ). Thus, stress-induced suppression of unconditioned avoidance behavior is not limited to innately aversive auditory stimuli, but also extends to a noxious somatosensory stimulus, thereby showing that impairment in the avoidance response to aversive stimuli in stressed rats to be a robust phenomenon that generalizes across stimulus modalities.

Stress impairs avoidance from, but increases freezing to, the conditioned stimulus in an auditory fear conditioning paradigm

Having demonstrated that exposure to chronic stress causes a deficit in the avoidance response to innately aversive unconditioned stimuli, we next asked if stress also impairs a conditioned avoidance response. To this end, we used a Pavlovian auditory fear conditioning paradigm, but with an additional behavioral readout (Fig. 2 ). In addition to testing for the recall of conditioned fear manifested as a freezing response in the usual testing context, we also assessed their conditioned avoidance response in the linear track (Fig. 2A , right). Rats were first habituated to the conditioning context for 20 minutes for two days. 24 h later, they were subjected to five presentations of the conditioned stimulus (CS) alone (tone habituation). This was immediately followed by auditory fear conditioning using seven pairings of the CS co-terminating with an unconditioned stimulus (US, 0.7 mA foot shock; Fig. 2A , conditioning). After the end of conditioning, control rats showed robust acquisition of fear memory, as evidenced by significantly higher freezing relative to tone habituation (Fig. 2B ). A day later, these rats were divided into two groups to assess their behavioral responses to the tone CS either in their home cage or in the linear track (Fig. 2A , right). During fear recall in their home cage, control rats exhibited significantly higher freezing to the CS (Fig. 2C ). The other group of control rats were first allowed to get habituated to the track for 10 minutes without the CS (habituation), wherein they spent comparable amounts of time in both halves (Fig. 2D , left). This was followed by five presentations of the same tone CS through a speaker at one end of the track (Fig. 2A ), identical to the earlier USV playback experiments. During this test in the linear track, CS presentations triggered a strong avoidance reaction in control rats (Fig. 2D , right). When stressed animals were subjected to the same sequence of training and tests, their behavioral response to the CS was similar to their control counterparts except for in the linear track. Stressed rats also exhibited robust acquisition of fear memory (Fig. 2E ). Stressed rats exhibited significantly higher levels of freezing than their control counterparts during fear acquisition (Supplementary Fig. 11 ). 24 h later, when tested for recall of conditioned fear in their home cages, one group of stressed rats also showed CS-induced freezing that was significantly higher than that shown by control rats (Fig. 2F ). However, in the linear track, the same CS failed to elicit avoidance behavior in the other group of stressed rats as they spent comparable amounts of time in both the proximal and distal halves (Fig. 2G , right). Further, we confirmed that the CS by itself was not innately aversive because it did not elicit avoidance behavior in experimentally naive rats (Supplementary Fig. 5A ). Also, while motility, measured as the overall distance traveled along the track, of control and naive rats during habituation and CS presentation was comparable, stressed rats showed lower motility (Supplementary Fig. 5B ). More detailed trial-by-trial analyses of time spent by the rats along the track revealed that control rats spent significantly greater time in the distal half of the track from the 2nd trial onwards. In contrast, stressed and naive rats spent comparable time in either halves of the track in all trials (Supplementary Fig. 5C ).

A Experimental design. ( B , E ) Freezing response during first pretone, tone habituation, first and last trials of conditioning. B Control: One-way RM ANOVA, Tukey’s multiple comparisons test, F 3, 84 = 50.22 p < 0.0001, N = 29; ( E ) Stress: One-way RM ANOVA, Tukey’s multiple comparisons test, F 3, 60 = 50.1 p < 0.0001, N = 21. C , F Freezing response to CS before (in conditioning context) and 24 h after (during fear recall in home cage) fear conditioning: ( C ) Control: Paired t-test, t 13 = 3.74, p < 0.01, N = 14; ( F ) Stress: Paired t-test, t 10 = 4.29, p < 0.01, N = 11. Fear recall: Control vs. Stress: Unpaired t-test, t 26 = 2.37, p < 0.05. D , G Time spent in proximal and distal halves during fear recall in linear track. D Control: Two-way RM ANOVA, Sidak’s multiple comparisons test, location: F 1, 14 = 10.29, p < 0.01, CS : F 1, 14 = 3.50, p > 0.05, location X CS: F 1, 14 = 8.93, p < 0.01, N = 15; ( G ) Stress: Two-way RM ANOVA, Sidak’s multiple comparisons test, location: F 1, 9 = 0.53, p > 0.05, CS : F 1, 9 = 0.01, p > 0.05, location X CS: F 1, 9 = 1.00, p > 0.05, N = 10.

Together, these results reveal that stress selectively suppresses avoidance behavior in response to the CS in the linear track, while enhancing conditioned freezing to the same CS in the home cage.

Targeted inactivation of the basolateral amygdala in control rats blocks avoidance behavior elicited by playback of aversive USV calls

Since aversive social calls are used by rodents to warn conspecifics about potential threats and the amygdala plays a role in defensive responses to threatening stimuli, we hypothesized that amygdalar activity might be necessary for mediating the avoidance behavior seen in the present study. Hence, we carried out bilateral in vivo infusions of the GABA A -receptor agonist muscimol directly into the BLA of control rats to test its impact on avoidance behavior triggered by the playback of 22-kHz USV calls (Fig. 3A , Supplementary Fig. 7 ). Rats infused with vehicle spent equal time in both halves of the track during habituation, but spent significantly more time in the distal half of the track during USV playback (Fig. 3 B, 3D ). Thus, vehicle infusion into the BLA did not interfere with these rats’ ability to exhibit avoidance behavior during USV playback. On the other hand, rats infused with muscimol spent equal time in the proximal and distal halves of the track during both habituation and playback (Fig. 3 C, 3E ). Thus, activity in the BLA is necessary for the expression of avoidance behavior evoked by aversive USV playback.

A Experimental design. B , C Time spent by an exemplar vehicle-infused ( B ) and muscimol-infused rat ( C ) along the track during habituation (left) and playback (right). D , E Time spent in proximal and distal halves and distance traveled. D Top: Representative photomicrograph showing infusion sites in the BLA (red arrows). Bottom: Left: Vehicle: Two-way RM ANOVA, Sidak’s multiple comparisons test, location: F 1, 12 = 4.82, p < 0.05, playback: F 1, 12 = 1.00, p > 0.05, location X playback: F 1, 12 = 5.13, p < 0.05, N = 13; Bottom: Right: Paired t-test, t 12 = 10.87, p < 0.0001. E Muscimol: Left: Two-way RM ANOVA, Sidak’s multiple comparisons test, location: F 1, 10 = 0.43, p > 0.05, playback: F 1, 10 = 1.00, p > 0.05, location X playback: F 1, 10 = 0.08, p > 0.05, N = 11. Right: Paired t-test, t 10 = 3.10, p < 0.05.

Playback of aversive calls increases cFos expression in the basolateral amygdala of control but not stressed rats

Results presented so far show that inactivation of the BLA prevents the avoidance reactions (Fig. 3 ) to 22-kHz USV playbacks. Interestingly, chronic stress has the same effect on avoidance behavior. Does this mean that stress blocks avoidance behavior by suppressing neural activity in the BLA? We addressed this question by testing whether differences in avoidance behavior are reflected in changes in BLA neuronal activity in control and stressed rats. The expression of the immediate early gene c-fos , and its protein product cFos, is a reliable marker for neuronal activation [ 50 , 51 , 52 , 53 ]. Thus, to assess how the playback of aversive calls affect cFos expression in the BLA (Fig. 4A ), control and stressed rats were either exposed to the linear track alone (control and stress track, Fig. 4 B, 4C , left), or subjected to the aversive call playback on the linear track (control and stress playback, Fig. 4 B, 4C , right). These rats exhibited the same behavioral response as depicted in Fig. 1 (Supplementary Fig. 13 ). Approximately 90 minutes after the behavioral sessions on the track, rat brains were prepared for quantification of cFos-labeled cells in the BLA (Supplementary Materials and Methods ; Fig. 4A ). USV aversive calls elicited a significant increase in cFos expression in the BLA of control rats relative to those exposed only to the track (Fig. 4 B, 4D ). Strikingly, this increase in BLA cFos expression was not seen in stressed rats (Fig. 4 C, 4D ). Also, the density of cFos positive nuclei was similar in the control and stressed rats that were only exposed to the track, suggesting that basal activity in BLA neurons was not affected by stress (Fig. 4 B, 4 C, 4D ). Additional analyses revealed cFos expression in the CA1 sub-region of the dorsal hippocampus to be similar across control and stressed animals subjected to the same playback of aversive USV calls (Supplementary Fig. 12 ). Overall, this analysis revealed that aversive call playback recruits lower numbers of BLA neurons in stressed rats compared to control rats. Hence, the increase in BLA cFos expression in control, but not stressed rats, mirrors their behavioral response to the aversive USV playback (Fig. 1 B– 1E ).

A Experimental design. B , C Top: Sub-groups for estimating cFos expression in BLA. ( B ) Control; ( C ) Stress. Bottom: Representative images (4X and 20X magnified) showing cFos expression in BLA from different sub-groups. ( B ) Control; ( C ) Stress. Scale bar measures 500 μm and 50 μm for 4X and 20X magnified images. D cFos expression in BLA of control and stressed rats. Two-way ordinary ANOVA, Sidak’s multiple comparisons test, playback: F 1, 12 = 6.44, p < 0.05, stress: F 1, 12 = 17.10, p < 0.01, playback X stress: F 1, 12 = 14.03, p < 0.01, N = 4.

