Animals Who Fear Too Much

Anxiety and Panic Disorders

If having a soul means being able to feel love and loyalty and gratitude, then animals are better off than a lot of humans.

—JAMES HERRIOT

When Mindy, an eight-year-old spayed female dog, came to me at Tufts, her owner wrote down “stranger anxiety” on the admission survey as a description of her dog’s problem.

Mindy’s past made her ripe for behavior issues. She was adopted from a shelter when she was between three and five months old. She had then undergone a two-month quarantine period because of parvovirus infection and had probably not been socialized properly when young. Until the time of her adoption, Mindy had negative or at least inconsistent interactions with people and her isolation in quarantine at a formative time of her life had exacerbated her fearfulness and insecurity.

All these influences came together to produce a dog who was deathly afraid of all strangers. It was pitiful to see Mindy in the consulting room. To start with, she stayed close to her kindly owner or pressed herself close against a wall. Her whole demeanor was one of mistrust. She eyed everyone in the room with furtive sideways glances. When her owner moved away from her, she hid under my desk and refused to come out, not even when lured with offers of food.

Because of her overwhelming fear of strangers, Mindy had been treated with mood-stabilizing medication for most of her life. Her owner tried to wean her off the medication at one point, but Mindy had gotten much worse and had to be put back on it again. My job was to optimize Mindy’s medications, to tweak her drug regimen, to try to make her a little more social. I also advised her owner on how to modify his pet’s behavior and coax Mindy out of her shell. Mindy somehow had to learn that not all people are to be feared. During the office visit, we had some success with Mindy eventually taking food treats from her safe place under my desk.

Although she improved considerably after our first encounter, Mindy still remained far from confident in the company of people. I should have predicted such an outcome, because, sadly, fears once acquired are not easily forgotten.

Anxiety can express itself in many different ways, including situational anxiety, social anxiety, stranger-induced anxiety, and generalized anxiety. There are as many brands of anxiety as there are of fear. Anxiety also underlies obsessive-compulsive disorder. For such a varied condition, it’s odd that the diagnosis of anxiety can still be controversial.

I once read a behavioral pharmacology textbook that confidently labeled fear as a major component of anxiety. That’s obvious, right? Yet many experts take exception to this as an overly liberal linking of the two concepts. But I think it has some merit. Fear and anxiety are related in their underlying neural mechanisms, though we—and animals—obviously express them somewhat differently.

Fear and anxiety can be situational and temporary, or ongoing and debilitating. Fear occurs when a potentially noxious stimulus is actually present, right there in front of us—animal or person. Anxiety, on the other hand, is an anticipatory type of fear. A pet fears that something bad may happen, or that something highly desired, like an owner’s return, may not come to pass. With anxiety, a direct stimulus is not present, so we call it objectless.

If a primate sees something scary, he naturally reacts with a “fear response.” It’s a natural protective reaction designed to prepare the animal for fight or flight. The stimulus might be a snake, fear of which is innate and anchored deep in our biology. As a primate, you really don’t want to step on that possibly poisonous snake in the grass or have it drop on you from a tree.

Primates and many other animals are genetically predisposed to react with fear to various triggers, including snakes in the grass, hawks circling overhead, and spiders. Nature knows best. So we have genetically determined causes of fear, and we also learn certain fears. When an animal is scared by an event or object, memories are stored for future reference. This “fear learning” is adaptive, in the sense that it is good for an individual’s survival. All of us mammals share this ability to learn from experience—and the tendency to react fearfully to and want to avoid a remembered negative experience.

Fear responses include the proverbial fight-or-flight reaction, freezing in position so as not to attract attention (as does a deer in headlights), hiding from the source of terror, or seeking the protection of another person, animal, or group. Another fear response goes by the tongue-twisting label of “thigmotaxic behavior.” With thigmotaxic behavior, a common strategy for rodents, animals hug the borders of a containment area, putting their backs to the wall, so to speak. Unfortunately, not all strategies work well for animals in the modern world. Freezing in the headlights of a car, for example, does not bode well for either the animal or vehicle.

In addition to these outward or operant behaviors, as these fear responses are called, automatic internal responses occur to prepare the animal to deal with the threat. These include increased heart rate, blood pressure, respiratory rate, hair standing on end, increased muscle tone, sweating, and, in dogs, salivation.

