Is the HM story only a 'remote memory'? Some facts about hippocampus and memory in humans

In this review, we argue that a number of current data support the notion t hat the hippocampal formations play an important role in episodic memory in humans. We will focus on data gathered from three topics within this field : (1) the neuropsychological study of memory in degenerative diseases, whic h provides striking dissociations of processes, as a function of the locati on of cerebral lesions and of their functional consequences; (2) the descri ption of patients' memory difficulties after unilateral medial temporal lob ectomy. Given the visuo-verbal dissociation, we may anticipate that the stu dy of the effects of such lesions may help in the understanding of the role of the hippocampus in memory, in terms of. (i) the stage of memory process ing where the hippocampus is really involved (encoding, consolidation and/o r retrieval); (ii) the specificity of the impairments as a function of the nature (verbal vs. visuo-spatial) of the to-be-remembered material; (3) rec ent evidence from imaging studies: (i) the morphological approach, which pr ovides interesting information with the study of correlations between the v olumes of diverse cerebral regions particularly the volume of the hippocamp us-and episodic memory performance and other cognitive measures; (ii) metab olic studies, using PET scan, which were first designed for correlational a nalyses between performance in episodic memory tasks and glucose utilizatio n at rest in diverse regions of interest, such as the hippocampal formation s, (iii) activation studies with PET and functional MRI, which are actually more straightforward, since they allow correlations between the metabolism in regions of interest and performance on line (e.g. during encoding or re trieval of information). In our view, inasmuch as such different approaches - degenerative diseases, lesions or imagery-provide convergent information , they give renewed weight to the notion according to which the hippocampal formations are critically concerned in episodic memory processes. (C) 2001 Elsevier Science BN. All rights reserved.