Aversive USV calls increase theta power in the BLA of control, but not stressed rats

Our post-mortem analysis of cFos expression suggests that the same aversive USV calls that elicit robust activation of BLA neurons in control rats, fail to do so in stressed animals. Therefore, in the final set of experiments, we probed the neural correlates of this in the intact BLA of freely behaving rats. Relatively little is known about neural activity in the amygdala in response to either playback of social calls [ 22 , 54 ] or vocalizations of conspecifics in free social interactions [ 55 ], and the impact of stress on such processes remains unexplored. Hence, rats were unilaterally implanted with in vivo electrodes to record local field potentials (LFPs) from the BLA (Fig. 5A , Supplementary Fig. 6 ). Upon recovery from surgery, these implanted rats were randomly assigned to either control or stress groups. On day 11, LFPs were recorded while rats were subjected to 100 presentations of single 22-kHz USV calls (Fig. 5B ). Relative to the baseline period, there was a significant increase in theta power in the BLA of control rats triggered by the 22-kHz USV (Figs. 5 C, 5D ). Notably, no such enhancement in BLA theta power was observed in stressed rats (Figs. 5 E, 5F ). Alterations in the power of distinct theta sub-bands in the amygdala have been correlated with distinct behavioral and internal states, and have been hypothesized to underlie distinct functions in a context-dependent manner [ 56 , 57 , 58 ]. Hence, we carried out a more detailed analysis of two different theta sub-bands––2–6 Hz and 8–12 Hz [ 56 , 57 , 58 , 59 ]. This revealed that while increased theta power in response to the aversive USV was specific to the 8–12 Hz frequency range in control rats (Fig. 5D , right), neither of the two sub-bands in stressed rats showed any significant change (Fig. 5F , right). In addition to the BLA, we recorded LFPs from the dorsal medial PFC (dmPFC), in the same rats, while presenting them with aversive USV calls. Similar to what was seen in the BLA, we observed a smaller but still significant increase in theta band activity in dmPFC of control rats (Supplementary Fig. 9A , 9B , left). But, this was not seen in stressed rats (Supplementary Fig. 9C , 9D , left). Unlike the changes in BLA, the increase in theta band activity in dmPFC during aversive call presentations was not exclusive to any frequency sub-band (Supplementary Fig. 9B , 9D , right). Also, during aversive call presentations, we found enhanced BLA-dmPFC theta synchrony (measured as magnitude-squared coherence) in control but not stressed rats (Supplementary Fig. 10 ). This finding is consistent with a potential role for BLA-dmPFC communication in mediating the appropriate avoidance responses in control rats that is impaired in stressed animals.

A Recording sites in BLA. Left: Representative photomicrograph showing recording site (red arrow head). Right: Schematic BLA coronal sections showing recording sites. B Experimental design for recording LFPs in BLA. C , E Left: Trial-averaged raw power spectrum from an exemplar control ( C ) and stressed ( E ) rat showing changes in BLA theta band power (blue vertical arrow). Thick solid and shaded lines represent mean and ±s.e.m. respectively. Right: Spectrogram showing baseline-corrected trail-averaged power in BLA of a representative control ( A ) and stressed ( E ) rat. Stimulus onset and offset are marked by vertical dashed black lines. Stimulus duration is marked by a horizontal solid red line. Vertical white arrow points to changes in theta band power. D , F Left: Baseline-corrected trial-averaged BLA theta band power. D Control: Paired t-test, t 13 = 3.63, p < 0.01, N = 14. F Stress: Paired t-test, t 15 = 0.52, p > 0.05, N = 16. Right: Baseline-corrected trial-averaged power in theta sub-bands. D Control: Paired t-test, t 13 = 4.10, p < 0.01. F Stress: Paired t-test, t 15 = 1.52, p > 0.05.

This study is one of the first attempts to examine the effects of repeated stress on avoidance behavior triggered by innately aversive stimuli, and a role for the basolateral amygdala (BLA) in such behavior. We found that playback of aversive USV social calls elicited avoidance reactions in rats, but prior exposure to chronic stress suppressed this. On the other hand, both control and stressed rats exhibited an initial approach behavior in response to playback of an appetitive USV calls. Unlike control rats, however, stressed rats also showed a late avoidance response to the appetitive call, suggesting a switch in the perception of the emotional valence of the calls from positive to negative. Notably, stress-induced impairment of avoidance also extended to other aversive stimuli – white noise and electric shock in an inhibitory avoidance task. During recall of conditioned fear, stressed rats exhibited higher conditioned freezing to the CS auditory tone compared to controls. However, avoidance reactions to the same CS tone was impaired in stressed but not control rats. This reveals that the same stress can have contrasting effects on the expression of defensive responses – impaired avoidance responses together with increased conditioned fear. This contrast led us to explore a role for the BLA because it not only plays a central role in conditioned fear, but is also affected by chronic stress. USV playback increased BLA neural activity, as evidenced by enhanced cFos expression and theta activity in control rats. Conversely, inactivation of the BLA prevented the avoidance response. Consistent with the stress-induced impairment in the avoidance behavior, both measures of enhanced USV-induced neural activity in the BLA were also suppressed by stress. Together, these findings add a new dimension to earlier work that focused primarily on how stress modulates learned behaviors, such as recall and extinction of conditioned fear, as well as appetitive conditioning tasks.

A role for amygdalar activity and its behavioral consequences

Our analyses identifying a role for the BLA in mediating the avoidance response adds to evidence on the presence of neural correlates for both appetitive and aversive USs in this brain area [ 60 , 61 ]. This is also in agreement with a role for the BLA in aversive conditioning and avoidance learning [ 62 , 63 , 64 , 65 , 66 ]. Further, our electrophysiological data are in line with an earlier report that 22-kHz USV increased single-unit firing rates in the BLA [ 22 ]. Future studies will be needed to examine whether BLA activity alone is sufficient to trigger avoidance responses, as well as potential contributions from other areas like the central amygdala [ 67 , 68 ]. In this context it is also worth noting that while previous studies assessing the facilitating effects of stress on conditioned fear reported stressed-induced potentiation of BLA activity [ 69 , 70 ], we found attenuated amygdalar activity in stressed rats in response to innately aversive social call playbacks. Similarly, exposure to chronic stressors, such as maternal maltreatment or prenatal stress, was reported to impair behavioral responses to social stimuli and reduce neural activity in the BLA [ 71 , 72 ]. Whether the blunted amygdalar responses seen in stressed rats are specific to innate fear cues or arise from a generalized attenuation in amygdalar responsiveness to social cues needs further investigation.

Exposure to aversive USV playback also increased cFos expression in the BLA of control rats, which is consistent with previous work showing enhanced cFos expression in the BLA and other brain areas induced by artificial and natural vocalizations [ 21 , 23 , 73 , 74 , 75 , 76 ]. On the other hand this increase in cFos expression was absent in stressed animals, which is similar to several earlier studies on stress-induced habituation of immediate early gene expression [ 77 , 78 , 79 , 80 , 81 , 82 , 83 ]. Further, while an acute bout of restraint stress was shown to increase expression of c-fos mRNA in multiple brain regions, repeated exposure to the same stress caused a habituation in c-fos mRNA expression [ 77 ]. This holds for audiogenic stress as well [ 80 ]. Finally, a novel acute stressor following a chronic exposure to homotypic stressor does not change c-fos expression in rodents [ 78 , 79 ]. Since the absence of stress-induced cFos expression in the BLA mirrored the impairment in avoidance behavior, we probed this further using in vivo recordings in awake, behaving rats. This part of our analysis was guided by previous studies on the roles of neural oscillations in the amygdala in the context of consolidation, retrieval and extinction of fear memories [ 56 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 ] and social behaviors [ 58 , 92 ]. Our findings on enhanced BLA theta activity elicited by aversive USV playback is in agreement with growing evidence regarding changes in theta rhythms during states of arousal, especially while responding to a fearful stimulus [ 93 ]. The specific increase in theta power in the 8–12 Hz range in the BLA, caused by the aversive USV, is interesting in light of a previous report on two divergent forms of arousal in rats caused by fearful and social stimuli [ 58 ]. While the fearful stimulus evoked a theta rhythm in the 3–7 Hz range, the social stimulus induced a distinct theta rhythm in the 7–10 Hz range. Other studies have also shown 2–6 Hz oscillations to overlap with freezing episodes during fear recall in mice [ 59 ]. This raises the possibility that enhanced BLA theta power in the 8–12 Hz range seen here may signal a heightened state of arousal associated with a social stimulus. Further, theta-range communication between the PFC and the BLA is also known to play an important role in fear discrimination. Hence, we also examined changes in BLA-dmPFC communication in mediating avoidance responses to aversive call playbacks. We found aversive USV playbacks to increase theta band activity in the dmPFC, as well as synchrony between BLA and dmPFC in the theta frequency band in control but not in stressed rats. This is consistent with a potential role for BLA-dmPFC communication in mediating the appropriate avoidance responses in control rats that is impaired in stressed animals.

While the use of innately aversive social calls in our study helped reveal stress-induced impairment in avoidance response, such ethologically natural stimuli also pose certain challenges. For instance, rats could be emitting aversive USVs during and after the 2-hour immobilization over the course of the chronic stress paradigm, thereby causing habituation to such USVs during subsequent behavioral tests in the linear track. Since the ability to vocalize is innate to the rats and a principal mode of communication for them, and given that rats are housed in the vivarium in colonies, it is quite challenging to control for this factor. Enhanced aversive vocalizations and reduced appetitive vocalizations have also been reported after exposure to chronic unpredictable stress or juvenile stress [ 94 , 95 ]. However, these vocalizations were recorded not when the rats were being stressed, rather when they were subjected to a separate behavioral paradigm. To the best of our knowledge, no such data exist with the chronic immobilization stress paradigm. Further, there are some aspects of our experimental design that are likely to have helped reduce the impact of such factors. Notably, we did not rely only on the 22-kHz aversive USV call playback to establish the key finding of stress-induced impairment in avoidance behavior. We used two other, very different, aversive auditory stimuli (white noise and the tone CS used in fear conditioning) to confirm that the same chronic stress also impaired avoidance in those experiments. The stressed rats were not repeatedly exposed to those auditory stimuli (CS/white noise) over the course of the 10-day paradigm, thereby ruling out habituation to those stimuli; yet they too exhibited impaired avoidance.

