Differential involvement of amygdala subsystems in appetitive conditioning and drug addiction.

Summary In this chapter, we review data from appetitive conditioning studies using measures of pavlovian approachbehaviour and of the effects of pavlovian conditioned stimuli on instrumental behaviour, including thepavlovian-to-instrumental transfer effect and conditioned reinforcement. These studies consistentlydemonstrate double dissociations of function between the basolateral area and the central nucleus of theamygdala. Moreover, these data show marked parallels with data derived from studies of aversive (fear)conditioning, and are consistent with the idea that these subsystems of the amygdala use differentassociative representations formed during conditioning, as part of a larger limbic cortico-striatal circuit. Wesuggest that the basolateral amygdala is required for a conditioned stimulus to gain access to the currentvalue of its specific unconditioned stimulus, while the central nucleus is responsible for conditionedmotivational responses using a simpler stimulus-response representation. Though these systems normallyoperate together, they modulate ongoing behaviour in distinct ways. We illustrate this by considering thecontributions of both systems to the process of drug addiction, using second-order schedules of intravenousdrug self-administration.