Joint Peer Victimization–Perpetration Trajectories and Cortical Thinning in Early Adolescence

Importance: Peer victimization and perpetration often co-occur and are associated with adverse psychosocial outcomes, but whether their joint temporal patterns are associated with adolescent brain development is unknown.Objective: To examine whether joint developmental trajectories of peer victimization and perpetration are associated with cortical thinning in social-affective brain regions during early adolescence.Design: Longitudinal cohort study using 2 years of follow-up data from the Adolescent Brain Cognitive Development (ABCD) Study, collected from 2018 to 2022 and analyzed from 2024 to 2026.Setting: The ABCD Study across 21 US research sites.Participants: Trajectory analyses included 8792 adolescents with peer experience data from at least 2 assessments; cortical thickness analyses included 2308 adolescents with MRI data at both visits.Exposures: Joint trajectories of self-reported peer victimization and perpetration assessed at the 2-, 3-, and 4-year follow-ups, spanning ages 11 to 14 years.Main Outcomes and Measures: Two-year change in MRI-derived cortical thickness across 7 prespecified social-affective brain regions between the 2- and 4-year follow-ups.Results: Longitudinal clustering (mean [SD] age, 12.08 [0.66] years; 4250 girls [48.3%]) identified 4 joint trajectories: stably low (62%), increasing (24%), decreasing (10%), and persistently high (4%) in both victimization and perpetration. In cortical thickness analyses (mean [SD] age, 11.98 [0.64] years; 1067 girls [46.2%]), no trajectory-group differences survived correction. Exploratory sex-moderation analyses identified persistently high versus stably low differences in the dorsal anterior cingulate cortex and lateral orbitofrontal cortex. Compared with the stably low group, the persistently high group showed little to no dorsal anterior cingulate cortex thinning among boys (β = 0.030; 95% CI, 0.012 to 0.048; P = .001) and greater lateral orbitofrontal cortex thinning among girls (β = −0.029; 95% CI, −0.055 to −0.002; P = .033).Conclusions and Relevance: Peer victimization and perpetration generally co-occurred and changed together over time in this US adolescent cohort. Exploratory findings suggested that persistently high, co-occurring victimization and perpetration may be neurodevelopmentally relevant, with sex-specific patterns in cortical regions implicated in threat detection, behavioral adaptation, and learning from negative consequences. These findings may inform prevention and early intervention efforts for adolescents persistently embedded in negative peer environments.