Puberty, not age, marks the start of adolescent brain structural remodeling

Many studies have shown that pubertal changes are associated with brain changes, but there lacks a clear understanding of what happens to the brain at puberty, and whether it opens the brain structural remodeling that characterizes adolescence. In this study, we used three longitudinal waves of structural MRI data from thousands of participants of the ABCD study aged 9-14 years to compare brain changes between age-matched children who had either reached or not reached a major pubertal milestone: menarche in females and fonarche (voice drop) in males. We found that only the children who had reached the milestone exhibited widespread contraction of cortical surface area and subcortical volume. The contraction was more pronounced in females, in line with previous evidence of how gonadal hormones regulate neuronal fine-tuning. Our findings suggest that reaching puberty, rather than reaching a particular age, begins the adolescent phase of structural brain development.