Recollection and familiarity in hippocampal amnesia

Currently, there is a general agreement that two distinct cognitive operations, recollection and familiarity, contribute to performance on recognition memory tests. However, there is a controversy about whether recollection and familiarity reflect different memory processes, mediated by distinct neural substrates (dual-process models), or whether they are the expression of memory traces of different strength in the context of a unitary declarative memory system (unitary-strength models). Critical in this debate is the status of recognition memory in hippocampal amnesia and, in particular, whether the various structures in the medial temporal lobe (MTL) contribute differentially to the recollection and familiarity components of recognition. The present study aimed to explore the relative contribution of recollection and familiarity to recognition of words that had been previously read or that had been previously generated in a group of severely amnesic patients with cerebral damage restricted to the hippocampus. A convergent pattern of results emerged when we used a subjective-based (remember/know; R/K) and an objective-based (process dissociation procedure; PDP) methods to estimate the contribution of recollection and familiarity to recognition performance. In both PDP and R/K procedures, healthy controls disclosed significantly higher recollection estimates for words that had been anagrammed than for words that had been read. Amnesic patients' recollection scores were not different for words that had been generated or that had been read, and the recollection estimate for words that had been generated was significantly reduced as compared to the group of healthy controls. For familiarity, both healthy controls and amnesic patients recognized as familiar more words that had been generated than words that had been read, and there was no difference between the two groups. These data support the hypothesis of a specific role of the hippocampus in recollection processes and suggest that other components of the MTL (e.g., perirhinal cortex) may be more involved in the process of familiarity.