The Laughing Species

Evidence that laughter is "hardwired" into our brains is found in the behavior of people suffering from various neurological disorders. Inappropriate, excessive laughter is an early symptom of kuru, a degenerative disease of the brain akin to "mad cow disease." This fatal malady, caused by an infectious protein called a prion, was observed in the Fore people of New Guinea, who, during the ritual cannibalism of dead relatives, sometimes consumed the infected brain tissue of the deceased. As in most cases of inappropriate laughter, the symptom probably results from the failure of some mechanism that inhibits laughter rather than from the direct activation of a laugh center in the brain.

Other disorders in which laughter may be a symptom include manganese poisoning, Wilson disease (a disorder caused by a recessive gene that leads to the accumulation of copper in the brain), some types of epilepsy, Alzheimer disease and the somewhat similar Pick disease, Rett disorder (a condition affecting only gifts, in whom a common symptom is solitary, nocturnal laughter), Angelman disorder (a genetic condition whose unfortunate victims were once dubbed "happy puppets"), Williams disorder (a genetic but not hereditary illness in which frequent laughter is part of an abnormally gregarious nature), and some kinds of schizophrenia. The symptom is also sometimes seen in lobotomy patients and other sufferers of frontal lobe damage and in victims of amyotrophic lateral sclerosis (Lou Gehrig's disease) and multiple sclerosis. In many of these pathologies, the laughter is not connected with feelings of mirth--the patient is as baffled and horrified as everyone else is when the errant brain causes him or her to bark out an emotionless sound. Curiously, laughter is not a symptom of Tourette's disorder, otherwise known for tics and vocal outbursts.

Laughter may be primed through the use of drugs such as marijuana or laughing gas (nitrous oxide), which can make things seem funnier, or stimulated by group conditions favoring mass hysteria or religious fervor. Some aspects of a person's style or frequency of laughing, if not his or her taste in humor, may even be inherited, as in the case of the "giggle twins"--female identical twins who were separated at birth, raised by relatively sober families, and reunited forty years later. Both had a similar predisposition to laughter.

One of the pleasures of my quest to understand laughter has been to escape from my windowless neurophysiology laboratory to seek laughing in all its contexts--bars, zoos, comedy clubs, acting classes, neurology clinics, city sidewalks, operas, TV laugh tracks, Pentecostal services, tickle wars. The study of laughter requires a catch-as-catch-can interdisciplinary approach and entails grappling with some of science's knottiest problems--the interrelationship of nature and nurture and the evolution of speech, language, and social behavior. Above all, studying laughter provides new insights into what it means to be and act human.