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Mental Disorders in Animals
The above is an image of a captive African gray parrot that suffers from excessive feather-plucking, or pterotillomania. People who work with captive parrots or own parrots as pets have probably at least heard of this disorder, or even observed it firsthand. The parrot may have an excellent diet and be in good physical condition, yet it will continue to pluck and pluck at its own feathers, shaving itself bald in places.
If the cause is not a disorder of the body, then, can we say that this is a symptom of a disorder of the mind?
That brings up another question, though: how can we possibly know what is happening in an animal’s head? How can we separate an animal’s behavior into that of bodily needs and that of mental needs? People like to point out all the time that you can’t sit a dog on a couch and ask him what his childhood was like; we don’t even know if a dog’s memory of his childhood exists in any form that a human would recognize. While I think most people would agree that animals have minds, they function- by necessity and evolution- in ways ours do not.
I think this has to be the focal point of the following discussion: animal minds and human minds are different. Am I saying animal minds are inferior? Certainly not. But I’d like to point out that a lot of the research on mental disorders in animals focuses on finding parallels with human mental disorders. Yet the underlying reasons for disordered behavior in animals may be because they have mental needs that humans do not. For example, a popular theory behind why parrots develop pterotillomania is because they are not given ample opportunities to perform normative food-foraging behaviors.
So what forms of mental disorders are present in animals, and what are biologists, psychologists, veterinarians, and pet owners doing to better understand them?
Below the cut I’ll be discussing several things that people may find distressing/triggering: animal suffering, mental illness (including references or descriptions of the most commonly diagnosed human mental disorders), and animal research. It’s an upsetting topic, which is why I’m writing about it much more formally than I normally do, but I think it’s both interesting and important.
Note: This post is also extremely long.
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How do we define a mental disorder?
While the point of this post isn’t really to prove one way or another that animals can get mental disorders like humans do, it’s important that we define what exactly a mental disorder is before we discuss them.
That, of course, is a little easier said than done. Much less define ‘mental disorder’ for animals, we’re barely able to settle on a definition for humans. Here’s how the DSM-V does it:


A mental disorder is a syndrome characterized by clinically significant disturbance in an individual’s cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning. Mental disorders are usually associated with significant distress in social, occupational, or other important activities. An expectable or culturally approved response to a common stressor or loss, such as the death of a loved one, is not a mental disorder. Socially deviant behavior (e.g., political, religious or sexual) and conflicts that are primarily between the individual and society are not mental disorders unless the deviance or conflict results from a dysfunction in the individual, as described above. (American Psychiatric Association, 2013)


It sounds confusing at first glance, but I do like it better than the previous definition in the DSM-IV. As troubled as the DSM is (and oh, it is, no doubt about that) I roughly agree with what the authors were trying to articulate here. A mental disorder is something that is long-term, that causes the affected individual to suffer, and that persists internally. I say ‘persists’ because some disorders are long-lasting results of a severe environmental disturbance. Soldiers with PTSD come to mind; though their postwar environment is ‘safe,’ their minds remain in that heightened ‘threat mode.’
But while I like this definition, I know there are a lot of people who have differing opinions. Some want hard neurological evidence for every mental disorder, some would rather focus entirely on self-reporting and analytical psychology, and there are some people who insist mental disorders don’t exist at all.
Though my goal is to keep it fairly neutral through this article, I think it’s evident that I have a low opinion of the last group. I have two mental disorders and my diagnoses were a profound relief and a gift to me- I could now understand why my behavior at times seemed out of my control, and that there were people out there that had the disorder as well and that I share experiences with.
I’m not saying that these labels don’t have stigmas and problems, but the people that insist that they shouldn’t exist and that my disordered thinking is a product of- what, I don’t know, my own desire to have myself suffer?- well, I’m not inclined to like them. Also, it’s very hard to treat something if you have no label to unify the symptoms under.
Anyway, I’d like to apply the DSM definition of mental disorder to animals, but it is obviously difficult. We cannot ask them about their thoughts or pasts- we can only observe their behavior. And since they are indeed animals and not humans, it is hard to discern what behavior is normal and what is abnormal. Furthermore, how do we separate normal animal stress responses are normal (correlate to the human grieving example in the DSM definition) and which ones are persistant and reflect a mental illness? We don’t always have the opportunity to remove an animal from a poor environment in captivity, so it is hard to say whether or not their behavior would snap back to ‘normal.’
(I keep using normal, too, but that’s also a nebulous word, because how do we even determine what is normal and what isn’t?)
In the end there are no simple answers, but I do consider it important to be able to identify and label different behavioral disorders in animals, particularly those in captivity. Without that, it will be much harder to know how to help them.
Animal Models of Mental Disorders
I suspect a lot of people who would insist that animals cannot have mental disorders do not realize that a large portion of laboratory animal research is dedicated to mental illness. In order to see if a certain drug reduces or eliminates symptoms of depression, for example, you first have to have an animal that exhibits those symptoms.
When I was in college, my adviser actually worked on some of the rat models of schizophrenia. Most animal models aren’t perfect copies of the human disorder- rather, they express one or more major symptoms of the disorder to understand a) what in the brain or the environment causes that symptom to appear and b) how that symptom can be treated.
My adviser was specifically studying prepulse inhibition- the tendency to react less to a loud sound when a softer sound is given first as a ‘warning.’ Human with schizophrenia (and several other mental disorders) tend not to show this inhibition- they are just as startled by the second sound as the first one.

Above: A sample visualization of the amount of startle response (usually measured by muscle movements) given by the subject without a prepulse stimulus and then with one.
While it may seem like a bizarre symptom to focus on, disrupted prepulse inhibition is actually an important indicator of a well-functioning nervous system- that is to say, individuals that lack prepulse inhibition have difficulty filtering out unnecessary stimuli, which is why it’s a symptom not only of schizophrenia but in some anxiety disorders such as obsessive-compulsive disorder. It’s also important because drugs that successfully treat this symptom often also treat other symptoms of schizophrenia.
Researchers have replicated this symptom in rats and mice via a number of pathways, which I won’t get into here, but essentially they involve either breeding rats with certain genetic disorders, introducing chemicals to the rat’s brain, or social deprivation at an early age. Like most symptoms of mental illnesses, disrupted prepulse inhibition can have both genetic and environmental causes- and often a combination of the two.
Symptoms of schizophrenia aren’t the only ones researchers use animals as models for. Others include anxiety disorders, ADD and ADHD, depression, bipolar disorder, eating disorders, and addiction (drugs, alcohol, smoking, and even gambling).
The research on generating depressive symptoms in animals is some of the most uncomfortable of all. Most people who have taken a psychology course know that learned helplessness is a factor in depression. The definition of learned helplessness is exactly as it sounds: the animal will be put into an unpleasant situation with no way out several times, and will eventually give up trying to escape. It is argued that this is similar to humans who live in abusive situations, as well as people on the receiving end of inescapable prejudice.
The most famous of the learned helplessness paradigms in animal models is the inescapable shock test performed by Seligman and Maier on domestic dogs. During the study, dogs were split into two groups. One group could turn off the electric shocks using a lever while the other received all the shocks the first group did but had no control over them. Soon differences emerged in the behavior of the second group of dogs: they took longer to recover from the traumatic experience than the first group.
But that wasn’t all. After the first series of tests, Seligman put the dogs into a second apparatus: a small box with a low barrier dividing the two sections. The section of floor the dog was first placed on began to give them electric shocks, while the section beyond the barrier did not. The dogs from the first group quickly learned to jump over the barrier. The dogs from the second group did not. In fact, they didn’t do anything, not even if Seligman and Maier coaxed them with both rewards and punishment to move. Even the ability to observe other dogs escaping did not affect their behavior. The only thing that eventually caused them to learn to jump the barrier was the researchers physically picking them up and placing them on the other side.

Learned helplessness is commonly induced in animals being used to test antidepressants. In rodents, tests like the forced swim test (where the animal is repeatedly put into a pool of water they cannot escape from and eventually stop trying to swim) and tail suspension test (where the rodent is taped to a bar by its tail again and again until it stops struggling to escape) are still commonly used.

The nicest thing I can say about these tests is that they are acute; that is, it is possible to make the animal recover from them with the right encouragement, and the effects are generally not long-term. This is obviously different from the depressive symptoms seen in humans, and is the focus of a lot of criticism surrounding these animal models as ways to mirror human depression.
The difference between a rat and a lab and a human being with depression is that the human isn’t usually undergoing a few forced swim tests- they are going through either systematic trauma for a long period in their lives, are experiencing a physical environment that can degrade their mental state (i.e., lack of exercise, lack of vitamin D), have a genetic component that predisposes them to depressive behaviors, or (most commonly) a little of all.
Animals can undergo these types of sustained traumas as well, but to examine them, we have to look beyond the experiments.
The Effects of Chronic Stress and Trauma on Animals

Although she is in good physical health, Rachel appears in almost constant distress. She rocks her head continuously, whimpers for extended periods of time, and isolates herself. She focuses on a body part, screams, and behaves as if her hand or foot is a foreign object. She positions her hand behind a chair and reacts as if her hand does not belong to her, attacking it violently or biting it so severely it bleeds. At other times, she hits herself continually in the head, loudly screaming for up to 20 minutes in repeated episodes throughout the day. She calms only when exhausted or when she sees blood. (Bradshaw et al., 2008)

Rachel is a chimpanzee, and she now lives at a Canadian sanctuary called Fauna Foundation. Before that, she was used in biomedical research at the Laboratory for Experimental Medicine and Surgery in Primates (LEMSIP), the same place that the famous Nim Chimpsky was sold after he was no longer needed for language studies.

