DISSOCIATION OF HIPPOCAMPAL AND STRIATAL CONTRIBUTIONS TO SPATIAL NAVIGATION IN THE WATER MAZE

Two experiments were conducted to compare the effects of fornix/fimbri a and caudate-putamen lesions in Long-Evans hooded rats (Rattus norveg icus) trained on two water maze tasks that differed in the type of spa tial localization required for optimum solution. In Experiment 1, the lesioned rats and surgical controls were trained on the standard place task in the water maze (Morris, 1981) and given two postacquisition t ests (a platform removal probe and platform relocation test). In Exper iment 2, rats with similar lesions and control rats were trained on a modified cue navigation task. Fornix/fimbria lesions impaired a late s tage of place task acquisition but did not impair acquisition of the c ue task. Caudate-putamen lesions resulted in a severe place acquisitio n impairment and a transient cue acquisition impairment, both of which were characterized by an initial tendency to swim near the wall of th e pool. Post-hoc analyses of the direction and angles of departure fro m the start points suggested that rats with fornix/fimbria lesions use d non-allocentric spatial strategies to solve the place task. These ra ts also demonstrated a significantly weakened spatial bias for the for mer training quadrant on the platform removal probe and reduced flexib ility in navigating to a novel platform location on the platform reloc ation test. In contrast, rats with caudate-putamen lesions showed a si gnificant spatial bias for the former training quadrant but failed to cross the exact location within the quadrant where the platform was fo rmerly positioned. The results suggest that the hippocampus mediates t he allocentric spatial component of the water maze place task while th e dorsomedial striatum may play an important role in the acquisition o f the procedural aspects of both place and cue versions of the task. ( C) 1996 Academic Press, Inc.