What are the boundary zones between normal aging and Alzheimer's disease (AD)? Are many elderly people whom we regard as normal actually in the early stages of AD? Alzheimer's disease does not develop overnight; the early phases may last for years or even decades. Recently, clinical investigators have identified a transitional condition between normal aging and and very early Alzheimer's disease that they have called mild cognitive impairment, or MCI. This term typically refers to memory impairment beyond what one would expect in individuals of a given age whose other abilities to function in...