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UI researchers find link between amygdala and social judgment

IOWA CITY, Iowa -- Damage to a brain structure called the amygdala impairs the ability to judge the trustworthiness of others, researchers in the University of Iowa College of Medicine report in the June 4 issue of the journal Nature.

Investigators in the UI department of neurology studied patients with a rare type of damage to the amygdala (a brain region known to be involved with emotion and social behavior), as well as people with undamaged brains and people with other types of brain damage. They found that bilateral damage to the amygdala prevents patients from judging that other people look unapproachable or untrustworthy. As a result, patients choose to approach and to trust individuals one might normally avoid.

The study, conducted by Drs. Ralph Adolphs, assistant professor of neurology, Daniel Tranel, professor of neurology, and Antonio R. Damasio, Van Allen Professor and head of neurology, builds on previous investigations by the same researchers. The idea that the amygdala serves to trigger knowledge and behaviors associated with negative emotions was developed in Damasio's book "Descartes' Error." The hypothesis has been supported by numerous studies from several laboratories. Previously, the group discovered that patients with amygdala damage cannot recognize fear in other people's facial expressions.

"Taken together, all these findings show that emotion and social behavior depend on specific brain systems in humans as well as in animals," Adolphs says. "The amygdala is one critical structure, without which we cannot recognize certain emotions or judge trustworthiness from other people's faces."

Adolphs adds that the findings are especially convincing because the patients have entirely normal vision. "They can see other people's faces perfectly fine but they are unable to judge, from looking at someone's face, if the person should be approached or should be trusted."

Damasio and his colleagues already have studies under way, using state-of-the-art imaging methods, that will further explore how the human brain processes emotion and social information.

"Over the next few years, it will be possible to identify which brain systems process different human emotions," Damasio says. "The new findings will help design novel approaches to disorders of emotion and mood, and to better understand the social dimension of those disorders."