Rachel. (faunafoundation.org)
LEMSIP was opened in 1965 and closed in 1998. Rachel stayed there for fifteen years, starting from when she was three and a half. Before that, she was hand-reared by human parents (like the vast majority of ‘pet’ chimpanzees, her adoptive ‘parents’ changed their minds when she got too big for them to handle).
The conditions for chimps in research in the 80s and 90s were fairly horrible, especially for a chimp coming in from the relative freedom of living in a human household. The cages were extremely small (one of the reasons LEMSIP may have closed down was because it would have cost them too much to upgrade to USDA standard cage sizes). Rachel was housed singly as well, likely with little access to enrichment.
I focus on Rachel’s environmental conditions more than the actual testing she experienced because the testing itself would have been an acute trauma- like the forced-swimming tests- terrifying, but not constant. Most animals, including ourselves, are more or less adapted to deal with acute stressors. But the confinement and lack of stimulation were constant stressors.
From the description above, we can see that even after Rachel was placed in the sanctuary, with space, enrichment, and the opportunity for social interaction, she maintained her symptoms, which included psychotic episodes, stereotyped behavior, and self-injurious behavior (SIB).
Stereotyped Behaviors
Stereotyped behaviors, often called stereotypies, are simple and repetitive movements that do not appear to have a goal. The most familiar example would be that of a big cat or bear pacing back and forth in a small cage. Other behaviors like rocking, swaying, jumping, head-bobbing, etc. are frequently-seen stereotypies. Stable vices in horses are another example.
Here’s a video with examples of different animals performing stereotypies.

Zoo elephant showing stereotyped behavior.
In humans, stereotypies are most commonly seen in individuals diagnosed with autism or neurological disorders such as tardive dyskinesia. In autism it is also often referred to as ‘stimming’- that is, it is a way of providing comforting sensory input.
In animals it most commonly relates to spending long periods of time in deprived or enrichment-poor environments. The term is also used to describe normal animal behaviors that consist of repeated movements- such as chewing- but here I use it only to refer to the maladaptive behaviors caused by deprivation.
Some animal stereotypies can be reduced or eliminated by offering the animal appropriate enrichment. However, many do not stop despite the presence of enrichment, suggesting that the stereotypies can lead to permanent neurological alteration. (This brings up the important note that if you see an animal with a stereotypy, it may be due to past neglect and have nothing to do with the animal’s current housing situation.)
The type of stereotypy performed by an animal often relates to its species-typical behavior. For example, the stereotypy that most commonly affects wild felines and bears is pacing. In the wold, these animals maintain large territories and normally spend their days foraging long distances in search of food, which might explain why they are still driven to keep moving even in a small enclosure. We can imagine a stereotypy occurring as a result of frustration due to the inability to perform a normal behavior.
Some maladaptive behaviors such as over-grooming are sometimes a little too complex to be referred to as a stereotypy even though they can have similar causes. In the beginning of this article I discussed a possible cause for feather-plucking or pterotillomania: when unable to forage for food, a bird overcompensates in its grooming. Since the motions in pterotillomania are not mechanically repetitive but always lead to the same inappropriate goal (plucking itself bald), this is termed a compulsive behavior.

A salmon-crested cockatoo that has created a bald patch on its chest due to compulsive over-grooming.
Some animals go much farther with compulsive behaviors than just over-grooming themselves, however.
Self-Injurious Behavior
Self-injurious behavior (SIB) is just like it sounds: it is when an animal actively injures itself. This can occur when the animal grooms or picks at itself until it bleeds, hits itself or slams itself against walls, or when an animal bites itself. I have even heard a case in which an African elephant would repeatedly drive her tusks into her rear legs.

Jenny developed self-mutilating stereotypical behavior during the reconstruction of elephant exhibit, 1995, during which she was exposed to heavy equipment activity and locked inside for extended period of time. She would often use her tusk to strike her right rear leg. Wounds had developed into abscesses that required intensive treatment…
…She stands on three legs, and raises and holds one of the rear legs at the bend of her front ‘elbow.’ She has to sort of contort to do this. It is so bizarre you can’t miss it. This is another strenuous activity that means something is very wrong. It is also one we need to worry about, because it places her rear foot in perfect position for her to ‘peg’ at it with her tusks. If you see this, the supervisor needs to be called immediately. (Dallas Zoo, 2003)


Jenny, who still lives in the Dallas zoo today.
Hearing about self-injurious behavior in animals often startles people, because they assume- somewhat correctly- that such a maladaptive trait would never be allowable by evolution. In other words, it takes a brain like a human’s, not a bundle of instincts like an animal’s, to want to hurt yourself.
Obviously the above statement is problematic for a number of ways, but you see my point. But animal self-injurious behavior is well-known to both researchers and zookeepers. It’s hard to say that an animal’s intent is to cause itself pain when these behaviors occur- it’s hard to assume anything about what an animal’s ‘intent’ is- but the actions are frequently repeated and end when self-harm occurs.
Self-injurious behavior is also a common comorbid phenomenon in humans with chronic anxiety and other severe mental illnesses. Individuals who intentionally cut, burn, and otherwise harm themselves are often viewed with the stigma of “doing it for attention” by society at large, but in the scientific community it is understood that these behaviors have biological as well as emotional motivators.
Human self-injurious behavior can be both compulsive and impulsive; it can be highly ritualized with no necessary trigger, or it can be triggered by stress. Patients often describe a mounting sense of anxiety up until they self-harm, and then a sense of relief and release when they do.
It was research on nonhuman primates showing SIB that was used to begin to describe the physiological components behind the behaviors. A small proportion of rhesus macaques used in research display self-biting behaviors. Studies on these animals found that heart rate and cortisol levels would go down after the self-directed bites occurred, indicating that like the human self-harmers, the monkeys experienced a reduction in anxiety after hurting themselves.

The areas that the monkeys would bite are also telling- namely, they would target the same areas of their bodies that would release endogenous opioids. Endogenous opioids are a family of peptides that include endorphins and are naturally released in the body to help with pain and stress management. Some forms of cultural self-mutilation and techniques such as acupuncture actually take advantage of the areas of the body that trigger release of these chemicals when injured.
So there is mounting evidence that the reasons self-injurious behaviors persist are actually somewhat rooted in biology rather than some sort of pathological self-hatred. Nevertheless, SIB appears to occur in animals largely in a way to deal with extreme, chronic stress that may alter their brain development, possibly resulting in dysregulation of systems such as the HPA axis. The rhesus macaques that displayed SIB were ones that experienced traumatic early experiences (such as early social isolation) coupled with frequent acute stressors (such as more veterinary procedures). Sometimes housing these monkeys with others was enough to significantly reduce the incidence of SIB, but it often took treatment with antidepressants to have a real effect on stopping them.
Modern animal husbandry now includes enrichment along with other life-sustaining necessities such as food, water, and shelter. The best enrichment is dynamic and changing, includes social as well as environmental interaction, and plays into an animal’s naturally fulfilling behaviors. But animals like chimpanzees, elephants and parrots often live for over fifty years, and even rhesus macaques live about twenty years. These animals, still living today, often cannot overcome the trauma inflicted on them by their early experiences in captivity and maintain their adverse behaviors.
The long-lasting behavioral effects of these traumas in animals is now leading to a relatively new phenomenon of attempting to diagnose individual animals with psychological disorders.
Do PTSD and Depression manifest in Animals?
In 2010 a military service dog named Gina made the news. Gina, deployed to Iraq to help soldiers detect IED explosives, had come back home terrified of any loud sounds, new people, and new experiences. She became the poster child for a new phenomenon- “canine PTSD.”

Gina has since been rehabilitated and may return to active combat zones.
I say new, but Gina’s behavioral symptoms aren’t really new; they’re seen in dogs coming from all sorts of traumatic situations. In this video, for example, you can view some of the behaviors of a dog rescued from a hoarding situation before and after treatment.
It’s important to note that the idea of “canine PTSD” only caught on around 2009, and while it’s endorsed by many veternairians, there’s been little scientific research done on the topic. There is no official standard for diagnosing a dog with canine PTSD, though there are a few unofficial versions floating about.
Similarly, there are few ‘official’ mental illness standards directed towards diagnosing animals. There is no animal version of the DSM-V. However, in a 2011 study, several researchers attempted to explore the possibility that they could apply human diagnostic criteria for depression and PTSD to captive chimpanzees. They examined case studies from the scientific literature using a slightly modified version of the DSM’s criteria for PTSD and depression, which you can view here and here. Symptoms such as the patient describing recurring thoughts were necessarily deleted.

