Sleep-like slow waves in ADHD: Regional specificity in combined type

The diagnosis of Attention Deficit/Hyperactivity Disorder (ADHD) remains challenging due to the lack of objective neurophysiological markers, particularly for distinguishing clinical subtypes. Here, we investigated whether sleep-like slow wave activity (SWA) during wakefulness could serve as a subtype-specific neural marker for ADHD. Using EEG recordings during the Attention Network Test (ANT), we analyzed behavioral and neurophysiological data from 120 children, including healthy controls (HC), inattentive-type (ADHD-I), and combined-type (ADHD-C) participants. Our research findings indicated that SWA existed in all groups during task participation, but was significantly elevated in both subtypes of ADHD, particularly in ADHD-C, where the maximum negative peak amplitude increased, duration prolonged, and slow wave slope became steeper. Although global SWA parameters distinguished ADHD from typical development, only topographic analysis showed that local frontal lobe abnormalities distinguished ADHD-C from ADHD-I. Notably, SWA features in the prefrontal region were selectively associated with executive control and orientation deficits in the ADHD-C group, but not in the ADHD-I. Moderation analyses further demonstrated that ADHD subtype significantly modulated the relationship between SWA and behavioral performance. These results provided compelling evidence that sleep-like slow wave dynamics reflected underlying differences in attentional processing between ADHD subtypes and could inform future efforts toward neurophysiological stratification and targeted intervention.