THAT'S THE WHY: Hands up if you are ticklish. Or maybe don't put your hand up, because it would expose a palm, armpit and ribs which, along with the soles of the feet and under the chin, rank among the most tickle-responsive parts of the body.
A tickle arises from the mild stimulation of something moving across the skin and there are generally two types of sensation: an irritating crawl known as “knismesis” that prompts rubbing and withdrawal and the more laugh-inducing “gargalesis” that comes from stronger, more playful tickling in sensitive areas.
Theories about the origins of the light tickle suggest it may have been a mechanism to quickly detect “non-self” (such as an insect) touching our skin. More pleasurable tickles may have tied in with grooming between individuals and persist today as a game between trusted carer and child.
Brain imaging technology has offered insights into another mystery: why you can’t effectively tickle yourself.
A University of London study found that a region of the brain called the cerebellum can predict when you are about to lightly stroke a piece of soft foam over the palm of your hand.
This prediction appears to dampen down responses in other regions of the brain that normally register touch and pleasant sensations.
The study also found you can respond to a tickle of your own command if a robot does it with a slight delay, but where’s the fun in that?
– CLAIRE O’CONNELL
