Diverse Effects of Conditioned Threat Stimuli on Behavior.

Aversive Pavlovian memory coordinates the defensive behavioral response to learned threats. The amygdala is a key locus for the acquisition and storage of aversive associations. Information about conditioned and unconditioned stimuli converge in the lateral amygdala, which is a hot spot for the plasticity induced by associative learning. Central amygdala uses Pavlovian memory to coordinate the conditioned reaction to an aversive conditioned stimulus. Aversive associations can also access the brain networks of instrumental action. The offset of an aversive conditioned stimulus can reinforce behavior, recruiting a pathway that includes the lateral and basal amygdala, as opposed to the lateral and central amygdala circuit for Pavlovian reactions. Aversive conditioned stimuli can also modulate ongoing behavior, suppressing appetitive actions and facilitating aversive actions. Facilitation depends on an amygdalar network involving the lateral and central, as well as medial, nuclei. Thus, aversive Pavlovian memory has wide-reaching effects on defensive behavior, coordinating reactive to active responses to environmental threats.