Stress and learned helplessness

What are the potential implications of the surprising finding that stress impaired, rather than enhanced, avoidance behavior evoked by a range of innately aversive auditory and somatosensory stimuli in stressed rats? Interestingly, these results are reminiscent of several earlier behavioral observations. For instance, rats and mice experiencing chronic immobilization stress [ 96 , 97 ] and inescapable foot shocks [ 98 ] exhibited impaired active defensive responses like avoidance in a conditioned avoidance response [ 96 , 97 ] or to innately aversive looming stimulus [ 98 ]. Taken together, these results suggest that repeated encounters with an inescapable stressor might tip the balance in favor of passive defensive responses (e.g. freezing) over active ones (e.g. flight or avoidance). This would be consistent with previous observations that stressed rats show enhanced fear recall (i.e. higher freezing), yet impaired avoidance responses as reported here and elsewhere [ 96 , 97 , 98 ]. Moreover, the impaired avoidance behavior may also be indicative of “learned helplessness” [ 99 ] wherein an organism, when challenged repeatedly with inescapable stressors, eventually learns that avoidance reactions are fruitless [ 99 , 100 , 101 ]. In such a framework, chronic immobilization stress would serve as the inescapable stressor inducing a state similar to “learned helplessness” such that when they are subsequently faced with aversive/stressful experiences, they no longer exhibit avoidance behaviors. Hence, it would be interesting to further explore the utility of this behavioral paradigm as an animal model of learned helplessness. While our results were obtained using male rats, growing evidence highlights the importance of sex differences in the effects of stress on fear and anxiety-like behavior, and their neural underpinnings in the amygdala [ 29 , 102 , 103 , 104 ]. However, the impact of sex difference in stress-induced modulation of innate fear and avoidance behavior remains unexplored and the findings presented here offer a framework to address this gap in knowledge.

Clinical implications for affective symptoms of stress disorders

In conclusion, the paradigm presented here combines an animal model of stress with natural, social calls to reveal amygdala-dependent behavioral changes akin to learned helplessness. These findings suggest future directions of enquiry that may be of clinical relevance. For instance, pioneering studies by Seligman and colleagues had explored the possibility of learned helplessness serving as a laboratory model of clinical depression [ 105 , 106 ]. As depression-like symptoms are often precipitated by some form of stress, animal models of stress have been used to elucidate the neural mechanisms of depression. These studies underscored the importance of stress-induced plasticity in corticolimbic structures, such as the amygdala, that are thought to contribute to emotional symptoms of depression [ 107 ]. Moreover, neuroimaging studies in depression patients also implicate many of the same brain areas, thereby providing convergence between animal models and clinical observations. Interestingly, similar to the stress-induced suppression of avoidance behavior and BLA activity seen here, blunted amygdalar activity was associated with depression severity in treatment-resistant depression [ 108 ]. In another clinical study, while depressed children exhibited a blunted response in the amygdala to fearful faces, children with anxiety disorders showed an exaggerated amygdala response to fearful faces compared with healthy children [ 109 ]. In this context, it is worth noting that the chronic stress paradigm used here also enhanced anxiety-like behavior in earlier studies [ 30 , 110 ] (Supplementary Figs. 1B–F ). This suggests that assessing the impact of the same stressor with a diverse range of behavioral readouts, such as those involving learned versus innate behaviors, can help capture a wider constellation of amygdala-dependent changes that, in turn, can be mapped to distinct stress disorder symptoms in humans. Together such analyses may offer a more comprehensive understanding of how severe stress leads to symptoms of affective disorders and possible therapeutic interventions to reverse them.

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Acknowledgements

We thank Prof. Gregory J. Quirk, Dr. Mohammed Mostafizur Rahman and Dr. Rajnish P. Rao for helpful advice and discussions. We also thank Dr. Rajnish P. Rao for generously sharing the recordings of 50-kHz USV calls with us. The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication. This work was supported by intramural funds from the Tata Institute of Fundamental Research, Department of Atomic Energy, Government of India. The authors declare no financial interests or potential conflicts of interests.

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AS and SC designed the study. AS conducted the experiments and analyzed data. AS and SC interpreted the results and wrote the paper.

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Shukla, A., Chattarji, S. Stressed rats fail to exhibit avoidance reactions to innately aversive social calls. Neuropsychopharmacol. 47 , 1145–1155 (2022). https://doi.org/10.1038/s41386-021-01230-z

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Received : 01 August 2021

Revised : 01 October 2021

Accepted : 30 October 2021

Published : 30 November 2021

Issue Date : May 2022

DOI : https://doi.org/10.1038/s41386-021-01230-z

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The paradoxical effects of chronic stress on avoidance: a role for amygdala-dorsomedial prefrontal cortex dialogue.

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Neuropsychopharmacology (2022)

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Incredible Experiment Reveals How Rats Use Their Imagination

Rats use their imaginations in a similar way to humans, a new study shows – meaning their thoughts aren't always fixed on what's immediately in front of them, but can also travel in space and time.

It's something that we do naturally, transporting ourselves to other places, recalling past events, or visualizing future scenarios in our minds. This seem to mostly take place in a part of the brain called the hippocampus , and researchers have now shown similar activity in the hippocampus of rats, too.

A team from the Howard Hughes Medical Institute (HHMI) used virtual reality (VR) combined with a brain-machine interface to determine if the rodents could think about traveling to a certain location to pick up a reward of water, even if they weren't actually moving there.

"To imagine is one of the remarkable things that humans can do," says neurologist Albert Lee from HHMI. "Now we have found that animals can do it too, and we found a way to study it."

Here's how the experiments worked: the researchers fitted a custom brain-machine interface to the rats, which mapped their movements through a virtual reality environment via 'imagined' activity in their hippocampus. The rats were placed on top of a spherical treadmill, so they could navigate in VR without actually moving from the same spot.

As the rats 'moved' around, their brain activity was monitored and translated into a personalized "thought dictionary" that linked places in virtual reality with hippocampus activity . This meant that the researchers could link certain patterns of activity to certain places in the virtual space – giving them a window into what was on the minds of the rats.

The setup was then tweaked so that physical movement on the treadmill didn't influence the VR world. It forced the rats to intentionally and voluntarily imagine moving to certain places or moving objects to certain places to get their water – and the brain scans suggested this is indeed what they were doing.

"The rat can indeed activate the representation of places in the environment without going there," says neuroscientist Chongxi Lai, from HHMI.

"Even if his physical body is fixed, his spatial thoughts can go to a very remote location."

The inference is that if the rats can imagine being in a different place, they might also imagine something in the future or remember something from the past – though it's still difficult to be certain about what's going on in the minds of animals . This VR system could enable future research in this area.

Also of note is the fact that the animals didn't need much training to imagine moving through VR, and that they could keep up their mental activity for around 10 seconds, a significant length of time.

"The stunning thing is how rats learn to think about that place, and no other place, for a very long period of time, based on our, perhaps naïve, notion of the attention span of a rat," says biochemist Timothy Harris, from HHMI.

The research has been published in Science .

The threshold for intracranial self-stimulation does not increase in rats exposed to chronic unpredictable stress, a systematic review and meta-analysis

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The chronic unpredictable stress model is a laboratory rodent model of stress-induced anhedonia. The sucrose preference test, often used to validate it, suffers from being unreliable. Intracranial self-stimulation offers an alternative and is often cited as supporting evidence of the validity of the model. Our aim was to assess whether an increased self-stimulation threshold is found after stress and if such a change correlates with decreases in sweet consumption. We searched PubMed, Embase, and Web of Science for studies in rats exposed to chronic unpredictable stress that employed intracranial self-stimulation. Thresholds, for stressed and control animals, in 23 experiments (11 studies) were pooled. Over 50% of the data was contributed by one research group, so a three-level meta-analytical random effects model was fit to account for methodological differences between different networks of researchers. After this adjustment, we did not find that the self-stimulation thresholds were increased in stressed rats. Pioneering experiments with positive results failed to be replicated by others, although no specific factor could be pointed to as a likely explanation. What is more, the available evidence suggests a lack of connection between sweet preference and self-stimulation, although this relationship has been seldom investigated. Methods known to mitigate biases were frequently absent, as was a transparent report of crucial study details. Our findings challenge the claim made in support of the validity of the model. Further efforts would be well-invested in assessing how reliably other tests of anhedonia have found the effects of the chronic unpredictable stress model.

Competing Interest Statement

The authors have declared no competing interest.

we made some changes to the introduction and discussion sections of the paper in order to further explain the purpose and aims of the study and the implications of the results.

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Can Cats and Rats Be Friends? Our Vet Answers & Explains

Image Credit: Etienne Outram, Shutterstock

Last Updated on February 27, 2024 by Catster Editorial Team

VET APPROVED

Dr. Luqman Javed

DVM (Veterinarian)

The information is current and up-to-date in accordance with the latest veterinarian research.

Rats don’t get much love from pop culture or social media. But that’s not fair because these rodents can be loving, caring, and gentle pets. Cats, in contrast, are everyone’s favorites. More importantly, they are a threat to rats; cats kill, eat, or just hunt the little guys for fun.

So, does that mean these two can never be friends?

