Region-function specificity of structural brain alterations associated with non-suicidal self-injury in young people.

BACKGROUND: Non-suicidal self-injury (NSSI) is prevalent among young people and has been theoretically associated with mentalizing - the capacity to understand behavior in terms of mental states. However, the structural correlates of this capacity, and their relationship to different NSSI motivations, remain unknown. METHODS: We examined the structure of brain regions implicated in mentalizing and region-function specificity in 173 young people (aged 10-24; NSSI group, n = 117; non-NSSI comparison group, n = 56). Structural MRI data (n = 132) were analyzed across seven a priori mentalizing network regions: inferior parietal lobule (IPL), supramarginal gyrus, medial orbitofrontal cortex, posterior cingulate cortex, superior temporal gyrus, and corpus callosum (CC) genu and splenium. RESULTS: The NSSI group showed reduced CC splenium volume (d = 0.58, pFDR = 0.029) and IPL thickness (d = 0.42, pFDR = 0.029). A region-function specificity pattern emerged: IPL thinning was selectively associated with intrapersonal NSSI functions (emotion regulation and self-punishment; p = 0.005), whereas CC splenium volume reduction was selectively linked to interpersonal functions (social communication and help-seeking; p = 0.003). CONCLUSIONS: These findings reveal regional structural reductions within mentalizing-related brain regions in NSSI, and suggest that distinct neurobiological pathways may underlie different NSSI motivations, with implications for function-based personalized interventions.