Why We Laugh

And why we sometimes can't stop:

The areas that control laughing lie deep in the subcortex, and in terms of evolutionary development these parts of the brain are ancient, responsible for primal behaviours such as breathing and controlling basic reflexes. This means laughter control mechanisms are located a long way away from brain regions that developed later and control higher functions such as language or even memory. Perhaps this explains why it is so hard to suppress a laugh, even if we know it is inappropriate. Once a laugh is kindled deep within our brains these ‘higher function’ brain regions have trouble intervening.