The rate of change in hypomanic traits longitudinally predicts the development of problematic smartphone use.

Problematic smartphone use (PSU) is an important behavioral health concern, but its longitudinal psychological, neural, and molecular correlates remain unclear. In a two-wave longitudinal study, 50 university students completed questionnaire and structural MRI assessments. Annualized changes in hypomanic excitement, fear of missing out (FoMO), PSU severity, gray matter volume (GMV), and morphometric similarity (MS) gradients were examined. Excitement change was positively associated with PSU change, whereas the association between FoMO change and PSU change did not survive multiple-comparison correction. Whole-brain analysis identified a left frontal pole (FP) cluster in which GMV change was negatively associated with PSU change. Exploratory mediation analysis identified an adjusted indirect association between excitement change and PSU change through FP GMV change. PSU change was also associated with local, but not global, prefrontal MS-gradient changes. A highly exploratory serial mediation analysis further identified an unadjusted indirect association linking excitement change to PSU change through FP GMV change and local second-gradient reorganization in the FP. Imaging transcriptomic analysis linked the PSU-related GMV pattern to spatial gene-expression profiles associated with energy metabolism, myelin- and axon-related processes, transcriptional regulation, and neurodevelopment. These findings associate hypomanic excitement change with longitudinal PSU change and localized prefrontal structural reorganization, while providing an indirect molecular annotation of the associated GMV pattern.