I am highly ticklish yet cannot tickle myself. To be sure, I can give myself the chills but tickling remains evasive, and now I know why. Turns out my cerebellum is able to predict whether the tickling stimulus is coming from an entity other than myself.
If the tickle comes from me then laughter is not a necessary reaction because my brain knows the intent is not to surprise or harm. If the tickle comes from an entity other than me, then laughter is a highly likely response because my brain is anticipating the intent of the action along with what will happen upon being touched.
The science behind tickling is explained in the HowStuffWorks article Why can’t you tickle yourself? as well as A Ticklish Question at Neuroscience for Kids. Tom Stafford and Matt Webb have written a book, Mind Hacks ~ Tips & Tools for Using Your Brain. Hack #65 is all about Why Can’t You Tickle Yourself?
Laughter plays an important role in our ability to make ourselves feel good. I am intrigued with the connection between tickling (a physical act of touching) and laughing (a cognitive act of understanding as well as a physical one of acting out the laugh). At Neuroscience for Kids you can read more about What’s So Funny and Why: Laughter and the Brain.
By the way, we are not the only ones to laugh upon being tickled. Apparently we are in the company of rats when it comes to laughing at being tickled.