La maladie d’Alzheimer et la mémoire humaine

Abstract

Memory disorders observed in Alzheimer's disease gave rise, from the eighties, to a detailed analysis into the framework of cognitive neuropsychology which aimed at describing the deficits of very specific processes. Beyond their clinical interest, these studies contributed to the modelisation of human memory thanks to the characterization of different memory systems and their relationships. The first part of this paper gives an overview of the memory deficits in Alzheimer's disease and insists on particular cognitive phenomena. Hence, several examples are developed in the domains of semantic memory (such as hyperpriming and hypopriming effects) and autobiographical memory. Recent results highlight the existence of severe autobiographical amnesia observed in all neurodegenerative diseases, though with contrasting profiles: Ribot's gradient in Alzheimer's disease (showing that remote memories are better preserved than recent ones), reverse gradient in semantic dementia and no clear gradient in the frontal variant of frontotemporal dementia. The second part of this article presents advances in cognitive neuroscience searching to disclose the cerebral substrates of these cognitive deficits in Alzheimer's disease. The studies using functional imaging techniques are the most informative regarding this problematic. While showing the dysfunctions of an extended network, they emphasize the selectivity of cerebral damages that are at the root of very specific cognitive dysfunctions, coming close in that way to the conceptions of cognitive neuropsychology. These neuroimaging studies unravel the existence of compensatory mechanisms, which until recently were clearly missing in the literature on neurodegenerative diseases. These different researches lead to a wide conception of human memory, not just limited to simple instrumental processes (encoding, storage, retrieval), but necessarily covering models of identity and continuity of the subject, which interact in a dynamic way with eminently changing memory representations.