EPISODIC AND DECLARATIVE MEMORY - ROLE OF THE HIPPOCAMPUS

The fact that medial temporal robe structures, including the hippocamp us, are critical for declarative memory is firmly established by now. The understanding of the role that these structures play in declarativ e memory, however, despite great efforts spent in the quest, has elude d investigators so far. Given the existing scenario, novel ideas that hold the promise of clarifying matters should be eagerly sought. One s uch idea was recently proposed by Vargha-Khadem and her colleagues (Sc ience 1997; 277:376-380) on the basis of their study of three young pe ople suffering from anterograde amnesia caused by early-onset hippocam pal pathology. The idea is that the hippocampus is necessary for remem bering ongoing life's experiences (episodic memory), but not necessary for the acquisition of factual knowledge (semantic memory). We discus s the reasons why this novel proposal makes good sense and why it and its ramifications should be vigorously pursued. We review and compare declarative and episodic theories of amnesia, and argue that the findi ngs reported by Vargha-Khadem and her colleagues fit well into an epis odic theory that retains components already publicized, and adds new o nes suggested by the Vargha-Khadem et al. study. Existing components o f this theory include the idea that acquisition of factual knowledge c an occur independently of episodic memory, and the idea that in antero grade amnesia it is quite possible for episodic memory to be more seve rely impaired than semantic memory. We suggest a realignment of organi zation of memory such that declarative memory is defined in terms of f eatures and properties that are common to both episodic and semantic m emory. The organization of memory thus modified gives greater precisio n to the Vargha-Khadem et al. neuroanatomical model in which declarati ve memory depends on perihippocampal cortical regions but not on the h ippocampus, whereas episodic memory, which is separate from declarativ e memory, depends on the hippocampus. (C) 1998 Wiley-Liss, Inc.