Negra met alternative criteria for depression and PTSD. According to reports, she had persistent depressed hunched posture, and she was socially withdrawn. Negra slept excessively during the daytime, and she lacked interest in play, food, other individuals, and grooming. She also demonstrated poor attention to tasks. She was described as slow and sluggish, and at times, she appeared anxious. In response to an unexpected touch, she would “threat bark,” scream, or run away. Compared with other chimpanzees, she demonstrated less variability in her facial expressions. Caretakers reported that her face was expressionless, “like a ghost,” for at least a month after she arrived at the sanctuary. She seldom, if ever, exhibited a play face. She was tested for a thyroid disorder and assessed for other medical causes of her clinical presentation, but all laboratory tests were within normal limits. (Ferdowsian et al., 2011)


Negra. (Chimpanzee Sanctuary Northwest)
Within the papers they examined, they found that a staggering 58% of chimpanzees living in sanctuaries met their criteria for depression, and 44% met their criteria for PTSD. By contrast, when they examined accounts of chimpanzees living in the wild, 3% met the criteria for depression, and less than 1% met the criteria for PTSD.
It is important to emphasize that these criteria were modified from the human version- symptoms that the patient could self-report were obviously out, and other symptoms, like anhedonia, had to have slightly modified criteria like a lack of interest in grooming, for example. The normal chimp behaviors were never going to perfectly mirror the human ones.
Elephants have also been another subject of possible PTSD/depression diagnoses, though again, there is no official standard. The case of elephants is more intriguing because much of the research has actually occurred on wild elephants, not just captive elephants. Studies have shown that poaching, particularly for older males and females, is correlated with serious adverse effects on the behavior of juvenile elephants years later. Male elephants become more aggressive and violent- in one case, male elephants that had grown up without older males began attacking and killing rhinoceroses. Female elephants in herds that had lost their matriarchs and older females give birth earlier and have higher infant mortality rates and infant neglect. Both sexes displayed decreased social skills and apathy.
Some researchers, including Dr. Gay Bradshaw, argue that this is evidence enough that elephants can suffer the same kinds of severe negative symptoms that humans diagnosed with depression and PTSD do.
I would put in the caveat that elephants might suffer from elephant PTSD, but not human PTSD. Like the chimpanzees, their normal behaviors and needs are different from ours, and the proximate causes behind their abnormal behaviors are different too. In the case of the rhinoceros-killing elephants, the lack of older males prevented normal hormonal suppression from taking place. The young males entered musth- a normal hormonal state related to breeding- earlier than they would have with the presence of older males. Similarly, the young females that were reproducing earlier than normal were not being reproductively suppressed by their elders.
Lack of positive social modeling, of course, no doubt also contributed to the adverse behaviors of these elephants, and we could argue all day about whether or not reproductive suppression also occurs in humans. The point is that slapping a label for a human disorder onto an animal is misleading and possibly unethical. Can elephants experience a range of symptoms that are very similar to those of a human experiencing PTSD? I’d say yes. But in order to treat them for it, we have to go in with the understanding that they are elephants and not humans.
Animal-Specific Behavioral Disorders
There are a number of behavioral disorders that are already well-known in various species of animals in captivity that do not occur in humans, though they sometimes have qualities of similar human disorders. I’ve already spoken about pterotillomania in birds, which bears obvious similarities to the human hair-pulling disorder, trichotillomania. However, it is doubtful that humans begin pulling out their hair because they don’t have enough opportunities to forage for their food. Similarly, the causes for many of the disorders I’m about to discuss may have to do with species-specific needs that humans don’t have.
Separation Anxiety Disorder

Most of us with dogs are familiar with what separation anxiety is, and a good proportion of the dog owners reading this may actually have a dog with this disorder- it affects about 14-29% of pet dogs. Cats also experience their own version of separation anxiety disorder.
Separation anxiety disorder manifests as it sounds- the dogs affected by it become extremely anxious when their owner is not present, sometimes even when the owner is just in the next room. This can lead to several behavioral issues, such as barking and whining, digging and chewing, and urinating and defecating. Owners with dogs with this disorder get used to coming home to a house in a state of destruction. Some dogs have such severe separation anxiety that they attempt to maintain physical contact with their owners at all times and perform such behaviors as excessive licking and pawing, and begin showing anxiety as soon as their owners start preparing to leave. Some dogs even become aggressive towards their owners when they see them performing actions like picking up their keys or putting on their coat.
It is normal for separation anxiety to occur in young puppies around 1-2 months of age, but it is considered a disorder if it persists for a long time after that. In fact, the disorder can actually become more common as dogs get older, perhaps because they become less able to adapt to changes in their environment.
The disorder is also more common in dogs that have been adopted from a shelter. The loss of their first (or second, or third) families may lead to these dogs becoming more anxious in the absence of their new owners. There also may be genetic and personality components to the disorder, considering it is more likely to develop in dogs that have other anxiety disorders such as noise or storm phobias.
Owners often inadvertently make separation anxiety disorder even worse when they punish their dogs when they return home (leading to further anxiety and fear) or attempt to solve the issue by adopting a second animal. The latter often does not help because the anxiety is caused by a specific attachment to one person- the owner- not general loneliness.
Separation anxiety disorder in dogs is often treated with SSRIs, but the most effective methods of reducing it have been found to be a combination of medication and behavior modification.
Separation anxiety disorder occurs less frequently in cats than dogs, but usually manifests as hypervocalization and elimination outside the litter box. Compulsive grooming to the point of raw skin or bleeding is also common.
The fact that separation anxiety disorder is seen so often in both dogs and cats is hypothesized by many to be partially due to the neotonization process that both species went through during domestication. The retention of juvenile behaviors like excessive vocalization, affection and playfulness could also lead to the retention of a more juvenile-like psychology, i.e., the need for the parental figure to be around all the time.
Pica

An x-ray showing rocks in a dog’s stomach.
Pica is the consumption of non-edible substances, such as dirt or glass. It is not a species-specific phenomenon, and does also occur in humans. It is also not always considered a disorder, because many animals are naturally driven to consume non-edible substances like clay to obtain nutrients that they aren’t getting in their conventional diet.
Where pica becomes classified as a disorder is when an animal compulsively eats non-edible objects that have no nutritive value. Sometimes the disorder can still relate to a physiological need- for example, many dogs that display pica may have thyroid problems. However, what starts as a response to a thyroid problem or other medical or diet issue may continue even after the problem is treated, leading to a long-term behavioral disorder. In cats, some of the most common objects ingested are string or wool, while in dogs it can be rocks or gravel.

Objects removed from one cat’s stomach.
Pica in dogs can also manifest as coprophagia, or feces-eating. Mother dogs do naturally eat the feces of their newborns, an adaptation to help hide them from predators, and some dogs will eat their own feces to make an area cleaner (particularly if in a cramped crate or cage). Some dogs, however, show compulsive coprophagia- that is, they will eat any feces they come across, dog or otherwise.
I’ve known several dogs with such intense pica that they had to wear muzzles at all times when they weren’t being supervised. One such case, in a standard poodle, resulted in tragedy- she got her muzzle off and ate a sock, which got lodged in her intestinal tract. She had to be euthanized.
Pica as a behavioral disorder is an extremely difficult behavior to correct once it starts, and can be life-threatening, but little research has been done to understand why it is such a prevalent problem in domestic cats and dogs. Some evidence exists to suggest that pica can be a response to stress, such as separation anxiety, and there may be a genetic correlation to certain types of pica such as coprophagia and wool-sucking, but for the most part it remains a mystery.
Anorexia
Much like with self-harm, it often surprises people that animals can experience anorexia; however, many of us are familiar with a dog or cat that stops eating due to anxiety. Anorexia actually simply refers to self-starving behavior, while anorexia nervosa specifically refers to the human eating disorder.
Like pica, anorexia in animals can occur due to dietary or health issues, and becomes a disorder when it occurs in a healthy animal with access to good-quality food. It most frequently manifests as a result of stress or anxiety, and many different animals, from rats to sheep, experience different variations of it. I’ll briefly go over one version of this- thin sow syndrome.
Thin sow syndrome is an eating disorder that affects female pigs, most commonly either just after they give birth or just after they have finished weaning their piglets. The sows begin eating less food and may show other symptoms such as hyperactivity, chain-chewing, and pica. Despite sufficient food being constantly available, pigs will become emaciated and eventually die without intervention.

