Longitudinal Development of Human Brain Wiring Continues from Childhood into Adulthood

TLDR

Brain white matter development continues through childhood and adolescence, but it is unclear whether these changes cease in late adolescence. The study tracked 103 healthy participants aged 5–32 years with diffusion tensor tractography, measuring fractional anisotropy and mean diffusivity in 10 major white matter tracts across 221 scans. White matter tracts exhibited nonlinear FA and MD trajectories, with most children and early adolescents showing significant changes that plateaued by late adolescence for projection and commissural tracts, while association tracts continued to mature postadolescently, driven mainly by decreasing perpendicular diffusivity and increasing parallel diffusivity, and volume gains were independent of diffusion changes, indicating microstructural rather than gross anatomical maturation.

Abstract

Healthy human brain development is a complex process that continues during childhood and adolescence, as demonstrated by many cross-sectional and several longitudinal studies. However, whether these changes end in adolescence is not clear. We examined longitudinal white matter maturation using diffusion tensor tractography in 103 healthy subjects aged 5–32 years; each volunteer was scanned at least twice, with 221 total scans. Fractional anisotropy (FA) and mean diffusivity (MD), parameters indicative of factors including myelination and axon density, were assessed in 10 major white matter tracts. All tracts showed significant nonlinear development trajectories for FA and MD. Significant within-subject changes occurred in the vast majority of children and early adolescents, and these changes were mostly complete by late adolescence for projection and commissural tracts. However, association tracts demonstrated postadolescent within-subject maturation of both FA and MD. Diffusion parameter changes were due primarily to decreasing perpendicular diffusivity, although increasing parallel diffusivity contributed to the prolonged increases of FA in association tracts. Volume increased significantly with age for most tracts, and longitudinal measures also demonstrated postadolescent volume increases in several association tracts. As volume increases were not directly associated with either elevated FA or reduced MD between scans, the observed diffusion parameter changes likely reflect microstructural maturation of brain white matter tracts rather than just gross anatomy.