Smiling Faces, Sometimes, Make Brains Light Up

Thu Jun 20, 2:03 PM ET

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - Seeing smiling faces makes the brains of extroverted people light up more than the brains of shy people, researchers said on Thursday in a study they believe could help shed light on the biology of personality differences.

Specifically, the amygdala, a small region of the brain associated with emotional response, lights up when an outgoing person sees a picture of a smiling face, the team at the State University of New York in Stony Brook and at Stanford University in California found.

Turhan Canli, a psychologist and behavioral neuroscientist who led the research, said it is not clear whether outgoing people actually get more pleasure out of looking at a smiling face. "You are certainly more reactive to a happy face. I don't know if it feels better," he said in a telephone interview.

"This study shows for the first time that the same facial expression can be processed differently by different people, according to their personality," he added.

"This opens the door to use brain imaging to study the biology of personality and even personality disorders. The next big step will be to understand why the brains of different people process the same stimuli differently."

Canli's team used functional magnetic resonance imaging to watch the amygdalas of 15 volunteers in response to a series of photographs of faces. They were looking for differences in response to fearful faces.

They found everyone responds in the same way to a fearful face -- the amygdalas all activated with similar patterns.

It was when the volunteers looked at happy faces that the differences became apparent, Canli reports in Friday's issue of the journal Science.

Now Canli has to answer a chicken-and-egg question -- are extroverts outgoing because they are hard-wired to get pleasure out of smiling faces, or do they respond to smiling faces because they are outgoing?

Canli pointed out that this report focuses on the amygdala only. His team has seen other actions in other brain structures, although he is not ready to report on these details.

The volunteers were shown standardized faces with expressions that have been proven, over the years, to mean about the same thing to people the world over. No matter what the culture, people all recognize the same expressions as meaning happiness, sadness, fear, anger and disgust.

The volunteers, mostly college students, also filled out standard personality questionnaires.

"They are asked things like 'I like to laugh a lot, I like to meet new people, I worry a lot about things'," Canli said.

The research adds to a growing body of evidence that shows personality and biology are linked. Other imaging studies have found the brains of depressed people are overactive in some places and underactive in others.

On Monday a team at the University of Wisconsin reported that they had found abused children viewing similar standardized faces saw anger in expressions that other children interpreted more neutrally.