Eyeblink classical conditioning in H.M.: delay and trace paradigms

Abstract

H.M., a well-known subject with bilateral removal of medial-temporal-lobe structures and profound amnesia, performed eyeblink classical conditioning (EBCC) for 21 90-trial sessions in the 400-ms delay and 900-ms trace paradigms. A 2nd amnesic subject with temporal lobe lesions and 2 normal control subjects (NCSs) were also conditioned. Acquisition occurred in both paradigms for all subjects. Acquisition in the delay paradigm was prolonged in H.M. (perhaps because of his cerebellar degeneration in the vermis and hemispheres), but not in the 2nd amnesic subject. Amnesic subjects and NCSs showed more rapid acquisition in the trace than in the delay paradigm. Two years after initial EBCC, H.M. attained learning criterion in the trace paradigm in 1/10th as many trials. No recollection of the experimenters, apparatus, instructions, or procedure was manifested by H.M. Results suggest that humans can condition in the 400-ms delay and 900-ms trace EBCC paradigms with the hippocampus radically excised.