Dissociating space and trace in dorsal and ventral hippocampus.

Emerging evidence suggests that the hippocampus can be anatomically and functionally dissociated along its septotemporal axis into dorsal and ventral subregions. With respect to function, we have recently demonstrated that pre-training excitotoxic lesions of ventral, but not dorsal, hippocampus impair the acquisition of trace fear conditioning, whereas post-training lesions of either dorsal or ventral hippocampus impair the subsequent expression of trace fear conditioning (Yoon and Otto (2007) Neurobiol Learn Mem 87:464-475). In addition to trace fear conditioning, dorsal and ventral hippocampus appear to be differentially involved in a number of spatial memory tasks. The present study examined the effects of temporary inactivation of dorsal or ventral hippocampus on the acquisition and expression of trace fear conditioning and on performance of a spatial delayed reinforced alternation task. The findings demonstrate a double dissociation of dorsal and ventral hippocampal function: inactivation of ventral, but not dorsal, hippocampus attenuated the acquisition and expression of trace fear conditioning, whereas inactivation of dorsal, but not ventral, hippocampus dramatically impaired performance in the delayed reinforced alternation task. These data further support the notion that dorsal and ventral hippocampus contribute differentially to performance in a variety of paradigms.