"From the resulting brain activity, she concluded that whenever we move our limbs, the brain’s cerebellum produces precise predictions of the body’s movements, and then sends a second shadow signal that damps down activity in the somatosensory cortex – where tactile feelings are processed. The result is that when we tickle ourselves, we don’t feel the sensations with the same intensity as if they had come from someone else, and so we remain calm rather than writhing with that familiar mix of discomfort and pleasure that comes when someone else tickles us."
“Your inability to tickle yourself suggests neurologically based definitions of self and other,”
Tickling has always been a fun activity, and I've always found this phenomena weird. ^^