Rat hippocampus and memory for places of changing significance.

Abstract

Rats were tested once daily on a 4-choice delayed match from sample task with a water reward. Each day the correct place changed, and a single exposure to it was provided on information trials. Lesions of the hippocampal formation that involved the fornix, or dorsal hippocampus bilaterally, produced a severe impairment in the performance of previously trained rats; lesions of the ventral hippocampus did not preclude reacquisition of the place-memory task. Some otherwise impaired rats with fornical lesions were able to find the water when aided by nonplace cues that consistently signaled reward. Reducing the number of choices from 4 to 2 did not aid the impaired rats. Certain lesions of the hippocampal formation in the rat produced amnesia; this is consistent with a role for the hippocampus in processing of place information and shows some parallels to the amnesia seen in persons with temporal lobe lesions.