NEUROTOXIC LESIONS OF BASOLATERAL, BUT NOT CENTRAL, AMYGDALA INTERFERE WITH PAVLOVIAN 2ND-ORDER CONDITIONING AND REINFORCER DEVALUATION EFFECTS

Considerable evidence suggests that various discrete nuclei within the amygdala complex are critically involved in the assignment of emotion al significance or value to events through associative learning. Much of this evidence comes from aversive conditioning procedures. For exam ple, lesions of either basolateral amygdala (ABL) or the central nucle us (CN) interfere with the acquisition or expression of conditioned fe ar. The present study examined the effects of selective neurotoxic les ions of either ABL or CN on the acquisition of positive incentive valu e by a conditioned stimulus (CS) with two appetitive Pavlovian conditi oning procedures. In second-order conditioning experiments, rats first received light-food pairings intended to endow the light with reinfor cing power. The acquired reinforcing power of the light was then measu red by examining its ability to serve as a reinforcer for second-order conditioning of a tone when tone-light pairings were given in the abs ence of food. Acquisition of second-order conditioning was impaired in rats with ASL lesions but not in rats with CN lesions. In reinforcer devaluation procedures, conditioned responding of rats with ABL lesion s was insensitive to postconditioning changes in the value of the rein forcer, whereas rats with CN lesions, like normal rats, were able to s pontaneously adjust their CRs to the current value of the reinforcer. The results of both test procedures indicate that ABL, but not CN, is part of a system involved in CSs' acquisition of positive incentive va lue. Together with evidence that identifies a role for CN in certain c hanges in attentional processing of CSs in conditioning, these results suggest that separate amygdala subsystems contribute to a variety of processes inherent in associative learning.