In most instances, allowing pet cats and rats to interact with each other isn’t advised. In some unique circumstances, exceptions do exist; with early socialization, it’s sometimes possible (but not guaranteed) to turn things around. You will need to put a lot of effort into supervision, of course, and it may not always work as rats intrinsically fear cats. But ultimately, this is a risk at best, and therefore, not something that’s advised. Can rats and cats coexist? Let’s find out!

Why Do Cats Hunt Rats in the First Place?

In the wilderness, cats are obligate carnivores and need to have meat as their primary food source. So, it’s only natural for them to hunt small rodents as they are the main source of food for felines in the wild. Without a steady supply of meat protein, cats won’t be able to grow, reproduce, and repair body tissues.

Rodents aren’t the only thing on the menu; cats also hunt birds, other small mammals, lizards, and smaller snakes too. Now, cats hunt for two reasons: to get food or to hone their hunting skills. This applies to both wild and domestic kitties. That’s why any small animal that’s rendered by a cat as prey won’t be safe living under the same roof as the cat.

Are They Good at Killing Rats?

The short answer is no, cats aren’t that great at chasing or catching these rodents down. However, cats are useful deterrents for rats. Humans have been using felines as the ultimate remedy against rodents for thousands of years. However, recent research 1 highlights that cats rarely attempted to catch large (>300 grams) rats when they had alternatives (in the form of smaller prey). Another study found similar results, where cats preferred smaller rats to go after 2 .

Nonetheless, cats were observed stalking rats, and the presence of cats led to the rats moving to different locations. This apparent movement of rats is what humans might perceive as a cat being an effective rat controller.

The fact that the rats chose to occupy areas with fewer cats is fascinating because, in experiments involving rats 3 , they appeared more defensive even if they could just smell (but not see) predators such as cats. This has implications for pets, as your pet rat may be able to smell your cat even if they’re physically separated from each other.

Felines and Rodents as Friends: Is It Possible?

Well, the prevailing opinion is that this shouldn’t be encouraged. Exceptions exist and at times, you might notice the two species interacting on social media. This largely depends on their personalities and the way they were brought up. If you adopt both pets as kits and provide plenty of supervision, this could happen. However, it’s important to keep in mind that social media is a glimpse into someone else’s life, and what you see might not be a full-time occurrence.

What’s important is that cats don’t necessarily have a need for friendship with other species. Cats are solitary, and though feral cats may form colonies (known as clowders or glarings), they still hunt individually. As pets, multiple cats can generally get along if each cat feels like their needs are sufficiently met.

Furthermore, when pet cats are playing, they’re in fact hunting. Therefore, it’s not beyond the realm of possibility that your pet cat would injure your rat during a session of play, even if they don’t necessarily think they’re going to eat a large pet.

Therefore, though this is possible, it’s certainly not something that we advise or encourage.

The Cat’s Background: Does It Matter?

Not really. Genetics can play a role in your cat’s behavior and disposition to some extent 4 . Therefore, some of your cat’s behavior idiosyncrasies might be breed-related. However, all cats can hunt, and can definitely play rough enough to injure a pet rat. Furthermore, as previously mentioned, even the smell of a cat can cause behavioral changes in rats.

Rats Can Fight Back and Harm Cats

This might come as a surprise, but felines often take huge risks when attacking prey. Prey can fight back, causing serious injuries to the feline. Rats do carry a powerful bite, and will bite if startled or captured. And if they carry an infection, they can pass it on to your cat.

In fact, this is a strategy some parasites that infect cats use 5 – when these parasites are present in rodents, they cause them to lose their fear of cats, increasing the likelihood of a cat capturing the rodent and ingesting the parasite. Therefore, a rat that seemingly is “comfortable” around a cat might not be friendly and tolerate the cat involuntarily.

Do Rats Attack Cats? What About Kittens?

Here’s another fact that you might not know: rats can kill cats and even dogs even without passing a parasite to them! This only applies to kittens and puppies, of course, and rats usually attack the smallest breeds. Therefore, if your cat recently gave birth to a bunch of adorable kittens and you have a big, mighty pet rat, they could attack those babies. That happens rarely, but you still need to be careful.

So, Can These Pets Co-exist Peacefully?

In all fairness, it would be best to not consider housing these pets together, even in separate rooms. Ideally, these pets should never coexist, as that may end badly for the rodent . Though it would hypothetically be possible to physically separate the two animals in a house, your rat would only have to smell your cat to develop adverse behaviors and physiological changes. This includes smelling your cat after you’ve petted your cat and moved into the same room as your rat – your cat’s scent would be on your body and clothes.

A friendship between a cat and a rat is not a common thing. Cats are natural-born hunters and may inadvertently injure or hurt a rat. The rat would also be stressed by the cat’s presence and therefore, it isn’t considered wise or ethical to house them together, even if they are physically separated. Instead, you should get pets that are safer to keep together with your pet cat or rat.

Behavioral changes induced by Toxoplasma infection of rodents are highly specific to aversion of cat odors
Breed differences of heritable behaviour traits in cats
Predator odor induced defensive behavior in wild and laboratory rats: A comparative study .
Temporal and Space-Use Changes by Rats in Response to Predation by Feral Cats in an Urban Ecosystem
Trophic Garnishes: Cat–Rat Interactions in an Urban Environment – PMC

Featured Image Credit: Etienne Outram, Shutterstock

About the Author

Dr. Luqman Javed DVM (Veterinarian)

Dr. Luqman (also known as Dr. Lucky) grew up with an immense passion for animals of all kinds. By becoming a veterinarian , he turned his childhood dream into reality. Now, his goals are focused on providing help to cats all around the world by helping to cat owners understand their feline friends better to ensure the best quality of life for them. His passions are wildlife, exotic pets, pet owner education, and animal welfare. He graduated with his DVM from the Universiti Putra Malaysia in 2020. He has worked with a variety of animal species and has decades of personal experience with keeping many different types of exotic pets , such as turtles, hamsters, freshwater fish, chickens, songbirds, and parrots (and he has extensive skills in training parrots, too).

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Feline Fine: How Acupuncture Works, Part Three

Don’t Be Afraid to Experiment—and Even Fail—to Make DEI Advances

During my years working at technology companies, it’s been clear to me that reframing failure in a productive way reflects a shared commitment to experimentation. This mindset applies to diversity, equity, and inclusion strategies as much as to other business initiatives.

From reserving offsite time for strategy and development to regular postmortems and actionable steps, each of the companies I’ve worked for highly protected the space around experimentation. This empowered individuals to lean into ambitious new ideas, and our teams were willing to try to execute on them.

Start With Intentionality

Other touchstones have emerged over the course of years I spent addressing how organizations can incorporate DEI values.

First, you need intentionality. Organizations should start with a specific and shared goal. From there, you can develop a programmatic approach with data-driven results.

Defining a specific goal is a multifaceted task, involving a number of viewpoints and constituencies; and diversity and inclusion takes many forms. For example, talent processes, compensation practices, and other employee development practices often take center stage in developing sustainable growth of DEI initiatives.

When leaders align on a shared organizational goal, managers can bring intentionality into delegating work assignments, which, in turn, balances critical components of success for employees.

Employee resource groups can become a welcome place of belonging and support, and further elevate voices in the organization. A chief diversity officer also brings a voice to the table, building coalitions as an executive-level leader of DEI initiatives.

Core business goals within an organization often already align with DEI. These can include year-over-year metrics in a corporate social responsibility report, or an environmental, social, and governance report that communicates company impact on the environment and community.

Not One-Size-Fits-All

No universal goal or solution fits all. A shared journey began simply when I served as executive sponsor and initial advisory board member of my company’s diversity and inclusion council. We intentionally allocated regular time and space for open conversation. These dialogues created a sense of belonging, sparked ideation, and produced specific programming opportunities and longer-term initiatives for consideration.

We found that clear commitments from leadership and across the organization were crucial to understanding some challenges in establishing a talent pipeline and data collection. Over time, we were able to make adjustments in recruitment to neutralize bias.

For example, we learned through our data that we needed to expand our pool of candidates, particularly in certain areas of the company. As a result, we identified schools and school fairs focusing on majors aligned with job opportunities and incorporated these into our recruiting practices.

For some “expertise” roles, we also conducted skills evaluations on resumes and removed identifying features. This required alignment in defining those skills, and limited implicit bias based on other candidate characteristics apparent on a resume.

I worked for another organization where our ESG philosophy reflected the company’s core business tenets. The organization was able to develop programmatic opportunities, such as regular meetings with business leaders, to ensure that its business investments and strategy were appropriately articulated in overall ESG goals. We also developed internal key performance indicators to consistently measure and analyze metrics.

Then in a volunteer role as DEI co-chair of a diverse legal association, achieving intentionality became more nuanced and required more frequent, smaller steps. With a membership that included a large number of microcommunities, achieving intentional goals required a further awareness, appreciation, and understanding of those communities, their experienced microaggressions, and backgrounds in intersectionality. Our work was action-oriented and focused on creating panels, educational material, and programs to build dialogue in the legal industry.

Support Innovation

Companies should consistently support innovation that aligns with company values and create a space that destigmatizes failure and encourages experimentation. When I was member of an informal ERG at a former company, we shared our own success stories about retaining talented individuals and found areas of opportunity. This dialogue resulted in data gathering and a public commitment to collaborative talent staffing, which opened more pathways to retain talent and provide managers with opportunities to cross-train.

Our CEO underscored these values regularly in company town halls, signaling that a key to our success was our commitment to innovation, which featured inclusion of diverse views and valuable talent.

In a different organization, the team—in concert with executive coaches and national legal leaders—developed a leadership series that focused on management agility and included a specific module incorporating best practices in managerial feedback and inclusivity. Our objective was to share effective managerial techniques and create support opportunities and spaces for legal teams.

Regardless where an organization’s journey begins, the investment in defining a space and redefining goals creates greater alignment. And bringing people of differing views together to find common ground toward a shared goal is, quintessentially, creating a culture of growth.

