Constituents of grapes have been studied for their antioxidant, anti-inflammatory, and anticarcinogenic properties. In the past decade, there has been emerging evidence regarding a potential role for grapes in slowing cognitive decline and other effects of aging. Furthermore, evidence has been obtained in vivo that supplementation of aged rats with grape seed extract improves cognitive performance. Despite the promising accumulating data supporting the use of grapes as a safe and effective strategy for delaying the incidence of dementia, it remains unclear how grape intake would be useful with respect to factors such as dose schedule or stage of dementing illness. In general, well-controlled experimental data obtained in human subjects is in need of much further development. The investigators aim to measure effects of grape intake on cerebral metabolism and cognitive function, and to determine whether initial patterns, and magnitude of change, of cerebral metabolism assessed by positron emission tomography (PET) can serve respectively as a predictor of, and biomarker for, the magnitude of cognitive changes resulting from intake of grapes.