Sometimes we humans (and some animals too, come to think of it), respond to our environment in a peculiar way.

Under certain conditions, our body performs "rhythmic, vocalised, expiratory, and involuntary actions" [Brittanica 1999]. Fifteen facial muscles contract and there is electrical stimulation of the zygomatic major muscle in particular. Currents of varying intensity, produce a wide range of facial responses. The respiratory system is upset by the epiglottis half-closing, so that air intake occurs in irregular gasps, rather than calm breaths. Under extreme circumstances, the tear ducts are activated, so that while the mouth is opening and closing and there is a struggle for a sufficient amount of oxygen intake, the face becomes moist and often red. Noises often accompany this odd behaviour "ranging from controlled snickers, escaped chortles, and spontaneous giggles, to ridiculous cackles, noisy hoots, and up-roarious guffaws." [Wooten, P., 1996, pg. 3]

For a video of someone laughing, click here! (Real Video format)

Laughter is contagious!

This process that all of us have been through in varying degrees is the physiological response, commonly known as laughter. However, laughter itself is more than simply a response to humor. There are many situations where we may break out in laughter in respnse to a situation which isn't anything like a joke.

Robert Provine, a professor of psychology and neuroscience at the University of Maryland has undertaken a detailed study of laughter. A significant difficulty he faced in approaching this study was that laughter disappears just when you are ready to observe it - especially in the laboratory. One of his studies looked at the sonic structure of laughter. Provine used the facilities of the National Zoo in Washington DC to study laughter. He discovered that all human laughter consists of variations on a basic form that of short vowel-like notes repeated every 210 milliseconds. Laughter can be the "ha-ha-ha" type or the "ho-ho-ho" type, but not a mixture of both. He pointed out that apes also laugh in similar situations to humans in play. The noises they make however are very different to the sounds that humans make. Provine also suggested that humans have a detector that is specifically devoted to laughter. This responds to laughter by triggering other neural circuits in the brain that generates more laughter. This explains why laughter is so contagious.