Passage: The question as to why a person could not tickle themselves was raised by the Greek philosopher Aristotle.Knismesis may represent a vestige of the primitive grooming response, in effect; knismesis serves as a "non-self detector" and protects the subject against foreign objects. Perhaps due to the importance of knismesis in protection, this type of light touch is not dependent on the element of surprise and it is possible for one to induce self-knismesis, by light touching.Gargalesis, on the other hand, produces an odd phenomenon: when a person touches "ticklish" parts on their own body no tickling sensation is experienced. It is thought that the tickling requires a certain amount of surprise, and because tickling oneself produces no unexpected motion on the skin, the response is not activated. A recent analysis of the "self-tickle" response has been addressed using MRI technology. Blakemore and colleagues have investigated how the brain distinguishes between sensations we create for ourselves and sensations others create for us. When the subjects used a joystick to control a "tickling robot", they could not make themselves laugh. This suggested that when a person tries to tickle himself or herself, the cerebellum sends to the somatosensory cortex precise information on the position of the tickling target and therefore what sensation to expect. Apparently an unknown cortical mechanism then decreases or inhibits the tickling sensation.While the reasons for the inhibition of the tickling sensation during self-tickling remain unknown, research shows that the human brain is trained to know what sensation to expect when the body moves or performs an action.  Another reason may be the lack of awareness of many sensations arising from self-movement, such as not paying attention to one's own vocal cords.  When we try to tickle ourselves by grabbing our sides, the brain foresees this contact between body and hand and prepares itself for it.  This removes the feeling of unease and panic, causing the body to not react to...

Question: What happens when someone tries to tickle themself?
the cerebellum sends to the somatosensory cortex precise information on the position of the tickling target