The surface of the body, the skin, is this year’s theme at the Festival of Spirituality in Turin, where I will tell something about tickling and conscience.
There is this phrase from Freud that I like very much: “The ego is ultimately derived from bodily sensations, especially from the sensations coming from the surface of the body.” Why should the sense of identity derive from the sensations that come from the surface of the body? And what does all this have to do with tickling?
I wrote a booklet on these issues, which has a somewhat odd title – Thoughts of the fly with a crooked head (Adelphi) – the meaning of which is revealed only around page one hundred and thirteen, when an experiment conducted in 1950 by the neuroscientist Erich is described. von Holst with his student Horst Mittelstaedt. The experiment involved rotating the head of a drone fly (those flies that emulate the appearance of bees) by one hundred and eighty degrees to study its visual-motor responses. The experiment led to the idea of an “efferent copy”: every time an animal performs an action, the motor command that starts from the nervous system is sent, in addition to the muscles, in carbon copy also to the sensory system itself, to alert it of those stimulations which are produced by the movement of the animal itself. This fundamental distinction between what happens to the body as a result of an active movement as opposed to what happens as a result of the passive encounter with a stimulus could represent the trigger for conscious experience.
The argument develops from an idea that dates back to the eighteenth-century Scottish philosopher Thomas Reid, who spoke of a “double province of the senses”: what happens to me and what happens out there. Reid said: «The external senses have a double mission: to make us feel and make us perceive. They provide us with a variety of sensations, some pleasant, some painful, and some indifferent; at the same time they give us an invincible conception and conviction of the existence of external objects ».
In the Essay on the Intellectual Powers of Man Reid states that “When I smell a rose, there is both sensation and perception in this operation. The pleasant smell I feel, considered in itself without relation to any external object, is only a sensation … Its very essence consists in being felt; and when it does not feel it is not. There is no difference between the sensation and the feeling of it – they are the same. ‘ In short, according to Reid, sensation is equivalent to what we call conscious experience, while perception is the (invincible) conception of the existence of the external object, which, however, does not need to be conscious.
This idea was taken up by the brilliant British neuroscientist Nicholas Humphrey with the first identification of a neurological condition, known as blindsight, in which an organism can provide an appropriate motor response to a stimulus (therefore perceiving it) while denying the at the same time to have a conscious experience of the stimulus itself (therefore without feeling it).
The moment in which the need arises for a distinction between the things that happen to me, on the surface of my body, on the border between me and not me, and the things that happen out there is linked in biological organisms to the appearance of movement. Try to think about when moving a finger you go to meet an object or the condition in which your finger is passively stimulated by the object. Locally, the tactile stimulation is the same: there is no way, it would seem, to distinguish the two conditions. In reality there is a way, it is provided precisely by the efferent copy mechanism and it is also the reason why we cannot tickle ourselves. When we stimulate ourselves, for example by touching the sole of the foot or the hollow of an armpit with a finger, the carbon copy efferent signal relating to our own movement cancels the sensation of tickling, which cannot be deleted from any efferent copy if the movement leading to the stimulation was performed by someone else. In short, Renato Rascel was right when he observed that tickling should be done in the brain, not in the armpits.
Understanding how exactly the efferent copying mechanism can produce conscious experience requires reading a few pages of the book, but in brief the idea is the following. Up to now we have conceived the efferent signal (which is originally motor) as something that must be compared with the sensory signal. For example, how come when we move our eyes we don’t see the world moving? After all, the situation is not unlike that in which the excitation produced on the photoreceptors by an external moving stimulus moves on the surface of the retina, while the eyes are still. The reason is that when the eye muscles (extraocular, they call each other) receive the motor command to contract or release, the same carbon copy signal arrives at a comparator that evaluates the creep signal of the stimulation on the retina. If the sliding is produced by the movement of the extraocular muscles, the sensation is canceled. In fact, if these muscles are blocked pharmacologically, when the brain sends the motor command the sensation that the patient experiences, very unpleasant, is that the environment around him is rotating.
However, we imagine that originally the response of organisms to stimuli consisted of a local reaction on the surface of the body. This bodily reaction, as a motor action, may have had an associated efferent copy, to be compared not with the sensory stimulation, but with the active movements of the organism. So, for example, when you move a finger, the local body reaction, which would then be your feeling, would be annihilated by the encounter with the motor command necessary for the movement of the finger. The result is that you do not feel something on the surface of your body, but the presence of an object out there – a perception that, as in blindsight patients, we know does not need to be accompanied by a conscious experience. On the contrary, if with your eyes closed you let yourself be touched by a finger, you feel that something has happened to you, to your body. It is perhaps the ego derived from the bodily sensations of which Freud spoke.
The skin, the feeling of tickling and the birth of consciousness