Activation of the left amygdala to a cognitive representation of fear

We examined the neural substrates involved when subjects encountered an eve nt linked verbally, but not experientially, to an aversive outcome. This in structed fear task models a primary way humans learn about the emotional na ture of events. Subjects were told that one stimulus (threat) represents an aversive event (a shock may be given), whereas another (safe) represents s afety (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 r esponse as measured by skin conductance. Additional activation observed in the insular cortex is proposed to be involved in conveying a cortical repre sentation of fear to the amygdala. These results suggest that the neural su bstrates that support conditioned fear across species have a similar but so mewhat different role in more abstract representations of fear in humans.