Conditional discrimination learning in patients with bilateral medial temporal lobe amnesia

The ability of bilateral medial temporal lobe amnesic patients (MT; n = 8) and normal participants (NC; n = 8) to acquire a conditional discrimination in trace and delay eyeblink conditioning paradigms was investigated. Experiment 1 assessed trace conditional discrimination learning by using a light conditional stimulus (S+/S-) and tone conditioned stimulus (CS) separated by a 1-s trace. NCs responded differentially on S+ trials (mean percent conditioned responses = 66) versus S- trials (30), whereas MTs were impaired in their acquisition of the conditional discrimination (S+ = 51, S- = 43). In Experiment 2, the temporal separation was eliminated. NCs acquired the conditional discrimination (S+ = 70, S- = 29). MTs were unable to respond differentially (S+ = 42, S- = 37). The findings indicate that the hippocampal system is essential in acquiring a conditional discrimination, even in a delay paradigm.