animal instincts

Tourette’s in the Stable

Dr. Samuel Johnson, the British poet, biographer, and lexicographer, is said to have suffered from a neurological condition characterized by involuntary movements and vocalizations. Faced with a doorway, he would stop, count his steps precisely, and finally leap over the threshold, whooping and gesticulating. Today, we know that Dr. Johnson probably had Tourette’s syndrome (TS), a disorder that affects perhaps one in a thousand to one in a hundred people.

But you don’t have to be human to have TS. Working with Louis Shuster, professor emeritus of pharmacology, biochemistry, and neuroscience at Tufts medical school, I have studied horses that exhibit the same kinds of symptoms. The first horse we ever saw with what we now call equine TS was an Arabian stallion that constantly made large sweeping movements with his neck, glancing anxiously at his flank as if flies were biting him.

Since that first case, we have encountered many other afflicted horses and have published a report on them. It turns out the clinical signs of the equine disorder are similar to those of human TS on at least a dozen points. Motor tics are present in all cases. Some horses also exhibit loud, spontaneous squeals. Upon hearing the noises, even experienced equestrians say, “What the heck was that?” We have dubbed these sounds “equine vernacular” and believe they may be analogous to the obscenities that some human Touretters utter (so-called coprolalia).

The age of onset for TS in horses is usually equivalent to that for TS in humans. It occurs primarily in males, as is also the case with humans. And there appears to be a strong genetic predisposition. Both the sire and the sibling of one stallion we encountered were affected.

The sire used to kick savagely. In fact, this symptom—hemiballismus, which refers to the flying out of a limb—is another one that people, too, experience. In both humans and horses, hemiballismus is chronic and persistent, typically striking many times a day, and stress and sexual thoughts exacerbate it. For example, a stallion may be set off if a mare in heat passes by. Equine TS, like the human version, is ameliorated by absorbing activities and suppressed by chemical castration.

The condition is also associated with obsessive-compulsive disorder. Horses and humans alike become preoccupied with the boundaries of their environment and often engage in compulsive sniffing. And just as thresholds would provoke tics in Samuel Johnson, they sometimes cause horses with TS to rear. One of our students had his shoulder dislocated when a TS stallion he was leading reared up at an entrance (the student should have let go of the lead shank).

In a way that seems almost uncanny, horses and humans with TS seem to recognize each other. We witnessed this when we introduced two horses with TS, one on either side of a barrier. Both animals immediately went into a flat spin (that’s another one of the things they do) and began to bite at their flanks. Some time after that we introduced a person with TS to a horse with TS, again placing a barrier between the two. The horse began to spin, bite itself, and kick. The person broke into a bout of whooping and gesticulating.

I find it fascinating that animals and people exhibit almost identical disorders. The only human psychiatric condition we have not yet found in animals is schizophrenia, and even here further evaluation might be in order. Similarly, disturbed animals respond to the same drugs as disturbed humans. To Dr. Johnson, animals were perfect creations that “exhibit evidences of infinite wisdom, bear their testimony to the supreme reason, and excite in the mind new raptures of gratitude and incentives to piety.” Today, he would have to concede that all species are cut from the same frail cloth.

NICHOLAS DODMAN directs the Animal Behavior Program at the Cummings School of Veterinary Medicine and has written four bestsellers in the field. He is the editor of Puppy’s First Steps: The Whole Dog Approach to Raising a Happy, Healthy, Well-Behaved Puppy (Houghton-Mifflin, 2007). He is a pet expert for Time Inc. and Life magazine.