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Why laughter is contagious

Dec. 12, 2006
Courtesy Wellcome Trust
and World Science staff

Laugh­ter is con­ta­gious: you can catch it with­out ask­ing for it, or even nec­es­sar­i­ly want­ing it. Now, sci­en­tists say they have an idea of why.

Re­search­ers at Uni­ver­si­ty Col­lege Lon­don and Im­pe­ri­al Col­lege Lon­don have found that pos­i­tive sounds such as laugh­ter or a tri­um­phant “woo hoo!” trig­ger a strong re­sponse in the lis­ten­er’s brain.

The pre­mo­tor cor­ti­cal ar­ea, shad­ed in blue in this im­age of a brain as seen from the left. Cer­tain cells in this re­gion are be­lieved to be in­volved in int­en­tion or prep­a­ra­tion for move­ment. They then in­flu­ence the ac­tu­al move­ment through con­nec­tions with the pri­ma­ry mo­tor cor­tex, the sligh­tly dark­er-shaded zone di­rect­ly to the right of the blue ar­ea. This zone gov­erns the ac­tu­al ex­e­cu­tion of move­ment.
This re­sponse oc­curs in a brain ar­ea that’s ac­ti­vat­ed when we smile, as though pre­par­ing our fa­cial mus­cles to laugh, the sci­en­t­ists said. The find­ings ap­pear in the Dec. 12 is­sue of The Jour­nal of Neu­ro­science.

“It seems that it’s ab­so­lute­ly true that ‘laugh and the whole world laughs with you’,” said So­phie Scott of Uni­ver­si­ty Col­lege Lon­don, one of the re­search­ers. 

“We’ve known for some time now that when we are talk­ing to some­one, we of­ten mir­ror their be­hav­i­our, cop­y­ing the words they use and mim­ick­ing their ges­tures. Now we’ve shown that the same ap­pears to ap­ply to laugh­ter, too—at least at the lev­el of the brain.”

The re­search team played a se­ries of sounds to vol­un­teers while scan­ning their brains with func­tion­al mag­net­ic res­o­nance im­ag­ing, a tech­nol­o­gy that meas­ures brain act­i­vi­ty based on blood flow in the brain. 

Some of the sounds were pos­i­tive, such as laugh­ter or tri­umph; oth­ers were un­pleas­ant, such as scream­ing or retch­ing. All were found to trig­ger ac­ti­vi­ty in the brain’s pre­mo­tor cor­ti­cal re­gion, which pre­pares the mus­cles in the face to re­spond ac­cord­ing­ly. But the re­sponse was great­er for pos­i­tive sounds, sug­gest­ing that these were more con­ta­gious than neg­a­tive sounds, ac­cord­ing to the group.

The re­search­ers be­lieve this ex­plains why we re­spond to laugh­ter or cheer­ing with an in­vol­un­tary smile. “We usu­al­ly en­coun­ter pos­i­tive emo­tions, such as laugh­ter or cheer­ing, in group sit­u­a­tions, wheth­er watch­ing a com­e­dy pro­gramme with fam­i­ly or a foot­ball game with friends,” said Scott. 

“This re­sponse in the brain, au­to­mat­i­cally prim­ing us to smile or laugh, pro­vides a way of mir­roring the be­hav­iour of oth­ers, some­thing which helps us in­ter­act so­cially. It could play an im­por­tant role in build­ing strong bonds be­tween in­di­vid­u­als in a group.”

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Laughter is contagious: you can catch that condition without asking for it, or even necessarily wanting it. Now, scientists say they understand why. Researchers at University College London and Imperial College London found that positive sounds such as laughter or a triumphant “woo hoo!” trigger a strong response in the listener’s brain. This response occurs in brain area that’s activated when we smile, as though preparing our facial muscles to laugh, the scientists said. The findings appear in the Dec. 12 issue of the Journal of Neuroscience. “It seems that it’s absolutely true that ‘laugh and the whole world laughs with you’,” said Sophie Scott of University College London. “We’ve known for some time now that when we are talking to someone, we often mirror their behaviour, copying the words they use and mimicking their gestures. Now we’ve shown that the same appears to apply to laughter, too—at least at the level of the brain.” The research team played a series of sounds to volunteers whilst measuring their brain’s response using functional magnetic resonance imaging, a scanning technology. Some of the sounds were positive, such as laughter or triumph; others were unpleasant, such as screaming or retching. All triggered a response in the brain’s premotor cortical region, near the head’s top-side area, which prepares the muscles in the face to respond accordingly. But the response was greater for positive sounds, suggesting that these were more contagious than negative sounds, according to the group. The researchers believe this explains why we respond to laughter or cheering with an involuntary smile. “We usually encounter positive emotions, such as laughter or cheering, in group situations, whether watching a comedy programme with family or a football game with friends,” said Scott. “This response in the brain, automatically priming us to smile or laugh, provides a way of mirroring the behaviour of others, something which helps us interact socially. It could play an important role in building strong bonds between individuals in a group.”