Dissociable amygdala and orbitofrontal responses during reversal fear conditioning.

The neural mechanisms underlying the persistence and plasticity of human emotional learning are unknown. Here we describe dissociable neural responses in amygdala and orbitofrontal cortex during acquisition and reversal of discriminatory fear conditioning. During acquisition, increased responses in bilateral amygdala were elicited by a face stimulus (A = CS+) predictive of an aversive noise compared to another nonpredictive face (B = CS-). With subsequent reversal of the conditioning contingency, face B (new CS+) elicited enhanced responses in right orbitofrontal cortex, while face A (old CS+) continued to evoke increased responses in right ventral amygdala. Thus, while orbitofrontal cortex exhibited rapid reversal of acquired fear responses, ventral amygdala showed a persistent, nonreversing "memory" for previous fear-related stimulus associations.