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Description
Introduction: Adolescence is a period of ongoing brain reorganization that is essential to biological and psychosocial maturation, but also to mental health (Paus et al., 2008). Adolescent brain maturation as captured via neuroimaging follows two main modes: 1) conservative strengthening of initially strong inter-regional similarities, or 2) disruptive remodeling, i.e. strengthening of initially weak inter-regional similarities and vice versa (Váša et al., 2020). While adverse experiences and psychopathological processes can alter maturational trajectories (Stenson et al., 2021), adolescent reorganization may also hold potential for flexible adaptation to risk factors. Thus, normative maturation facilitating psychosocial skills may also aid well-being through resilience to adversity.
Methods: We analyzed age-related changes in myelin-sensitive Magnetic Transfer (MT) and microstructural profile covariance (MPC) in a longitudinal cohort of individuals aged 14-26 (n=295; 512 scans; 50.8% female). MPC reflects inter-regional similarity of intracortical MT profiles sampled at ten cortical depths. We first identified maturational modes by correlating the whole-brain MPC pattern of each region at age 14 with the age-related changes of this pattern (14-26y; computed via edge-wise linear mixed effect models). Positive correlations indicate conservative and negative correlations disruptive development. To disentangle this pattern further, we applied non-linear dimensionality reduction to MPC age effects and identified an underlying axis along which regions vary in similarity of their MPC maturational profile (Paquola et al., 2019). Next, we investigated whether adolescent resilience to adverse life events is associated with altered maturational patterns. We predicted general distress from several adversity measures and - conceptualizing resilience as better than expected wellbeing given the adversity faced - extracted residuals as resilience scores. We then contrasted the maturational index and the principal axis of MPC change in adaptive versus susceptible individuals.
Results: We observed conservative MPC development in dorsal/sensorimotor and ventral/temporal cortex, whereas disruptive MPC development was characteristic of a frontoparietal heteromodal midline. The MPC maturational index showed a U-shaped relationship with the MPC axis of age-related change, indicating re-organization of the heteromodal midline towards ventral and dorsal ‘anchors’. Resilient individuals showed more conservative / less disruptive development in confined regions in the frontal and parietal cortex, indicating that age-related change in MPC was more closely coupled to patterns already set up during early adolescence. Moreover, resilience was related to an expansion and bimodal distribution of loadings along the identified underlying axis, reflecting a clearer MPC differentiation of the heteromodal fronto-parietal midline with age.
Conclusion: In sum, our analyses underline a benefit of stability in microstructural maturation through differentiation that follows paths already set up during early adolescence more closely. Inter-individual differences in resilience were associated with altered microstructural development in association and paralimbic cortex. These regions are known to show protracted plasticity linked to both socio-cognitive refinement and psychopathological alterations (Sydnor et al., 2021) and may point to an inherent link between cognitive resources and resilience capacities. However, future studies shall further investigate to which degree adaptive brain development may be a resilience factor in itself, or a consequence of protective environmental factors.
