Our sense of touch is not equally distributed throughout all parts of our body , some parts being much more sensitive than others. For example, the soles of the feet are not particularly sensitive, but the hands and lips occupy very large areas of the somatosensory cortex.
To measure the sensitivity of our sense of touch, the researchers limited themselves to prodding the subject with a double-ended instrument , thus checking the minimum distance that these points could be while still being recognized as separate pressure sources.
The somatosensory cortex is configured as a map of the body mapped according to the areas from which it receives information, so it contains a region of the feet (which processes stimuli from the feet), a region of the arms, etc.
Our touch, as well as the rest of the senses, can be victims of illusions or misinterpretations. One of the most striking is the so-called Aristotle illusion, which Dean Burnett explains in his book The Idiot Brain :
Part of our ability to identify things by touching them occurs because the brain is aware of how our fingers are arranged, so if we touch something small (a marble, for example) with the index and middle fingers, we will feel a single object . But if we cross those two fingers and close our eyes, we will feel rather two different objects.
This is a secondary effect of the fact that there is no communication between the somatosensory cortex that processes touch and the motor cortex, which moves its fingers to signal the contradiction to the former. Obviously, the eyes must be closed so that we cannot provide information to clarify this incorrect conclusion .
The tato, in addition to not being regularly spread by our body, also has different classes of receptors, which have been called by the name of their discoverers:
Pacini’s corpuscles for pressure (described by Filippo Pacini, in the year 1830). Meissner’s corpuscles for touch (Georg Meissner, 1853). Krause’s terminal bulbs for cold (Wilhelm Krause, 1860). The endings for the Ruffini heat (Angelo Ruffini, 1898).