Pubertal timing is a critical dimension of adolescent brain vulnerability

Adolescence is a period of rapid brain development, during which biological maturational timing varies substantially between individuals. This variability may drive specific developmental vulnerabilities to adverse experiences with long-term consequences, warranting early identification of at-risk individuals. We utilized ultrasonic bone age measurements to track pubertal maturity, classifying participants by adolescent biological maturity relative to chronological age (accelerated, average, decelerated). Brain hierarchy was quantified as the irreversibility of brain signals in resting state electroencephalography, providing a brain-based method to detect vulnerability patterns. The COVID-19 pandemic presented a unique opportunity to also assess alterations in brain hierarchy following external disruption. We mapped maturity-defined trajectories and rates of hierarchical organization, and their post-pandemic deviation from expected development, capturing two distinct vulnerability forms. First, early maturing adolescents showed persistent reduction in brain hierarchy. Second, those undergoing their fastest phase of development - specifically, decelerated adolescents - showed the strongest disruption in brain hierarchy following the pandemic. These findings suggest that pubertal timing is a critical dimension of individual variation in adolescent brain development and vulnerability. They also emphasize the need for objective maturity measurements to tailor support to individual pubertal timelines, particularly given the secular trend toward earlier puberty and ongoing global ecological crises.