The syndrome has genetic components, as it appears more often in lines of pigs bred for leaner meat, and is more likely to occur in conditions that are overcrowded, or when the sow in question is moved to a new social group. It appears to be related to extreme stress, and is difficult to reverse by behavioral methods alone. There has been limited success in treating the sows with antidepressants and anti-anxiety drugs.
Canine Compulsive Disorder
I discussed compulsive grooming and self-injurious behavior earlier in the article, and both are symptoms of canine compulsive behavior. However, other symptoms are vastly varied, and include movement stereotypies, repetitive pica, excessive light-chasing, flank-sucking or wool sucking, tail-chasing, snapping at the air, upward gazing, and a host of other bizarre rituals.
Any of these behaviors could be seen as ordinary if performed infrequently, but in a compulsive dog they occur constantly and almost out of the animal’s control. Watch this video to see what I mean.
Canine compulsive disorder is diagnosed when the compulsive behaviors interfere with the dog’s ability to get through its day to day life, like in the video I liked above.
There are a number of proposed causes for these repetitive behaviors. The main one, of course, is stress and trauma in early life. The compulsion might arise due to an inability to perform normative behaviors, such as when a dog is kept in a small crate for long periods of time, unable to walk or run. The compulsive behavior can occur as a redirection of frustration and become ‘wired in’ with enough repetition. Then the dog in the crate may continue to perform the compulsion even when the crate door is opened.
Some types of compulsions, such as flank-sucking, wool sucking, and forms of pica, may also be due to early weaning and maternal deprivation, where the animal never loses its early oral fixation.
Other compulsions appear with no apparent environmental cause at all. Genetics also plays an important role in the disorder. Many specific compulsions are more common in certain breeds. In dobermans, a gene has been found that correlates to flank-sucking behavior. Here’s a video of a doberman unable to stop flank-sucking. You can see that the behavior occurs on a couple of occasions immediately after the dog is stopped from doing something else like jumping up.

Certain compulsions, particularly those related to apparent hallucinations (snapping at the air and staring upwards) or repetitive motor activity (spinning) may also be due to neurological diseases and partial seizures. In truth, canine compulsive disorder is probably similar behavior with many different proximate causes lumped together under an umbrella term.
Whatever the cause, canine compulsive disorder is extremely difficult to successfully treat, which can be problematic. Some compulsions may merely be annoying, like spinning, but many are actively harmful to the dog’s health. Acral lick dermatitis is one of these- the dog will lick itself in a specific spot until the skin is raw and bleeding, and often can only be stopped by putting it in a muzzle or cone.
Behavioral modification through training alone almost never reduces the symptoms of canine compulsive disorder, and often worsens it, as the owner either increases stress through punishment or inadvertently reinforces the behaviors by rewarding them. As with separation anxiety disorder, a combination of medication and training may help, along with a regular schedule and reduction of confinement or restriction of normal behavior. However, even with all that, severe cases of CCD may only show mild reduction of symptoms.
Conclusions: Do Animals Suffer From Mental Disorders?
I’m not really going to try to answer that question; I’ll let you guys decide for yourselves. I think instead the keyword is ‘suffer’- that is, many, many animals suffer from pain that seems to come from nowhere else besides the mind. Veterinarians and animal researchers are already well aware of this; it is the public that seems to have a hard time catching up.
Many people are strangely resistant to the idea that animals should be put on things like antidepressants or anti-anxiety medication, despite the fact that they have been used to manage captive animal behavior since at least the 80s. I won’t deny that it’s more desirable to fix the issue through behavioral modification alone, as it is with humans, but the persistent denial that behavioral drugs should be used on animals to me almost smacks of a refusal of the idea that animals can experience long-term mental suffering.
And it is a shame, because many animals that show these behavioral issues are simply put down in the end, because people aren’t willing to put in the time and energy to try and find a way to treat them.
Many animals in captivity suffer mentally because of things we have done, and I think that it is our responsibility to try as hard as we can to help them.
References (suggested reading is starred)
American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: American Psychiatric Publishing.
*Bradshaw, G. A., Capaldo, T., Lindner, L., & Grow, G. (2008). Building an inner sanctuary: complex PTSD in chimpanzees. Journal of Trauma & Dissociation, 9(1), 9-34.
Bradshaw, G. A., & Schore, A. N. (2007). How elephants are opening doors: developmental neuroethology, attachment and social context. Ethology, 113(5), 426-436.

Burke, T.; Page, B.; Van Dyk, G.; Millspaugh, J.; & Slotow, R. (2008). Risk and ethical concerns of hunting male elephant: behavioural and physiological assays of the remaining elephants. PLoS One 3: e2417.
Cox, W. T., Abramson, L. Y., Devine, P. G., & Hollon, S. D. (2012). Stereotypes, Prejudice, and Depression The Integrated Perspective. Perspectives on Psychological Science, 7(5), 427-449.
Dallas Zoo. (2003). Animal Profiles: Jenny. 
*Dao, James. (2011). More military dogs show signs of combat stress. New York Times Magazine. 
Dodman, N. H., Karlsson, E. K., Moon-Fanelli, A., Galdzicka, M., Perloski, M., Shuster, L., … & Ginns, E. I. (2010). A canine chromosome 7 locus confers compulsive disorder susceptibility. Molecular psychiatry, 15(1), 8-10.
*Ferdowsian, H. R., Durham, D. L., Kimwele, C., Kranendonk, G., Otali, E., Akugizibwe, T., … & Johnson, C. M. (2011). Signs of mood and anxiety disorders in chimpanzees. PLoS One, 6(6), e19855.
Fernando, A. B. P., & Robbins, T. W. (2011). Animal models of neuropsychiatric disorders. Annual review of clinical psychology, 7, 39-61.
*Garner, J. P. (2005). Stereotypies and other abnormal repetitive behaviors: potential impact on validity, reliability, and replicability of scientific outcomes. ILAR journal, 46(2), 106-117.
Geyer, M. A., Krebs-Thomson, K., Braff, D. L., & Swerdlow, N. R. (2001). Pharmacological studies of prepulse inhibition models of sensorimotor gating deficits in schizophrenia: a decade in review. Psychopharmacology, 156(2-3), 117-154.
Gobush, K. S., Mutayoba, B. M., & Wasser, S. K. (2008). Long‐Term Impacts of Poaching on Relatedness, Stress Physiology, and Reproductive Output of Adult Female African Elephants. Conservation Biology, 22(6), 1590-1599.
Hewson, C. J., Luescher, U. A., & Ball, R. O. (1998). Measuring change in the behavioural severity of canine compulsive disorder: the construct validity of categories of change derived from two rating scales. Applied animal behaviour science, 60(1), 55-68.
Holden, J. E., Jeong, Y., & Forrest, J. M. (2005). The endogenous opioid system and clinical pain management. AACN Advanced Critical Care, 16(3), 291-301.
*Landsberg, G. M., Hunthausen, W. L., & Ackerman, L. J. (2012). Behavior Problems of the Dog and Cat. Elsevier Health Sciences.
Lumeij, J. T., & Hommers, C. J. (2008). Foraging ‘enrichment’as treatment for pterotillomania. Applied animal behaviour science, 111(1), 85-94.
McKeown, D., Luescher, A., & Machum, M. (1988). Coprophagia: Food for thought. The Canadian Veterinary Journal, 29(10), 849.
Nagasawa, M., Mogi, K., & Kikusui, T. (2012). Continued distress among abandoned dogs in Fukushima. Scientific reports, 2.
*Nestler, E. J., & Hyman, S. E. (2010). Animal models of neuropsychiatric disorders. Nature neuroscience, 13(10), 1161-1169.
Nind, M., & Kellett, M. (2002). Responding to individuals with severe learning difficulties and stereotyped behaviour: challenges for an inclusive era. European Journal of Special Needs Education, 17(3), 265-282.
Novak, M. A. (2003). Self‐injurious behavior in rhesus monkeys: new insights into its etiology, physiology, and treatment. American Journal of Primatology, 59(1), 3-19.
Overall, K. L., & Dunham, A. E. (2002). Clinical features and outcome in dogs and cats with obsessive-compulsive disorder: 126 cases (1989-2000). Journal of the American Veterinary Medical Association, 221(10), 1445-1452.
Overmier, J. B., & Seligman, M. E. (1967). Effects of inescapable shock upon subsequent escape and avoidance responding. Journal of comparative and physiological psychology, 63(1), 28.
Paylor, R., Nguyen, M., Crawley, J. N., Patrick, J., Beaudet, A., & Orr-Urtreger, A. (1998).  α7 nicotinic receptor subunits are not necessary for hippocampal-dependent learning or sensorimotor gating: a behavioral characterization of Acra7-deficient mice. Learning & Memory, 5(4), 302-316.
*Schwartz, S. (2003). Separation anxiety syndrome in dogs and cats. Journal of the American Veterinary Medical Association, 222(11), 1526-1532.
Seligman, M. E., & Maier, S. F. (1967). Failure to escape traumatic shock. Journal of experimental psychology, 74(1), 1.
Simeon, D., & Favazza, A. R. (2001). Self-injurious behaviors. Self-injurious behaviors, assessment and treatment, 1-28.

