The concept of cognitive reserve (CR) suggests that innate intelligence or aspects of life experience like educational or occupational attainments may supply reserve, in the form of a set of skills or repertoires that allows some people to cope with progressing Alzheimer's disease (AD) pathology better than others. There is epidemiological evidence that lifestyle characterized by engagement in leisure activities of intellectual and social nature is associated with slower cognitive decline in healthy elderly and may reduce the risk of incident dementia. There is also evidence from functional imaging studies that subjects engaging in such leisure activities can clinically tolerate more AD pathology. It is possible that aspects of life experience like engagement in leisure activities may result in functionally more efficient cognitive networks and therefore provide a CR that delays the onset of clinical manifestations of dementia.The CR hypothesis suggests that there are individual differences in the ability to cope with AD pathology (Stern, 2002). For example, Katzman et al. (1989) described cases of cognitively normal, elderly women who were discovered to have advanced AD pathology in their brains at death. They speculated these women did not express the clinical features of AD because their brains were larger than average. About 25% of subjects who during autopsy fulfill pathologic criteria for AD and were assessed and followed in wellcharacterized cohorts were clinically intact during life (Ince, 2001). Similarly, most clinicians are aware of the fact that a stroke of a given magnitude can produce profound impairment in 1 patient and while having minimal effect on another. Something must account for the disjunction between the degree of brain damage and its outcome, and the concept of reserve has been proposed to serve this purpose.Innate intelligence or aspects of life experience like educational or occupational attainment may supply reserve, in the form of a set of skills or repertoires that allows some people to cope with pathology better than others.Epidemiological data supporting the CR hypothesis include observations that lower educational and occupational attainment is associated with increased risk for incident dementia (Stern et al., 1994). Similarly, lower linguistic ability (as expressed by idea density and grammatical complexity) in early life and childhood mental ability scores are strong predictors of poor cognitive function and dementia in late life (Snowdon et al., 1997;Whalley et al., 2000). This is consistent with the prediction that people with more reserve can cope with advancing AD pathology longer before it is expressed clinically. In addition it has been shown that AD patients with higher educational and occupational attainment have more rapid cognitive decline than those with lower attainment, consistent with the idea that,