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Laughter Laughter is the biological reaction of humans to moments or occasions of humor: an outward expression of amusement. Laughter is subcategorised into various groupings depending upon the extent and pitch of the laughter: giggles, clicks (which can be almost silent), chortles, chuckles, hoots, cackles, sniggers and guffaws are all types of laughter. Smiling may be considered a mild silent form of laughter. Some studies indicate that laughter differs depending upon the gender of the laughing person: women tend to laugh in a more "sing-song" way, while men more often grunt or snort. Babies start to laugh at about 4 months of age. Philosopher John Morreall theorises that human laughter may have its biological origins as a kind of shared expression of relief at the passing of danger. The relaxation we feel after laughing may help inhibit the fight-or-flight response, making laughter a behavioral sign of trust in one's companions. On the other hand, laughing at somebody is ridiculing him or her. Laughter is a part of human behavior regulated by the brain. It helps humans clarify their intentions in social interaction and provides an emotional context to our conversations. Laughter is used as a signal for being part of a group — it signals acceptance and positive interactions. Laughter is contagious and the laughter of one person can itself provoke laughter from others. This may account in part for the popularity of laugh tracks in situation comedy television shows. A particularly dramatic demonstration of contagious laughter was the Tanganyikan laughter epidemic, which demonstrated that laughter can also be difficult to control and can occur, unpleasantly, when people are severely stressed. Certain medical theories attribute improved health and well-being to laughter as it triggers the release of endorphins. A study demonstrated neuroendocrine and stress-related hormones decreased during episodes of laughter, which provides support for the claim that humor can relieve stress. Research has shown that parts of the limbic system are involved in laughter. The limbic system is a primitive part of the brain that is involved in emotions and helps us with basic functions necessary for survival. Two structures in the limbic system are involved in producing laughter: the amygdala and the hippocampus. Researchers frequently learn how the brain functions by studying what happens when something goes wrong. People with certain types of brain damage produce abnormal laughter. This is found most often in people with pseudobulbar palsy, gelastic epilepsy and, to a lesser degree, with multiple sclerosis, ALS, and some brain tumors. Inappropriate laughter is considered symptomatic of psychological disorders including dementia and hysteria. In most people, laughter can be induced by tickling, a phenomenon in itself. Laughing gas is sometimes used as a painkiller. Other drugs, such as cannabis, can also induce episodes of strong laughter. The December 7, 1984 Journal of the American Medical Association describes the neurological causes of laughter as follows: "Although there is no known "laugh center" in the brain,
its neural mechanism has been the subject of much, albeit inconclusive,
speculation. It is evident that its expression depends on neural paths
arising in close association with the telencephalic and diencephalic centers
concerned with respiration. Wilson considered the mechanism to be in the
region of the mesial thalamus, hypothalamus, and subthalamus. Kelly and
co-workers, in turn, postulated that the tegmentum near the periaqueductal
gray contains the integrating mechanism for emotional expression. Thus,
supranuclear pathways, including those from the limbic system that Papez
hypothesized to mediate emotional expressions such as laughter, probably
come into synaptic relation in the reticular core of the brain stem. So
while purely emotional responses such as laughter are mediated by subcortical
structures, especially the hypothalamus, and are stereotyped, the cerebral
cortex can modulate or suppress them."
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