(a) Linear mixed-effects modelling of unstandardized WASI intelligence matrix subscore over all scans and subjects revealed increase of abilities over visits (left plot, t = 4.8, p = e-5, df = 516, statistics from fixed-effects coefficient, two-sided, n = 522/292 observations/subjects in a and c) and with higher age of subject (right plot, t = 2.4, p = .017, df = 516). This supports that cognitive ability differences and changes might be a hidden variable for compulsivity/impulsivity related associations presented in the main findings. However, this is unlikely since our study revealed no evidence for intelligence being related to either compulsivity (b) (n = 481/252 observations/subjects, df = 472, two-sided) or impulsivity (c) (n = 522/292 observations/subjects, df = 513, two-sided), supporting that our main finding can be considered rather independent of cognitive development in late adolescents. All plots show effects of interest and data adjusted for effects of no interest (that is covariates and confounds). (d) Here we illustrate the main finding of reduced longitudinal growth of cortical MT with higher compulsivity (top row) and impulsivity (bottom row) (main results Figs. 3a and 4a) when additionally accounting for between-subject covariates and their time/visit interactions for alcohol consumption, substance consumption, and ethnicity during longitudinal Sandwich Estimator modelling. Last two columns show similar accounting for fully time-varying WASI intelligence sub-scores matrix and vocabulary as covariates. Here, surface projections for Z-maps (p < .05, voxelwise FDR, one-sided Wald-test) are shown, testing for negative trait by visit/time interaction (age_mean, sex, socioeconomic status, interactions and confounds fixed in all analyses, n = 497/288 scans/subjects).