Age-related changes in fibre composition of the human corpus callosum: Sex differences

WE found positive correlations between the number of myelinated callosal fibres > 1 mu m in diameter and age in humans. The relatively abundant axons with diameters between 1 and 3 mu m correlated with age only in females, while the scarce fibres > 3 mu m in diameter correlated significantly with age only in males. When analysing different callosal segments, it was found that in the midbody (but not in the splenium) of females the number of fibres > 3 mu m also increased with age. In males, the relationship between these large diameter fibres and age disappeared after dividing the callosum into distinct segments. There may, therefore, be sex differences in the course of callosal fil;re growth and myelination during the normal lifespan.