Inhibition in children with attention-deficit/hyperactivity disorder: a psychophysiological study of the stop task

Background: The purpose of the study was to investigate and identify abnormal brain activity, as revealed by event-related potentials (ERPs) concurring with deficient inhibitory control in children with attention-deficit/hyperactivity disorder (ADHD). Methods: Performance and ERPs from 16 children with ADHD and 16 control subjects were compared in the stop-signal paradigm. Results: The ADHD children showed a lower inhibition percentage and their (estimated) response time to the stop signal was disproportionally longer compared to the slowing of reaction times to primary-task stimuli. In normal control subjects, fronto-central positivity (100–400 msec) after the onset of the stop-signal was larger in case of successful inhibition, relative to failed inhibition; this was less so in ADHD children. A late positive wave (500–700 msec), maximal at Oz on failed inhibition trials, and possibly related to error-detection, was smaller in ADHD children. Conclusions: These results point to abnormalities in brain processes involved in motor inhibition and error-detection in ADHD children.