Synchrony between brain age and internalising and externalising symptoms across adolescence.

Background: Adolescence is a period of rapid neurobiological and behavioural change, yet it remains unclear how deviations from normative brain maturation relate to the development of internalising and externalising symptoms. Methods: Using data from the Adolescent Brain Cognitive Development (ABCD) Study, we combined brain age prediction with bivariate latent growth curve (BLGC) models to test whether deviations in brain maturation - indexed by the brain age gap (BAG) - relate to mental health development across late childhood and adolescence. Brain age was estimated using T1-weighted, diffusion (dMRI), resting-state fMRI, and multimodal MRI data across four waves (ages ~8.3-17.5). Internalising and externalising symptoms were assessed across ten waves with the self-report Brief Problem Monitor (BPM). Results: Across T1, dMRI, and multimodal models, deviations from age-expected brain maturation and internalising and externalising symptoms showed coordinated nonlinear development across adolescence. Adolescents whose brains increasingly diverged from age-expected maturation over time also showed increasing symptom trajectories. These associations were small to moderate in magnitude and were most consistent for internalising symptoms in females ( Conclusion: These results indicate that adolescent development of mental health problems is more strongly linked to nonlinear changes in how individuals diverge from age-expected brain trajectories, rather than to fixed differences in brain age. Shifts in brain maturational tempo may therefore be a key feature underlying vulnerability to psychopathology in youth.