This article does not necessarily reflect the opinion of Bloomberg Industry Group, Inc., the publisher of Bloomberg Law and Bloomberg Tax, or its owners.

Author Information

Amy Yeung has served in senior and executive legal leadership, counseling fast-growth private and Fortune 1000 public companies. Yeung has also served in leadership capacities in legal operations, DEI, and innovative leadership, including in her current positions as past chair of the Law Department Management Network of the Association of Corporate Counsel and a fellow of the College of Law Practice Management.

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To contact the editors responsible for this story: Jessie Kokrda Kamens at [email protected] ; Alison Lake at [email protected]

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Behavioral Expression of Contextual Fear in Male and Female Rats

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The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The study of fear conditioning has led to a better understanding of fear and anxiety-based disorders such as post-traumatic stress disorder (PTSD). Despite the fact many of these disorders are more common in women than in men, the vast majority of work investigating fear conditioning in rodents has been conducted in males. The goal of the work presented here was to better understand how biological sex affects contextual fear conditioning and expression. To this end, rats of both sexes were trained to fear a specific context and fear responses were measured upon re-exposure to the conditioning context. In the first experiment, male and female rats were given context fear conditioning and tested the next day during which freezing behavior was measured. In the second experiment, rats were trained and tested in a similar fashion while fear-potentiated startle and defecation were measured. We found that males showed more freezing behavior than females during a fear expression test. The expression of fear-potentiated startle did not differ between sexes, while males exhibited more defecation during a test in a novel context. These data suggest that the expression of defensive behavior differs between sexes and highlight the importance of using multiple measures of fear when comparing between sexes.

Introduction

The prevalence of some fear and anxiety-based psychopathologies differs between sexes, including post-traumatic stress disorder (PTSD), which is about twice as common in women as it is in men (Breslau et al., 1998 ; Kilpatrick et al., 2013 ). The traumatic event that initiates the dysregulated fear response characteristic of PTSD is readily identifiable and is akin to a Pavlovian fear conditioning procedure with cues present at the time of trauma becoming associated with the traumatic experience (Parsons and Ressler, 2013 ). One hallmark of PTSD is that fear responses are not restricted to the cues present at the time of trauma, but instead generalize to stimuli not originally associated with trauma (Jovanovic et al., 2012 ; Kaczkurkin et al., 2017 ). Much of the ability to restrict fear responses to the appropriate stimuli has to do with the successful recognition of contextual cues (Maren et al., 2013 ). Thus, studying contextual fear conditioning in rodents might offer some insight into this key aspect of PTSD.

Contextual fear conditioning describes when an organism learns to associate an aversive stimulus with the context in which it was delivered. Contextual fear conditioning has been studied in the laboratory for several decades leading to many advances in both the understanding of fear behavior and its underlying neural systems. A handful of studies have compared contextual fear conditioning between sexes, and the results of these are equivocal. Some studies have found that male rats show higher levels of contextual fear when compared to female rats (Maren et al., 1994 ; Wiltgen et al., 2001 ; Chang et al., 2009 ; Barker and Galea, 2010 ), others have shown no differences (Kosten et al., 2006 ; Dachtler et al., 2011 ; Keiser et al., 2017 ), and some have reported that females showed more contextual fear than males (Fenton et al., 2016 ). These discrepancies likely reflect the influence of multiple factors including parametric differences among studies (e.g., Wiltgen et al., 2001 ). Another factor complicating the comparison of males and females is that there is evidence that the behavioral expression of fear differs between sexes (Dalla et al., 2008 ; Gruene et al., 2015 ). If the behavioral expression of fear differs between males and females, then in some cases differences between sexes in fear conditioning might be attributable to differences in behavioral performance, and not necessarily learning.

The approach adopted here was chosen with the hope that it might offer some clarity with respect to sex differences in contextual fear learning. Prior work (Archer, 1975 ; Blanchard et al., 1991 ; Dalla et al., 2008 ; Gruene et al., 2015 ) indicates that defensive behaviors between sexes in rodents differ in important ways, but less is known about how contextual fear conditioning and expression differ between male and female rodents. Our hypothesis was that if contextual fear conditioning differed between males and females then this difference should be observed on all measures of fear. If instead, differences in freezing behavior were influenced by performance variables, then differences between males and females might be specific to certain measures of fear. To test our hypothesis, male and female rats were exposed to two contextual fear conditioning procedures with identical training and testing parameters. Fear was assessed by measuring freezing behavior, fear-potentiated startle, and conditioned defecation. Fear-potentiated startle and freezing behaviors are two commonly measured defensive behaviors activated by learned fear, and both are thought to be part of the post-encounter defensive mode (Fanselow, 1994 ). Variability in the expression of these, and other behaviors in rodents is relevant to the variability in response to trauma in humans (Cohen et al., 2003 , 2004 ; Yehuda and LeDoux, 2007 ). This is especially true for acoustic startle, which is known to be exaggerated in PTSD (Morgan et al., 1995 ; Grillon and Baas, 2003 ; Pole et al., 2009 ). By keeping parameters consistent while assessing multiple measures of fear, we hoped to be able to determine whether males and females show different levels of contextual fear learning that would be observed across all measures, or whether any potential differences were specific to certain fear responses. Our findings indicate that differences in contextual fear were observed when measuring freezing behavior, with males showing higher freezing levels during testing in the conditioning context. However, levels of both fear-potentiated startle and defecation did not differ between sexes when rats were tested in the conditioning context. Our data indicate that sex differences in contextual fear are not observed broadly across all measures, suggesting that the behavioral expression of contextual fear, but not learning per se , differs between male and female rats.

Thirty-three, adult, male Sprague–Dawley rats (300–325 g upon arrival) and 35, adult, female Sprague–Dawley rats (200–225 g upon arrival), obtained from Charles River Laboratories (Raleigh, NC, USA) served as subjects (approximately 8–10 weeks of age). The rats were housed in pairs in plastic boxes, with food and water freely available, on a 12 h light/dark cycle (lights on at 7 am). All experiments took place during the light portion of the light/dark cycle. All procedures were approved by the Stony Brook University Institutional Animal Care and Use Committee and were in accordance with the National Institutes of Health guidelines for the care and use of laboratory animals.

Behavioral Apparatus

Experiment 1: freezing.

The apparatus for all experiments has been described in detail elsewhere (Russo and Parsons, 2017 ). Experiment 1 took place in conditioning chambers (Clever Systems Inc., Reston, VA, USA) located within sound-attenuating isolation boxes. The conditioning chambers contained shock grid floors and stainless steel and Plexiglas walls, 28-V, incandescent, house light bulbs, and were wiped down with 5% acetic acid. Overhead cameras recorded behavioral sessions and the video signal from each chamber fed into a software program (FreezeScan 2.00) which automatically scored freezing behavior based on pixel change. Parameters for scoring were chosen such that the computer-scored freezing behavior closely matched hand-scored behavior by a trained observer, and the motion parameters were set as follows (noise filtering radius = 1, interframe motion < 100 pixels, Freeze N = 24, Freeze M = 22, Move N = 10, Move M = 8).

Experiments 2 and 3: Fear-Potentiated Startle and No-Shock Controls

Experiments 2 and 3 took place in sound-attenuating cabinets (Startle Monitor II, Kinder Scientific, Poway, CA, USA). Fear conditioning and a context fear test took place in Context A, where rats were placed in cages made of Plexiglass and a stainless-steel shock-grid floor, the house lights in the cabinets were turned on, the ceiling lights in the lab were turned off, and the cages were wiped down with 5% ammonium hydroxide. Baseline startle response and a second context fear test took place in Context B, where rats were placed in restrainers made with a stainless-steel rod cover and a plastic floor, the house lights in the cabinets were turned off, the ceiling lights in the lab were turned on, and the cages were wiped down with 70% EtOH.

Both the shock cages and the restrainers sat on top of load cell sensing platforms inside the cabinets. Startle amplitude was reported in Newton (N) through a single-pulse calibrator interfaced to a PC. Startle amplitude was defined as the peak N that occurred during the 500 ms following the onset of a white noise burst. Startle responses were elicited by 50 ms, 95 dB, white noise bursts which were delivered through speakers mounted on the ceilings of the cabinets. Shocks were delivered through a grid floor.

Behavioral Procedures

Rats were handled for 5 min per day for 7 days before behavioral procedures began. The first 4 days of handing occurred in the colony room. For the final 3 days, rats were carted into the laboratory and handled. On the first day of the experiment, rats ( n = 14 of each sex) were placed into the conditioning chambers where they were exposed to three, 1 mA, 1 s foot shocks (20 s ITI) following a 4 min baseline period. Rats were returned to their home cages 2 min following the last shock. The following day, all rats were placed back into the conditioning chamber for a 10 min context test. Approximately half of the male rats ( n = 8) and half of the female rats ( n = 8) were run by a female experimenter, while the remaining male rats ( n = 6) and female rats ( n = 6) were run by a male experimenter.

Experiment 2: Fear-Potentiated Startle

The same handling procedure was used as described above. On the first 2 days of the experiment, baseline startle was measured by placing rats ( n = 14 females, n = 11 males) into startle chambers (Context B) and exposing them to 30, 95 dB, 50 ms, white noise bursts (30 s ITI) following a 5 min baseline period. The following day, rats were placed into Context A and were exposed to three, 1 mA, 1 s foot shocks (20 s ITI) following a 4 min baseline period. Rats were returned to their home cages 2 min following the last shock. Three male rats were excluded from the analysis due to a technical malfunction on the conditioning day. The next day, rats were tested for fear-potentiated startle in Context A for 10 min. During this session, rats were exposed to 20, 95 dB, 50 ms, white noise bursts (30 s ITI) following a 30 s stimulus-free period. On the last day of the experiment, rats were tested for fear-potentiated startle in Context B with stimuli identical to those presented during the Context A test. The number of fecal boli produced by each rat was recorded after each testing session. Approximately half of the male rats ( n = 5) were run by a male experimenter, while the remaining male rats ( n = 6) and all of the female rats ( n = 14) were run by a female experimenter.

