Matteo Cerri, neurophysiologist
Every living organism of minimal complexity uses its senses to explore its surroundings. There are senses such as sight, hearing and smell which enable us to interact with our environment from a distance. They are passive, in the sense that the environment reveals itself through them independent of our volition. However, there is one sense which cannot operate at a distance and which is often associated with a conscious intention to explore our environment: touch. It is difficult to say which sense is the most important, but if we were asked to rank them, there is little doubt that we would be very unlikely to find touch at the top of the list. But this might be the result of our failure to understand and truly appreciate this wonderful sense. Its complexity and significance had been grasped, though, by Aristotle: in his treatise On the Soul, he identifies it as the sense which distinguishes man from the animals.
To understand the importance of touch, let’s try to imagine what it would be like without it. Unlike sight and hearing, whose absence we can briefly simulate, to try to imagine life without touch is extremely difficult, almost impossible. It is touch which sends a costant flow of information to the brain, even though we are unaware of much of it. The unpleasant sensation of losing our sense of feeling is what we have when the dentist gives us a local anaesthetic. That odd numb sensation is caused precisely by the interruption to the flow of information which our brain is accustomed to receive; numbness is what we feel when feeling has been deadened.
But there are many other reasons why touch is such an extraordinary sense. To begin with, we would be failing to recognize its complexity if we treated it as a single sense. What we experience is one, integrated tactile sensation, but in fact the sense of touch does not exist per se. What exists are many types of tactile sensations, each with its own receptors and properties. For example, the ability to distinguish surfaces and their edges is characteristic of the Merkel nerve endings. It is thanks to them that it is possible to read Braille. The distribution of these corpuscles on the skin enables certain areas, like the lips and fingertips, to read it; other areas are blind to Braille precisely because they are without the receptors needed to see it tactilely. The sense of touch is also linked intrinsically and inextricably to our emotions. In the emotional sphere, any touch can kindle a range of different sensations according to the expectations we harbour. Our sense of touch is in fact our ultimate safeguard. If something touches us without our knowledge, that something could represent a threat to our security and it is our sense of touch which triggers the alarm. If, though, that touch was expected, even desired, such as a mother caressing her child, then not only will it not seem threatening, but positively pleasurable. Yet we live in a society which has a phobia of touching. So much so that we have found it necessary to create a Global Hug Day (21st January), as if this gesture needed a justification. And yet, subconsciously we recognise its value. For example, doctors who touch their patients more frequently during a medical examination are credited by the patients themselves with being the better doctors. But nowadays it is not generally considered good manners to touch someone without permission; and even when this permission exists, as in the case of a pair of lovers, our behaviour is determined to a large degree by social conditioning. In Puerto Rico couples come into physical contact on average 150 times an hour, in Paris 110 times, in Florida twice and in London not even once. It must have something to do with the proverbial British self control. There is, though, a stage in our lives when it is very important to experience the sensation of touch: in infancy. Children who grow up deprived of physical contact with their parents suffer from much higher levels of stress. Indeed, touch is the first sense to develop and it is already active by the eighth week, when the embryo is a mere 1.5 cm. long.
Besides tactile sensations as such, touch is the realm which accounts for our perception of heat and cold, pain and, obviously, emotion. These sensory impressions can access our emotions and condition our behaviour even when we are unaware of it. For instance, it is enough to have a cup of warm tea in our hands to feel more kindly disposed towards others. In fact the idea of warmth envelops much of our emotional code because it is the emotion of human warmth or of the warmth of an embrace which fuses this sensory modality with the emotion of contact itself. It is hardly surprising that we describe a sensitive, discreet person as “tactful”, from the Latin tactus, meaning “sense of touch”. In conclusion, touch is nothing short of a symphonic sense, generating an emotional melody by calling into play the range of sensory instruments at its disposal; like an orchestra in which the instruments, singly and in combination, colour the music with which we are brought into contact. And contact is very much the operative word.