Appetitive behavior: impact of amygdala-dependent mechanisms of emotional learning

In this chapter, we review data from studies involving appetitive conditioning using measures of pavlovian approach behavior and the effects of pavlovian conditioned stimuli on instrumental behavior, including the pavlovian-to-instrumental transfer effect and conditioned reinforcement. These studies consistently demonstrate double dissociations of function between the basolateral area and the central nucleus of the amygdala. Moreover, the data show marked parallels with data derived from aversive (fear) conditioning studies and are consistent with the idea that these subsystems of the amygdala mediate different kinds of associative representation formed during pavlovian conditioning. We hypothesize that the basolateral amygdala is required for a conditioned stimulus to gain access to the current affective value of its specific unconditioned stimulus, whereas the central nucleus mediates stimulus-response representations and conditioned motivational influences on behavior. Although these systems normally operate together, they can also modulate behavior in distinct ways. In many circumstances, then, emotional behavior can be seen as a coordinated combination of processing by these amygdaloid sub-nuclei, reflecting the superimposition of a phylogenetically recent basolateral amygdala subsystem that encodes and retrieves the affective value of environmental stimuli and thereby directs complex, adaptive behavioral responses onto a phylogenetically older central amygdala subsystem that enables cortical structures (including the basolateral amygdala) to recruit incentive motivational processes and thereby invigorate emotional responding.