These fearful operant and autonomic responses are similar to what happens when an animal is anxious, but less well defined. Classic manifestations of anxiety include attempting to escape from an acute anxiety-promoting situation, avoiding contact with a disquieting person or other animal, hypervigilance, nervous pacing, stomach upsets, and digestive disorders.

Both fear and anxiety can be functional, that is, they can help an animal or person be properly prepared for challenges that they encounter. But fear and anxiety can also become overreactions. Excessive and dysfunctional fearfulness, phobias, or excessive anxiety caused by overactivity in certain brain circuits, can interfere with daily life and cause debilitating psychological problems.

Many people ask whether animals can experience anxiety, to which my answer is a resounding yes. Of course, you can’t ask an animal whether it is feeling anxious and hope to get a definitive answer. But by all other assessments—by outward behavior and measurement of internal responses—anxiety in pets is as real an entity as pain. Anyone who lives with animals knows this. Pet owners more readily accept that animals can feel anxiety than some purist behavioral scientists.

Because of the constraints of Morgan’s Canon, some scientists balk at the concept of an animal feeling anxiety. Real scientists, they believe, should always find a way of explaining behavior in basic mechanistic or reflexive terms, rather than attributing what they see to a cognitive process.

Research data on brain function, unavailable to Morgan when he formulated his canon, now show that the neurological centers governing fear and anxiety are similar in people and animals. The amygdala, the brain’s Grand Central Terminal for both fear and anxiety, lights up on PET imaging scans in anxious and fearful animals and people.

A long-term memory center, the hippocampus, is also involved in propagating the response. Connections between the amygdala, hippocampus, and hypothalamus facilitate release of stress hormones, like epinephrine and cortisol. Epinephrine increases heart rate, blood pressure, and the caliber of the respiratory passages. Pupils dilate widely. Depending on the species, the mouth of some animals goes dry because of lack of saliva, and dogs drool a thick viscid saliva. In addition, endorphins are released in reaction to fear.

So in both people and nonhuman animals, the same neurotransmitters are released in brain regions that deal with anxiety and similar behaviors result. The similarities of people’s and other animals’ responses are quite clear to me. Morgan’s Canon be damned.

Why would nonhuman animals not be self-aware? Why would they be incapable of projecting bad outcomes for themselves? Recall the Harvard research studies that strongly suggest that dogs possess “theory of mind,” demonstrating that some other creature knows something that they don’t know. Other studies show that dogs can be jealous and that dogs laugh, making a happy huffing sound when they are amused. Kenneled dogs calm down and stop barking when exposed to sounds of other dogs huffing with laughter.

Finally, dogs have been reported by scientists at Bristol University to have either optimistic or pessimistic character traits. Joy is the primary emotion underlying optimism and sadness is the primary emotion underlying pessimism. By this score, laughter should occur more often in optimistic canines and anxiety may occur more frequently in sadder, more pessimistic dogs. Which is exactly what the research shows.

Put a dog in an anxiety-promoting situation, or leave him alone in a strange place, and observe him pacing, whining, and breathing hard. Measure his heart rate, blood pressure, and stress hormones such as cortisol and endorphins, and you will find them all elevated. Then reverse this whole situation with a known antianxiety medication.

Other than anxiety, what explanation can there possibly be for the similar brain activity and physical behavior? To me it’s a no-brainer, so to speak. Dogs can be anxious, cats can be anxious, horses can be anxious. All animals can be anxious.

In people, a common type of anxiety occurs as a panic attack, in which intense feelings of fear or discomfort are accompanied by several physical signs of distress, like sweating, trembling, and shaking. These attacks can be so severe that sufferers often believe that they are going crazy or are about to die. They feel an overwhelming instinct to flee from wherever they are, but sometimes are so overwhelmed that they pass out. Panic attacks can arise unexpectedly or they can be provoked by certain environmental factors.

I am not sure that dogs have panic attacks that occur with no specific trigger, but they surely experience such attacks in situations that scare them. One dog I treated had “panic attacks”—as described by his owner—several times a day.

