THE EFFECTS OF HIPPOCAMPECTOMY ON PERFORMANCE BY RATS OF A RUNNING RECOGNITION TASK USING LONG LISTS OF NONSPATIAL ITEMS

Unoperated rats, or rats with cortical control lesions or hippocampal aspiration lesions, were trained on a non-spatial delayed non-matching-to-sample task. Once the non-matching rule had been learned, the task was modified so as to assess list memory, with list lengths of up to 32 items. Hippocampectomy induced a significant drop in choice accuracy, that was independent of list length; nonetheless, hippocampectomised rats still performed at better than chance levels. The cortical control lesion appeared to induce an intermediate (though generally non-significant) deficit. It was concluded that hippocampectomy leaves rats still capable of choosing with considerable accuracy on non-spatial working memory tasks that use trial-unique or 'pseudo-trial-unique' stimuli, even under experimental conditions in which a heavy memory load is imposed.