Abstract: In this article, I discuss the cognitive transition from normal aging to dementia -- a period often referred to as the preclinical phase of dementia. Research shows marked preclinical cognitive deficits several years before diagnosis in both Alzheimer´s disease and vascular dementia. The most pronounced prodromal impairment is observed for measures of episodic memory, speed, and executive functioning. The global nature of the impairment is consistent with neurobiological evidence that multiple lesions in limbic and neocortical regions. Despite large mean-level differences between cases and controls long before diagnosis, the performance distributions for the two groups overlap to a large degree. An important task for future research is to find means by which to decrease this overlap. This could be accomplished by combining cognitive and other (e.g., brain-based, genetic, clinical, social) markers into the prediction models. Other pressing issues for future research include (a) delineating the point at which precipitous decline normally occurs during the preclinical period; (b) asesssing individual differences in rate of change from preclinical to clinical dementia; and (c) determining how the strength of the association between a certain factor and subsequent dementia varies as a function of time to diagnosis.

Key words: aging, cognitive functions, episodic memory, preclinical dementia, Alzheimer´, s disease, vascular dementia