Spock earned his name because of his large, batlike ears. Unlike his namesake, Spock was emotionally over the top, and illogically so. He would become totally hysterical several times a day, pacing, panting, and vocalizing for several minutes at a time. In this specific case, the trigger turned out to be the remote sound of any form of power equipment in a nearby neighbor’s house.

Another dog exhibited the same type of behavior several times a day, but only in his owner’s home, never when at a friend’s house. The trigger in this case, determined later by a process of exclusion, was the owner’s own parrot, whose screeching terrified the poor dog. Another pooch reacted to the sound of steam blasts emitted from a clothes iron.

Some people who have panic attacks also have agoraphobia. They may panic when home alone, as the definition includes being in any inescapable situation, not simply being in a wide open space. The separation anxiety that dogs suffer resembles a panic attack, with affected dogs showing physical signs of severe anxiety.

Separation anxiety occurs in some 15 to 17 million of the nation’s 78 million dogs. Certainly some dogs seem to inherit a tendency to develop separation anxiety, so nature possibly plays a part, but inadequate nurture at an early stage of life seems to be the most important factor. At Tufts, when a dog comes in with separation anxiety, we ask the owner a series of simple questions regarding the pet’s early upbringing.

• Was the dog separated from his mother and littermates too early, i.e., before eight weeks?

• Has he had multiple owners?

• Did you acquire him from a shelter?

Almost always, positive answers to these questions indicate that the dog had a dysfunctional early puppyhood. Young dogs should not have to face these stresses. There’s a basic rule: The more consistent the attention paid to a youngster in an early sensitive period of development, the more confident the adult animal will be. The opposite also tends to be true. Less attention and more disruptive environments lead to anxiety-related behavior issues. It’s the same for people.

At least half the dogs with separation anxiety come from a shelter. When this is not the case, I can usually identify periods when the dog, as a puppy, was isolated, frightened, or psychologically traumatized.

Two responses to psychological trauma are common in people: they either seek to take greater control of a situation or they lose self-esteem or confidence. Dogs with separation anxiety have little confidence. They can make for the sweetest pets, following at their owner’s heels everywhere around the house. They are generally worried or anxious, offer frequent appeasement gestures, and live in mortal dread of their owner’s absence. Whenever their owner does prepare to leave, they become extremely anxious, pacing, whining, hiding, or shaking with fear. After the owner leaves, they pace, whine, bark, or howl, and sometimes panic. Those who try to escape may damage doors, windowsills, or blinds. Others act out their frustration with displacement behavior, destroying couches and cushions, cupboard doors, or other wholly innocent targets. Some dogs throw up because of the anxiety. Few pay any attention to food, displaying so-called psychogenic anorexia. Many have “accidents,” soiling the house.

Unwitting owners quite often attempt to resolve the hallmark destructive behavior by crating their dog. That may solve the owner’s immediate problem, but it does not usually address the pet’s underlying issues. Some dogs become even more hysterical when crated, damaging themselves and the crate in sometimes successful attempts to escape their confinement. In the midst of crate panic, it’s as if the pet entered the phone booth as Clark Kent and emerged as Superdog, developing the strength of ten. Superdog will bend and buckle the metal bars of crates as if they were made of putty. In the process, they may chip teeth, bloody their mouths, or break off claws. Owners who try the confinement solution might return to find their dog still in the crate but bathed in blood and standing in a pool of saliva. One crated dog barked so hard and for so long that he jumped his crate across the floor with the vibrations. Reaching the door where his owner’s purse was hanging, he sucked it in through the bars and ripped it open, strewing its contents—makeup included—around the inside of the crate. Then he continued to bark and managed to jump the crate back to its original position. When the owner came back, she was stunned with what she saw—the torn purse inside the crate, not where she had left it, and the dog enthusiastically welcoming her home with lipstick all over his face. It was a sight for sore eyes.

Separation anxiety can be a burden for owners and neighbors, who may complain about the dog’s continuous barking when alone. Owners often have costly property damage. Many owners are angered by the behavior and damage, but others feel sympathy for their pet. As bad as all this is for owners, it is worse for the dog. Many of these traumatized pets are exiled to shelters, some to face euthanasia.

