Sex differences in cortical thickness in middle aged and early old-aged adults: Personality and Total Health Through Life study

The study investigated sex differences in cortical thickness in middle-aged (MA, 44-48 years old, n = 397) and early old-aged (OA, 64-68 years old, n = 398) adults in a community-based sample. T1-weighted three-dimensional structural magnetic resonance imaging scans were acquired in a Fast Field Echo sequence, and cortical thickness was measured with a surface-based segmentation procedure (http://surfer.nmr.mgh.harvard.edu). Results showed that after correcting for age, MA males had predominantly thicker superior temporal cortices, while MA females had thicker occipital, posterior cingulate, precentral, and postcentral cortices. Sex differences in OA adults were less prominent than those in MA adults with females showing thicker temporal and posterior cingulate cortices and males showing thicker rostral middle frontal regions. Between-cohort comparisons revealed that when compared with MA males, OA males showed many regions with significantly thinner cortices, but this pattern was less pronounced for OA females. Our results suggest that sex differences in cortical thickness are age specific, as larger differences in cortical thickness were found in MA compared to OA adults. The results of the present study indicate that the inconsistencies in sexual dimorphism that have been reported in the literature are partly due to the variable and transitory nature of cortical thickness differences with age.