Laughter is Contagious

Have you ever seen two people laugh at a joke you haven't heard - and you laughed or smiled anyway?

According to a study published in Journal of Neuroscience in 2007, positive sounds like laughter trigger a response in the area of the listener's brain activated when we smile, as though preparing facial muscles to laugh.

Using an MRI scanner, volunteers were subjected to various sounds (laughter, triumph, screaming, retching) while measuring brain responses. All triggered a response in the premotor cortical region of the brain, which prepares facial muscles to respond accordingly. The response was greater for positive sounds however, suggesting that these were more contagious than negative sounds. The researchers believe this explains why we respond to laughter or cheering with an involuntary smile.