One dog with the most severe separation anxiety I have ever seen leaped clean out of a window—except the window was shut. He broke right through the glass and fell to the ground below. The neighbors heard the crash and ran outside to see what was going on. When they saw the broken window smeared with blood, they concluded a vicious crime had been committed and called the police. The owners later found the dog wandering, cut up and bleeding profusely. When I saw the dog, he was covered with bandages like an Egyptian mummy.

The causes and symptoms of feline separation anxiety are similar to those of dogs. Cats vocalize and pant and pace. They don’t usually make enough noise to disturb the neighbors and are not powerful enough to trash micro blinds or destroy doors and window moldings. Anxious urine marking occurring only in an owner’s absence is a cardinal feature of the condition in cats.

Children get separation anxiety, too, a state of affairs that would be easy to predict even if it had been never before described. Separation anxiety is one of those situational anxieties that are well-recognized in human kids, especially when it comes time to leave Mom and go to school for the first time. My now fully grown and wonderful daughter Keisha had a bout of separation anxiety when she was very young, when we enrolled her in day care. Her symptoms of crying, inappetence, and panic were similar to those I see in my canine patients. She was too young to try to escape day care in order to get to her mom but otherwise the parallels were undeniable.

To prevent separation anxiety for children and dogs, it is best to train independence gradually, in order to avoid the sudden loss of an attachment figure. My daughter recovered from her separation anxiety and is now confidently living away from home, having graduated from medical school. Puppies are all too often taken too early from their mothers in puppy mills and stuffed into pet stores. We can help dogs with separation anxiety by avoiding prolonged absences from home, independence training, environmental enrichment, and, when necessary, antianxiety medication.

Another kind of anxiety is social anxiety, which the chronically cowering Mindy displayed. Genetics probably plays a role in setting up animals for this condition, but improper socialization leading to lack of confidence in social settings is the precipitating factor.

One study found that cats not exposed to people in the first seven weeks of life were always on edge in the presence of people. This sensitive period is crucially important to normal feline development, too. Certainly cats who have not been socialized can form close relationships with one or two trusted individuals, though total acceptance of people apart from those of their inner circle is not a realistic expectation. When these cats are around even well-intentioned, nonthreatening strangers, their anxiety is practically palpable. Mostly they simply hide under furniture and remain stressed and hypervigilant until the person they see as a potential threat is long gone.

Socially anxious canines also become stressed in the presence of unfamiliar people. They are not aggressive, just anxious. Dogs may squat and urinate around strangers or even their owners. Although commonly misunderstood by owners, submissive urination is a gesture of appeasement, designed to assuage the perceived threat. Getting angry or impatient with a dog who does this makes the problem worse.

Dogs with social anxiety dread crowds, even when nothing bad is actually happening. Underexposure to people in the sensitive period of development causes dogs to develop social anxiety. A severely circumscribed life, as occurs in brood bitches in puppy mills, will totally destroy self-confidence in dogs and lead to social anxiety.

Adult humans may suffer from social anxiety and there is some evidence that genetic factors play a role in its development. But, again like dogs and cats, environmental factors are more intimately involved. Children with social anxiety dread all interactions in a public setting, often worrying that they will be judged negatively by other people. They also are afraid of strangers. Stranger anxiety typically occurs in children under one year of age when they are looked at or approached by a total stranger. It is so common for children to have this fear at this stage of life that it is considered almost normal. At this early point in development, stranger anxiety is certainly not considered a phobia.

Young puppies and kittens may go through a similar stage. A stranger in the house might cause fear, flight, hiding, or overly extreme and abjectly submissive reactions. With good management, this is a fleeting phase of development. In both people and pets, if stranger anxiety persists into adulthood, it is termed social anxiety.

Generalized anxiety disorder (GAD) is a psychiatric diagnosis that we frequently use to describe some generally nervous or fearful pets. The fourth edition of the DSM states that, for diagnosis of this condition, people must experience chronic anxiety and excessive worry, almost daily, for at least six months. They also must have three or more defined symptoms, including “restlessness or feeling keyed up or on edge, being easily fatigued, difficulty concentrating or mind going blank, irritability, muscle tension, sleep disturbance.”

