Eyes-Open Fronto-Central Alpha Activity as an Electrophysiological Correlate of Working Memory in Children with Predominantly Inattentive ADHD

Background/Objectives: This study aimed to identify resting-state quantitative electroencephalography (QEEG) correlates of cognitive performance in children with attention-deficit/hyperactivity disorder (ADHD). Methods: ADHD diagnoses were established according to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition. Cognitive performance was evaluated using the Wechsler Intelligence Scale for Children, Fourth Edition, focusing on the Working Memory Index (WMI) and Processing Speed Index (PSI). Following at least 24 h medication washout, QEEG recordings were collected during both the eyes-open (EO) and eyes-closed (EC) resting states. The absolute spectral power across four frequency bands (delta, theta, alpha, and beta) was analyzed within seven predefined scalp regions. Associations between QEEG measures and cognitive indices were assessed using Spearman’s rank correlation with false discovery rate (FDR) correction. Results: A total of 45 children with ADHD were included: 29 with predominantly inattentive ADHD (ADHD-I) and 16 with combined ADHD (ADHD-C). No significant associations between the QEEG measures and cognitive performance were observed in the overall ADHD cohort. However, within the ADHD-I presentation, EO alpha power was positively correlated with WMI scores across bilateral frontal and central regions (Spearman’s ρ = 0.535–0.582, FDR-corrected q = 0.014–0.028). In contrast, no significant alpha–WMI associations were identified in the ADHD-C presentation. Furthermore, no significant correlations were observed during the EC condition, and no EEG-PSI associations survived the FDR in either presentation. Conclusions: Our findings demonstrate presentation-related differences in QEEG–cognitive relationships and suggest that EO frontocentral alpha activity may represent an electrophysiological correlate of working memory performance in pediatric ADHD-I, though limited by the lack of healthy controls.