The common touch

The common touch

Even though our skin is our largest organ, weighing about the same as a bowling ball, touch is our most commonly overlooked sense. Yet touch not only connects us to other people, it may even help us develop our own identities.

There is a well-known experiment about our sense of our own body. The subject’s hand is hidden from their view, and a rubber hand put in its place. The rubber hand is then stroked at the same time as the real hand, whilst out of view. The effect of this is for people to experience the rubber hand as their own. So powerful is this effect that the rubber hand doesn’t even have to be realistic – even an inflated rubber glove will be incorporated into the subject’s sense of self.

As if this were not an intriguing enough insight into how we develop our sense of our physical selves, the experiments revealed something else. The effect was heightened when the stroking mimicked that of low force, low speed, gentle stroking.

Researchers have found that we have a two speed system for transmitting our sense of touch. The higher speed signals are carried on nerves called A fibres. These relay immediate information to the brain to allow us to move around and interact safely with our environment.

There is a second category of nerves, called C fibres, which carry information to the brain at the relatively leisurely pace of four miles an hour. At first it was thought that these simply carried the secondary information – for instance dull aches instead of A fibres’ sharp pains. However in the late 1990s researchers discovered another category of C fibres – called CT, or C-tactile fibres.

Whereas most touch receptors are found around the mouth, lips and fingers, the receptors for CT fibres are found solely in areas of hairy skin. Though everywhere except the lips, palms and soles of the feet they’re concentrated on the scalp, upper torso, arms, and thighs. These receptors have a heightened response to low force, low speed, gentle stroking – exactly the kind found in social and emotional physical contact.

It’s thought that this actually begins before birth. As the amniotic fluid washes over the fine lanugo hair on the foetus it helps the brain to develop a mental map of the body and sense of physical self. This continues outside of the womb after birth, through affectionate touch from others. Here touch helps the young infant to learn where they stop and others begin, the foundation for developing relationships and social networks.

Social touching has been shown to activate the same pathways in the brain as grooming does in primates, pathways that trigger the release of endorphins. So fundamental is touch to this that the density of individuals’ endorphin receptors vary according to the size of their social networks.

The link between touch and the sense of self is pointing to different techniques in the treatment of strokes. Results from trials have shown that stroking the affected limb on a regular basis can shorten peoples’ recovery times. The parallel development of the sense of touch, and social interaction, also points to insights into autism. One idea is that the brains of babies who respond differently to touch might form the basis of a test for autistic spectrum disorder.

And on a much more trivial note watch out for people who misuse the power of touch to engineer the sense of an emotional connection. The salesman who guides you with a hand on your back, or the acquaintance who touches your arm as they ask for yet another favour – it’s too embedded to stop it working, but you can be aware of how they’re using it.

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