NONREVERSAL AND REVERSAL SHIFTS IN THE HIPPOCAMPECTOMIZED RAT

Hippocampectomized, neocortically damaged and unoperated rats (N=45) were trained on a light/dark discrimination with irrelevant tactile and position cues. After reaching criterion a nonreversal shift was required, i.e., the tactile dimension became the relevant dimension. During the tactile discrimination the previously correct light cue was present but irrelevant for half the rats in each group. For the remaining rats the light cue was not available. Finally, all rats were trained on a reversal of the tactile discrimination. Hippocampectomized rats were not impaired on either nonreversal problem. Nor were they impaired on the reversal problem with only the position cue irrelevant. These results contradict the interference hypothesis that hippocampectomized animals have difficulty in restraining the influence of prior learning on present performance. Hippocampectomized rats were impaired in acquisition of the original light/dark discrimination and on the reversal problem with multiple irrelevant cues. The hypothesis behavior of the hippocampectomized rats on these problems, however, did not indicate overresponding to the additional irrelevant cue or to the previously rewarded cue. © 1979.