Brain Measures Trust-
worthiness by Face Value
Excerpt By Merritt McKinney, Reuters Health

NEW YORK (Reuters Health) - Our minds may be more suspicious than we think. New research indicates that some brain regions involved in evaluating trustworthiness are activated even when a person is not consciously making a judgment about someone else.

"The human brain is more adept at making apparently complex judgments about unfamiliar faces than we might have expected," study author Dr. Joel S. Winston of the Institute of Neurology in London, UK, told Reuters Health.

"The fact that our brains show responses to untrustworthy faces, regardless of whether or not we are thinking about making such a judgment," reveals the sort of evolutionary pressures that shaped the development of the brain, according to Winston.

He said the research also suggests the importance of social awareness in human survival.

A report on the findings appears in the advance online edition of the journal Nature Neuroscience.

Exactly how the brain makes judgments about other people has been uncertain, but prior research suggests that a brain region called the amygdala may be involved. When the amygdala in both sides of the brain is damaged, people tend to make unusual judgments about other people.

To get a better idea of what parts of the brain are involved in evaluating trustworthiness, Winston and his colleagues showed photos of unknown faces to a group of people. In some cases, participants were asked to say whether the person in the photo seemed trustworthy. In others, participants were asked to guess the person's age but not to make a judgment about his or her trustworthiness.

During the experiments, the researchers monitored participants' brain activity using a tool called functional magnetic resonance imaging (fMRI).

When participants were asked to evaluate trustworthiness, fMRI detected increased activity in several parts of the brain. But some of these brain regions were activated even when participants were not asked to make judgments about trustworthiness.

The amygdala on both sides of the brain, as well as the right insula, were activated when participants viewed photos of people they thought to be untrustworthy even when they were not being asked to evaluate these people. In contrast, a part of the brain called the right superior temporal sulcus was activated only when a person was asked to evaluate trustworthiness.

The findings suggest that the brain's ability to judge other people is partly automatic and partly intentional, according to the researchers.

But the question of what types of faces seem untrustworthy remains unanswered, Winston noted.

It would be fascinating, he said, to see how the findings apply to people with disorders that affect social interactions, such as autism.

SOURCE: Nature Neuroscience advance online publication 2002;10.1038/nn816.

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