When the nerve endings under your skin are stimulated by a light touch, they send a signal through the nervous system to your brain. Using functional magnetic resonance imaging machines (fMRI), researchers have determined that two areas of the brain create that tickle sensation: the somatosensory cortex, the area responsible for analysing touch, and the anterior cingulate cortex which is involved in creating pleasurable feelings.
But tickle also activates the hypothalamus, the area of the brain that regulates the fight or flight response. Researchers suggest that laughing when tickled could be a defensive mechanism. We may have evolved to send this signal out to show our submission to an aggressor and to prevent us from getting hurt.
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