[Plurality of patterns of cognitive impairment in normal aging and in dementia]

Normal aging, as well as most of the degenerative diseases of the central nervous system characterizing old age, have an impact on cognitive abilities which are obvious as well as increasingly understood. Cognitive changes in normal ageing realize a plurality of possible patterns of cognitive disabilities. Dementias are also well known to be characterized by a plurality of cognitive impairments patterns. The different cognitive patterns are likely to be due to distinct levels of impairments of different domains of cognition, or of different components within one given domain of cognition. These differences are such that in some cases they can even realize double dissociations. The plurality of cognitive impairments patterns in normal aging and in dementia will be discussed as well as the different factors that could contribute to such a plurality. Some of these factors relate to pre-morbid characteristics of the individuals known to influence the functional organization of the brain for cognition. Others--of major importance--are related to the nature and the distribution of the pathophysiological processes underlying normal ageing or a given degenerative disease. It is also reminded that some or many of these factors can interact with more general cognitive factors, such as speed of execution. It is however suggested that, despite of their presence, these general factors partly contribute to the cognitive impairments in neurodegenerative dementia. In this case, the impact of different disease-related factors over a general cognitive factor is probably much greater than in the case of normal aging.