Contribution of positron emission tomography to functional neuroimaging inAlzheimer's disease.

When combined with cognitive investigations, functional neuroimaging method s such as positron emission tomography allow to depict the neural substrate s that underlie the neuropsychological alterations in Alzheimer's disease. Capitalising on the variance in both cognitive performances and resting cer ebral metabolic rate of glucose (CMRGIc) in Alzheimer's disease, it is poss ible to correlate these two quantitative variables on a pixel-by-pixel basi s and to generate maps showing the significant correlations in stereotaxic space. Some examples using this approach in the domain of memory disorders are presented in this brief review. We notably show that the localisation of the significant correlations diffe rs from one memory system to another as evaluated by clinical memory tasks. This approach also unravels the compensatory mechanisms that take place wi th evolution of the disease. Over and above its interest in clinical neurop sychology, this method constitutes a new source of inferences complementary to the classic activation paradigm in normal subjects, as the latter ident ifies the cerebral structures that are involved with, but not necessarily i ndispensable for, the normal execution of the task. This approach highlight s the interest of combining functional neuroimaging and neuropsychology to better understand the neural substrates of cognitive deficits in both patie nts with memory disorders and elderly normal subjects.