Perseveration on place reversals in spatial swimming pool tasks: further evidence for place learning in hippocampal...

Animals with damage to the fimbria-fornix (FF) or cells of the hippocampus (HIP) can learn a place problem but cannot learn matching-to-place problems, which feature a series of place "reversals." The two experiments described in the present report were designed to examine the causes of impairment on reversal learning. In experiment 1, control, HIP, and FF groups were trained to asymptote on a place problem, and then the location of the platform was moved. Control rats learned the reversal response more quickly than the initial response; the HIP rats learned both problems at the same rate. Swim analysis showed that the impairment in the lesion group on the reversal response was aggravated by perseverative returns to the first learned place. In experiment 2, control and FF groups were trained on a task in which the platform was visible on three daily trials and hidden on one daily trial. After 10 days, the platforms were moved. In the reversal response, the FF group showed enhanced performance on the cue trials and severely impaired performance on the place trials relative to initial learning and control performance. Swim analysis showed that FF rats perseverated on the initial place response in place trials. These experiments provide further evidence for place learning in hippocampal rats and show that perseverative responses contribute to impairments in new learning. The results are discussed in relation to the idea that the hippocampus mediates spatial mapping and/or uses self-movement cues to solve spatial problems.