Why can't a person tickle himself?

Ever wonder why you are unable to tickle yourself no matter how hard you try?

The answer lies at the back of the brain in an area called the cerebellum, which is involved in monitoring movements. The cerebellum can predict sensations when your own movement causes them but not when someone else does. When you try to tickle yourself, the cerebellum predicts the sensation and this prediction is used to cancel the response of other brain areas to the tickle.

Source: Scientific American
Image: Spamily / Flickr
Tags: Tickle | Brain