Experiment 3: No-Shock Controls

The same handling procedure was used as described above. Baseline startle was measured by placing rats ( n = 8 males, n = 7 females) into startle chambers on consecutive days (Context B) and exposing them to 30, 95 dB, 50 ms, white noise bursts (30 s ITI) following a 5 min baseline period. The following day, rats were placed into Context A for 7 min, however, no shock was delivered. As in Experiment 2, the next day rats were tested in Context A for 10 min, and 24 h later were given a test in context B. One female rat was excluded from the analysis due to a technical malfunction on the conditioning day. Acoustic startle and defecation were measured during both of the test sessions, as described in Experiment 2. All of the male rats were run by a male experimenter, while all of the female rats were fun by a female experimenter.

Data Analysis

Average time spent freezing during the baseline period and the post-shock period of the fear conditioning session was averaged for each animal. Likewise, the average time spent freezing during the 10 min context test was computed for all rats. Shock reactivity and post shock activity bursts were analyzed by computing motion (defined by the number of pixel changes/frame) during the 5 s before shock, the 1 s during shock, and the 5 s after shock. Independent samples t -tests (one-tailed) were used to compare freezing between groups.

Experiment 2 and 3: Fear-Potentiated Startle and No-Shock Controls

Baseline startle values were calculated by taking the average of startle responses across the 2 days of baseline startle testing. Context fear-potentiated startle was calculated by first subtracting the average baseline startle response from the startle response during the test sessions to produce a difference score, and then dividing the difference score by the baseline startle mean and multiplying by 100 to produce a fear-potentiated startle percentage. Independent samples t -tests (one-tailed) were used to compare between groups, and repeated measures ANOVAs were used for within-and between-subject comparisons. Mann–Whitney U tests were used to compare males and females in fecal boli counts. Results were considered significant when p < 0.05 for all statistical tests. For each t -test reported, Cohen’s d is also reported, with 0.2, 0.5, and 0.8 being considered small, medium, and large effect sizes, respectively.

All rats were given a fear conditioning session followed 24 h later by a test session in the training context ( Figure 1A ). We first compared freezing levels across groups during the fear conditioning session by averaging freezing levels during the baseline and post-shock periods for all rats ( Figure 1B ). A t -test revealed that baseline freezing did not differ between groups ( t (26) = 1.02, p > 0.05, d = 0.38). A similar analysis on the data from the post-shock period revealed a significant effect of group ( t (26) = −1.76, p < 0.05, d = 0.67), with female rats showing higher freezing levels overall.

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Male ( N = 14) and female ( N = 14) were given contextual fear conditioning and freezing behavior was assessed during a 10 min test session the next day (panel A depicts the timeline of the experiment). (B) Freezing behavior during the baseline and post-shock periods during the fear conditioning session. The inset graph shows average baseline freezing and minute-by-minute freezing during the last 3 min of the conditioning session. (C) Shock reactivity and post shock activity burst as measured by the average number of pixel changes per frame for male and female rats during the 5 s before the shock (left panel), during the 1 s duration of the shock (middle panel), and during the 5 s after the shock (right panel). Freezing behavior during the context test session in male and female rats (D) . For all graphs, symbols reflect individual subject values and error bars reflect the standard error of the mean. * p < 0.05.

Shock reactivity was analyzed for male and female rats ( Figure 1C ). Motion levels were similar for males and females during the 5 s prior to the shock ( t (26) = −1.18, p > 0.05, d = 0.45), but males showed significantly more motion during the 1 s shock ( t (26) = −3.85, p < 0.001, d = 1.46) and during the 5 s after the shock ( t (26) = −2.37, p < 0.05, d = 0.90).

For the testing data ( Figure 1D ), freezing levels were averaged across the 10 min session. A t -test on these data showed a significant difference between groups ( t (26) = 1.91, p < 0.05, d = 0.72), with males showing higher freezing levels during the test session. Because males showed higher reactivity to shock during conditioning and higher levels of freezing during the context test, we examined whether or there was a relationship between the two measures. We computed correlation coefficients using Pearson’s r in both males and females. There was no significant correlation between shock reactivity and freezing during the context test in either males ( r = −0.20, p > 0.05) or females ( r = −0.20, p > 0.05), suggesting that differences in shock reactivity were not driving the differences in freezing behavior during the test session.

Next, we analyzed the data from rats given contextual fear conditioning and which were subsequently tested in the conditioning context and in a context in which shock was not delivered ( Figure 2A ). Fear-potentiated startle was assessed on both test days. We first analyzed baseline startle responses ( Figure 2B ) using a repeated measures ANOVA with session as a within-subjects factor and sex as a between-subjects factor. Results from this analysis showed that there was no effect of the session ( F (1,23) = 1.00, p > 0.05), indicating that startle responses did not change across the 2 days of testing. There was a significant effect of sex ( F (1,23) = 5.30, p < 0.05) with males having higher amplitude startle responses, and a significant session by sex interaction ( F (1,23) = 5.87, p < 0.05) owing to a further divergence in startle responses between sexes on day 2. Next, we analyzed testing data ( Figure 2C ) using a repeated measures ANOVA with context as a within-subjects factor and sex as a between-subjects factor. Results from this analysis revealed a significant effect of context ( F (1,23) = 9.68, p < 0.01) driven by a greater fear-potentiated startle in the context in which the animals were shocked. There was no context by sex interaction ( F (1,23) = 0.13, p > 0.05) and no main effect of sex ( F (1,23) = 0.18, p > 0.05). We also used t -tests to individually compare males and females for both test sessions. Results from these tests showed no differences between sexes for the test session in Context A ( t (23) = 0.434, p > 0.05, d = 0.18) and Context B ( t (23) = 0.11, p > 0.05, d = 0.04). Finally, we compared the number of fecal boli ( Figure 2D ) collected during both test sessions using a repeated measures ANOVA. Results showed a significant effect of context with a higher number of fecal boli during the test in Context A ( F (1,23) = 23.46, p < 0.001). There was no interaction between sex and context ( F (1,23) = 0.002, p > 0.05), but there was a significant effect of sex ( F (1,23) = 6.89, p < 0.05). Mann–Whitney U tests were used to compare males and females in fecal boli production in both test sessions. There was no significant difference between males and females in the number of fecal boli during the test in Context A ( U = 53, p > 0.05, d = 0.59), however, males showed significantly more fecal boli than females during the test in Context B ( U = 35, p < 0.01, d = 1.27).

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Male ( n = 11) and female ( n = 14) rats were given baseline startle tests on consecutive days and the next day they were exposed to contextual fear conditioning. Rats were then exposed to the training context (Context A) and the next day re-exposed to the startle context (Context B) for 10 min during which fear-potentiated startle was assessed (panel A depicts the timeline of the experiment). (B) Average baseline startle amplitude in males and females during both days of startle testing. (C) Fear potentiated startle in the training context (Context A, right panel) and during a test in the startle chamber (Context B, left panel). (D) The number of fecal boli in males and females during the respective test sessions.

Finally, we analyzed the data from rats which were treated identically to those in Experiment 2 but were not administered shock on the conditioning day ( Figure 3A ). First, we used a repeated measures ANOVA to compare baseline startle responses ( Figure 3B ) across the 2 days of startle testing. There was no effect of session ( F (1,13) = 0.76, p > 0.05) and the session by sex interaction was also not significant ( F (1,13) = 0.13, p > 0.05). There was a significant main effect of sex ( F (1,13) = 4.72, p < 0.05) with male rats showing higher startle values overall, consistent with our observation in Experiment 2. For the test sessions ( Figure 3C ), a repeated measures ANOVA with context and sex as factors showed no effect of context ( F (1,13) = 0.35, p > 0.05), no sex by context interaction ( F (1,13) = 1.12, p > 0.05), and no effect of sex ( F (1,13) = 0.17, p > 0.05). We also used t -tests to individually compare males and females for both test sessions. Results from these tests showed no differences between sexes for the test session in Context A ( t (13) = 1.21, p > 0.05, d = 0.63) and Context B ( t (13) = −0.23, p > 0.05, d = 0.12). Finally, we analyzed the fecal boli data ( Figure 3D ) using a repeated measures ANOVA. We found no effect of context ( F (1,13) = 1.76, p > 0.05), no interaction ( F (1,13) = 1.76, p > 0.05), and no effect of sex ( F (1,13) = 1.76, p > 0.05). Because females produced 0 fecal boli in Context A, and both males and females produced 0 fecal boli in context B, Cohen’s d is not reported for these comparisons. Mann–Whitney U tests were used to compare males and females in fecal boli production in both test sessions. There were no significant differences between males and females in fecal boli in Context A ( U = 21, p > 0.05) or Context B ( U = 28, p > 0.05).

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Male ( n = 8) and female ( n = 7) rats were given baseline startle tests on consecutive days and the next day they were exposed to a fear conditioning chamber with no shock presented. Rats were then exposed to the training context (Context A) and the next day re-exposed to the startle context (Context B) for 10 min during which fear-potentiated startle was assessed (panel A depicts the timeline of the experiment). (B) Average baseline startle amplitude in males and females during both days of startle testing. (C) Fear potentiated startle in the training context (Context A, right panel) and during a test in the startle chamber (Context B, left panel). (D) The number of fecal boli in males and females during the respective test sessions.