There is no doubt that GAD also exists in pets. Some dogs seem locked into a perpetual state of worry and display ongoing anxiety in three areas: anxiety around people, anxiety concerning certain sights and sounds, and one or more situational anxieties. This is a behavioral “full house” as far as anxiety is concerned. These animals may develop fears to the level of phobias or manifest the anxiety-based condition of obsessive-compulsive disorder.

Brood mothers from puppy mills frequently have the behavioral full house of anxiety that I classify as GAD. Practically afraid of their own shadows, brood bitches from a puppy mill will cower around people, seemingly terrified of everyone and everything. They often remain silent, never barking at all, and do not wag their tails. They don’t know how to play. Most do not recognize or climb stairs, have no idea about cars or car travel. They are, in general, totally wretched. Their cruel fates have robbed them of their normal canine selves.

Fortunately, something can be done to address such ongoing anxiety. It takes time, patience, and positive training methods. In the right hands, GAD dogs can be usefully rehabilitated in about a year. They are not “cured” in the absolute sense of the term, but they have been coaxed out of their fear and into something resembling normal doghood.

About twenty years ago, I was talking to my next-door neighbor, John, in his front yard. John told me he had been experiencing anxiety as a result of a number of unfortunate experiences occurring simultaneously. He had been trying to hold down three jobs and become unable to sleep properly as anxiety spilled over into the nighttime hours. John found himself caught in a catch-22. Because he couldn’t sleep, he couldn’t do his work well and feared losing his primary employment as a school chemistry teacher. This made him worry even more. His doctor put him on the antianxiety medication buspirone, which was brand-new at the time and it had worked beautifully. Now he could sleep and handle his multiple jobs. Because he felt better, he worried less. He was a new man.

Using buspirone in a veterinary situation was somewhat novel at the time, but when I found that it worked as an antianxiety treatment in my animal patients, I decided to apply for a US patent. The patent examiner, however, was apparently a man ahead of his time. He declined the patent application. The grounds? Such a use was “obvious to one skilled in the art.” Of course an antianxiety treatment for people would also be effective in animals. The idea was too baldly apparent to warrant protection. The examiner turned out to be an early One Medicine proponent, probably without even being aware of the fact.

There was one part of the application that he did approve. I was granted a patent for the use of buspirone to treat anxiety-related urine marking in cats. Considering the logic the examiner was applying, it was odd that even that claim was allowed.

The anxiety-related conditions that occur in people and the equivalent ones in animals, all respond to similar behavioral modification therapy and identical medications. Buspirone and serotonin reuptake inhibitors, such as Prozac, Paxil, and clomipramine, are effective for treating anxiety in people as well as dogs, cats, and horses. Two of these medications, fluoxetine (human brand name Prozac) and clomipramine, are licensed by the FDA for the treatment of separation anxiety in dogs. It moves me to ask a question of the scientists who adhere to Morgan’s Canon: What part of One Medicine don’t you understand?

The bottom line regarding animal anxiety is that, if it looks like anxiety, has similar internal changes as the ones that occur in human anxiety, and can be successfully treated with the same medications as people with anxiety, then it probably is anxiety.

Help for treating animals suffering from anxiety came from an unexpected quarter. One of the most celebrated people with autism is the scientist, animal activist, and best-selling author, Temple Grandin. When I worked with Temple a few years ago, I learned a lot about how to reduce anxiety and stress reactions in animals.

I first met Temple when she was a PhD student at the University of Illinois, researching environmental enrichment in young piglets and its effects on brain development. An expert on farm animal behavior, especially the behavior of cows and horses, Temple had risen to become an academic star and visited Tufts to give a lecture.

Temple’s relationship with animals is in some ways otherworldly. She seems to intuitively understand animals and their behavior, and she is able to build up nonverbal rapport with almost every creature she meets. If she sits down in the middle of a field of cows, the cows will be drawn to mill around her. They appear to recognize her empathy, and they react accordingly.

Temple has high-functioning autism—sometimes referred to as Asperger’s syndrome. Her remarkable skill in understanding animal behavior has made her, perhaps paradoxically, one of the world’s most sought-after designers of slaughterhouse facilities.

Her philosophy is that, since people are always going to eat animals, we should see to their welfare and, when their day comes, ensure they experience as little stress as possible. Not only is it the humane thing to do, but stress can trigger surges of adrenaline and other stress hormones, which can negatively affect the taste of meat. A careful, respectful send-off works for both the stock animals and the meat purveyors.

