WHAT IS LAUGHTER ?

Laughter is one of the least understood of human behaviors. Scientists have found that during a good laugh three parts of the brain light up: a thinking part that helps you get the joke, a movement area that tells your muscles to move, and an emotional region that elicits the "giddy" feeling. But it remains unknown why one person laughs at your brother's foolish jokes while another chuckles while watching a horror movie. John Morreall, who is a pioneer of humor research at the College of William and Mary, has found that laughter is a playful response to incongruities - stories that disobey conventional expectations. Others in the humor field point to laughter as a way of signaling to another person that this action is meant "in fun." One thing is clear: Laughter makes us feel better

/Live Science