We show that white matter tracts are differentially positioned in the cortical hierarchy to support specific cognitive functions, and that tracts spanning the hierarchy connect regions with greater cognitive diversity. Moreover, tracts situated within the same hierarchical level connect biologically similar regions, while those crossing the hierarchy bridge distinct biological milieux to support diverse cognitive functions. The placement of tracts in the cortical hierarchy also reflects developmental variation in tract microstructure and individual differences in cognition.

The Adolescent Brain Cognitive Development (ABCD) Study is the largest U.S. effort to track brain development in adolescence. Diffusion MRI (dMRI) offers a powerful window into white matter, but large, multi-site datasets are difficult to process and analyze. We address this with the ABCD-BIDS Community Collection (ABCC, release 3.1.0): an open resource of 24,000+ fully processed dMRI scans. ABCC includes analysis-ready data, detailed quality metrics, advanced microstructural measures, and individualized white matter tractography. Using these data, we show that newer dMRI metrics outperform traditional measures in detecting developmental change—and are more robust to differences in image quality. We also demonstrate that harmonizing data across scanners improves the consistency of findings across sites. ABCC lowers barriers to large-scale neuroimaging and provides a powerful, open foundation for studying adolescent brain development.

Brain-behavior associations in humans are typically small. Although socioeconomic factors have long been linked to brain structure and function, their pervasiveness and magnitude have often been overlooked in human neuroscience. Here we highlight recent findings that suggest that the childhood environment is a major source of variation in human neuroscience that may be essential for understanding brain organization.