Physical-Digital and social-nonsocial extracurricular engagement: differential effects on brain development and...

Extracurricular activities shape children's development, yet how the interaction between their modality (digital/physical) and social context (social/non-social) impact mental health and neurodevelopment remains unclear. This study examined these relationships and their bidirectionality, as well as mediation by brain structural changes. Using baseline and one-year follow-up data from 8230 children in the Adolescent Brain Cognitive Development Study, we analyzed self-reported screen time for six digital activities (three social, three non-social), caregiver-reported participation in 28 extracurricular activities (11 social, 17 non-social), mental health via the Child Behavior Checklist and Kiddie Schedule for Affective Disorders and Schizophrenia, and gray matter volume using T1-weighted MRI. Distinct interaction patterns between modality and social context emerged. Physical-social activities were linked to fewer psychiatric symptoms, particularly withdrawn/depressed behaviors, and increased frontoparietal gray matter. In contrast, digital non-social activities were associated with higher psychiatric risk, especially rule-breaking behaviors, and reduced temporal gray matter. Physical non-social and digital-social activities demonstrated mixed effects on developmental measures. Longitudinal analyses revealed bidirectional activity-mental health associations, with brain volume changes mediating 3.7-5.0% of these relationships. These findings highlight the interactive role of activity modality and social context in children's development and provide neurobiological evidence informing guidelines for beneficial developmental outcomes.