You may have heard that you can ‘hypnotize’ large predators like sharks or alligators by rubbing their bellies. There’s some truth behind this. Tonic Immobility is a reflex characterized by a state of immobility and apparent paralysis. This behavior has been reported in a variety of animals, from insects to fish to mammals.
Tonic immobility is often associated with a response to a threat such as a predator. It can be induced by physically restraining an animal on its side or back. In some animals, it can also be caused by pinching the skin at the nape of the neck.
Mesmerizing Sharks and Rays
Tonic immobility has been induced in many species of sharks and rays by inverting the animal. Sharks usually enter a tonic state within a minute and can remain like that for up to 15 minutes before righting themselves and swimming away. During tonic immobility, the breathing and muscle contractions become steadier and more relaxed.
Tonic immobility is used as an aid in shark husbandry in aquariums and when handling wild sharks to minimize struggling by the animal and reduce the possibility of injury to all parties.
But people might not be the only ones to exploit tonic immobility in sharks. In 1997, eyewitnesses watched a female orca off the coast of California seemingly induce tonic immobility purposely in a great white shark. The orca held the shark upside down, inducing tonic immobility, and kept the shark still for 15 minutes, which caused it to suffocate to death. Another instance of orcas purposely inducing tonic immobility in prey was documented with stingrays in New Zealand.
It’s unclear why apex predators such as sharks would have evolved tonic immobility, as it is usually used as an anti-predator behavior. They don’t appear to enter a tonic state as a fear response, as other animals do. It’s still an open question why sharks demonstrate this behavior.
Chicken and Rabbit Trances
There are several ways to “mesmerize” a chicken. You can lay it on its side, tuck its head under its wing and gently rock it, or put it on its back and stroke its sternum. You can wave your finger in front of its face — starting with your finger close to its beak and then pulling your finger slowly straight back. The chicken will focus on your finger.
Another method is to put the chicken on the ground on its stomach and then draw a line in the dirt with a stick or your finger. If you start the line right in front of the chicken’s beak and draw it straight out, the chicken will focus on the line and remain immobile anywhere from 15 seconds to 30 minutes.
Tonic immobility in chickens is thought to be a defensive mechanism caused by fear. It’s been used by scientists studying farm animal welfare to determine when chickens are most fearful; for instance, hens in cages are more fearful than those in pens, and hens on the top tier of battery cages are more fearful than those on the lower levels.
Tonic immobility in rabbits is also associated with fear. When confronted by a predator, feigning death by falling into a tonic state may cause the predator to lose interest and allow the animal to escape.
In rabbits, tonic immobility can be induced by turning the animal onto its back and restraining it. When a rabbit is first captured, its heart rate and blood pressure shoot up. But once in a tonic state, they fall back down to levels experienced during relaxation, and continue to gradually decrease.
Cat ‘Clipnosis’
Many cat owners know that cats and kittens can be immobilized by picking them up by the scruff of the neck, or even pinching the skin from the neck to the shoulder blades. Colloquially called “clipnosis,” in the scientific literature it is referred to as pinch-induced behavioral inhibition (PIBI).
In one study, scientists induced PIBI in cats by placing standard 2-inch binder clips along the loose skin at the napes of their necks. The majority of the cats had a positive response to the treatment, becoming passive, curling their spines, and dipping their tails between their legs.
PIBI seems to be different from tonic immobility. It’s not a fear or pain response; the cats didn’t show any dilated pupils, increased heart rate, or faster breathing. Also unlike an animal in a tonic state, the cats remained responsive.
The researchers concluded that the response to PIBI makes it easier for mother cats to carry their kittens. Another recent study supports this idea. In 2013, scientists found that in both mice and humans, a mother carrying an infant causes three similar responses in the infant: passivity, a decreased heart rate, and a cessation of crying. In evolutionary terms, this makes sense: a quiet, compact baby is easier for a mother to carry away from danger.
Tonic Immobility in Humans?
Tonic immobility has been hypothesized to happen in humans who are facing an intense trauma such as sexual assault. In one study, participants with post-traumatic stress disorder listened to descriptions of their own traumas as scientists took physiological measurements. Some participants reported immobility while listening to the description, and this was associated with increased heart rate and diminished heart rate variability. The researchers say this suggests that tonic immobility is preserved in humans as an involuntary defensive strategy.
References and Other Resources:
Carli, G. (1974). Blood Pressure and Heart Rate in the Rabbit During Animal Hypnosis. Electroencephalography and Clincical Neurophysiology 37: 231-237. doi: 10.1016/0013-4694(74)90026-1.
Esposito, G., et al. (2013). Infant calming responses during maternal carrying in humans and mice. Current Biology 23(9): 739-745. doi: 10.1016/j.cub.2013.03.041.
Gallup, Gordon G. Tonic immobility: The role of fear and predation. The Psychological Record 27: 41-61.
Gilman, T.T., Marcuse, F.L. and Moore, A.U. (1960). Animal hypnosis: a study of the induction of tonic immobility in chickens. Journal of Comparative Physiology and Psychology, 43: 99-111. doi: 10.1037/h0053659.
Henningsen, A.D. (1994). Tonic immobility in 12 elasmobranchs – use as an aid in captive husbandry. Zoo Biology 13:325-332. doi:10.1002/zoo.1430130406.
Jones, B. and Faure, J.M. (1981). Tonic immobility (“righting time”) in laying hens housed in cages and pens. Applied Animal Ethology 7: 369-372. doi: 10.1016/0304-3762(81)90063-8.
Pozza, M.E., Stella, J. L., Chappuis-Gagnon, A., Wagner, S. O., and Buffingotn, C. A. T. (2008). Pinch-induced behavioral inhibition (‘clipnosis’) in domestic cats. Journal of Feline Medicine and Surgery 10: 82-87. doi:10.1016/j.jfms.2007.10.008
Volchan, E. et al. (2011). Is there tonic immobility in humans? Biological evidence from victims of traumatic stress. Biological Psychology 88(1): 13-19. doi: 10.1016/j.biopsycho.2011.06.002.
No comments:
Post a Comment