Brain perks up to uncertain threats

The brain shows particular sensitivity to facial expressions that convey ambiguous threats rather than clear ones, according to a new brain-imaging investigation.

In their study, Reginald B. Adams Jr. of Dartmouth College in Hanover, N.H., and his coworkers assumed that an angry facial expression indicates a clear threat to an observer if it’s combined with eyes looking straight ahead, but an ambiguous threat if combined with eyes looking away. They also assumed that a fearful face with eyes looking to one side indicates clearly to an observer where a nearby threat is located, whereas eyes looking directly at an observer from a fearful face portray a vague threat.

Functional magnetic resonance imaging of the brains of 11 adults supports this perspective, Adams’ team reports in the June 6 Science. The left-hemisphere portion of the amygdala, an inner-brain structure regulating emotion, exhibited intense blood flow–an indirect sign of vigorous brain-cell activity–when volunteers looked at faces conveying the unspecified threats.

Modest amygdala activity occurred when participants viewed faces indicative of direct threats. The imaging data indicate that the brain takes special note of vague threats as it strives to identify just what the danger is, the researchers say.

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