We investigated the relationship between age, structural properties of selected cerebral regions, and cognitive performance in healthy adults, 18 to 78 years old. Spin-lattice relaxation time (T1), measured by nuclear magnetic resonance, was used to describe the structural composition of the brain tissue. Temporal lobe white-matter T1 showed age-related prolongation best described by a quadratic polynomial. There was a significant cubic trend in the association of hippocampal (gray-matter) T1 with age. In the examined regions of the medial temporal lobes, normally observed differentiation between gray- and white-matter T1 diminished linearly with age and dis-appeared almost completely in the elderly. Age and the ratio of gray-to white-matter T1 accounted for 53% of the variance in a measure of fluid intelligence (Cattell Culture Fair Test); the unique contributions of age and of gray-white-matter T1 ratio were 23% and 3%, respectively. The largest share of the variance in fluid intelligence (27%) was explained by the common influence of age and gray-white-matter T1 ratio. The same set of variables explained no significant proportion of the variance in crystallized intelligence. The possible mechanisms underlying age-related changes in gray-white-matter differentiation, their relationship to age-related selective deterioration of cognitive functions, and the implications of the findings for research on biological markers of aging are discussed.
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Raz et al. (1990) studied this question.
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