Female advantage in verbal memory: Evidence of sex-specific cognitive reserve.

OBJECTIVE: We investigated sex differences in verbal memory across different levels of neural dysfunction, measured by temporal lobe glucose metabolic rates (TLGluMR).
METHODS: Three hundred ninety controls and 672 participants with amnestic mild cognitive impairment (aMCI) and 254 with Alzheimer disease (AD) dementia from the Alzheimer's Disease Neuroimaging Initiative completed the Rey Auditory Verbal Learning Test (RAVLT) and [18F]-fluorodeoxyglucose-PET. Cross-sectional analyses were conducted using linear regression to examine the sex by TLGluMR interaction on RAVLT performance in the overall sample and within diagnostic groups adjusting for age, education, and APOE ε4 genotype.
RESULTS: Across groups, female sex and higher TLGluMR and their interaction were associated with better verbal memory (p values ≤ 0.005). The female advantage in verbal memory varied by TLGluMR such that the advantage was greatest among individuals with moderate to high TLGluMR and minimal or absent among individuals with lower TLGluMR. Diagnosis-stratified analyses revealed that this interaction was driven by the aMCI group (p values = 0.009). The interaction was not significant in control and AD dementia groups.
CONCLUSIONS: Women show better verbal memory than men in aMCI despite similar levels of brain hypometabolism. The lifelong advantage that females show over males in verbal memory might represent a form of cognitive reserve that delays verbal memory decline until more advanced pathology, as indexed by TLGluMR. This issue is clinically important because verbal memory scores are used in diagnosing aMCI and AD dementia.