In this set of experiments male and female rats were given contextual fear conditioning and we measured different fear responses when rats were re-exposed to the context in which shock was delivered. Our results show that males exhibited higher levels of freezing compared to females when they were returned to the conditioning chamber a day following contextual fear conditioning. This was the case even though freezing levels after shock administration during conditioning were higher in females. When fear-potentiated startle or defecation was measured, males and females did not differ in their levels of contextual fear. Prior work from our lab has also uncovered sex differences in cued fear extinction that were specific to certain measures of fear (Voulo and Parsons, 2017 , 2019 ). The results from those studies are complicated by the fact that the parameters used to induce cued fear differed in the experiments comparing freezing to fear-potentiated startle. Here, we were able to avoid this potential complication by keeping the training and testing parameters identical across experiments. The fact that sex differences in contextual fear are not consistently observed across all measures of fear suggests that the difference in contextual fear seen between males and females when freezing is measured may reflect an effect of behavioral performance, and not of differences in learning.

Although our results are consistent with a behavioral performance interpretation, several alternative explanations and factors that may be affecting our results should be discussed. First, it is possible that the relatively mild training parameters used in the current study resulted in a floor effect in the fear-potentiated startle experiment, obscuring a potential difference between sexes. Some prior studies (McNish et al., 1997 ) have trained rats with stronger conditioning parameters, and it would be worthwhile to compare males and females under such conditions. Another important consideration is whether or not our results were influenced by presenting the rats with loud startle stimuli, which can serve as an unconditioned stimulus capable of supporting contextual fear conditioning (Cranney, 1987 ). If so, it is possible that the startle stimulus served as UCS and that the increased startle we observed when rats were trained might reflect generalized fear from having received startle stimuli in Context B. However, we think this is unlikely given that prior studies have shown that low intensity (90–100 dB) startle stimuli are less able to support contextual fear (Cranney, 1987 ; Perusini et al., 2016 ) and that our data showed that levels of potentiated startle in un-shocked controls did not differ in Context A compared to Context B, suggesting that enhanced startle in A is not simply a result of having received startle trials in B. Finally, while we kept the key conditioning parameters consistent across experiments, it is possible that differences in the apparatus cues might have affected our results. Namely, the size of the chambers in which freezing or fear-potentiated startle was measured were different, and prior work (Rosen et al., 2008 ) has shown that levels of freezing behavior can be influenced by the size of the testing chambers.

Several prior studies have compared males and female rodents’ performance in contextual fear conditioning and collectively the results are ambivalent. Some studies have reported males showing stronger context fear conditioning (Maren et al., 1994 ; Wiltgen et al., 2001 ; Chang et al., 2009 ; Gresack et al., 2009 ; Barker and Galea, 2010 ; Mizuno et al., 2012 ; Colon et al., 2018 ; Colon and Poulos, 2020 ) whereas others showed equivalent levels of contextual fear in males and females (Kosten et al., 2006 ; Dachtler et al., 2011 ; Keiser et al., 2017 ), and some studies have even reported stronger context fear conditioning in females (Fenton et al., 2016 ; Blume et al., 2017 ; Zambetti et al., 2019 ). Nearly all of these prior studies have used freezing behavior to assess learning, meaning that the discrepant results are not simply because these studies used different measures of fear. It is likely that some combination of parametric inconsistencies and/or differences across studies in species or strain can account for the discordant findings, as these variables are known to influence whether sex differences in contextual fear are observed (Pryce et al., 1999 ; Wiltgen et al., 2001 ). Our results cannot be explained by parametric differences because the conditioning and testing parameters were identical across experiments.

For the prior studies that have reported higher levels of contextual fear in males than in females, the possibility that this difference reflects an effect of behavioral performance has typically been addressed by measuring cued fear in the same animals (e.g., Maren et al., 1994 ). The reasoning follows that if cued fear does not differ between sexes, but contextual fear does, then the deficit in contextual fear is likely one of learning and not of behavioral performance. However, it is possible that the differential outcomes seen in prior studies comparing males and females on cued and contextual fear reflect a “ceiling effect” in performance to the discrete cues and that this masks a potential parallel deficit in cued fear in female rodents. In fact, one prior study reported deficits in cued and contextual fear in some rat strains (Pryce et al., 1999 ). The extent to which these prior findings can be reconciled by whether the behavioral performance was at ceiling is unclear, however, one approach to address this issue would be to vary the intensity of the conditioning session and determine if cued fear deficits are observed in females when performance is sub-asymptotic. This basic approach was taken by Maren et al. ( 1994 ) and their results showed a sex difference in contextual fear when rats were trained with a single trial, but not with three trials. In the same rats, freezing levels to a discrete cue were not different regardless of the number of trials. This would seem to argue against a performance effect interpretation, however levels of freezing to the discrete cue in animals trained with a single trial were very low, raising the possibility of a floor effect. In addition to the ceiling effect issue, another important consideration is whether or not prior studies of cued fear, which by and large only measured freezing behavior, might have revealed a different pattern of findings had other measures of fear been taken. A prime example is the recent characterization of “darting” during cued fear, a behavior that is predominant in females (Gruene et al., 2015 ).

One limitation of the current study is that the estrous cycle phase was not accounted for in the female animals. Our decision to not assess the estrous phase was motivated by a desire to equate handling conditions between sexes and the fact that our prior work with fear-potentiated startle showed that the estrous phase did not affect the expression or extinction of cued fear (Voulo and Parsons, 2017 ). Some prior studies have reported differences in contextual fear across stages of the estrous cycle (Markus and Zecevic, 1997 ; Lynch et al., 2013 ), although this is an inconsistent finding as others have reported lower levels of contextual fear in females regardless of the estrous phase (Chang et al., 2009 ). Some other studies (Gresack et al., 2009 ; Fenton et al., 2016 ) have found sex differences in contextual fear that are not directly attributable to the estrous phase, and our results are perhaps most readily compared to these reports. While we cannot rule out the possibility that the estrous phase affected our findings, if this were the case, we would have expected greater variability in females than in males, which was not consistently observed in any of the experiments.

The primary goal for this study was to determine if sex differences were present in contextual fear when multiple measures of fear were taken. However, for the experiment in which we assessed fear-potentiated startle, rats were also tested in a context in which shock was not presented, making it akin to a test of contextual discrimination. A number of recent studies (Lynch et al., 2013 ; Keiser et al., 2017 ; Asok et al., 2019 ) have reported that female rodents show a deficit in contextual fear discrimination, where they exhibit higher levels of fear in a novel context compared to males. While our results indicate similar levels of discrimination between sexes, they are not necessarily inconsistent with prior work. First, in two of the prior studies (Lynch et al., 2013 ; Asok et al., 2019 ) the deficit in discrimination was only seen when the tests occurred several days or more after training. In our study, testing occurred on consecutive days 1 day after training. Second, one of the studies (Asok et al., 2019 ) showed a test order effect such that the deficit in discrimination in females was observed when they were first tested in the novel context, but not if they were tested first in the training context. All rats in our study were first tested in the training context, making it likely that the testing order favored discrimination. Another factor supporting discrimination in this experiment was the fact that other than background noise levels, the novel chamber did not share any features with the training chamber. Prior work (Keiser et al., 2017 ) indicates that rats of both sexes can readily discriminate dissimilar contexts, but that females lose the ability to discriminate when the novel context shares some features with the training context. Finally, the primary motivation behind including a test in a novel chamber in the fear-potentiated startle experiment was not to test for discrimination, but to rule out the possibility that the increase in startle when the rats were tested in the training chamber was simply sensitization of the startle reflex by prior shock exposure, a phenomenon known to occur under certain circumstances (Davis, 1989 ; Hitchcock et al., 1989 ; Gewirtz et al., 1998 ). The fact that startle amplitudes were lower in the novel context than in the conditioning context indicates that the conditioning session did not lead to a long-term sensitization of the startle reflex.

Although we found that males showed higher levels of freezing during the test session, females showed higher levels of freezing during the period after shock during the conditioning session. We examined this further first by assessing freezing levels in each of the 3 min following shock. This showed that the difference between sexes was driven largely by lower freezing in males during the first 2 min, with freezing levels becoming similar by the final minute. Next, we examined activity levels around the time of shock. This analysis revealed that males exhibited higher levels of activity both during the shock period and in the 5 s aftershock. This result is somewhat surprising given that several prior studies have not detected sex differences in shock reactivity (Wiltgen et al., 2001 ; Greiner et al., 2019 ; Hoffman et al., 2020 ) and one showing the opposite pattern as reported here (Gruene et al., 2015 ). Nonetheless, this suggests that the difference in freezing during the post-shock period can be explained, at least partially, by the fact that males react more to the shock and show a more pronounced post-shock activity burst. Importantly, levels of freezing during the context test did not appear to be driven by differences in shock reactivity as there was no significant correlation between the two measures.

The main finding we report here is that males show higher levels of contextual fear when freezing is measured, but not when fear-potentiated startle or defecation is used to assess fear. Importantly, these results cannot be explained by parametric differences as key parameters were equated across experiments. Our results suggest that deficits in contextual fear in female rats may reflect differences in behavioral performance, and not learning. This suggestion is supported by other studies indicating that the expression of defensive behavior in rodents differs in male and female rodents (Dalla et al., 2008 ; Gruene et al., 2015 ; Shansky, 2018 ). This factor needs to be carefully considered when comparing across sexes in studies of learned fear.

Data Availability Statement

Ethics statement.

The animal study was reviewed and approved by Stony Brook Institutional Animal Care and Use Committee.

Author Contributions

AR and RP designed the experiments, collected and analyzed the data, and wrote the manuscript. All authors contributed to the article and approved the submitted version.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We thank Meagan Voulo for assistance with the data collection.

Funding. This research was supported by startup funds from Stony Brook University, The Stony Brook Foundation, and grants R21 MH121772 (to RP) from the U.S. National Institutes of Health (National Institute of Mental Health).

