THE EFFECTS OF HUMAN HIPPOCAMPAL RESECTION ON THE SERIAL POSITION CURVE

The purpose of this study was to examine the contribution of the human hippocampal formation to the classic serial position curve. Seventy-s even patients who underwent anterior temporal lobectomy (ATL) (47 left , 30 right) were administered a list learning task before and after su rgery, and changes in the serial position curve were examined. Forty n onsurgical patients with complex partial seizures were tested at compa rable intervals and served as controls. Changes in the serial position curve were seen only after left ATL, and almost exclusively among pat ients without hippocampal sclerosis. Patients without left hippocampal sclerosis, and who therefore underwent resection of hippocampus that was to a considerable degree structurally (and presumably functionally ) intact, showed significant declines in recall from the primacy and m iddle portions of the list compared to all other groups. There was no change in the recency portion of the list. Patients with left hippocam pal sclerosis showed only a modest decline in recall from the middle r egion compared only to the control group, and the right ATL groups did not show any significant changes in serial position recall. These fin dings demonstrate the contribution of the left hippocampus ro those di screte portions of the serial position curve which rely on secondary m emory, and have implications for assessing the effects of ATL on memor y function.