Spontaneous Pupillary Dynamics as Biomarkers of ADHD-Related Traits in Preschool and Early School-Aged Children without a Diagnosis

Attention-deficit/hyperactivity disorder (ADHD) often emerges in early childhood; however, objective biomarkers for its early detection remain limited. In this study, we aimed to identify pupil-based physiological markers associated with ADHD-related traits in preschool-and early school-aged children. To this end, we recorded the pupil diameters of typically developing children without an ADHD diagnosis during a simple fixation task. From these data, we extracted multiple features, including the mean pupil size, temporal variability, and interocular asymmetry in both magnitude and variability. ADHD-related tendencies were assessed using the ADHD Rating Scale-5 (ADHD-RS-5). Among the features analysed, only the temporal variability of interocular asymmetry (VarLRdiff) showed a significant positive correlation with ADHD-RS-5 total and subscale scores. This association likely reflects the combined effects of immature autonomic regulation and functional asymmetry in the neural circuits involving the locus coeruleus. In contrast, other pupil-based indices showed no significant correlations, potentially because of developmental ceiling effects and the short evaluation duration. These findings suggest that VarLRdiff may serve as a promising physiological marker of ADHD-related traits in young children. Future studies incorporating longer recordings, advanced analytical methods, and longitudinal or multimodal neuroimaging approaches are warranted to validate their utility for early ADHD screening.