Topographic changes of ERP during a CPT-AX task at pre- and post-medication of methylphenidate in children with ADHD

Abstract To examine cerebral process of motor control in children with Attention-Deficit/Hyperactivity Disorder (ADHD; mean age, 11 years), event-related potentials (ERPs) during a cued continuous performance test (CPT-AX) were recorded from ADHD children an hour after psychostimulant (methylphenidate) dosage (Medicated ADHD), and without psychostimulants (Non-Medicated ADHD). These data were compared with ERPs in unmedicated age-matched normal controls (Non-ADHD). Hit rate in Non-medicated ADHD was significantly lower than that in Non-ADHD. However, their performance improved significantly due to psychostimulant medication, up to levels comparable to those of Non-ADHD subjects. In the ERP elicited by nontargets, P2 amplitudes in Non-Medicated ADHD were smaller than in Non-ADHD. Due to medication, P2 amplitudes increased and became comparable to that in Non-ADHD. Medication also improved a delayed onset of the P2 brain electric field in ADHD. Reduced amplitude of ERP in Non-Medicated ADHD suggests a lower activation at this relatively early stage of visual information processing in ADHD. In contrast, enhancement of ERP in Medicated ADHD implies that the medication contributes to allocate resources for orienting their attention to distinguish stimulus relevance, and to inhibit later processing of irrelevant stimuli properly. These results imply that methylphenidate improves response control in ADHD.