Apparent Gray Matter Loss in Early Adolescence Cannot Be Explained by White Matter Growth

Poster Session E - Monday, April 15, 2024, 2:30 – 4:30 pm EDT, Sheraton Hall ABC

Jordan A. Chad^1,2, Catherine Lebel²; ¹Rotman Research Institute at Baycrest, ²University of Calgary

A fundamental puzzle about brain development is why the volume of gray matter (GM) apparently declines as white matter (WM) grows when children enter adolescence. The prevailing theory posits that an expanded distribution of myelin causes the inner edge of the GM to “whiten” while total brain volume remains steady, shifting the MRI-measured WM:GM boundary closer to the brain’s outer surface. This theory inherently predicts that GM volume loss is concurrent with WM volume growth across regions, within sexes and over time, although these predictions have yet to be explicitly tested. In this study, we test these predictions by mapping regional GM and WM volumetric changes in 2,333 participants of the Adolescent Behavioral Cognitive Development (ABCD) study aged 9-14 years who each received three MRI scans two years apart. We show that average GM and WM volume changes follow distinct spatial, temporal, and sex-specific patterns, indicating that GM volume loss is not balanced by WM volume growth, although cortical GM thinning is weakly correlated with WM growth in some regions. We conclude that myelin is not the main source of measured GM volume loss, and we propose alternative candidates.

Topic Area: NEUROANATOMY