Slotow, R.; Balfour, D.; & Howison, O. (2001). Killing of Black and White Rhinoceroses by African Elephants in Hluhluwe-Umfolozi Park, South Africa. Pachyderm 41, 13-20.
Swaisgood, R. R., & Shepherdson, D. J. (2005). Scientific approaches to enrichment and stereotypies in zoo animals: what’s been done and where should we go next? Zoo Biology, 24(6), 499-518.
*Tiefenbacher, S., Novak, M. A., Lutz, C. K., & Meyer, J. S. (2005). The physiology and neurochemistry of self-injurious behavior: a nonhuman primate model. Front Biosci, 10(1), 1-11.
*Treasure, J. L., & Owen, J. B. (1997). Intriguing links between animal behavior and anorexia nervosa. International Journal of Eating Disorders, 21(4), 307-311.
*Yenkosky, J. P., & McCarthy, E. (2010, August). Post-Traumatic Stress Disorder among parrots in captivity: Treatment considerations. In ASSOCIATION OF AVIAN VETERINARIANS (p. 17).

Mental Disorders in Animals

The above is an image of a captive African gray parrot that suffers from excessive feather-plucking, or pterotillomania. People who work with captive parrots or own parrots as pets have probably at least heard of this disorder, or even observed it firsthand. The parrot may have an excellent diet and be in good physical condition, yet it will continue to pluck and pluck at its own feathers, shaving itself bald in places.

If the cause is not a disorder of the body, then, can we say that this is a symptom of a disorder of the mind?

That brings up another question, though: how can we possibly know what is happening in an animal’s head? How can we separate an animal’s behavior into that of bodily needs and that of mental needs? People like to point out all the time that you can’t sit a dog on a couch and ask him what his childhood was like; we don’t even know if a dog’s memory of his childhood exists in any form that a human would recognize. While I think most people would agree that animals have minds, they function- by necessity and evolution- in ways ours do not.

I think this has to be the focal point of the following discussion: animal minds and human minds are different. Am I saying animal minds are inferior? Certainly not. But I’d like to point out that a lot of the research on mental disorders in animals focuses on finding parallels with human mental disorders. Yet the underlying reasons for disordered behavior in animals may be because they have mental needs that humans do not. For example, a popular theory behind why parrots develop pterotillomania is because they are not given ample opportunities to perform normative food-foraging behaviors.

So what forms of mental disorders are present in animals, and what are biologists, psychologists, veterinarians, and pet owners doing to better understand them?

Below the cut I’ll be discussing several things that people may find distressing/triggering: animal suffering, mental illness (including references or descriptions of the most commonly diagnosed human mental disorders), and animal research. It’s an upsetting topic, which is why I’m writing about it much more formally than I normally do, but I think it’s both interesting and important.

Note: This post is also extremely long.

How do we define a mental disorder?

While the point of this post isn’t really to prove one way or another that animals can get mental disorders like humans do, it’s important that we define what exactly a mental disorder is before we discuss them.

That, of course, is a little easier said than done. Much less define ‘mental disorder’ for animals, we’re barely able to settle on a definition for humans. Here’s how the DSM-V does it:

A mental disorder is a syndrome characterized by clinically significant disturbance in an individual’s cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning. Mental disorders are usually associated with significant distress in social, occupational, or other important activities. An expectable or culturally approved response to a common stressor or loss, such as the death of a loved one, is not a mental disorder. Socially deviant behavior (e.g., political, religious or sexual) and conflicts that are primarily between the individual and society are not mental disorders unless the deviance or conflict results from a dysfunction in the individual, as described above. (American Psychiatric Association, 2013)

It sounds confusing at first glance, but I do like it better than the previous definition in the DSM-IV. As troubled as the DSM is (and oh, it is, no doubt about that) I roughly agree with what the authors were trying to articulate here. A mental disorder is something that is long-term, that causes the affected individual to suffer, and that persists internally. I say ‘persists’ because some disorders are long-lasting results of a severe environmental disturbance. Soldiers with PTSD come to mind; though their postwar environment is ‘safe,’ their minds remain in that heightened ‘threat mode.’

But while I like this definition, I know there are a lot of people who have differing opinions. Some want hard neurological evidence for every mental disorder, some would rather focus entirely on self-reporting and analytical psychology, and there are some people who insist mental disorders don’t exist at all.

Though my goal is to keep it fairly neutral through this article, I think it’s evident that I have a low opinion of the last group. I have two mental disorders and my diagnoses were a profound relief and a gift to me- I could now understand why my behavior at times seemed out of my control, and that there were people out there that had the disorder as well and that I share experiences with.

I’m not saying that these labels don’t have stigmas and problems, but the people that insist that they shouldn’t exist and that my disordered thinking is a product of- what, I don’t know, my own desire to have myself suffer?- well, I’m not inclined to like them. Also, it’s very hard to treat something if you have no label to unify the symptoms under.

Anyway, I’d like to apply the DSM definition of mental disorder to animals, but it is obviously difficult. We cannot ask them about their thoughts or pasts- we can only observe their behavior. And since they are indeed animals and not humans, it is hard to discern what behavior is normal and what is abnormal. Furthermore, how do we separate normal animal stress responses are normal (correlate to the human grieving example in the DSM definition) and which ones are persistant and reflect a mental illness? We don’t always have the opportunity to remove an animal from a poor environment in captivity, so it is hard to say whether or not their behavior would snap back to ‘normal.’

(I keep using normal, too, but that’s also a nebulous word, because how do we even determine what is normal and what isn’t?)

In the end there are no simple answers, but I do consider it important to be able to identify and label different behavioral disorders in animals, particularly those in captivity. Without that, it will be much harder to know how to help them.

Animal Models of Mental Disorders

I suspect a lot of people who would insist that animals cannot have mental disorders do not realize that a large portion of laboratory animal research is dedicated to mental illness. In order to see if a certain drug reduces or eliminates symptoms of depression, for example, you first have to have an animal that exhibits those symptoms.

When I was in college, my adviser actually worked on some of the rat models of schizophrenia. Most animal models aren’t perfect copies of the human disorder- rather, they express one or more major symptoms of the disorder to understand a) what in the brain or the environment causes that symptom to appear and b) how that symptom can be treated.

My adviser was specifically studying prepulse inhibition- the tendency to react less to a loud sound when a softer sound is given first as a ‘warning.’ Human with schizophrenia (and several other mental disorders) tend not to show this inhibition- they are just as startled by the second sound as the first one.

Above: A sample visualization of the amount of startle response (usually measured by muscle movements) given by the subject without a prepulse stimulus and then with one.

While it may seem like a bizarre symptom to focus on, disrupted prepulse inhibition is actually an important indicator of a well-functioning nervous system- that is to say, individuals that lack prepulse inhibition have difficulty filtering out unnecessary stimuli, which is why it’s a symptom not only of schizophrenia but in some anxiety disorders such as obsessive-compulsive disorder. It’s also important because drugs that successfully treat this symptom often also treat other symptoms of schizophrenia.

Researchers have replicated this symptom in rats and mice via a number of pathways, which I won’t get into here, but essentially they involve either breeding rats with certain genetic disorders, introducing chemicals to the rat’s brain, or social deprivation at an early age. Like most symptoms of mental illnesses, disrupted prepulse inhibition can have both genetic and environmental causes- and often a combination of the two.

Symptoms of schizophrenia aren’t the only ones researchers use animals as models for. Others include anxiety disorders, ADD and ADHD, depression, bipolar disorder, eating disorders, and addiction (drugs, alcohol, smoking, and even gambling).

The research on generating depressive symptoms in animals is some of the most uncomfortable of all. Most people who have taken a psychology course know that learned helplessness is a factor in depression. The definition of learned helplessness is exactly as it sounds: the animal will be put into an unpleasant situation with no way out several times, and will eventually give up trying to escape. It is argued that this is similar to humans who live in abusive situations, as well as people on the receiving end of inescapable prejudice.

The most famous of the learned helplessness paradigms in animal models is the inescapable shock test performed by Seligman and Maier on domestic dogs. During the study, dogs were split into two groups. One group could turn off the electric shocks using a lever while the other received all the shocks the first group did but had no control over them. Soon differences emerged in the behavior of the second group of dogs: they took longer to recover from the traumatic experience than the first group.

But that wasn’t all. After the first series of tests, Seligman put the dogs into a second apparatus: a small box with a low barrier dividing the two sections. The section of floor the dog was first placed on began to give them electric shocks, while the section beyond the barrier did not. The dogs from the first group quickly learned to jump over the barrier. The dogs from the second group did not. In fact, they didn’t do anything, not even if Seligman and Maier coaxed them with both rewards and punishment to move. Even the ability to observe other dogs escaping did not affect their behavior. The only thing that eventually caused them to learn to jump the barrier was the researchers physically picking them up and placing them on the other side.

