by Matthew Cobb
Everyone knows that kittehs love being stroked. Indeed it’s something that is common to many mammals. But why and how? A paper in Nature by Sophia Vrontou and co-workers addresses the “how” question – that is, what are the underlying mechanisms – looking at mice. The opening sentences are limpid:
Stroking of the skin produces pleasant sensations that can occur during social interactions with conspecifics, such as grooming:. Despite numerous physiological studies, molecularly defined sensory neurons that detect pleasant stroking of hairy skin in vivo have not been reported.
They identified a particular set of sensory neurons that innervate hairy skin in mice and are activated by stroking, not pinching, and were able to show that this stimulation is apparently rewarding for the mice.
I won’t go into it any more, because Nature has made an excellent LOLcat video which explains everything about the mechanism [MAKE SURE YOU WATCH IT RIGHT TO THE END]. The issue now is to try to understand where and when this sense evolved in the mammalian lineage.
The article even made the cover!
Sophia Vrontou, Allan M. Wong, Kristofer K.Rau, H.Richard Koerber & David J. Anderson (2013) Genetic identification of C fibres that detect massage-like stroking of hairy skin in vivo. Nature 493:669–673
h/t My ex-PhD student @marvel_matt
Fascinating. So many different kinds of neurons.
Adorable and informative vid by Nature–great job! Thanks, Matthew.
“The issue now is to try and understand where and when this sense evolved in the mammalian lineage.”
I also would like to know how varied the response is to stroking: some animals, including humans, like it more than others. I suppose the response is an impossible-to-tease-out combined influence of nature and nurture.
It’s a ticklish problem…
Might seem like ‘soft’ science right now, but the stimulus does have a reproducible response. One can probably look for resulting changes in heart rate, breathing rate, maybe endorphins. I would like to see brain activity imaging while being stroked, and I would especially want to see what is going on in the limbic system.
Anyone want to stick a cat into a CAT scan? 😉
Reblogged this on Mark Solock Blog.
Great video. Thanks for posting
The Ohio Players knew about the importance of this topic. As Billy Beck (the keyboardist) tells his girl in “Fire” in the previous post, he’s gonna “tighten up my stroke”!
The Beach Boys song “Good Vibrations” is science?
Interesting. When I was a grad student at Rutgers, there was a Princeton post-doc in Physics who had a B/W cat named Dirac. Dirac seemed to enjoy being vigorously scratched on the head. Then I tried using a big door key. He liked that too, and that was great for me because cat dander and I don’t get along. It got to the point that all I had to do was produce the key and hold it stationary – he’d but his head against it.
Also noted in passing, for a short while & long ago Koerber’s (the fourth au) lab was down the hall from mine at Pitt.
I found the same with the neighbours’ cat the other night. A very handsome orange-and-white tabby, he’s usually quite nervous, he was wandering across our driveway, I managed to approach him, as soon as I touched the top of his head he was right into it – I hardly had to move my fingers, he was rubbing vigorously up against my hand, all shyness gone. He kept going for about five minutes.
The leap from mice to cats (or humans) seems fairly reasonable and expected. We might not be quite as hairy but many people enjoy the feel of someone running fingers through their hair or over their skin, etc…
I’m curious about our more aquatic cousins like dolphins and whales. Is there much grooming or stroking style behvaviour in such species? Parents petting their kids, or as a lead-up or follow-up to mating, or just plain friends bonding?
Perhaps flippers aren’t as well suited for it as hands are but dolphins are adept at headbutting and cats are quite good at that for petting purposes 😛
Hmm, I saw Michael Fisher allude to tickling earlier which you can’t do to yourself. Do cats get this stroking response when they’re stroking themselves with a tongue bath?
There’s still plenty of science to do! 😀
I’ve neither read not done any science on the subject, but regarding tickling:
As you point out you can’t really tickle yourself. Equally important to note is that ticklish areas tend to be vulnerable areas of the body: stomach, neck, etc.
Could the ticklish response be a form of protection?
