Deficits in inhibitory processes in normal aging and patients with Alzheimer's disease: a review

Empirical data suggest that inhibitory processing is impaired in normal aging. A decrease in inhibitory processing may also play an important role in the cognitive changes occurring in the early stages of Alzheimer's disease. The comparison of inhibitory deficits in Alzheimer's disease and normal aging emphasizes the need to discriminate quantitative changes in inhibitory functioning from qualitative changes which may be specifically related to the disease process. Inhibitory deficits in normal old adults and patients with Alzheimer's disease, suggest different levels of implication of the inhibitory processes. In the cognitive literature, the construct of inhibition, frequently used, is however difficult to define as it refers to many different phenomena. The question of whether or not inhibitory processes are to be considered as a single unit is challenging, and many authors suppose the existence of several distinct inhibitory mechanisms. A taxonomy of inhibition, based on proposals from Nigg and Soltzfus et al., is proposed to facilitate studies of inhibitory dysfunction. Such approach allows a clarification between inhibition deficits specific to normal aging and to Alzheimer's disease.