The Riddle of Laughter: Neural and Psychoevolutionary Underpinningsof Joy

Modest advances are being made in understanding the neurology and functions of laughter. The discovery of tickle-induced "laughter" in animals should facilitate the characterization of this basic emotional response of the mammalian brain. The existence of such vocal activities in species other than humans (e.g., rats) suggests that the fundamental brain processes for joyful affect may have emerged early in vertebrate brain evolution. Here, I summarize the little that we know about the evolutionary and brain sources of laughter, and how the accompanying positive emotions may solidify social bonds within the mammalian brain. Discovery of unique neurochemistries that specifically promote laughter and joy may provide clues for development of new classes of antidepressants.