History and experience: the direction of Alzheimer's disease.

As the global population is projected to age substantially in coming decades, the number of individuals who will develop Alzheimer disease (AD) is expected to rise dramatically. We have come to understand that AD is likely to be multidetermined through interactions between heritable causal and susceptibility genes, environmental exposures, midlife health status, and lifestyle choices. In addition, mounting evidence suggests that the neuropathological processes characteristic of AD can be detected several years before the onset of clinical symptoms. Thus, AD is now considered to have presymptomatic, prodromal (mild cognitive impairment), and dementia phases. Through cerebrospinal fluid biomarkers, volumetric neuroimaging, functional neuroimaging, and cognitive stress tests, individuals at significant risk for developing dementia can now be identified with greater sensitivity and specificity. Consequently, there is growing attention to identify interventions to halt or delay the onset of AD. The biological capacities of neurogenesis and neuroplasticity and the related concepts of brain and cognitive reserve provide a rationale for developing techniques to maintain or enhance the cognitive abilities of older persons to sufficiently prevent dementia. This has led to the emergence of a new "brain fitness" commercial industry in which "products" are being marketed and sold to consumers to "keep your brain sharp." However, most available brain fitness products have scant scientific evidence to support their effectiveness. Nevertheless, ongoing research advances do support the potential for memory and other intellectual functions to be strengthened and maintained through cognitive training, physical exercise, dietary choices, social engagement, and psychological stress reduction.