Laughter Without a Joke

Tickle laughter is driven largely by the hypothalamus and other deep, reflexive parts of the brain, not the regions that handle actual humor. It is a reflex, not amusement, which is why people can laugh hard while genuinely hating it.

Some researchers think tickling also has a social side, since most people feel they would not be tickled by a stranger. But this is debated: when scientists had people tickled by what they believed was a machine, the response was nearly identical to being tickled by a person. That hints the real trigger is unpredictable touch, not who is delivering it.