Activation of the left amygdala to a cognitive representation of fear.

We examined the neural substrates involved when subjects encountered an event linked verbally, but not experientially, to an aversive outcome. This instructed fear task models a primary way humans learn about the emotional nature of events. Subjects were told that one stimulus (threat) represents an aversive event (a shock may be given), whereas another (safe) represents safety (no shock will be given). Using functional magnetic resonance imaging (fMRI), activation of the left amygdala was observed in response to threat versus safe conditions, which correlated with the expression of the fear response as measured by skin conductance. Additional activation observed in the insular cortex is proposed to be involved in conveying a cortical representation of fear to the amygdala. These results suggest that the neural substrates that support conditioned fear across species have a similar but somewhat different role in more abstract representations of fear in humans.