Emerging left-right asymmetry of white matter brain pathways in humans: Fetal, neonatal, and toddler stages

Abstract

Little is known about the emergence of structural asymmetry of white matter (WM) tracts during early human brain development. In this study, we examined the emergence and developmental trajectory of structural hemispheric asymmetry in select WM tracts from ages 15 gestational weeks (GW) to 3 years. The outcomes of interest included WM tract volume and measures of apparent diffusion coefficient and fractional anisotropy. Age-related development of laterality was not observed in a migration stream from the ganglionic eminence nor in two limbic pathways, the cingulum bundle and the fornix. Among the studied corticocortical association pathways (inferior longitudinal fasciculus [ILF], inferior frontooccipital fasciculus, and arcuate fasciculus), only the ILF showed development of age-related laterality emerging as early as the second trimester. These results suggest that asymmetry in WM pathways arises substantially later than asymmetry in the related cortical areas described in the literature.