by E.L. Miller

Created on: October 11, 2007

When I was young, my father would need only point his finger at my side to elicit a giggling fit. The anticipation of his "counting my ribs" was enough to call to mind the tickling sensation that made me curl into a ball and laugh uncontrollably. My efforts to reciprocate were usually unproductive; he seemed immune to tickling, smiling more due to my feeble attempts than any physiological response. Which begs the question: What's so funny about being tickled?

Laughter as a reaction to tickling remains one of science's great mysteries, despite the musings and research of legendary academics such as Aristotle, Plato and Darwin. Theories abound, from its functions as an evolutionary response to protect oneself to a form of physical bonding between individuals in familial or intimate relationships. What scientists do know is that the ticklish feeling is a result of two factors: the physical stimulation of nerve fibers linked to both pain and touch, and the mental reaction of nervousness.

On the physical side, tickling can occur in two ways. The feeling that results from a light touch, such as that of a bug crawling on your skin, is called knismesis. Laughter-inducing tickling, or gargalesis, occurs as a response to heavier contact, with the most ticklish areas often being under the chin or arms, the torso and the soles of people's feet. Mentally, the touch activates a nervous response of both surprise and discomfort, though facial expressions and laughter portray pleasant expressions.

The combination of the physical and mental responses results, somewhat inexplicably, in laughter. However, other factors must also be present to ensure chuckles from the person being tickled. First, the tickler and ticklee usually must have a favorable relationship, such as parent-child, sibling or romantic interest. Otherwise, the touch is more likely to be deemed offensive, even sexually aggressive. Second, the most laughter is the result of uncertainty, as in not knowing where exactly on one's person will be tickled, and what degree of pressure will be applied. This explains why it is difficult, if not impossible, to tickle oneself.

These theories, derived from many studies on the topic, still leave the question unanswered: Why do we laugh when we're tickled? Is it funny? Is it torture? Does it feel good? Does it hurt? People have different reactions to tickling even in what is considered the optimal tickling situation, the right touch in a ticklish spot by a person known and sufficiently friendly to the person being tickled. Some people aren't really ticklish at all.

As I now practice my father's tickle technique on my daughter, I see her reaction is similar to mine, and just as confounding to scientists. Just the idea of being tickled sparks giggles. An actual rib-counting makes her crumple to the floor in hysterics. She always shouts, "Stop! Stop!" between laughter, but when I stop, she begs me to do it again. She enjoys it, can't stand too much, then wants to repeat the enjoyment. She finds it similarly funny to tickle me in return. This continues until we are both exhausted from laughter and I have to use my escape clause: "I can't do it anymore, my ticklers are tired!"

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