A funny bit of research reveals how laughter is contagious

According to a new study, laughter truly is contagious: the brain responds to the sound of laughter and preps the muscles in the face to join in the mirth.

"It seems that it's absolutely true that 'laugh and the whole world laughs with you," said Sophie Scott, a neuroscientist at the University College London. "We've 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. Now we've shown that the same appears to apply to laughter, too–at least at the level of the brain."

Scott and her fellow researchers played a series of sounds to volunteers and measured the responses in their brain with an fMRI scanner. Some sounds, like laughter or a triumphant shout, were positive, while others, like screaming or retching, were negative. All of the sounds triggered responses in the premotor cortical region of the brain, which prepares the muscles in the face to move in a way that corresponds to the sound. The response was much higher for positive sounds, suggesting they are more contagious than negative sounds–which could explain our involuntary smiles when we see people laughing.

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