Dimensional association between ADHD traits and gray matter volume in young adults: A voxel‐based morphometry study

Abstract Aim Prior structural magnetic resonance imaging (MRI) studies of attention‐deficit/hyperactivity disorder (ADHD) have primarily focused on clinically diagnosed samples, whereas the neuroanatomical correlates of dimensional ADHD traits in healthy young adults (aged 18–27 years) remain insufficiently characterized, and it is unclear whether neuroanatomical patterns reported in clinically diagnosed samples generalize to subclinical trait variability in young adulthood. We therefore examined whole‐brain voxelwise associations between gray matter volume (GMV) and the Conners' Adult ADHD Rating Scales (CAARS) Hyperactivity/Restlessness subscale as the primary analysis, and evaluated associations with other CAARS scales on an exploratory basis, using voxel‐based morphometry (VBM). Methods Participants were 534 healthy young adults (304 males, 230 females; aged 18–27 years) without an ADHD diagnosis. ADHD traits were assessed using CAARS. High‐resolution T1‐weighted structural MRI data were acquired on a 3‐Tesla scanner. GMV was analyzed using VBM implemented in SPM12. Voxelwise multiple‐regression analyses were conducted, with Hyperactivity/Restlessness as the primary scale of interest and other CAARS scales examined in separate exploratory models. Statistical significance was set at p < 0.05 (cluster‐level family‐wise error [FWE]‐corrected), using a voxelwise cluster‐forming threshold of p < 0.001 (uncorrected). Results GMV in the right dorsolateral prefrontal cortex (DLPFC) showed a small but statistically significant positive association with Hyperactivity/Restlessness scores (cluster‐level FWE‐corrected p = 0.017). No significant associations were observed for other CAARS subscales, and no significant sex‐stratified effects were detected. Conclusion These findings are consistent with a dimensional perspective on ADHD‐related traits and suggest that interindividual differences in Hyperactivity/Restlessness may be reflected in subtle GMV variation in the right DLPFC among healthy young adults. Further multimodal and longitudinal studies are warranted to clarify developmental and mechanistic interpretations.