Abstract
Objective: Childhood peer abuse is a developmentally salient form of interpersonal adversity, yet its role in shaping links between peripheral biological stress markers and brain structure remains poorly understood. The present cross-sectional study examined whether retrospectively reported childhood peer verbal and physical abuse moderated associations of systemic inflammatory burden and hair cortisol with subcortical brain volume.Methods: Participants from a community sample completed the Maltreatment and Abuse Chronology of Exposure scale and structural magnetic resonance imaging. Inflammatory burden was indexed by a composite of standardised IL-6, IL-8, TNF-alpha, and C-reactive protein values (n = 292), and hair cortisol was available in a subsample (n = 172). Bilateral amygdala, hippocampus, putamen, and caudate volumes were extracted from FreeSurfer segmentation. Linear regression models adjusted for gender, age, parental education, and estimated total intracranial volume; false discovery rate correction was applied across the four ROI tests within each marker-by-moderator family.Results: Peer verbal abuse moderated associations of inflammatory burden with bilateral amygdala volume (β = -.095, pFDR = .032) and bilateral putamen volume (β = -.115, pFDR = .017). Peer physical abuse moderated the association between hair cortisol and bilateral amygdala volume (β = .227, pFDR = .035). Caudate models did not survive correction. Core findings remained significant after sensitivity adjustment for broader childhood adversity and current depression/anxiety symptoms.Conclusions: Associations differed across brain regions, biological markers, and peer-abuse subtypes. These findings identify peer adversity as an important interpersonal context for understanding stress-related brain differences.