Are you ticklish?
As all people with older siblings know, a few seconds of well-placed tickling can reduce a person to a laughing, gasping wreck. Ticklish areas (neck, underarms, feet) typically contain more nerve endings than normal. Usually responsible for detecting pain or temperature changes, a light touch to these overly sensitive areas will send signals to the pleasure areas of the brain, evoking an uncontrollable laughter response.
While it seems like an odd weakness for us to have, ticklishness evolved as a way for young children to practice their self-defence skills. Some of the most ticklish areas are also the most vulnerable. For example, the neck houses the trachea which delivers air to the lungs and the underarms contain several vital arteries. Tickle fights offer children a relatively safe and enjoyable training ground to learn to protect these key areas instinctively in actual combat situations, while encouraging early bonding between family and friends at the same time.
But why is it impossible to tickle oneself? Well the brain knows that it is your own movements producing the tickling sensation, so it ignores the resulting feelings of pleasure. This makes sense if tickling is a method of learning self-defence. What would be the point in learning to protect from oneself?
Image Courtesy of Sham Hardy on Flickr.