Learned helplessness is commonly induced in animals being used to test antidepressants. In rodents, tests like the forced swim test (where the animal is repeatedly put into a pool of water they cannot escape from and eventually stop trying to swim) and tail suspension test (where the rodent is taped to a bar by its tail again and again until it stops struggling to escape) are still commonly used.

The nicest thing I can say about these tests is that they are acute; that is, it is possible to make the animal recover from them with the right encouragement, and the effects are generally not long-term. This is obviously different from the depressive symptoms seen in humans, and is the focus of a lot of criticism surrounding these animal models as ways to mirror human depression.

The difference between a rat and a lab and a human being with depression is that the human isn’t usually undergoing a few forced swim tests- they are going through either systematic trauma for a long period in their lives, are experiencing a physical environment that can degrade their mental state (i.e., lack of exercise, lack of vitamin D), have a genetic component that predisposes them to depressive behaviors, or (most commonly) a little of all.

Animals can undergo these types of sustained traumas as well, but to examine them, we have to look beyond the experiments.

The Effects of Chronic Stress and Trauma on Animals

Although she is in good physical health, Rachel appears in almost constant distress. She rocks her head continuously, whimpers for extended periods of time, and isolates herself. She focuses on a body part, screams, and behaves as if her hand or foot is a foreign object. She positions her hand behind a chair and reacts as if her hand does not belong to her, attacking it violently or biting it so severely it bleeds. At other times, she hits herself continually in the head, loudly screaming for up to 20 minutes in repeated episodes throughout the day. She calms only when exhausted or when she sees blood. (Bradshaw et al., 2008)

Rachel is a chimpanzee, and she now lives at a Canadian sanctuary called Fauna Foundation. Before that, she was used in biomedical research at the Laboratory for Experimental Medicine and Surgery in Primates (LEMSIP), the same place that the famous Nim Chimpsky was sold after he was no longer needed for language studies.

Rachel. (faunafoundation.org)

LEMSIP was opened in 1965 and closed in 1998. Rachel stayed there for fifteen years, starting from when she was three and a half. Before that, she was hand-reared by human parents (like the vast majority of ‘pet’ chimpanzees, her adoptive ‘parents’ changed their minds when she got too big for them to handle).

The conditions for chimps in research in the 80s and 90s were fairly horrible, especially for a chimp coming in from the relative freedom of living in a human household. The cages were extremely small (one of the reasons LEMSIP may have closed down was because it would have cost them too much to upgrade to USDA standard cage sizes). Rachel was housed singly as well, likely with little access to enrichment.

I focus on Rachel’s environmental conditions more than the actual testing she experienced because the testing itself would have been an acute trauma- like the forced-swimming tests- terrifying, but not constant. Most animals, including ourselves, are more or less adapted to deal with acute stressors. But the confinement and lack of stimulation were constant stressors.

From the description above, we can see that even after Rachel was placed in the sanctuary, with space, enrichment, and the opportunity for social interaction, she maintained her symptoms, which included psychotic episodes, stereotyped behavior, and self-injurious behavior (SIB).

Stereotyped Behaviors

Stereotyped behaviors, often called stereotypies, are simple and repetitive movements that do not appear to have a goal. The most familiar example would be that of a big cat or bear pacing back and forth in a small cage. Other behaviors like rocking, swaying, jumping, head-bobbing, etc. are frequently-seen stereotypies. Stable vices in horses are another example.

Here’s a video with examples of different animals performing stereotypies.

Zoo elephant showing stereotyped behavior.

In humans, stereotypies are most commonly seen in individuals diagnosed with autism or neurological disorders such as tardive dyskinesia. In autism it is also often referred to as ‘stimming’- that is, it is a way of providing comforting sensory input.

In animals it most commonly relates to spending long periods of time in deprived or enrichment-poor environments. The term is also used to describe normal animal behaviors that consist of repeated movements- such as chewing- but here I use it only to refer to the maladaptive behaviors caused by deprivation.

Some animal stereotypies can be reduced or eliminated by offering the animal appropriate enrichment. However, many do not stop despite the presence of enrichment, suggesting that the stereotypies can lead to permanent neurological alteration. (This brings up the important note that if you see an animal with a stereotypy, it may be due to past neglect and have nothing to do with the animal’s current housing situation.)

The type of stereotypy performed by an animal often relates to its species-typical behavior. For example, the stereotypy that most commonly affects wild felines and bears is pacing. In the wold, these animals maintain large territories and normally spend their days foraging long distances in search of food, which might explain why they are still driven to keep moving even in a small enclosure. We can imagine a stereotypy occurring as a result of frustration due to the inability to perform a normal behavior.

Some maladaptive behaviors such as over-grooming are sometimes a little too complex to be referred to as a stereotypy even though they can have similar causes. In the beginning of this article I discussed a possible cause for feather-plucking or pterotillomania: when unable to forage for food, a bird overcompensates in its grooming. Since the motions in pterotillomania are not mechanically repetitive but always lead to the same inappropriate goal (plucking itself bald), this is termed a compulsive behavior.

A salmon-crested cockatoo that has created a bald patch on its chest due to compulsive over-grooming.

Some animals go much farther with compulsive behaviors than just over-grooming themselves, however.

Self-Injurious Behavior

Self-injurious behavior (SIB) is just like it sounds: it is when an animal actively injures itself. This can occur when the animal grooms or picks at itself until it bleeds, hits itself or slams itself against walls, or when an animal bites itself. I have even heard a case in which an African elephant would repeatedly drive her tusks into her rear legs.

Jenny developed self-mutilating stereotypical behavior during the reconstruction of elephant exhibit, 1995, during which she was exposed to heavy equipment activity and locked inside for extended period of time. She would often use her tusk to strike her right rear leg. Wounds had developed into abscesses that required intensive treatment…

…She stands on three legs, and raises and holds one of the rear legs at the bend of her front ‘elbow.’ She has to sort of contort to do this. It is so bizarre you can’t miss it. This is another strenuous activity that means something is very wrong. It is also one we need to worry about, because it places her rear foot in perfect position for her to ‘peg’ at it with her tusks. If you see this, the supervisor needs to be called immediately. (Dallas Zoo, 2003)

Jenny, who still lives in the Dallas zoo today.

Hearing about self-injurious behavior in animals often startles people, because they assume- somewhat correctly- that such a maladaptive trait would never be allowable by evolution. In other words, it takes a brain like a human’s, not a bundle of instincts like an animal’s, to want to hurt yourself.

Obviously the above statement is problematic for a number of ways, but you see my point. But animal self-injurious behavior is well-known to both researchers and zookeepers. It’s hard to say that an animal’s intent is to cause itself pain when these behaviors occur- it’s hard to assume anything about what an animal’s ‘intent’ is- but the actions are frequently repeated and end when self-harm occurs.

Self-injurious behavior is also a common comorbid phenomenon in humans with chronic anxiety and other severe mental illnesses. Individuals who intentionally cut, burn, and otherwise harm themselves are often viewed with the stigma of “doing it for attention” by society at large, but in the scientific community it is understood that these behaviors have biological as well as emotional motivators.

Human self-injurious behavior can be both compulsive and impulsive; it can be highly ritualized with no necessary trigger, or it can be triggered by stress. Patients often describe a mounting sense of anxiety up until they self-harm, and then a sense of relief and release when they do.

It was research on nonhuman primates showing SIB that was used to begin to describe the physiological components behind the behaviors. A small proportion of rhesus macaques used in research display self-biting behaviors. Studies on these animals found that heart rate and cortisol levels would go down after the self-directed bites occurred, indicating that like the human self-harmers, the monkeys experienced a reduction in anxiety after hurting themselves.

The areas that the monkeys would bite are also telling- namely, they would target the same areas of their bodies that would release endogenous opioids. Endogenous opioids are a family of peptides that include endorphins and are naturally released in the body to help with pain and stress management. Some forms of cultural self-mutilation and techniques such as acupuncture actually take advantage of the areas of the body that trigger release of these chemicals when injured.

So there is mounting evidence that the reasons self-injurious behaviors persist are actually somewhat rooted in biology rather than some sort of pathological self-hatred. Nevertheless, SIB appears to occur in animals largely in a way to deal with extreme, chronic stress that may alter their brain development, possibly resulting in dysregulation of systems such as the HPA axis. The rhesus macaques that displayed SIB were ones that experienced traumatic early experiences (such as early social isolation) coupled with frequent acute stressors (such as more veterinary procedures). Sometimes housing these monkeys with others was enough to significantly reduce the incidence of SIB, but it often took treatment with antidepressants to have a real effect on stopping them.

Modern animal husbandry now includes enrichment along with other life-sustaining necessities such as food, water, and shelter. The best enrichment is dynamic and changing, includes social as well as environmental interaction, and plays into an animal’s naturally fulfilling behaviors. But animals like chimpanzees, elephants and parrots often live for over fifty years, and even rhesus macaques live about twenty years. These animals, still living today, often cannot overcome the trauma inflicted on them by their early experiences in captivity and maintain their adverse behaviors.

