I Didn’t Know That

Q: Why can’t we tickle ourselves?

A: Neuroscientists have debated that question for a long time without arriving at a compelling answer. Recent studies of brain chemistry among people trying to tickle themselves by a team from University College in London, however, suggest that a specific part of the brain called the cerebellum unconsciously tells the rest of the brain, in effect, “It’s just you. Don’t get excited.” Previous studies have shown that the cerebellum tells the rest of the brain what to expect to feel when the body does something. In that manner, the brain can ignore expected sensations, like pressure on the soles of the feet while walking, and save its attention for unexpected things, like stepping on a stone. The London team reported in a recent issue of Nature Neuroscience that, during self-tickling, the cerebellum tells a brain area called the somatosensory cortex what sensation to expect, and that this dampens the tickling sensation. This unconscious mechanism doesn’t come into play, however, when we are tickled by another person.