Hippocampal formation size in normal human aging: a correlate of delayed secondary memory performance.

Although mild progressive memory impairment is commonly associated with normal human aging, it is unclear whether this phenomenon can be explained by specific structural brain changes. In a research sample of 54 medically healthy and cognitively normal elderly persons (ages 55-87, x = 69.0 +/- 7.9), magnetic resonance imaging (MRI) was used to derive head-size-adjusted measurements of the hippocampal formation (HF) (dentate gyrus, hippocampus proper, alveus, fimbria, subiculum), the superior temporal gyrus (STG), and the subarachnoid cerebrospinal fluid (CSF) (to estimate generalized cerebral atrophy). Subjects were administered tests of primary memory (digit span) and tests of secondary memory with immediate and delayed recall components (paragraph, paired associate, list recall; facial recognition). Separate composite scores for the immediate and delayed components were created by combining, with equal weighting, the subtests of each category. The WAIS vocabulary subtest was used as a control measure for language and intelligence. A highly significant correlation (P < 0.001), independent of age, gender, and generalized cerebral atrophy was found between HF size and delayed memory performance. No significant correlations were found between HF size and primary or immediate memory performance. STG size was not significantly correlated with any of the composite memory variables. These results suggest that HF atrophy may play an important independent role in contributing to the memory loss experienced by many aging adults.