You cannot tickle yourself
A self-produced touch is cancelled by a prediction from the cerebellum. The same touch from someone else is not, and it tickles.
Established2 min read
Blakemore, Wolpert, and Frith had people tickle their own palms with a robot arm, then inserted a delay. With no delay the touch felt dull. As the delay grew, the tickle returned. The nervous system was using a copy of the motor command — an efference copy — to predict the sensation and damp it.
The damping is useful. It keeps you from being startled by your own footsteps. Tickle is what prediction fails to cancel. You cannot surprise the part of you that issued the order.
Caveats
- Some people with lesions that disrupt this prediction can be more ticklish to themselves. The healthy case is the cancellation.
Sources
- 1Blakemore S. J., Wolpert D. M., Frith C. D.. Central Cancellation of Self-produced Tickle Sensation. Nature Neuroscience 1, 1998.