Objective: To examine the electrophysiological effects of methylphenidate (MPH) on inhibitory control in children with attention deficit/hyperactivity disorder (ADHD).
Method: Twelve children with ADHD performed the Stop Signal Task (SST) while event related potentials (ERP) were obtained. Each child completed two testing sessions, once on placebo and again on an individualized dose of MPH, with the order of medication administration counterbalanced. The following ERP parameters were studied: the N200, often seen as a measure of the activation of the inhibitory process, and the NoGo-P3, which may represent the degree of performance monitoring and/or error detection.
Results: MPH significantly improved behavioral performance on the SST. During successful inhibitions, MPH also significantly increased the amplitude of the right frontal N200, while during unsuccessful inhibitions MPH increased the amplitude of the NoGo-P3.
Conclusions: MPH may improve inhibitory control by enhancing brain mechanisms that trigger the inhibitory process and make stopping a motor act more probable (reflected by increased N200) and by increasing attentional resources to the task when unsuccessful inhibitions occur (as reflected by increased NoGo-P3). These results are consistent with functional imaging studies suggesting a role for the right frontal inferior cortex and the cingulate cortex in the pathophysiology of ADHD.