Away from their home barns or pastures, animals clearly feel great amounts of fear, uncertainty, even terror. Temple has noted the calming effect of controlled restraint of animals with mechanical devices. For example, in slaughterhouses, pigs are transported from point A to point B on a conveyor belt and squeal in fear. When they are restrained in a V-shaped contraption called a V-trough, however, their squealing is effectively eliminated. The effect of the V-trough seems profoundly sedating. Even when the workers leave the plant for lunch and turn off the machinery, any pigs suspended in transit in the V-troughs remained relaxed and silent, almost falling asleep.

At Tufts, we used V-troughs to calm and restrain pigs prior to anesthesia. A raucous, violently struggling 100-pound swine is a tough animal to control, as county fair greased pig contests can attest, but once installed in a V-trough a pig becomes serene, almost mesmerized. The effect is as dramatic as hoodwinking a bird, hypnotizing a chicken, hobbling a horse, or scruffing a cat.

Babies, too, are soothed when swaddled tightly. When she herself was young, Temple did not like being hugged by well-meaning relatives, although she felt comforted when she wrapped herself tightly in the blankets of her bed. This type of gentle, persistent, and controlled pressure generates feelings of well-being.

When in college, Temple designed and developed a squeeze machine for herself, a boxlike structure in which an average person can sit, with inflatable pads that can be controlled to exert pressure on the torso. The effect is calming but not stifling. With just the right amount of pressure for just the right amount of time—about twenty minutes—Temple would emerge from the machine relaxed and happy, able to go through her day with less stress and with a lot more focus. She shared this technology with various autistic centers around the country so that they, too, could use them in therapy for autistic children. Dr. Oliver Sacks, who wrote about Temple Grandin in his book, An Anthropologist from Mars, tried Temple’s machine and reported feeling perfectly relaxed afterward.

Just what exactly was going on, in terms of biochemistry, when a pressure is calming? After her talk, Temple and I discussed her V-troughs and my work with cribbing horses. The cribber’s repetitive actions cause the brain to release endorphins, which help the horse cope with the stress of confinement. Endorphins, natural morphine-like substances released by reward centers in the brain, cause feelings of warmth and pleasure.

Temple asked, “Do you think that the pressure effect of the squeeze machine releases endorphins?”

“Could be,” I said.

“Maybe that’s why I find the squeeze machine addictive,” she said. “I make a point of limiting my use of it to twenty minutes a day. I tell that to people in the autistic centers, too, that they shouldn’t let people get too fond of it. It’s easy to get addicted to a behavior. That’s what happened with your horses, isn’t it?”

“Do you think we could run an experiment together?” I asked. “We could try blocking the temporary squeeze-induced bliss in pigs, for example, using an opioid antagonist.”

Temple liked this idea. “It’s easy to work with pigs,” she said. “You’ve got some on the campus, haven’t you?”

“We have pigs in a place called Hog Heaven. Perhaps they would volunteer to be our subjects?”

“They may even enjoy it,” Temple said drily. “I’ll draw up plans for a pig-size squeeze machine and you can have the machine made. Then we’ll run a score of pigs through that machine, give half of them saline for control, and the other half we’ll give your blocker drug . . .”

“Naltrexone,” I said.

We had a plan. That is, as long as the pigs agreed.

A few days later, Temple’s blueprint plans for a pig squeezer arrived, a marvel of draftsmanship. One of Temple’s many extraordinary gifts is an ability to draw up and read blueprint designs as if they were three-dimensional objects. Her drawings were works of art.

I gave the plans to the university carpenter, who fabricated a very fine-looking portable squeeze chute for pigs, a padded V-trough with a lever. When the lever was pressed, the sides of the V came closer together to produce gentle pressure on each side of the pig’s body. With the machine completed, we were ready to try our experiment. Temple flew in from her home in Illinois.

The temperature was already in the midnineties that summer day. The piggery at Tufts is buried deep in the woods surrounding the campus. I slid open the door to the piggery and we struggled to get the squeeze machine through the small door, eventually managing to position it in the center of the aisle that divided two rows of pens. By this point the pigs were squealing in anticipation. Human visitors usually meant food.