The long-lasting behavioral effects of these traumas in animals is now leading to a relatively new phenomenon of attempting to diagnose individual animals with psychological disorders.

Do PTSD and Depression manifest in Animals?

In 2010 a military service dog named Gina made the news. Gina, deployed to Iraq to help soldiers detect IED explosives, had come back home terrified of any loud sounds, new people, and new experiences. She became the poster child for a new phenomenon- “canine PTSD.”

Gina has since been rehabilitated and may return to active combat zones.

I say new, but Gina’s behavioral symptoms aren’t really new; they’re seen in dogs coming from all sorts of traumatic situations. In this video, for example, you can view some of the behaviors of a dog rescued from a hoarding situation before and after treatment.

It’s important to note that the idea of “canine PTSD” only caught on around 2009, and while it’s endorsed by many veternairians, there’s been little scientific research done on the topic. There is no official standard for diagnosing a dog with canine PTSD, though there are a few unofficial versions floating about.

Similarly, there are few ‘official’ mental illness standards directed towards diagnosing animals. There is no animal version of the DSM-V. However, in a 2011 study, several researchers attempted to explore the possibility that they could apply human diagnostic criteria for depression and PTSD to captive chimpanzees. They examined case studies from the scientific literature using a slightly modified version of the DSM’s criteria for PTSD and depression, which you can view here and here. Symptoms such as the patient describing recurring thoughts were necessarily deleted.

Negra met alternative criteria for depression and PTSD. According to reports, she had persistent depressed hunched posture, and she was socially withdrawn. Negra slept excessively during the daytime, and she lacked interest in play, food, other individuals, and grooming. She also demonstrated poor attention to tasks. She was described as slow and sluggish, and at times, she appeared anxious. In response to an unexpected touch, she would “threat bark,” scream, or run away. Compared with other chimpanzees, she demonstrated less variability in her facial expressions. Caretakers reported that her face was expressionless, “like a ghost,” for at least a month after she arrived at the sanctuary. She seldom, if ever, exhibited a play face. She was tested for a thyroid disorder and assessed for other medical causes of her clinical presentation, but all laboratory tests were within normal limits. (Ferdowsian et al., 2011)

Negra. (Chimpanzee Sanctuary Northwest)

Within the papers they examined, they found that a staggering 58% of chimpanzees living in sanctuaries met their criteria for depression, and 44% met their criteria for PTSD. By contrast, when they examined accounts of chimpanzees living in the wild, 3% met the criteria for depression, and less than 1% met the criteria for PTSD.

It is important to emphasize that these criteria were modified from the human version- symptoms that the patient could self-report were obviously out, and other symptoms, like anhedonia, had to have slightly modified criteria like a lack of interest in grooming, for example. The normal chimp behaviors were never going to perfectly mirror the human ones.

Elephants have also been another subject of possible PTSD/depression diagnoses, though again, there is no official standard. The case of elephants is more intriguing because much of the research has actually occurred on wild elephants, not just captive elephants. Studies have shown that poaching, particularly for older males and females, is correlated with serious adverse effects on the behavior of juvenile elephants years later. Male elephants become more aggressive and violent- in one case, male elephants that had grown up without older males began attacking and killing rhinoceroses. Female elephants in herds that had lost their matriarchs and older females give birth earlier and have higher infant mortality rates and infant neglect. Both sexes displayed decreased social skills and apathy.

Some researchers, including Dr. Gay Bradshaw, argue that this is evidence enough that elephants can suffer the same kinds of severe negative symptoms that humans diagnosed with depression and PTSD do.

I would put in the caveat that elephants might suffer from elephant PTSD, but not human PTSD. Like the chimpanzees, their normal behaviors and needs are different from ours, and the proximate causes behind their abnormal behaviors are different too. In the case of the rhinoceros-killing elephants, the lack of older males prevented normal hormonal suppression from taking place. The young males entered musth- a normal hormonal state related to breeding- earlier than they would have with the presence of older males. Similarly, the young females that were reproducing earlier than normal were not being reproductively suppressed by their elders.

Lack of positive social modeling, of course, no doubt also contributed to the adverse behaviors of these elephants, and we could argue all day about whether or not reproductive suppression also occurs in humans. The point is that slapping a label for a human disorder onto an animal is misleading and possibly unethical. Can elephants experience a range of symptoms that are very similar to those of a human experiencing PTSD? I’d say yes. But in order to treat them for it, we have to go in with the understanding that they are elephants and not humans.

Animal-Specific Behavioral Disorders

There are a number of behavioral disorders that are already well-known in various species of animals in captivity that do not occur in humans, though they sometimes have qualities of similar human disorders. I’ve already spoken about pterotillomania in birds, which bears obvious similarities to the human hair-pulling disorder, trichotillomania. However, it is doubtful that humans begin pulling out their hair because they don’t have enough opportunities to forage for their food. Similarly, the causes for many of the disorders I’m about to discuss may have to do with species-specific needs that humans don’t have.

Separation Anxiety Disorder

Most of us with dogs are familiar with what separation anxiety is, and a good proportion of the dog owners reading this may actually have a dog with this disorder- it affects about 14-29% of pet dogs. Cats also experience their own version of separation anxiety disorder.

Separation anxiety disorder manifests as it sounds- the dogs affected by it become extremely anxious when their owner is not present, sometimes even when the owner is just in the next room. This can lead to several behavioral issues, such as barking and whining, digging and chewing, and urinating and defecating. Owners with dogs with this disorder get used to coming home to a house in a state of destruction. Some dogs have such severe separation anxiety that they attempt to maintain physical contact with their owners at all times and perform such behaviors as excessive licking and pawing, and begin showing anxiety as soon as their owners start preparing to leave. Some dogs even become aggressive towards their owners when they see them performing actions like picking up their keys or putting on their coat.

It is normal for separation anxiety to occur in young puppies around 1-2 months of age, but it is considered a disorder if it persists for a long time after that. In fact, the disorder can actually become more common as dogs get older, perhaps because they become less able to adapt to changes in their environment.

The disorder is also more common in dogs that have been adopted from a shelter. The loss of their first (or second, or third) families may lead to these dogs becoming more anxious in the absence of their new owners. There also may be genetic and personality components to the disorder, considering it is more likely to develop in dogs that have other anxiety disorders such as noise or storm phobias.

Owners often inadvertently make separation anxiety disorder even worse when they punish their dogs when they return home (leading to further anxiety and fear) or attempt to solve the issue by adopting a second animal. The latter often does not help because the anxiety is caused by a specific attachment to one person- the owner- not general loneliness.

Separation anxiety disorder in dogs is often treated with SSRIs, but the most effective methods of reducing it have been found to be a combination of medication and behavior modification.

Separation anxiety disorder occurs less frequently in cats than dogs, but usually manifests as hypervocalization and elimination outside the litter box. Compulsive grooming to the point of raw skin or bleeding is also common.

The fact that separation anxiety disorder is seen so often in both dogs and cats is hypothesized by many to be partially due to the neotonization process that both species went through during domestication. The retention of juvenile behaviors like excessive vocalization, affection and playfulness could also lead to the retention of a more juvenile-like psychology, i.e., the need for the parental figure to be around all the time.

Pica

An x-ray showing rocks in a dog’s stomach.

Pica is the consumption of non-edible substances, such as dirt or glass. It is not a species-specific phenomenon, and does also occur in humans. It is also not always considered a disorder, because many animals are naturally driven to consume non-edible substances like clay to obtain nutrients that they aren’t getting in their conventional diet.

Where pica becomes classified as a disorder is when an animal compulsively eats non-edible objects that have no nutritive value. Sometimes the disorder can still relate to a physiological need- for example, many dogs that display pica may have thyroid problems. However, what starts as a response to a thyroid problem or other medical or diet issue may continue even after the problem is treated, leading to a long-term behavioral disorder. In cats, some of the most common objects ingested are string or wool, while in dogs it can be rocks or gravel.

Objects removed from one cat’s stomach.

Pica in dogs can also manifest as coprophagia, or feces-eating. Mother dogs do naturally eat the feces of their newborns, an adaptation to help hide them from predators, and some dogs will eat their own feces to make an area cleaner (particularly if in a cramped crate or cage). Some dogs, however, show compulsive coprophagia- that is, they will eat any feces they come across, dog or otherwise.

I’ve known several dogs with such intense pica that they had to wear muzzles at all times when they weren’t being supervised. One such case, in a standard poodle, resulted in tragedy- she got her muzzle off and ate a sock, which got lodged in her intestinal tract. She had to be euthanized.

Pica as a behavioral disorder is an extremely difficult behavior to correct once it starts, and can be life-threatening, but little research has been done to understand why it is such a prevalent problem in domestic cats and dogs. Some evidence exists to suggest that pica can be a response to stress, such as separation anxiety, and there may be a genetic correlation to certain types of pica such as coprophagia and wool-sucking, but for the most part it remains a mystery.

