Impaired sensitivity to Pavlovian stimulus-outcome learning after excitotoxic lesion of the ventrolateral neostriatum.

Subregions of the neostriatum have been dissociated according to their role in specific aspects of instrumental and Pavlovian learning. While the dorsomedial striatum is critical for the acquisition of goal-directed behaviours, the dorsolateral striatum has been shown to be necessary for the formation of habits. The ventrolateral subregion of the neostriatum (VLS), which supports a distinct cortical-subcortical circuitry, has not, however, been investigated within these paradigms. Thus, to determine whether the VLS is involved in the formation of action-outcome associations, Experiment 1 used a sensory specific devaluation procedure to assess the role of the VLS in the acquisition of goal-directed instrumental behaviours. Experiment 2 examined the ability of VLS lesion rats to form Pavlovian-outcome associations and to adjust responses according to the current incentive value of the reward by using a Pavlovian approach task, while Experiment 3 assessed the development and expression of habitual responding. Results indicated an intact ability of both sham and VLS lesion rats to form instrumental action-outcome associations and to use such representations to direct behaviour according to the incentive value of the outcome. VLS lesion rats equally demonstrated intact development of habitual lever press responses, which were shown to be impervious to lithium chloride devaluation treatment. VLS lesion rats did, however, demonstrate aberrant goal-directed responding to a Pavlovian auditory stimulus after outcome specific devaluation treatment. Thus, these results indicate that the VLS is necessary for utilising a representation of a Pavlovian stimulus-outcome association to direct behaviour according to the current incentive value of a reward.