The General and Outcome-Specific Forms of Pavlovian-Instrumental Transfer Are Differentially Mediated by the Nucleus Accumbens Core and Shell

Tests of Pavlovian-instrumental transfer (PIT) demonstrate that reward-predictive stimuli can exert a powerful motivational influence on the performance of instrumental actions. Recent evidence suggests that predictive stimuli produce this effect through either the general arousal (general PIT) or the specific predictions (outcome-specific PIT) produced by their association with reward. In two experiments, we examined the effects of pretraining lesions (Experiment 1) or muscimol-induced inactivation (Experiment 2) of either the core or shell regions of the nucleus accumbens (NAC) on these forms of PIT. Rats received Pavlovian training in which three auditory stimuli each predicted the delivery of a distinct food outcome. Separately, the rats were trained to perform two instrumental actions, each of which earned one of the outcomes used in Pavlovian conditioning. Finally, the effects of the three stimuli on performance of the two actions were assessed in extinction. Here we report evidence of a double dissociation between general and outcome-specific PIT at the level of the accumbens. Shell lesions eliminated outcome-specific PIT but spared general PIT, whereas lesions of the core abolished general PIT but spared outcome-specific PIT. Importantly, the infusion of muscimol into core or shell made immediately before the PIT tests produced a similar pattern of results. These results suggest that whereas the NAC core mediates the general excitatory effects of reward-related cues, the NAC shell mediates the effect of outcome-specific reward predictions on instrumental performance, and thereby serve to clarify reported discrepancies regarding the role of the NAC core and shell in PIT.