Dorsal and ventral hippocampus: Same or different?

Abstract

Previous work has suggested that the hippocampus (HPC) is not a functionally homogenous structure, because lesions of the septal pole have been found to produce more of a deficit in spatial navigation. To investigate whether this dissociation extends to configural-relational learning, we tested rats with dorsal or ventral HPC lesions in a modified version of the Morris water task and in a discriminative context-conditioning paradigm. Results indicated that dorsal HPC lesions were more efficient in impairing performance in the spatial navigation task but that ventral HPC lesions also had some effect. However, no differences between groups were found in the nonspatial context-conditioning task. Both lesion groups acquired discriminative freezing at a rate identical to that of the controls, but lesioned animals could not acquire preference for the safe environment even after three pairings with shock. Thus, comparison of multiple cues with different emotional valence requires integration along the septotemporal axis of the HPC. Reviewing previous studies, we conclude that although the dorsal HPC pole is more efficient than the ventral in supporting spatial navigation, the dissociation is not absolute. We also hypothesize that physiological activity along the longitudinal axis of the HPC might have particular behavioral relevance. Theoretical implications of this hypothesis are considered.