(a) Developmental volume changes and differences using longitudinal Voxel-Based Morphometry (VBM) analysis and sandwich estimator modelling. Shown are projections of statistical Z-maps (from one-sided Wald-test) testing for volume shrinkage (negative effect of study time/visits or age of subject) in cortical (top-row) and subcortical (2nd row) gray matter regions. Widespread cortical shrinkage was observed in lateral temporal (max z-value voxel [z = 9.02, p = .002 voxelwise FDR, p=.001 clusterwise FWE] in middle temporal gyrus [MNI: 65 −42 4], n = 494/285 scans/subjects apply for panels a-c, 51.9% female), inferior parietal and lateral frontal as well as cingulate cortex. Subcortical gray matter shrinkage was especially found in cerebellum (not shown) (max z-value voxel [z = 6.00, p = .003 voxelwise FDR, p = .001 clusterwise FWE] in cereb. exterior [20 −50 −13]), ventral striatum (regional peak voxel [z-value = 5.64, p = .001, voxelwise FDR, p = .001 clusterwise FWE] in [−7 13 −10]), posterior striatum, pallidum and thalamus. All shown Z-maps are peak/voxel level corrected, p < .05 (FDR). SPM results can be found in Supplementary Table 4. (b) Local volume trajectories show widespread nonlinearities during transitioning into adulthood. In particular, we observed an age-dependent deceleration of the (within-subject) shrinkage in posterior cingulate cortex (max z-value voxel [z = 5.18, p = .005 voxelwise FDR, p = .001 clusterwise FWE] in [4 −56 16]), precuneus, anterior prefrontal cortex, middle cingulate cortex, insula, inferior parietal cortex, lateral temporal regions, frontal pole, superior frontal sulcus, inferior frontal gyrus, and orbital gyrus. Statistical maps were obtained using a one-sided Wald-test for a positive time/visit by age_mean (mean age across visits) interaction (for fixed covariates, time/visits, age_mean, sex etc.). Left data plot shows gray matter volume in females/males with data (gray/black) and full model predictions (red/orange, all predictors) in posterior cingulate cortex. X-axis: age refers to the chronological age of each individual at each visit). Right data plot shows same plot with adjusted data (removing effects of covariates of no interest) and model predictions (red/orange, effect of interest: intercept, time/visit, age_mean, sex, age_mean by sex, age_mean squared, age_mean squared by sex, age_mean by time, age_mean by time by sex). (c) Developmental volume expansion in cortical and subcortical white matter regions. Shown are projections of statistical Z-maps testing for volume expansion (one-sided Wald-test for positive effects of study time/visits or age of subject) in cortical (left) and core (right) white matter areas. Widespread volume expansion was found in cortex adjacent white matter as well as in core white matter with strongest effects in bilateral pyramidal motor tracts (max z-value voxel [z-value = 4.95, p = .001 voxelwise FDR, p = .001 clusterwise FWE] in left upper pyramidal tracts [−19 −19 46]) and prefrontal white matter (max regional z-value voxel [z = 4.65, p = .001 voxelwise FDR, p = .006 clusterwise FWE] in right anterior medial prefrontal cortex [13 42 −5]). SPM results are shown in Supplementary Table 4. Left data plot shows adjusted data (removing effects of covariate of no interest) and model predictions (red/orange, effect of interest: intercept, time/visits, sex, sex by time) in pyramidal tract peak. Right panel shows corresponding plot in prefrontal white matter (red/orange, effects of interest: intercept, age_mean, sex, age_mean by sex, age_mean squared, age_mean squared by sex), a region showing strongest cross-sectional age-related growth (regional peak, z-value = 4.5, p = .017 voxelwise FDR). Y-axis: modulated local tissue volume (VBM); x-axis: time of scan in years relative to each subject’s mean age over all visits. age_mean refers to each individual’s mean age over all visits. (cf. methods and supplementary notes on modelling).