Differential effects of dorsal and ventral hippocampal lesions.

Several studies have demonstrated that dorsal, but not ventral, hippocampus is critical for spatial memory. The mnemonic role of the ventral hippocampus remains unclear. The existence of relatively direct connections between hypothalamic nuclei and ventral hippocampus suggests that the ventral hippocampus may be involved in acquisition of information regarding internal cues (e.g., hunger). Male Long-Evans rats received ibotenic acid-induced lesions of either dorsal or ventral hippocampus or underwent sham surgeries. After a 3 week recovery, subjects were tested on delayed alternation in a T-maze and on a task in which food-deprivation state was used as a contextual cue (Davidson and Jarrard, 1993). Rats with dorsal, but not ventral, lesions were impaired in delayed alternation, consistent with previous findings, but both groups were impaired in the learning of the internal state-shock association task.