Abstract
The transition from adolescence into adulthood is a period where rapid brain development coincides with a greatly enhanced incidence of psychiatric disorder. The precise developmental brain changes that might account for this emergent psychiatric symptomatology remains obscure. Capitalising on a unique longitudinal dataset, that includes in-vivo myelin-sensitive magnetization transfer (MT) MRI, we show this transition period is characterised by brain-wide growth in MT, within both gray matter and adjacent juxta-cortical white matter. The expression of common developmental psychiatric risk symptomatology in this otherwise healthy population, namely compulsivity and impulsivity, was tied to regionally specific aberrant unfolding of these MT trajectories. This was most marked in superior frontal/cingulate cortex for compulsivity, and in inferior frontal/insular cortex for impulsivity. The findings highlight a brain developmental linkage for emergent psychiatric risk features, evident in regionally specific perturbations in the expansion of MT-related myelination.