Fig. 3. Network development in youth unfolds along a functional hierarchy.
a We define functional hierarchy according to the widely used principal gradient of functional connectivity from Margulies et al. (2016), which describes each location on the cortex on a unimodal-to-transmodal continuum. b Between-network coupling is modeled for every network at each scale using Generalized Additive Models (GAMs) with penalized splines to account for linear and nonlinear effects of age. Each solid line represents the developmental pattern of one network at one scale; colors indicate the position of that network on the functional hierarchy. Dashed lines and corresponding brain maps represent estimated between-network coupling at each age, averaged across scales. Between-network coupling of sensorimotor networks (purple lines) increases with age, indicating increased integration. In contrast, the coupling of association networks (yellow lines) declines with age, reflecting increased segregation. c Age effects of each network (from b) are plotted versus their position on the functional hierarchy (from a). Networks that do not display significant change over development are shaded in gray (QFDR > 0.05). The position of each network on the functional hierarchy explains the majority of variance in age effects (r = −0.840, β = −0.012, pboot < 0.001, two-sided). d We quantified the duration, magnitude, and direction of maturational changes in coupling for each network using the derivatives of the fitted splines (from b). Top: annualized change in between-network coupling at 10, 16, and 21 years old, averaged across scales. Bottom: change per year in average between-network coupling of each network across the age range studied; as in b, each line represents the developmental pattern of a given network at a single scale. While integration of sensorimotor networks increases over the entire age range sampled, segregation of association networks generally plateaus near the end of adolescence.