This series of experiments compared the effects of lesions of the basolateral complex (BLA) and the central nucleus (CN) of the amygdala on a number of tests of instrumental learning and performance and particularly on the contribution of these structures to the specific and general forms of pavlovian-instrumental transfer (PIT). In experiment 1, groups of BLA-, CN-, and sham-lesioned rats were first trained to press two levers, each earning a unique food outcome (pellets or sucrose), after which they were given training in which two auditory stimuli (tone and white noise) were paired with these same outcomes. Tests of specific satiety induced outcome devaluation, and tests of PIT revealed that, although the rats in all of the groups performed similarly during both the instrumental and pavlovian acquisition phases, BLA, but not CN, lesions abolished selective sensitivity to a change in the reward value of the instrumental outcome as well as to the selective excitatory effects of reward-related cues in PIT. In experiment 2, we developed a procedure in which both the general motivational and the specific excitatory effects of pavlovian cues could be assessed in the same animal and found that BLA lesions abolished the outcome-specific but spared the general motivational effects of pavlovian cues. In contrast, lesions of CN abolished the general motivational but spared the specific effects of these cues. Together, these results suggest that the BLA mediates outcome-specific incentive processes, whereas CN is involved in controlling the general motivational influence of reward-related events.

In three experiments we examined the effect of bilateral excitotoxic lesions of the nucleus accumbens core or shell subregions on instrumental performance, outcome devaluation, degradation of the instrumental contingency, Pavlovian conditioning, and Pavlovian-instrumental transfer. Rats were food deprived and trained to press two levers, one delivering food pellets and the other a sucrose solution. All animals acquired the lever-press response although the rate of acquisition and overall response rates in core-lesioned animals were depressed relative to that in the shell- or sham-lesioned animals. Furthermore, in shell- and sham-lesioned rats, post-training devaluation of one of the two outcomes using a specific satiety procedure produced a selective reduction in performance on the lever that, in training, delivered the prefed outcome. In contrast, the core-lesioned rats failed to show a selective devaluation effect and reduced responding on both levers. Subsequent tests revealed that these effects of core lesions were not caused by an impairment in their ability to recall the devalued outcome, to discriminate the two outcomes, or to encode the instrumental action-outcome contingencies to which they were exposed. Additionally, the core lesions did not have any marked effect on Pavlovian conditioning or on Pavlovian-instrumental transfer. Importantly, although shell-lesioned rats showed no deficit in any test of instrumental conditioning or in Pavlovian conditioning, they failed to show any positive transfer in the Pavlovian-instrumental transfer test. This double dissociation suggests that nucleus accumbens core and shell differentially mediate the impact of instrumental and Pavlovian incentive processes, respectively, on instrumental performance.

Background Addictions are defined by a loss of flexible control over behavior. The development of response habits may reflect early changes in behavioral control. The following experiments examined the flexibility of alcohol-seeking following different durations of self-administration training and tested the role of the dorsal striatum in the control of flexible and habitual alcohol self-administration. Methods Rats were trained to lever-press to earn unsweetened ethanol (10%). The sensitivity of the lever-press response to devaluation was assessed by prefeeding the rats either ethanol or sucrose prior to an extinction test following different amounts of training (1,2,4, and 8 weeks). We subsequently tested the role of the dorsomedial striatum (DMS) and dorsolateral striatum (DLS) in controlling alcohol seeking using reversible inactivation techniques (baclofen/muscimol: 1.0/0.1mM, 0.3μl per side). Results We find that operant responding for ethanol early in training is goal-directed and reduced by devaluation, but after 8 weeks of daily operant training, control has shifted to a habit-based system no longer sensitive to devaluation. Further, following relatively limited training, when responding is sensitive to devaluation, inactivation of the DMS greatly attenuates the alcohol-seeking response whereas inactivation of the DLS is without effect. In contrast, responding that is insensitive to devaluation following 8 weeks of training becomes sensitive to devaluation following inactivation of the DLS, but unaffected by inactivation of the DMS. Conclusions These experiments demonstrate that extended alcohol self-administration produces habit-like responding and that response control shifts from the DMS to the DLS across the course of training.

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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 prior to 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.