Here's why people 'catch' smiles, frowns like flu

Smiles and frowns are usually contagious - they tend to wind up on everyone's face and now, a new research has revealed why.

Growing evidence shows that an instinct for facial mimicry allows us to empathize with and even experience other people's feelings. If we can't mirror another person's face, it limits our ability to read and properly react to their expressions.

In their paper, University of Wisconsin's Paula Niedenthal and Adrienne Wood and colleagues describe how people in social situations simulate others' facial expressions to create emotional responses in themselves.

For example, if you're with a friend who looks sad, you might "try on" that sad face yourself, without realizing you're doing so. In "trying on" your friend's expression, it helps you to recognize what they're feeling by associating it with times in the past when you made that expression. Humans extract this emotional meaning from facial expressions in a matter of only a few hundred milliseconds.

Niedenthal said that you reflect on your emotional feelings and then you generate some sort of recognition judgment and the most important thing that results is that you take the appropriate action, you approach the person or you avoid the person. Your own emotional reaction to the face changes your perception of how you see the face, in such a way that provides you more information about what it means.

"There are some symptoms in autism where lack of facial mimicry may in part be due to suppression of eye contact," Niedenthal says. In particular, "it may be overstimulating socially to engage in eye contact, but under certain conditions, if you encourage eye contact, the benefit is spontaneous or automatic facial mimicry."

The study appears in Trends in Cognitive Sciences.