Revue de neuropsychologie


Functional imaging studies of memory in early Alzheimer's disease: dysfunction and compensatory mechanisms Volume 2, issue 2, juin 2010

Inserm-EPHE-Université de Caen/Basse-Normandie, Unité de Recherche U923, GIP Cyceron, Caen

Over the past fifteen years, many task-related functional studies have been carried out in Alzheimer's disease and in the prodromal phase of dementia, especially in patients with mild cognitive impairment. These studies examine the cerebral substrates of cognitive disorders and attempt to pinpoint precursor signs of the pathology. They also enable the identification of potential brain compensatory mechanisms to cope with the neuropathological abnormalities. Most of the studies focussed on memory, notably on episodic memory, because of its early and predominant impairment in such patients. This review scopes the main findings obtained from patient studies over three broad memory systems: episodic memory, semantic memory and working memory. Results highlight functional disorders within the key structures associated with each memory system. These dysfunctions affect both brain activations and deactivations induced by the cognitive task. Furthermore, brain plasticity and functional reorganization phenomena are also observed. These functional modifications may reflect the implementation of compensatory mechanisms. At the prodromal stage, these mechanisms mainly rely on expected structures regarding the cognitive task and consist essentially in quantitative functional modifications. With the entrance into the dementia, qualitative functional modifications appear. Indeed, the compensatory network becomes less specific and more extended throughout the brain.