White matter development during late adolescence in healthy males: A cross-sectional diffusion tensor imaging study

Background: Previous MRI studies of healthy children have reported age-related white matter (WM) changes in language and motor areas of the brain. The authors investigated WM development in healthy adolescent males through age-associated changes in fractional anisotropy (FA), radial (λ_⊥) and axial (λ_||) diffusivity. Methods: Twenty-four healthy adolescent males (mean age = 16.6, SD = 2.5 years) were divided into two groups with an age split of 16.9 years and underwent a whole-brain voxelwise analysis. Results: At a threshold of p < 0.001 and extent threshold of 100 contiguous voxels, several clusters with increased FA and axial diffusivity and no differences in radial diffusivity were observed in older adolescents compared to the younger adolescents in the left arcuate fasciculus, bilateral posterior internal capsule/thalamic radiation, bilateral prefrontal gyrus, right superior temporal gyrus, and posterior corpus callosum. Increased FA and λ_|| of several clusters along the arcuate fasciculus significantly correlated with a test of language and semantic memory. Conclusions: These results suggest ongoing maturational changes especially in the arcuate fasiculus during late adolescence. Increased FA and λ_|| with no changes in radial diffusivity may reflect a developmental pattern of reduced tortuousity toward more straightened fibers and/or increased axonal fiber organization during late adolescence.