Contagious Laughter
The Tanzania Laughter Epidemic
Apparently, someone told someone else a joke and the three students involved in the joke became subject to uncontrollable fits of laughter. The fits didn't leave any permanent in but uncontrollable laughter meant few students could learn anything, so the school was shut down. As soon as the school was shut down, the students went home and the laughter epidemic spread across the region. After the school reopened a few weeks later, dozens of students became rapidly infected and the school shut down again.
By the time the "disease" finally ended in June 1964, the laughter epidemic had "infected" around 1000 people and caused the closure of 14 schools in the area. Just like a real epidemic, the only effective preventative measure seemed to be quarantining villages that had not been touched by the disease. Whatever it was, the epidemic was not cause by a virus or bacteria, or some chemical in the food supply or environment. In school, the disease did not follow any certain pattern (girls who shared rooms with infected students did not necessarily become infected themselves). Out of school, young females were first to be infected. They would then take the disease home to infect their mothers and other female relatives. Adult men seemed to be completely immune to the epidemic, which builds on the fact that women laugh more than men do.
Contagiousness
The contagiousness of others' laughter is rooted in the neurological mechanism of laugh detection. The fact that laughter is contagious raises the possibility that humans have an auditory laugh detector, or a circuit in the brain that responds only to laughter. Contagious yawning also involves a similar process in the visual area of the brain. Once triggered, the laugh detector turns on a laugh generator, which is a neural circuit that causes us to laugh. When we are talking to someone, we often mirror their behavior, copying the words they use and mimicking their gestures. The same applies for laughter; when the person you are talking to laughs, you feel the urge to laugh along with him/her; it helps us interact socially. When the laugh track was introduced in 1950, it was a way to compensate for the lack of a live studio audience. No matter how corny laugh tracks sound, they do increase the chances that we'll laugh at something. Because of contagious laughter, people are more likely to laugh and find jokes funny when the jokes are followed by a recorded sound of laughter.
Sources:
http://www.world-science.net/othernews/061212_laugh.htm
http://danzarrella.com/contagious-laughter.html#
http://health.howstuffworks.com/mental-health/human-nature/happiness/laughter-contagious.htm
http://men.webmd.com/features/why-we-laugh?page=2
http://www.suite101.com/content/the-laughter-epidemic-a46227
http://www.worktheworld.com/blog/mass-psychogenic-illness-–-the-tanzania-laughter-epidemic_1917
http://danzarrella.com/contagious-laughter.html#
http://health.howstuffworks.com/mental-health/human-nature/happiness/laughter-contagious.htm
http://men.webmd.com/features/why-we-laugh?page=2
http://www.suite101.com/content/the-laughter-epidemic-a46227
http://www.worktheworld.com/blog/mass-psychogenic-illness-–-the-tanzania-laughter-epidemic_1917
