Microstructural development across white matter from 9-13 years

Development in late childhood has been associated with microstructural changes in white matter (WM) that are hypothesized to underpin concurrent changes in cognitive and behavioral function. Restriction spectrum imaging (RSI) is a framework for modelling diffusion-weighted imaging that can probe microstructural changes within hindered and restricted compartments providing greater specificity than diffusion tensor imaging for characterizing intracellular diffusion. Using RSI, we modelled voxelwise restricted isotropic, N0, and anisotropic, ND, diffusion across the brain and measured cross-sectional and longitudinal age associations in a large sample (n=8,039) aged 9-13 years from the Adolescent Brain and Cognitive Development (ABCD) StudySM. Participants showed global increases in N0 and ND across WM with age. When controlling for global RSI measures (averaged across WM), we found smaller age-related associations in frontal regions, reflective of more protracted development of frontal WM. Moreover, variability in the development of restricted diffusion in subcortical regions and along particular gray-white matter boundaries was independent of the global developmental effect. Using the ABCD sample, we have unprecedented statistical power to estimate developmental effects with high precision. Our analyses reveal spatially-varying maturational changes for different regions, independent of global changes. This non-uniformity may reflect age-dependent development of distinct cognitive and behavioral processes.