Anorexia

Much like with self-harm, it often surprises people that animals can experience anorexia; however, many of us are familiar with a dog or cat that stops eating due to anxiety. Anorexia actually simply refers to self-starving behavior, while anorexia nervosa specifically refers to the human eating disorder.

Like pica, anorexia in animals can occur due to dietary or health issues, and becomes a disorder when it occurs in a healthy animal with access to good-quality food. It most frequently manifests as a result of stress or anxiety, and many different animals, from rats to sheep, experience different variations of it. I’ll briefly go over one version of this- thin sow syndrome.

Thin sow syndrome is an eating disorder that affects female pigs, most commonly either just after they give birth or just after they have finished weaning their piglets. The sows begin eating less food and may show other symptoms such as hyperactivity, chain-chewing, and pica. Despite sufficient food being constantly available, pigs will become emaciated and eventually die without intervention.

The syndrome has genetic components, as it appears more often in lines of pigs bred for leaner meat, and is more likely to occur in conditions that are overcrowded, or when the sow in question is moved to a new social group. It appears to be related to extreme stress, and is difficult to reverse by behavioral methods alone. There has been limited success in treating the sows with antidepressants and anti-anxiety drugs.

Canine Compulsive Disorder

I discussed compulsive grooming and self-injurious behavior earlier in the article, and both are symptoms of canine compulsive behavior. However, other symptoms are vastly varied, and include movement stereotypies, repetitive pica, excessive light-chasing, flank-sucking or wool sucking, tail-chasing, snapping at the air, upward gazing, and a host of other bizarre rituals.

Any of these behaviors could be seen as ordinary if performed infrequently, but in a compulsive dog they occur constantly and almost out of the animal’s control. Watch this video to see what I mean.

Canine compulsive disorder is diagnosed when the compulsive behaviors interfere with the dog’s ability to get through its day to day life, like in the video I liked above.

There are a number of proposed causes for these repetitive behaviors. The main one, of course, is stress and trauma in early life. The compulsion might arise due to an inability to perform normative behaviors, such as when a dog is kept in a small crate for long periods of time, unable to walk or run. The compulsive behavior can occur as a redirection of frustration and become ‘wired in’ with enough repetition. Then the dog in the crate may continue to perform the compulsion even when the crate door is opened.

Some types of compulsions, such as flank-sucking, wool sucking, and forms of pica, may also be due to early weaning and maternal deprivation, where the animal never loses its early oral fixation.

Other compulsions appear with no apparent environmental cause at all. Genetics also plays an important role in the disorder. Many specific compulsions are more common in certain breeds. In dobermans, a gene has been found that correlates to flank-sucking behavior. Here’s a video of a doberman unable to stop flank-sucking. You can see that the behavior occurs on a couple of occasions immediately after the dog is stopped from doing something else like jumping up.

Certain compulsions, particularly those related to apparent hallucinations (snapping at the air and staring upwards) or repetitive motor activity (spinning) may also be due to neurological diseases and partial seizures. In truth, canine compulsive disorder is probably similar behavior with many different proximate causes lumped together under an umbrella term.

Whatever the cause, canine compulsive disorder is extremely difficult to successfully treat, which can be problematic. Some compulsions may merely be annoying, like spinning, but many are actively harmful to the dog’s health. Acral lick dermatitis is one of these- the dog will lick itself in a specific spot until the skin is raw and bleeding, and often can only be stopped by putting it in a muzzle or cone.

Behavioral modification through training alone almost never reduces the symptoms of canine compulsive disorder, and often worsens it, as the owner either increases stress through punishment or inadvertently reinforces the behaviors by rewarding them. As with separation anxiety disorder, a combination of medication and training may help, along with a regular schedule and reduction of confinement or restriction of normal behavior. However, even with all that, severe cases of CCD may only show mild reduction of symptoms.

Conclusions: Do Animals Suffer From Mental Disorders?

I’m not really going to try to answer that question; I’ll let you guys decide for yourselves. I think instead the keyword is ‘suffer’- that is, many, many animals suffer from pain that seems to come from nowhere else besides the mind. Veterinarians and animal researchers are already well aware of this; it is the public that seems to have a hard time catching up.

Many people are strangely resistant to the idea that animals should be put on things like antidepressants or anti-anxiety medication, despite the fact that they have been used to manage captive animal behavior since at least the 80s. I won’t deny that it’s more desirable to fix the issue through behavioral modification alone, as it is with humans, but the persistent denial that behavioral drugs should be used on animals to me almost smacks of a refusal of the idea that animals can experience long-term mental suffering.

And it is a shame, because many animals that show these behavioral issues are simply put down in the end, because people aren’t willing to put in the time and energy to try and find a way to treat them.

Many animals in captivity suffer mentally because of things we have done, and I think that it is our responsibility to try as hard as we can to help them.

References (suggested reading is starred)

American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (5th ed.). Arlington, VA: American Psychiatric Publishing.

*Bradshaw, G. A., Capaldo, T., Lindner, L., & Grow, G. (2008). Building an inner sanctuary: complex PTSD in chimpanzees. Journal of Trauma & Dissociation, 9(1), 9-34.

Bradshaw, G. A., & Schore, A. N. (2007). How elephants are opening doors: developmental neuroethology, attachment and social context. Ethology, 113(5), 426-436.

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Cox, W. T., Abramson, L. Y., Devine, P. G., & Hollon, S. D. (2012). Stereotypes, Prejudice, and Depression The Integrated Perspective. Perspectives on Psychological Science, 7(5), 427-449.

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*Dao, James. (2011). More military dogs show signs of combat stress. New York Times Magazine.

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*Ferdowsian, H. R., Durham, D. L., Kimwele, C., Kranendonk, G., Otali, E., Akugizibwe, T., … & Johnson, C. M. (2011). Signs of mood and anxiety disorders in chimpanzees. PLoS One, 6(6), e19855.

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*Garner, J. P. (2005). Stereotypies and other abnormal repetitive behaviors: potential impact on validity, reliability, and replicability of scientific outcomes. ILAR journal, 46(2), 106-117.

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Hewson, C. J., Luescher, U. A., & Ball, R. O. (1998). Measuring change in the behavioural severity of canine compulsive disorder: the construct validity of categories of change derived from two rating scales. Applied animal behaviour science, 60(1), 55-68.

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*Landsberg, G. M., Hunthausen, W. L., & Ackerman, L. J. (2012). Behavior Problems of the Dog and Cat. Elsevier Health Sciences.

Lumeij, J. T., & Hommers, C. J. (2008). Foraging ‘enrichment’as treatment for pterotillomania. Applied animal behaviour science, 111(1), 85-94.

McKeown, D., Luescher, A., & Machum, M. (1988). Coprophagia: Food for thought. The Canadian Veterinary Journal, 29(10), 849.

Nagasawa, M., Mogi, K., & Kikusui, T. (2012). Continued distress among abandoned dogs in Fukushima. Scientific reports, 2.

*Nestler, E. J., & Hyman, S. E. (2010). Animal models of neuropsychiatric disorders. Nature neuroscience, 13(10), 1161-1169.

Nind, M., & Kellett, M. (2002). Responding to individuals with severe learning difficulties and stereotyped behaviour: challenges for an inclusive era. European Journal of Special Needs Education, 17(3), 265-282.

Novak, M. A. (2003). Self‐injurious behavior in rhesus monkeys: new insights into its etiology, physiology, and treatment. American Journal of Primatology, 59(1), 3-19.

Overall, K. L., & Dunham, A. E. (2002). Clinical features and outcome in dogs and cats with obsessive-compulsive disorder: 126 cases (1989-2000). Journal of the American Veterinary Medical Association, 221(10), 1445-1452.

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Paylor, R., Nguyen, M., Crawley, J. N., Patrick, J., Beaudet, A., & Orr-Urtreger, A. (1998). α7 nicotinic receptor subunits are not necessary for hippocampal-dependent learning or sensorimotor gating: a behavioral characterization of Acra7-deficient mice. Learning & Memory, 5(4), 302-316.

*Schwartz, S. (2003). Separation anxiety syndrome in dogs and cats. Journal of the American Veterinary Medical Association, 222(11), 1526-1532.

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Swaisgood, R. R., & Shepherdson, D. J. (2005). Scientific approaches to enrichment and stereotypies in zoo animals: what’s been done and where should we go next? Zoo Biology, 24(6), 499-518.

*Tiefenbacher, S., Novak, M. A., Lutz, C. K., & Meyer, J. S. (2005). The physiology and neurochemistry of self-injurious behavior: a nonhuman primate model. Front Biosci, 10(1), 1-11.

*Treasure, J. L., & Owen, J. B. (1997). Intriguing links between animal behavior and anorexia nervosa. International Journal of Eating Disorders, 21(4), 307-311.

*Yenkosky, J. P., & McCarthy, E. (2010, August). Post-Traumatic Stress Disorder among parrots in captivity: Treatment considerations. In ASSOCIATION OF AVIAN VETERINARIANS (p. 17).

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