Two girls laughing

Laughter is an audible expression or appearance of happiness, or an inward feeling of joy (laughing on the inside). It may ensue (as a physiological reaction) from jokes, tickling, and other stimuli. Inhaling nitrous oxide can also induce laughter; other drugs, such as cannabis, can also induce episodes of strong laughter. Strong laughter can sometimes bring an onset of tears or even moderate muscular pain.

Laughter is a part of human behaviour regulated by the brain, helping humans clarify their intentions in social interaction and providing an emotional context to conversations. Laughter is used as a signal for being part of a group — it signals acceptance and positive interactions with others. Laughter is sometimes seemingly contagious, and the laughter of one person can itself provoke laughter from others as a positive feedback. This may account in part for the popularity of laugh tracks in situation comedy television shows.

The study of humor and laughter, and its psychological and physiological effects on the human body is called gelotology.

Nature of laughter

Provine argues that “Laughter is primitive, an unconscious vocalization.” And if it seems you laugh more than others, Provine argues that it probably is genetic. In a study of the “Giggle Twins,” two exceptionally happy twins were separated at birth and not reunited until 43 years later. Provine reports that “until they met each other, neither of these exceptionally happy ladies had known anyone who laughed as much as she did.” They reported this even though they both had been brought together by their adoptive parents, whom they indicated were “undemonstrative and dour.” Provine indicates that the twins “inherited some aspects of their laugh sound and pattern, readiness to laugh, and perhaps even taste in humor.” WebMD 2002

Raju Mandhyan states "The physical and psychological benefits of laughter come second only to the physical and psychological benefits of sex."

Norman Cousins developed a recovery program incorporating megadoses of Vitamin C, along with a positive attitude, love, faith, hope, and laughter induced by Marx Brothers films. "I made the joyous discovery that ten minutes of genuine belly laughter had an anesthetic effect and would give me at least two hours of pain-free sleep," he reported. "When the pain-killing effect of the laughter wore off, we would switch on the motion picture projector again and not infrequently, it would lead to another pain-free interval." He wrote about these experiences in several books.

Laughter and the brain

Modern neurophysiology states that laughter is linked with the activation of the ventromedial prefrontal cortex, which produces endorphins after a rewarding activity.