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Little Albert experiment
Little Albert experiment. The Little Albert experiment was a study that mid-20th century psychologists interpret as evidence of classical conditioning in humans. The study is also claimed to be an example of stimulus generalization although reading the research report demonstrates that fear did not generalize by color or tactile qualities. [1]
Little Albert Experiment (Watson & Rayner)
The experiment was performed in 1920 and was a case study aimed at testing the principles of classical conditioning. Watson and Raynor presented Little Albert (a nine-month-old boy) with a white rat, and he showed no fear. Watson then presented the rat with a loud bang that startled Little Albert and made him cry.
The Little Albert Experiment
The Little Albert Experiment was a study conducted by John B. Watson and Rosalie Rayner in 1920, where they conditioned a 9-month-old infant named "Albert" to fear a white rat by pairing it with a loud noise. Albert later showed fear responses to the rat and other similar stimuli.
The Little Albert Experiment
The participant in the experiment was a child that Watson and Rayner called "Albert B." but is known popularly today as Little Albert. When Little Albert was 9 months old, Watson and Rayner exposed him to a series of stimuli including a white rat, a rabbit, a monkey, masks, and burning newspapers and observed the boy's reactions.
GoodTherapy
Albert was a 9-month-old baby who had not previously demonstrated any fear of rats. In the beginning of the experiment, when Albert was 11 months old, John Watson placed a rat (in addition to some ...
The Little Albert Experiment And The Chilling Story Behind It
YouTube Little Albert showed no fear toward the white rat at the beginning of the experiment. Watson and Rayner wanted to try to reproduce Pavlov's study in humans, and the Little Albert Experiment was born. The researchers presented a nine-month-old boy they called "Albert" with fluffy animals like a monkey, a rabbit, and a white rat ...
Using Rats to Trace Anatomy of Fear, Biology of Emotion
Like most animals, rats exhibit fear, an emotion that may help creatures escape from predators. In experiments over the last 15 years, Dr. LeDoux has traced fear inside the rat's brain -- from the ...
Cued and Contextual Fear Conditioning for Rodents
Fear conditioning to either a cue or a context represents a form of associative learning that has been well used in many species . The majority of the experiments reported in the literature involve the mouse; however, there is also a generous proportion of the literature devoted to the rat.
Ecological analysis of Pavlovian fear conditioning in rats
The absence of one-trial fear conditioning in a naturalistic setting may be analogous to "The Rat Park Experiment," where rats housed in an enriched environment with plants, trees, and social ...
Observational Fear Learning in Rats: Role of Trait Anxiety and
In this experiment, the rats were first submitted to a light-dark box test (Figure 1 a). Then, the rats were grouped with respect to their prospective roles (DEM, OBS, NAIVE; n = 16/group) in the upcoming observational fear learning experiment with the restriction that there must be two triads with DEM OBS and NAIVE rats per cage.
Fear or No Fear
The Experiment. Watson chose a nine-month old boy named Albert, and performed a series of tests to try and condition the Little Albert's fears: Little Albert was exposed to the following items: a white rabbit, a dog, a rat, a monkey, masks, cotton wool, and burning newspaper, among others. Little Albert was then placed on a mattress along ...
Rats sense their human handler's fear
Lab Animal - Rats sense their human handler's fear. ... In a final set of experiments, the investigators performed an observational fear learning procedure in humans, in which one participant in ...
Stress-Enhanced Fear Learning, a Robust Rodent Model of Post-Traumatic
This protocol describes the methodology required to conduct stress-enhanced fear learning (SEFL) experiments, a preclinical model of PTSD, in both rats and mice. ... For rat experiments, use the shock generator and scramblers to deliver 15 1-s, 1-mA footshocks randomly presented over 90 minutes (average ISI = 6 min) through the grid bars of the ...
Fearful Memories Passed Down to Mouse Descendants
Fearful Memories Passed Down to Mouse Descendants. Genetic imprint from traumatic experiences carries through at least two generations. By Ewen Callaway & Nature magazine. Mind & Brain. From ...
Observational Fear Learning in Rats: Role of Trait Anxiety and
In the first experiment, trait anxiety was assessed in a light-dark box test before the rats were submitted to the observational fear learning procedure. In the second experiment, ultrasonic vocalization was recorded throughout the whole observational fear learning procedure, and 22 kHz and 50 kHz calls were analyzed.
Pheromone-Induced Odor Associative Fear Learning in Rats
Conditioned fear can be transmitted to conspecifics in the absence of an aversive stimulus. In the first experiment, we tested whether the companion rats (O + /Comp) of the O + /S + conditioned ...
Curt Richter's rat hope experiment: Why did the first nine rats survive
The numbers you cite regarding the 3 versus 9 rats comes from his second run of the experiment where he tests whether trimming the whiskers in the rats would result in different times. The first rat swam around excitedly on the surface for a very short time, then dove to the bottom, where it began to swim around nosing its way along the glass wall.
Observational Fear Learning in Rats: Role of Trait Anxiety and ...
Rats can acquire fear by observing conspecifics that express fear in the presence of conditioned fear stimuli. This process is called observational fear learning and is based on the social transmission of the demonstrator rat's emotion and the induction of an empathy-like or anxiety state in the observer. The aim of the present study was to investigate the role of trait anxiety and ...
Baby Mice Can Inherit Fear of Certain Smells From Their Parents
In an experiment reminiscent of A Clockwork Orange, researchers trained male mice to fear a cherry blossom-like scent called acetophenone by inducing slight electric shocks every time the smell ...
A fear conditioned cue orchestrates a suite of behaviors in rats
We gave rats Pavlovian fear discrimination over a baseline of reward seeking. TTL-triggered cameras captured 5 behavior frames/s around cue presentation. Experiment 1 examined the emergence of danger-specific behaviors over fear acquisition. Experiment 2 examined the expression of danger-specific behaviors in fear extinction.
Stressed rats fail to exhibit avoidance reactions to innately aversive
Stressed rats exhibited significantly higher levels of freezing than their control counterparts during fear acquisition (Supplementary Fig. 11). 24 h later, when tested for recall of conditioned ...
Rats respond to aversive emotional arousal of human handlers ...
The human and rat findings presented here suggest a common brain circuit activating when humans and rats interact with humans subjected to fear conditioning. The results of human-rat and human-human studies are consistent with the previous reports showing similarities between the rodents' and humans' neural processing of the aversive ...
Incredible Experiment Reveals How Rats Use Their Imagination
Here's how the experiments worked: the researchers fitted a custom brain-machine interface to the rats, which mapped their movements through a virtual reality environment via 'imagined' activity in their hippocampus. The rats were placed on top of a spherical treadmill, so they could navigate in VR without actually moving from the same spot.
Long-lasting incubation of conditioned fear in rats
Exp. 1: Time course of fear incubation. We studied the time course of fear incubation in 4 groups of rats (n=10-15 per group). The rats were trained for fear conditioning over 10 sessions of tone-shock pairings, and then tested for conditioned fear 2, 15, 31, and 61 days (±1 day for days 30 and 60) after the last tone and shock exposure.
The threshold for intracranial self-stimulation does not ...
The chronic unpredictable stress model is a laboratory rodent model of stress-induced anhedonia. The sucrose preference test, often used to validate it, suffers from being unreliable. Intracranial self-stimulation offers an alternative and is often cited as supporting evidence of the validity of the model. Our aim was to assess whether an increased self-stimulation threshold is found after ...
Rats study tests whether photoluminescent fur is used in ...
In a world-first experiment, JCU researchers have been using the pelts of dead rats to test if the glow-in-the-dark fur of mammals is being used for secret nocturnal communication. The results are ...
Can Cats and Rats Be Friends? Our Vet Answers & Explains
Rats don't get much love from pop culture or social media. But that's not fair because these rodents can be loving, caring, and gentle pets. Cats, in contrast, are everyone's favorites.
Don't Be Afraid to Experiment—and Even Fail—to Make DEI Advances
Deputy GC Amy Yeung says DEI should spur creative solutions and that companies acting from intentionality don't fear missteps, and learn from them. ... Don't Be Afraid to Experiment—and Even Fail—to Make DEI Advances. Amy Yeung . Related Stories . Corporate DEI Isn't Dead. It's an Existential Moment for Change .
Behavioral Expression of Contextual Fear in Male and Female Rats
During this session, rats were exposed to 20, 95 dB, 50 ms, white noise bursts (30 s ITI) following a 30 s stimulus-free period. On the last day of the experiment, rats were tested for fear-potentiated startle in Context B with stimuli identical to those presented during the Context A test.
Researchers create realistic virtual rodent
To help probe the mystery of how brains control movement, scientists have created a virtual rat with an artificial brain that can move around just like a real rodent. The researchers found that ...

Little Albert Experiment (Watson & Rayner)

Little Albert Experiment

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Classical Conditioning

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The Little Albert Film

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The Little Albert Experiment

Who Was John B. Watson?

Who Was Little Albert?

What Happened to Little Albert?

The True Story of the Little Albert Experiment

Criticisms of the Little Albert Experiment

Other Controversial Studies in Psychology

The Robbers Cave Experiment

The Stanford Prison Experiment

The Milgram Experiment

The Monster Study

How Do Psychologists Conduct Ethical Experiments?

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Little Albert Experiment

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What Happened to Little Albert?

Classical Conditioning in Popular Culture

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Inside The Horrifying Little Albert Experiment That Terrified An Infant To The Point Of Tears

What Was The Little Albert Experiment?

The Controversy Surrounding The Little Albert Experiment

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Using Rats to Trace Anatomy of Fear, Biology of Emotion

Fear or No Fear – The Little Albert Experiment

Fearful Memories Passed Down to Mouse Descendants

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