Science Fair Project Encyclopedia
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 is a mild silent form of laughing. 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 of tension 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; often laughter alone will provoke laughter from others. This in part may account for the popularity of laugh tracks in situation comedy television shows. A particularly dramatic demonstration of contagious laughter was the Tanganyikan laughter epidemic, which also demonstrated that laughter can often 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 about 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 also considered symptomatic of psychological disorders including dementia and hysteria.
- "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."
Laughter is not confined to humans. Chimpanzees show laughter-like behavior in response to physical contact, such as wrestling, chasing, or tickling, and rat pups emit short, high frequency, ultrasonic vocalizations during rough and tumble play, and when tickled. Rat pups "laugh" far more than older rats. Chimpanzee laughter is not readily recognizable to humans as such, because it is generated by alternating inhalations and exhalations that sound more like breathing and panting. The differences between chimpanzee and human laughter may be the result of adaptations that have evolved to enable human speech.
- Goel, V. & Dolan, R. J. The functional anatomy of humor: segregating cognitive and affective components. Nature Neuroscience 3, 237 - 238 (2001).
- Bachorowski, J.-A., Smoski, M.J., & Owren, M.J. The acoustic features of human laughter. Journal of the Acoustical Society of America, 110 (1581) 2001
- Fried, I., Wilson, C.L., MacDonald, K.A., and Behnke EJ. Electric current stimulates laughter. Nature, 391:650, 1998 (see patient AK)
- Provine, R. R., Laughter. American Scientist, V84, 38:45, 1996.
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