The sense of somesthesia
This sense has long been called the "sense of touch" but this expression is not complete. If you use it as a verb, "touch" is an action with your hands towards something or someone. Touch does not mean either what I feel when I touch. Someone who has lost all feeling in their hands, for example due to cold or numbness, can still touch. So the sensations that a person feels when I touch them cannot be represented by the "sense of touch". If we use it as a name, it is to describe the way someone uses his hands (a musician, a therapist, etc.) or it can simply mean a contact (as in conspecific touch). So « touch », by itself, though sometimes beautiful, is not one of the five senses.
So we used the expression "tactile sense" to describe what we feel when we touch or what the person feels when he is touched. Its definition, in the dictionary Biology Online: "The tactile sense is one of the five traditional senses of the body. It is recognised by the organs of touch which are found mainly in the skin. The sensitivity varies from one part of the skin to another, e.g. the highly sensitive areas are the tactile sense on the forehead, temples, and the back of the forearm (H. N. Martin). Tactile sense is focused mainly on sense of pressure, traction and touch, excluding temperature and pain."(1) (2) Yet, something is missing, "tactile sense" beeing limited to skin. But what?
It lacks all those other sensations that we perceive with our body. It can be sensations of hot, cold or pressure, but also positioning in space (proprioception), tingling, itching, pain (nociception), pleasant touch, hunger, pulsation, peristalsis (viceroception), in short everything that one feels and that comes from outside or inside the body. These sensations, even those coming from the outside, subserve what Dr. Arthur D. Craig (3) calls interoception. This concept, although seemingly contradictory, will be better explained in future articles. It will be of paramount importance in understanding the therapist's work.
A definition of somesthesia found in the Thesaurus (4) : "The faculty of bodily perception; sensory systems associated with the body; includes skin senses and proprioception and the internal organs." Let me give you a more complete definition of somesthesia provided by the online French encyclopaedia, "Encyclopaedia Universalis": "The term "general somesthesic sensitivity" refers to the conscious sensations aroused by the stimulation of body tissues, sensations that are neither visual, auditory, gustatory nor olfactory. They are caused by the excitation of receptor nerve endings of various types, located in the skin lining and various more deeply located tissues: visceral connective tissue, capsules and joint ligaments. These receptors are sensitive to a number of specific stimulants: mechanical, thermal, painful. Within somesthesia, a distinction will therefore be made between tactile, thermal and painful sensitivities, as well as conscious kinaesthesia, which comes from the joints and provides information about the positions and movements of the different body segments in space." (5)
So what I mean by somesthesia includes all the receptors that make someone feel something. Many of these receptors are accessible to the therapist and it is through his action on these receptors that the therapist will be able to "talk" to the central nervous system (CNS).
(2) We notice that, according to the years, schools of thought and cultures, the definitions of "touch" and "tact" vary a lot. For example, in English the "tactile sense" does not include the sensation of temperature, whereas in French it is part of it.
(3) Craig, A.D. "How do you feel? An Interoceptive Moment with your Neurobiological Self",Princeton University Press, 2015