Double dissociation of function within the hippocampus: A comparison of dorsal, ventral, and complete hippocampal cytotoxic lesions

Rats with complete cytotoxic hippocampal lesions exhibited spatial memory i mpairments in both the water maze and elevated T maze. They were hyperactiv e in photocell cages; swam faster in the water maze; and were less efficien t on a nonspatial, differential reinforcement of low rates (DRL) task. Perf ormance on both spatial tasks was also impaired by selective dorsal but not ventral lesions; swim speed was increased by ventral but not dorsal lesion s. Both partial lesions caused a comparable reduction in DRL efficiency, al though these effects were smaller than those of complete lesions. Neither p artial lesion induced hyperactivity when rats were tested in photocell cage s, although both complete and ventral lesion groups showed increased activi ty after footshock in other studies (Richmond et al., 1999). These results demonstrate possible functional dissociations along the septotemporal axis of the hippocampus.