Activation of the amygdala by fearful faces compared to neutral faces has been relatively consistently reported in scientific literature, Canli said. What has not been consistently found is reaction to other emotional stimuli, particularly happy faces. "When people start looking at happy facial expressions, the verdict is split," said Canli. "Some have found activation; others haven't."

Canli thought that the inconsistent findings might be due to differences in the samples of volunteer subjects. For example, if people in a sample group tended to be outgoing, the amygdala would be more likely to respond or "turn on" to positive stimuli.

To test this theory, Canli and other researchers in Gabrieli's cognitive neuroscience lab recruited 15 student volunteers with no psychiatric histories. They were assessed for extraversion - the tendency to be optimistic and sociable, and neuroticism - the tendency to be anxious, worried or insecure. The two are not opposing personality traits and both can exist in one person, Canli said.

The participants, one by one, lay down on a bed attached to an fMRI scanner and looked at pictures of faces depicting a variety of expressions. They were given no instruction about how to respond beyond judging whether the faces were male or female - a task devised to keep them focused on the pictures, Gabrieli said. The fMRI recorded the brain's spontaneous response to each image.

The researchers found, as expected, that the amygdala in all participants responded to fearful faces. However, when subjects looked at happy faces, the amygdala "turned on" more in those with high extraversion scores. "We got this very clean association between amygdala reaction to two different kinds of emotional facial expressions," Canli said. As a result, he explained, "You can use extraversion as a factor that can explain or predict amy
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Contact: Lisa Trei
lisatrei@stanford.edu
650-725-0224
Stanford University
20-Jun-2002