Altered pre-stimulus alpha dynamics index sustained attention difficulties in ADHD

Sustained attention difficulties are a hallmark of Attention-Deficit/Hyperactivity Disorder (ADHD), yet the neural mechanisms underlying these difficulties remain insufficiently understood. In the current study, we analyzed EEG data collected during performance on a slow-paced 2-choice reaction time task, to examine time-on-task effects on prestimulus posterior alpha power-an index of attentional engagement-in adults with and without ADHD (ADHD: n = 24; age = 34.38 (SD = 10.21) years, 13/11 M/F; controls: n = 20; age = 36.55 (SD = 11.21) years, 11/9 M/F). Results revealed that while both groups showed a systematic increase in pre-stimulus alpha power over time, the ADHD group exhibited a significantly more pronounced increase, suggesting a greater decline in attentional engagement. Analyses on the temporal dynamics of alpha during the 5 s pre-stimulus interval showed a decrease of alpha power in adults without ADHD, representing increased attentional readiness to respond to the upcoming stimulus. Adults with ADHD showed this reduction only during the early stages of the task, but did not maintain this proactive preparation thereafter. Furthermore, irrespective of the time-on-task, lower pre-stimulus alpha predicted faster reaction times in adults without ADHD but not in adults with ADHD, indicating a decoupling between the neural preparatory attentional state and behavioral output. These findings suggest both a dynamic failure to regulate attentional states over time and a more stable difficulty with translating anticipatory attention into motor performance in ADHD. This study highlights the importance of including time-on-task analyses and neural measures to capture and explain sustained attention difficulties in ADHD.