Adults’ brains show temperamental side

Using brain-imaging techniques, psychologists have identified possible neural locations underlying shyness or gregariousness.

Thirteen people in their early 20s whom the psychologists had categorized as inhibited during infancy displayed much more amygdala activity when shown new faces versus familiar ones, say Carl E. Schwartz of Massachusetts General Hospital in Charlestown and his coworkers. In contrast, nine young adults who were uninhibited as infants didn’t show this difference in amygdala responses to novel and recognizable faces, the scientists report in the June 20 Science.

The amygdala, an inner-brain structure involved in regulating emotions, responds to novel social cues differently depending on the extent to which a person is reserved or outgoing, Schwartz’s group theorizes.

In the study, a magnetic resonance imaging scanner tracked neural blood flow, an indirect sign of brain-cell activity, as volunteers viewed new and familiar faces.

An inhibited temperament may be the prime reason for previous reports of heightened amygdala activity in people diagnosed with social phobia, a condition marked by constant fear and avoidance of unfamiliar people. In the new study, two people in the inhibited group had social phobia, but that condition didn’t further boost their amygdala responses.

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Bruce Bower has written about the behavioral sciences for Science News since 1984. He writes about psychology, anthropology, archaeology and mental health issues.

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