Learning versus performance impairments following regional administration of MK-801 into nucleus accumbens and dorsomedial striatum.

To further ascertain the relative contributions of nucleus accumbens (NAC) and dorsomedial striatum (DS) to cognitive behaviors, the comparative effects in rats of MK-801 microinjections into these regions on a multiple schedule of repeated learning (RL) and performance (P) were examined. The RL component required learning of a new three-member response sequence during each experimental session, while the P component required rote performance of a pre-learned response, thus permitting a more precise delineation of treatment-related cognitive vs. non-cognitive changes. MK-801 decreased overall accuracy in both the RL and P components of the schedule in both brain regions, indicating that in neither NAC nor DS are NMDA receptors exclusively involved in mediating acquisition processes. Decreases in overall accuracy were primarily due to increased perseverative errors which may have been the result of excessively accelerated responding, a type of motoric alteration. MK-801 administered into NAC also resulted in an additional increase in skipping errors at the 2.5 micrograms dose, a finding which could be consistent with disrupted learning resulting from an inability to encode spatial relationships. Collectively these findings suggest that NAC and DS mediate some behavioral functions in common, but that additional cognitive-related spatial processes are mediated by NAC.