Without any preliminaries, Temple hopped into the first pig’s cage, grabbed the animal by its hind legs, and lifted it onto the scale. This was no easy feat. Each piglet weighed sixty or seventy pounds. But Temple displayed impeccable pig-handling skills.

“Pig number 345, sixty-five pounds,” she hollered. “Ready for Solution A.”

I grabbed a prefilled syringe containing “Solution A,” aka saline, and injected it into the piglet’s buttock. The needle was so fine the pig didn’t seem even to notice the injection. Temple put the pig back in its pen and moved on to the next one.

“Pig number 581, sixty-two pounds,” she called out. “Ready for Solution B.”

“Solution B” was actually naltrexone, which blocks the action of endorphins in the brain. The experiment proceeded until we’d injected another ten pigs with either Solution A or Solution B.

About an hour after we’d begun, we returned to the first piglet. We attached ECG sticky pads onto the pig so that we could get an instantaneous measure of the animal’s heart rate and its rhythm. Temple heaved the animal up and over the bars of the pen, placing it in the padded V-trough. I engaged the lever to apply pressure, and at the same time hit the start button on a stopwatch.

We observed the pig closely for signs of relaxation, like fluttering eyelids, slow breathing, and loosened muscles. Just as Temple had predicted from her slaughterhouse observations, and just as I had noticed when I anesthetized pigs, each animal tested gradually began to relax into a soporific state once the pressure was applied. At the point of maximum relaxation, which came usually between two and five minutes, I hit the stopwatch button again and noted the time.

The first pig, who had been given Solution A, the saline, took 110 seconds to relax. Unfortunately for this blissed-out piglet, we then rudely awakened and hoisted him back into his pen. Clearly none the worse for wear, he rooted around in the straw bedding, grunted a few times, and then lay down, perfectly happy.

Temple grabbed the second piglet and we repeated the whole procedure. This pig had been given the drug that stops the endorphin rush. It remained alert in the V-trough, grunting and tense, for much longer than the first pig.

“I think it’s working,” Temple said.

When the second pig finally drifted into a dreamy state, I pressed the stop button on the stopwatch at 300 seconds.

“That’s nearly three times longer than the first one,” Temple said.

On we went until all the pigs had been tested. By the end of the day, our hair smelled of pigs, our hands smelled of pigs, our clothes smelled of pigs. Flies buzzed around us excitedly, unable to decide who to settle on, us or the pigs. But we had very interesting data to study, so we didn’t mind.

The next day, we used a different barnload of squealing piglets. We wrangled, injected, pressurized, and recorded, until we once again smelled like two large ungulates, and had additional data to analyze.

Temple flew back to Illinois, and called me the next morning, having entered the study data into her laptop on the flight home. She had also calculated the “means and standard deviations” of the relaxation times, comparing the results of the two groups of Solution A and Solution B pigs.

“Guess what?” Temple said. “Just as we thought. There is a significant difference.”

We had clearly proven that endorphins are involved in the calming effect of controlled squeezing. The pigs that received the saline injection relaxed much more quickly than did the pigs given the endorphin-blocking drug. We had taken a significant step forward in understanding how to alleviate stress, both in animals and people.

Autistic children seem to have roller-coaster-ride levels of endorphins throughout the day. When levels are low, our results suggest, the squeeze machine can help boost endorphin release and normalize their feelings. High levels of endorphins though may be responsible for the frantic head banging that is sometimes a feature of low-functioning autism. Endorphin blockers like naloxone are sometimes helpful in reducing this dangerous behavior.

Hugging may generate endorphins, too. It is a sign of affection, and may send a message through the medium of endorphins. Dogs who have generalized anxiety and thunderstorm phobia are now regularly suited up in tight-fitting vests or T-shirts, which produce about a 50 percent reduction in the signs of anxiety during storms. For dogs with separation anxiety when left by their owners in a kennel, vests lessened the rate of increase in heart rate.

While V-troughs, chutes, swaddles, and tightly wrapped arms are not exactly identical, each provides similar psychological benefits and comparable effects. Controlled pressure, both in animals and people, releases endorphins that lead to feelings of inner well-being or peace. The molecules of our emotions stress or comfort us in virtually the same ways.