Just as some people appear to have selective memories or selective hearing, a new brain imaging study reveals selective emotions of a sort. In this month's issue of Behavioral Neuroscience, Turhan Canli and colleagues of Stanford University report that personality traits can heavily influence the brain's response to emotional stimuli. In particular, extroverted people have stronger reactions to positive emotions, whereas neurotic people have stronger reactions to negative emotions. "Depending on personality traits, people's brains seem to amplify some aspects of experience over others," says co-author John Gabrieli.

The scientsts gave 14 healthy women aged 19 to 42 years-old a personality test to determine their levels of extroversion (defined as the tendency to be optimistic and sociable) and neuroticism (the tendency to be anxious, worried and socially insecure). Then they placed each subject in a functional magnetic resonance imaging (fMRI) scanner, and gave them photographs to look at: some pictures showed puppies, happy couples, ice cream and other scenes planned to evoke positive emotions, whereas the rest depicted crying or angry people, spiders, guns or cemeteries.

In response to the positive images, the women who scored high on extroversion showed increased activity in the frontal cortex, amygdala and anterior cingulate--all brain regions associated with emotional control. Women who scored low on extroversion, however, showed no similar increase. And those who scored high on neuroticism displayed heightened brain activity in response to the negative images. "All of the participants saw very positive and very negative scenes, but people's reactions were very different," Gabrieli notes. "One group saw the cup as being very full while the other group saw it as very empty."