Dissociable roles of the dorsal striatum and dorsal hippocampus in conditional discrimination and spatial alternation T-maze tasks.

The roles of the dorsal hippocampus (DH) and dorsal striatum (DS) in the learning and retention of conditional discrimination (CD) rules is a subject of debate. Although previous studies have examined the relationship between the DH and DS and the performance of CD tasks in operant chambers, the relative contributions of these two brain regions to the retention of CD rules requiring an association between a cue and a spatial location have not been characterized. We designed an experiment to assess the roles of the DH and DS in the retention of a visuospatial CD task by transiently inactivating either structure with muscimol in separate groups of rats and measuring performance on a previously learned CD task. The performance of two other groups of rats on a previously learned delayed spatial alternation (DA) task was also measured following inactivation of either DS or DH, which allowed us to control for any possibly confounding effects of spatial cues present in the testing room, length of the intertrial interval period on the performance of the CD task, and muscimol on sensorimotor or motivational processing. Muscimol inactivation of dorsal striatum, but not dorsal hippocampus, impaired CD performance, while inactivation of dorsal hippocampus, but not dorsal striatum impaired DA performance. These results demonstrate a double dissociation between the roles of the DH and DS in these two tasks, and provide a systematic characterization of the relationship between these two brain areas and CD performance.