Tickling is the body’s defense system. Scholars believe they arose in prehistoric times. Its function was not to make people laugh, but identify problems, like venomous insects. The animal’s rubbing against the skin provoked an unpleasant sensation of alertness, forcing the human being to scare it away (thus avoiding a fatal bite, for example). According to neuroscientist Robert Provine, author of Laughter: A Scientific Study, tickling also emerged as a mechanism to reinforce social ties. He cites as an example the light tickling that the mother usually does in the baby.
Oh, what an affliction!
Sensory stimulation causes extreme reactions from the body, including uncontrolled laughter.
1- Just under the skin, there are sets of tactile receptors – small endings connected to the nervous system, responsible for all the sensations of touch, such as textures, temperature, etc. For evolutionary reasons, there is a greater concentration of these receptors in the hands, neck, feet, abdomen, armpits, ears and groin. So these are the areas more susceptible to tickle.
2- The stimulus in these receptors is sent to the brain. The region of the postcentral gyrus, responsible for sensations, understands the signal as a surprise. In an instinctive reflex, the cerebral cortex activates the motor area, causing sudden body movements. (Another part, the cerebellum, prevents us from tickling ourselves – when it anticipates the movement, it inhibits its consequences).
3 – As a consequence, the ventral medial prefrontal cortex, involved with emotions and pleasure, activates the mechanism of laughter. “The diaphragm, the muscle that controls breathing, starts to work in rhythmic contractions, generating deep exhalations and inspirations”, says neurologist Susanie Rigatto. The more intense the tickle, the greater the brain area activated, and the greater the physical response.
Long tickling sessions were used as torture in feudal Japan and Nazi Germany.
The concentration of receptors also varies from person to person. That’s why some are more ticklish than others.