Scientists Decipher The Pleasure Of Gentle Touch

Doesn't even just reading the words "gentle touch" make you feel good? But why? What is it about a caress that is so deeply pleasurable? The answer may remain an ineffable mystery, but at least scientists have begun to figure out what goes on in our brains — or rather, the brains of tiny fruit flies — as they perceive that lovely sensation.

From the press release:

Stroke the soft body of a newborn fruit fly larva ever-so-gently with a freshly plucked eyelash, and it will respond to the tickle by altering its movement — an observation that has helped scientists at the University of California, San Francisco (UCSF) uncover the molecular basis of gentle touch, one of the most fundamental but least well understood of our senses.

Our ability to sense gentle touch is known to develop early and to remain ever-present in our lives, from the first loving caresses our mothers lavish on us as newborns to the fading tingle we feel as our lives slip away. But until now, scientists have not known exactly how humans and other organisms perceive such sensations.

In an article published online this week in the journal Nature, the UCSF team has identified the exact subset of nerve cells responsible for communicating gentle touch to the brains of Drosophila larvae— — alled class III neurons. They also uncovered a particular protein called NOMPC, which is found abundantly at the spiky ends of the nerves and appears to be critical for sensing gentle touch in flies.

Without this key molecule, the team discovered, flies are insensitive to any amount of eyelash stroking, and if NOMPC is inserted into neurons that cannot sense gentle touch, those neurons gain the ability to do so.

And a bit more fascinating background:

Though it is fundamental to our experience of the world, our sense of gentle touch has been the least well understood of our senses scientifically, because, unlike with vision or taste, scientists have not known the identity of the molecules that mediate it.

Scientists generally feel that, like those other senses, the sense of touch is governed by peripheral nerve fibers stretching from the spine to nerve endings all over the body. Special molecules in these nerve endings detect the mechanical movement of the skin surrounding them when it is touched, and they respond by opening and allowing ions to rush in. The nerve cell registers this response, and if the signal is strong enough, it will fire, signaling the gentle touch to the brain.

What has been missing from the picture, however, are the details of this process. The new finding is a milestone in that it defines the exact nerves and uncovers the identity of the NOMPC channel, one of the major molecular players involved—at least in flies.

The full article in Nature is here. And of course the question that arises: Once we fully understand the biology of the sensation of gentle touch, can we reproduce it artificially? Will we someday pop "gentle touch" capsules on sad, lonely, stressful days?