Hm... I heard another area f the brain was activated during tickling, but both proved the same anticipatory "non-tickling" reactions.
Also explains more about why/how schizophrenics actually can tickle themselves, as they have difficulties separating reality from dreams (so they may envision one of their 'mental voices' as the person tickling them, even when it's their own hand performing the motions). Not a guarantee, but a possibility.
I'm also unsure about the different tickle sensations: gargalesis and knismesis.