Lesions of the dorsolateral or dorsomedial striatum impair performance of a previously acquired simple discrimination task.

Previous evidence has suggested a specific role for the dorsal striatum, especially the dorsolateral region of the dorsal striatum, in stimulus-response learning. In a previous study, we found an impairment in animals with dorsolateral striatal lesions on a simple discrimination task (CS+/CS-), thought to require the involvement of both stimulus-reward and stimulus-response learning. It is possible that the generally poor performance of dorsolateral lesioned animals on this experiment precluded adequate exposure to stimulus-reward pairings necessary for solving this task, and, thus, had little to do with stimulus-response learning. To test this hypothesis, the performance of animals with dorsolateral and dorsomedial striatal lesions was assessed on a previously acquired simple discrimination task. To independently assess the effects of each lesion on the performance of stimulus-reward learning, dorsolateral and dorsomedial lesioned animals were assessed on a previously acquired conditioned place preference task (CPP). In agreement with our earlier experiment, and the stimulus-response interpretation of dorsolateral striatal function, animals with dorsolateral striatal lesions were found to be impaired during post-lesion performance of the simple discrimination task, but not CPP learning. Additionally, dorsomedial lesioned animals were found to be impaired in performance of the simple discrimination task, but not on the CPP task. Possible explanations for the differences between the role of the dorsomedial striatum in acquisition and expression of the simple discrimination task are proposed.