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They are related to the body’s reaction to situations of fear and panic. That’s why tickling often manifests itself through uncomfortable laughter. They are probably a primitive response, with the aim of making the body react in case, for example, there is an insect walking on it. The skin of certain more vulnerable parts of the body has sensitive receptors called free nerve endings. “These nerve receptors are the same ones that allow us to feel pain, itching and excessive heat or cold – that is, disturbing stimuli that make the body move away from them”, says neurologist Benito Pereira Damas, from Unicamp. When the skin is stroked in a certain way, these receptors transmit the stimulus to the brain’s pleasure center, located in the hypothalamus.
But when the stimulation is deep, fast and blunt, this reaction can have the opposite result, with nervous laughter, screams and sudden movements, signs that it has become a real torture. When a person does the same kind of stimulation to their own nerve endings, however, they cannot feel ticklish. This is due to the fact that the cerebellum – the brain’s motor control center – has already received a copy of the information about this movement even before it is completed, leaving the brain on alert and blocking unjustified feelings of fear.