Why can you not tickle yourself? It's the age old question, why can't we tickle ourselves? If you rub your fingers along your skin, sure there's sensation but you don't break down into a laughing fit (at least I don't :P), if someone else does it to you, you're rolling around on the ground begging them to stop tickling you. Why is it that other people can tickle us but we can't tickle ourselves by touch? (I'm aware that if you use a feather or foreign object on yourself you can be tickled by it so that doesn't count.)

In short, it's because your brain processes external and self-produced stimuli differently.

If someone tickles you, you feel that ticklish feeling, but when trying to tickle yourself, there is a reduction in the sensation. When you are tickled by someone, a part of your brain activates causing you to laugh, etc., but it seems that when you trying tickling yourself, your brain doesn't react the same way and that section of the brain does not activate as if someone were tickling you.

* Blakemore, S.J., D.M. Wolpert, and C.D. Frith. 1998. Central cancellation of self-produced tickle sensation. _Nature Neuroscience_ 1(7): 635–640. doi:10.1038/2870