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23-November 2013

The one myth about cats that's actually true

Most of us know at least one cat myth. Maybe it has to do with the width of their whiskers, or their purported ability to steal breath from a baby. Most of these myths are crap. But clipnosis? Clipnosis, it turns out, is a real thing.

For those unfamiliar with the term, "clipnosis" refers to the phenomenon whereby a cat is rendered suddenly immobile by a gentle squeezing of the loose skin on the back of its neck. It's a little like "scruffing," only gentler, but we'll get to that in a second.

When I first heard about clipnosis I was skeptical. The word itself is a portmanteau that makes direct reference to hypnosis, a loaded term that really sets my skeptic-senses tingling. The expression "animal hypnosis" is sometimes used to describe a variety of immobility behaviors triggered by a range of stimuli, though the use of the phrase is problematic for reasons encapsulated by the title of the 1974 paper "Animal hypnosis: factual status of a fictional concept" (written by Gordon G. Gallup, Jr., the psychologist best known for developing the famed, if somewhat controversial, mirror test).

Suffice to say I was a little surprised when, in searching for more information about clipnosis, I came across a scientific investigation in The Journal of Feline Medicine and Surgery that sought to explore the phenomenon empirically. Led by Tony Buffington, a professor of Veterinary Clinical Sciences at Ohio State University, the study examined the effectiveness of clipnosis by placing, what else?, standard 2-inch binder clips along the neck-skin of 31 cats. Much to my relief, Buffington and his colleagues referred to the phenomenon not as "clipnosis" but as "pinch-induced behavioral inhibition," or "PIBI." "PIBI is just a very clear description of exactly what it is," Buffington said. Not only does it describe the method and the response, it also avoids "the more anthropomorphic term 'hypnosis,'" while differentiating the technique from "scruffing", a more intense and, Buffington says, controversial method of feline-handling. "PIBI is really a much gentler form of scruffing," and relies on the initial stimulus of lightly pinching the skin on the back of the neck, he explains.

All but one of the cats in Buffington's study was shown to have a positive response to the binder clips, a "positive" response being one in which the cat becomes passive, its spine curls and its tail dips between its legs.

Further observations led Buffington and his colleagues to conclude that PIBI is neither a fear nor pain response. The cats' pupils did not dilate, a physiological response often seen in fearful animals, and their heart rates did not increase. Nor did their breathing quicken. The cats also remained responsive, in contrast with cats seen to exhibit what is called "tonic immobility," whereby the animal will freeze and become entirely unresponsive in the face of highly threatening stimuli. In the end, Buffington and his colleagues conclude that the physiological response seen with PIBI likely evolved to make it easier for mother cats to transport their kittens.

But Why Does it Work?

The maternal-carrying hypothesis suggested by Buffington and his colleagues echoes that of other researchers who study animal immobilization. In fact, PIBI-like physiological responses have been observed in quite the range of animals, including mice, rats, rabbits, dogs and guinea pigs, to name a few; searching Google Scholar for "dorsal immobility" or "transport immobility" pulls up close to 200 studies dating back several decades that have investigated this and similar phenomena in one animal or another, many of which make direct reference the maternal carrying hypothesis.

In contrast, comparably little has been said about why this method of immobilization is so effective, physiologically, that is. "One of the reasons we decided to call the response 'pinch induced behavioral inhibition,' is that [this description] doesn't assume a mechanism," said Buffington. In other words, "PIBI" doesn't presume to offer an explanation for why pinching induces behavioral inhibition, only that it does. While a handful of studies have provided limited insight into transport immobility's physiological underpinnings, those underpinnings have remained, for many years, largely undefined.

Earlier this year, however, there was a breakthrough. In a study published in the May 2013 issue of Current Biology, researchers led by Japanese neuroscientist and RIKEN Brain Institute researcher Kumi Kuroda conducted a study that compared a wide range of physiological responses of infants to maternal-carrying not just in mice, but in humans. Incredibly, Kuroda's team found that in both species, the act of a mother carrying an infant leads almost immediately to three very similar responses in the infant: a cessation of crying, passivity, and a decreased heart rate.

That inter-species discovery was impressive in its own right, but the study also provided some much needed insight into the neural mechanisms of maternal-carrying's calming effects. Science's Dennis Normile provides a tidy explanation of their findings:

With mice, the team was able to investigate the underlying mechanisms in experiments that could not be tried with human babies. They applied a local anesthesia to pups' necks and chemically blocked neural signals produced by motion. Depriving the pups of these sensory inputs inhibited the calming effect of being carried. Surgically removing parts of the brain and testing mice with neural abnormalities allowed the team to track the adoption of a compact pose to the cerebellar cortex, which, not surprisingly, is thought to be involved in controlling posture and balance. And they found that it took longer for mother mice to rescue pups that had been anesthetized, so that they could not curl up, or drugged, so that they would not become passive. "The evolutionary value and function [of the calming response] is quite clear," Kuroda says: A passive, quite, compact newborn would be easier for a mother to carry away from danger. What's more, by chemically targeting the mouse pups' sympathetic and parasympathetic nervous systems, the researchers were able to show that disrupting the latter inhibited the carrying-induced decrease in heart rate observed in normal pups, while still allowing them to be rendered immobile.

The upshot? The calming response elicited by pinching the nape of a mouse's neck is made possible by the coordinated regulation of several physiological systems, including tactile sensation, proprioception, and multiple upstream and downstream pathways of the central nervous system .

But perhaps the most important finding, in the context of our discussion regarding PIBI, has to do with the similarities between infant carrying in humans and in mice. Humans obviously don't tote their young around by their necks, but the fact that the same physiological responses were observed in a human infant as in a mouse pup suggests that the calming effects of maternal carrying are highly conserved among mammalian species, and offers still more evidence that "clipnosis," however unfortunate the name, is a real phenomenon.

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