Belly laugh with pals has chemical payoff

New York TimesNovember 11, 2012 

Jonathan Eisen is a professor __in the departments of evoluaØ,Ǩ¬a__tion and ecology and medical __microbiology at the University __of California at Davis.

KARIN HIGGINS — Karin Higgins/UC Davis

For the study published this year in Proceedings of the Royal Society B, researchers at Oxford University recruited a large group of undergraduate men and women and set out to make them laugh.

Most of us probably think of laughter as a response to something funny – as, in effect, an emotion. But laughter is fundamentally a physical action.

“Laughter involves the repeated, forceful exhalation of breath from the lungs,” said Robin Dunbar, a professor of evolutionary psychology at Oxford, who led the study. We’ve all heard the phrase “laugh until it hurts,” he points out. That pain isn’t metaphoric; prolonged laughing can be painful and exhausting.

Rather like a difficult workout. But does laughter trigger a physiological response similar to that of exercise and, if so, what might that reveal about the nature of exertion?

To find out, Dunbar and his colleagues had their volunteers watch, both alone and as part of a group, a series of short videos that were either comic or dryly factual documentaries. But first, the volunteers submitted to a test of their pain threshold, as determined by how long they could tolerate a tightening blood pressure cuff or a frozen cooling sleeve.

The decision to introduce pain into this otherwise fun-loving study stems from one of the better-established effects of strenuous exercise: It causes the body to release endorphins – natural opiates – and, like other opiates, induce a feeling of euphoric calm and well-being. (They are believed to play a role in “runner’s high.”)

In Dunbar’s experiments, pain thresholds did go up after people watched the funny videos, but not after they viewed the documentaries.

The only difference between the two experiences was that in one, people laughed, a physical reaction that the scientists quantified with audio monitors. They could hear their volunteers belly-laughing. Their abdominal muscles were contracting. Their endorphin levels were increasing in response, and their pain thresholds and general sense of enjoyment were on the rise.

In other words, it was the physical act of laughing – the contracting of muscles and resulting biochemical reactions – that prompted, at least in part, the pleasure of watching the comedy.

Or, as Dunbar and his colleagues write, “the sense of heightened affect in this context probably derives from the way laughter triggers endorphin uptake.”

Why should the interplay of endorphins and laughing interest those of us who exercise? As Dunbar points out, what happens during one type of physical exertion probably happens in others. Laughter is an infectious activity. In this study, people laughed more readily and lustily when they watched the comic videos as a group than when they watched them individually, and their pain thresholds, concomitantly, rose higher after group viewing.

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