More than just axons: A positive relationship between an intracellular isotropic diffusion signal and pubertal development in white matter regions in a massive adolescent cohort

Puberty is a key event in adolescent development that involves significant, hormone-driven changes to many aspects of physiology including the brain. Understanding how the brain responds during this time period is important for evaluating neuronal developments that affect mental health throughout adolescence and the adult lifespan. This study examines diffusion MRI scans from the cross-sectional ABCD Study baseline cohort, a large multi-site study containing thousands of participants, to describe the relationship between pubertal development and brain microstructure. Using advanced, 3-tissue constrained spherical deconvolution methods, this study is able to describe multiple tissue compartments beyond only white matter (WM) axonal qualities. After controlling for age, sex, brain volume, subject handedness, scanning site, and sibling relationships, we observe a positive relationship between an isotropic, intracellular diffusion signal fraction and pubertal development across a majority of regions of interest (ROIs) in the WM skeleton. We also observe regional effects from an intracellular anisotropic signal fraction compartment and extracellular isotropic free water-like compartment in several ROIs. This work suggests that changes during pubertal development elicit a complex response from brain tissue that cannot be completely described by traditional methods focusing only on WM axonal properties. This work brings in vivo human neuroimaging studies more into line with work performed on animal models, which describe an interaction between increased myelination, neurogenesis, angiogenesis, and glial cell proliferation in response to pubertal hormones.