Richard G. Petty, MD

Why is Laughter Infectious?

When I was a very young student Monty Python’s Flying Circus was being shown on TV for the first time. The TV room in the halls of residence would normally be home to one or two sleeping stalwarts. But on Monty P. nights we would have seventy or eighty of us crammed into a small room: the sharing of laughter made the whole show ten times funnier.

I think that we’ve all had the experience of infectious laughter. It’s easy enough to see that it can be a social lubricant. But how does it work?

We have known for some time that when we are talking to someone, we often mirror their behavior, copying the words they use and mimicking their gestures. You may know that deliberately copying other people is a technique that we use when we are trying to influence others. It has seemed likely that the same applies to laughter.

Researchers at University College and Imperial College in London have shown that positive sounds such as laughter or a rousing and triumphant “woo hoo!” trigger a response in the listener’s brain. This response occurs in the regions of the brain that are activated when we smile, as though preparing our facial muscles to laugh. The research, funded by the Wellcome Trust, Action Medical Research and the Barnwood House Trust, is published in the Journal of Neuroscience.

The research team played a series sounds to volunteers whilst measuring their brain’s response using an fMRI scanner. Some of the sounds were positive, such as laughter or the triumphant woo hoo’s, while others were distinctly unpleasant, such as screaming or retching. All of the sounds triggered a response in the volunteer’s brain in the region of the premotor cortex. This is part of the brain that prepares the facial muscles to respond to emotion. The response was greater for positive sounds, suggesting that these were more contagious than negative sounds. The researchers believe that this explains why we respond to laughter or cheering with an involuntary smile.

When we are in a group and encounter positive emotions, the brain responds by automatically priming us to smile or laugh. This gives us a way of mirroring the behavior of others, which in turn helps our social interactions. Presumably it plays an important role in building strong bonds between individuals in a group.

There is a global movement which started in India called the laughter clubs, in which people get together to have a really good belly laugh. It has been claimed that these group giggles reduce the chance of developing depression. The data is not good, but there’s one thing for sure: it’s unlikely to cause you much harm.

“Laugh and the world laughs with you; cry and you cry alone.”

–Horace (a.k.a. Quintus Horatius Flaccus, Roman Poet and Satirist, 65-8 B.C.E.)

“What a force is laughter.”
–Alexander Solzhenitsyn (Russian Writer and, in 1970, Winner of the Nobel Prize in Literature, 1918-)

“The arrival in town of a good clown is of more benefit to the people than the arrival of 20 asses laden with medicine.”
–Thomas Sydenham (English Physician and a Founder of Modern Clinical Medicine and Epidemiology, 1624-1689)

About Richard G. Petty, MD


3 Responses to “Why is Laughter Infectious?”
  1. Jim Pfrommer says:

    Don’t believe the positive affects have the market cornered on “affect contagion.”
    We wouldn’t want to forget crying at funerals, or God forbid, the sheer power of an angry lynch mob.

  2. Dear Jim,

    Excellent point!

    I wonder if you’ve ever attended a funeral in a culture in which massive out-pourings of grief are the cathartic norm? I wonder whether those good people get over their grief with less persistent dysphoria. I’ve not seen any studies on that, but it might make sense.

    As I was writing the piece on laughter I was waiting to see how my football team – Arsenal – was going to do this weekend, and thought about the amazing emotional power of the crowds. Or, for that matter, the way that everyone seemed to be swept up in the Nuremburg rallies.

    And by the way, you’d better try and patent “affect contagion,” or I’m going to steal it! I’ve used “emotional contagion” but I much prefer your term.

    Kindest regards,


  3. Jim Pfrommer says:

    No need to steal. Just use with credit. That’s what Nathanson and I did with so much of this stuff as we were making it up.

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