Longitudinal changes in T1w/T2w estimates of cortical myelin with age and pubertal timing.

Puberty may regulate changes in sensitive period plasticity during adolescence. Experience-dependent myelination is a mechanism that may underlie such changes in plasticity. Intracortical myelin can be indirectly indexed by the ratio of T1-weighted to T2-weighted MRI images (T1w/T2w). While age-related T1w/T2w changes have been documented, less is known about the contributions of pubertal timing (being earlier/later relative to peers). Using Bayesian hierarchical generalized additive models with longitudinal data from 9- to 18-year-olds in the Human Connectome Project in Development, we examined how age and pubertal timing relate to T1w/T2w. Results confirmed that age-related change is patterned along the sensorimotor-association axis, though longitudinal effects were smaller than prior cross-sectional estimates. Pubertal timing accounted for up to 1.8% of variance in T1w/T2w across parcels, with negligible effects in most parcels. Modest sex- and regionally specific effects were identified: Early pubertal timing was linked to greater T1w/T2w in sensorimotor regions and lower T1w/T2w in association areas (especially dorsolateral and frontopolar cortices) but only in females. In contrast, late puberty was linked to higher T1w/T2w in association areas in both sexes and reduced T1w/T2w in several mid-ranking parcels. Future work should replicate these effects and investigate associations with cognitive and psychosocial development.