Further Analysis of the Hippocampal Amnesic Syndrome: 14-year Follow-up Study of H.m.*

-The report attempts to delineatecertain residual learning capacities of H.M., a young man who became amnesic in 1953 following a bilateral removal in the hippocampal zone. In addition to being able to acquire new motor skills (CoRKIN [2]), this patient shows some evidence of perceptual learning. He also achieves some retention of very simple visual and tactual mazes in which the sequence of required turns is short enough to fit into his immediate memory span; even then, the rate of acquisition is extremely slow. These vestigial abilities, which have their occasional parallels in the patient's everyday life, are assessed against the background of his continuing profound amnesia for most on-going events, an amnesia that persists in spite of above-average intelligence and superior performance on many perceptual tasks. THE PRESENT repor t has three aims. In the first place, it describes the persis tent features of a severe amnesic syndrome acquired 14 years ago, fol lowing bi la tera l mesial t empora l lobec tomy (ScoVILLE [28]). Secondly, the repor t a t tempts to give further substance to our previous ly held belief tha t the pa t ien t ' s perceptua l and intel lectual capacit ies remain intact , as mani fes ted by no rma l or super ior pe r tb rmance on a fair ly wide range o f exper imental tasks. Thirdly , we are explor ing the na ture o f the m e m o r y detect in some detai l by trying to discover which learning tasks the pat ient can master , as c o m p a r e d with those on which he always fails. I N T E R V A L H I S T O R Y Since the onset of his amnes ia in 1953, we have twice had the oppor tun i ty o f br inging this pa t ien t under intensive observat ion. In 1962, he spent one week at the Mont rea l Neuro log ica l Inst i tute, and most results o f these and earl ier examinat ions have a l ready been repor ted (CoRK~N [1]; MILNER [16, 18, 19]). Extensive testing was again carr ied out in 1966, dur ing a two-week admiss ion to the Clinical Research Center at M.I .T. Findings ob ta ined dur ing that per iod, supplemented later by visits to the pa t ien t ' s home, form the basis of the present report . * From the Montreal Neurological Institute and from the Psychophysiological Laboratory and Clinical Research Center, M.I.T. "Ilais work was supported in part by the Medical Research Council of Canada, and in part by grants to H.-L. TEtmER from the John A. Hartford Foundation, NASA, and the National Institutes of Health (under MH-05673, and a Clinical Center Grant, FR88). The follow-up study of K.M. was supported by United States Public Health Small Grant M5774A to BRENDA MILNER.