Why You Can’t Tickle Yourself

It’s a well-known fact that you can’t tickle yourself. Try it; you (mostly) can’t. Brush your own fingers across the soles of your feet. You certainly feel a sensation, but it’s nothing like when someone else does it.

But why can’t you tickle yourself? The answer is that our brains have a basic function which is designed to tell whether some sensation is caused by ourselves, or whether it comes from outside.

Telling the difference between the two is important because otherwise your own touch might give you the same surprise as when someone comes up behind you and taps you on the shoulder. The human brain anticipates unimportant sensations, so it can focus on important input like, say, a tarantula crawling up your neck.

It lends support to the theory that the brain is constantly predicting what is about to happen, what sensations it’s about to receive. The cerebellum, which is involved in monitoring movements,  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.

Further studies using robots showed that the presence of a small delay between your own movement and the resulting tickle can make the sensation feel tickly. Indeed, the longer the delay, the more tickly it feels. So it might be possible to tickle yourself, if you are willing to invest in a couple of robots!

The reason is that the ‘robot’ has tricked the mind into thinking the source of the movement is external. And because it feels like someone else is causing the sensation, then it tickles!

Summing-up: The reaction to tickling is the brain’s response to an unexpected stimulus. If you try and tickle yourself, your brain is expecting it. When their brains expected a tap and the tap came as expected, the brain noticed it less.

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