Hi, Koryos! I was wondering if you have any insight on why animals enjoy petting so much? As a person, I personally don’t like the feeling of being petted. Is it just that I’m soothing little itches for them, or something else?

koryos:

Good question! The answer is quite complex, actually, starting with the fact that animals don’t always like to be petted, either. Of course, everyone probably knows this, and has experienced times when their pets have acted uncomfortable with physical contact. 

Petting, as a matter of fact, is a very specific type of touch. It’s different from poking, patting, or pinching. And I do mean literally different: gentle stroking on the skin actually activates different neurons than other forms of contact do. So petting isn’t just an arbitrary category- it’s a form of contact most mammals are primed to perceive differently.

Activating the “petting neurons” (called MRGPRB4+ fibers in the scientific literature, but let’s stick with “petting neurons”) feels good. In one study, researchers let mice choose between two chambers- one they preferred, and one they didn’t- and then activated the petting neurons in the non-preferred chamber. The mice went to that chamber as soon as they learned it would activate those neurons, and showed fewer stress responses to boot, entering a state of soothing mouse bliss.

Petting neurons occur on hair-covered areas of the skin, so the general consensus is that these neurons evolved to help give positive feedback to grooming behaviors. In other words, the act of cleaning our fur or hair feels good, which motivates us to keep cleaner and healthier fur or hair.

However, there’s another, additional reason animals enjoy being petted: social grooming, or allogrooming. Allogrooming occurs when one animal grooms another. Not only does this activate “petting neurons,” it also generates the release of the hormone oxytocin in both the groomer and the groomee. Oxytocin, among other things, can foster a feeling of connectedness and closeness between two individuals and is critically important for animals that form close pair-bonds. Social grooming also results in the release of pleasure-inducing endorphins, and inhibits the release of corticosteriods  (i.e., stress hormones). 

In fact, social grooming is so important for young mammals that those that are deprived of tactile contact when very young end up with abnormal concentrations of serotonin and TSH, both of which help manage the release of corticosteroids (those stress hormones again!). These animals- and humans- go on to be unusually anxious and asocial adults.

So, to sum up: petting activates specific neurons associated with pleasure, relaxation, and bonding, which is why so many animals appear to enjoy it. However, as I mentioned before, even if you’re doing the right kind of petting (not patting or tickling), animals don’t always enjoy the experience. Context matters very much, and if an animal isn’t in the mood to be petted, or doesn’t like to be touched in a particular area, it won’t matter how well you light up those neurons: they’re still going to hate it. Pay attention to what their body language is telling you.

Sources:

Crockford C., Wittig R.M., Langergraber K., Ziegler T.E., Zuberbuhler K. & Deschner T. (2013). Urinary oxytocin and social bonding in related and unrelated wild chimpanzees, Proceedings of the Royal Society B: Biological Sciences, 280 (1755) 20122765-20122765. DOI: 10.1098/rspb.2012.2765

Liu, Q., Vrontou, S., Rice, F. L., Zylka, M. J., Dong, X., & Anderson, D. J. (2007). Molecular genetic visualization of a rare subset of unmyelinated sensory neurons that may detect gentle touch. Nature neuroscience, 10(8), 946-948.

Liu, D., Diorio, J., Tannenbaum, B., Caldji, C., Francis, D., Freedman, A., … & Meaney, M. J. (1997). Maternal care, hippocampal glucocorticoid receptors, and hypothalamic-pituitary-adrenal responses to stress. Science, 277(5332), 1659-1662.

Spruijt, B.M.; Van Hooff, J.A.; Gispen, W.H. (1992). Ethology and neurobiology of grooming behavior. Physiological Reviews 72 (3): 825–852, PMID 1320764

Vrontou S., Wong A.M., Rau K.K., Koerber H.R. & Anderson D.J. (2013). Genetic identification of C fibres that detect massage-like stroking of hairy skin in vivo, Nature, 493 (7434) 669-673. DOI:10.1038/nature11810