Background: Aging is accompanied by a gradual deterioration in multiple cognitive abilities and brain structures. Both cognitive function and white matter (WM) structure are found to be associated with neurodegeneration diseases and correlated with sex during aging. However, it is still unclear whether the brain structural change could be attributable to sex, and how sex would affect cognitive performances during aging. Materials and Methods: Diffusion magnetic resonance imaging (MRI) scans were performed on 1127 healthy participants (age range: 21-89) at a single site. The age trajectories of the WM tract microstructure were delineated to estimate the turning age and changing rate between sexes. The canonical correlation analysis and moderated mediation analysis were used to examine the relationship between sex-linked WM tracts and cognitive performances. Results: The axon intactness and demyelination of sex-linked tracts during aging were multifaceted. Sex-linked tracts in females peak around 5 years later than those in males but change significantly faster after the turning age. Projection and association tracts (e.g., corticospinal tracts and parahippocampal cingulum) contributed to a significant decrease in visuospatial functions (VS) and executive functions (E). We discovered that there is a stronger indirect effect of sex-linked tracts on cognitive functions in females than in males. Conclusion: Our findings suggest that the vulnerable projection and association tracts in females may induce negative impacts on integrating multiple functions, which results in a faster decrease in VS and E. Impact statement By recruiting a healthy population for diffusion magnetic resonance imaging (MRI) scan, we demonstrated that the age-related changes of white matter (WM) integrity were manipulated by sex. Sex-linked tracts in females reached the turning age 5 years later, but change faster than those in males after the turning age. The most significant sex effect was found in projection and association tracts. Our results indicated that sex affected both WM microstructure and cognitive functions and was further involved in the mediation of the age-WM-cognition relationship. The vulnerability of projection and association tracts in females may induce negative impacts on visuospatial and executive functions.
Keywords: cognitive aging; diffusion tensor imaging (DTI); life span; sex differences; white matter microstructure.