Its on the net, somewhere, why we laugh
A Dr. Harris (Female) did some scientific studies with male and female (pant, heavy breathing) college students. It was strictly scientific in nature. She has written may papers on tickling and its relationship to pain, why one laughs, etc. The medical community is seriously looking into tickling because there is a current theory that tickling and pain are very closely related. If they can determine why one person is ticklish and another isn't, then they can figure a better way to control or eliminate pain. I don't remember her full name but her work has been published in Scientic American and other science journals. Maybe some other member has more information.