Heterogeneity of cognitive profiles in normal aging: implications for early manifestations of Alzheimer's disease.

This study explores the presence of homogeneous subgroups among 156 normal elderly subjects based on their performance on a battery of neuropsychological tests. Subjects ranged in age between 57 and 85 years and included 62 males and 94 females with a mean age 70.7 years, mean education 14.1 years, and mean Full Scale IQ of 117.2. Six clusters were extracted, three of which are likely to represent preclinical stages of the dementing process with distinct patterns of cognitive deficits. The results are discussed in light of different models of cognitive deterioration in DAT.