Stroking of the skin produces pleasant sensations…
That simply begs the question, which is: why are these sensations pleasant?
They sort of suggest that it simulates grooming and cleaning.
What I didn’t see in the video was evidence that this really is the connection. But it seems plausible that we’d have evolved a positive response to hygienic behavior.
My current cat seems to enjoy being petted even more than eating. She’s the only cat I’ve ever had who can be tempted away from the food dish by a hand offering a cuddle. When I try to get up from a cuddling session she grabs my hand with her front paws and tries to pull me back.
Several issues here:
Grooming is good for health – nits etc. do the skin no good, and nourish and reward the groomer, so surely mammals would be programmed to like grooming and being groomed without the need for special neurons to determine the nature of the stimulus?
I assume the horizontal and vertical stripes in rooms A and C were pure artistic licence. If they were really there they could be a confounding factor. (Dunno about mice, but I imagine cats and other predators with vertical slit irises – and hence more highly accurate perception of horizonal movement – might have a strong preference for horizontal or vertical stripes.)
Cats rub up against people, surely, because people reward cat behaviour that seems to be affectionate.
Excellent use of LOLcats to make science accessable to laypeople without patronising.
The stripes likely aren’t artistic license, it’s probably an obvious visual clue for the mice so they can learn which room is the one they felt stroked in vs which room they didn’t.
If the mice aren’t given some very clear way to distinguish them, there’s no way for the mice to prefer one room over the other and to do the final stage of the experiment to gauge preference.
The video doesn’t say this is what they did, but it would be trivially easy to have the “which room is the rewarding room” be randomly assigned too.
So sometimes the horizontal is the one that the mice get the drug in, and some mice get the drug in the vertical striped room.
Or if you don’t like random assignment(you should, it’s shiny!) you could do a pretest where the mice are given free access to all three rooms and see which they prefer. Then make that the saline room and see if administering the drug in the least-liked room is enough to switch their allegiance.
You say “obvious visual cue” but do we know horizontal vs vertical stripes are salient to mice?
(I was assuming that “turn left” vs “turn right” was salient enough. We know rats are very -handed, turning upside-down rather than put the “wrong” hand down a tube to reach out food. [They put the tube in a corner to force the choice.])
I don’t mind random assignment, but if the association is weak, you need to increase the number of subjects to ensure significance.
[” -handed”? Not sure if I have enhanced or retarded English by coining that. Is the word “chiral” applicable? The SOED says it means “not superposable on its mirror image”, which is not what I mean at all. “-handed” is much clearer.]
Sorry, you lost me here. How can an organism be programmed to prefer stimulus X over stimulus Y without some neurological mechanism for distinguishing X from Y?
I was assuming that grooming could be distinguished from other touch by strong vs weak, gentle vs rough, and the ongoing nearness, smell, sounds etc. of the other mammal, without the need for specialised neurons.
OK, but why shouldn’t “touching hairs” v. “poking or pinching skin” be part of that discrimination process? If in fact it turns out to be the most effective discriminator, then it’s the one that will predominate, whether it’s strictly necessary or not.
Bear in mind that follicular neurons most likely existed before grooming behavior evolved. So the sensory channel was already in place, and was co-opted by natural selection as part of the grooming reward system.
This is good …
now.msn.com/catshaming-meme-funny-cat-photos
Some of the intraspecific contact associated with courtship and mating, social aggregations, and (at least in birds) allogrooming look not unlike the kind of behaviour that these stroke-neurons are supposed to mediate in mammals. And not only intra: herp-keepers know that some lizards and snakes (once habituated to handling) respond well to stroking around the head and neck, and parrots love a good long head-scratch. So it would be interesting to compare the sensory neurons of mammals with those of other vertebrates, and see how deep in phylogeny the different types go.
Next question. Do mammals also enjoy stroking? Is there an evolved neurological response to reinforce stroking of others? People sure do seem to derive satisfaction from stroking their pets and other humans (if the right human anyway). It seems possible that other animals would as well, for various reasons.