METHYLPHENIDATE INFLUENCES ON BOTH EARLY AND LATE ERP WAVES OF ADHD CHILDREN IN A CONTINUOUS PERFORMANCE-TEST

Although it has frequently been reported that hyperactive children hav e abnormally small P3 amplitudes of the event-related potential (ERP), which are normalized by the stimulant drug methylphenidate (MPH), the literature is inconsistent concerning earlier ERP waves. The aim of t he present study was to investigate whether the normalizing effect of a 10-mg dose of MPH was also apparent on earlier waves, such as the N1 , the P2, and the N2, besides the P3. Twelve attention deficit with hy peractivity disorder (ADHD) children performed a Continuous Performanc e Test involving a button-press response to the letter X (CPT-X) under the influence of MPH in a double-blind placebo controlled acute dosag e design. ERPs were recorded at Oz, Pz, Cz, and Fz. The expected incre ase of the parietal P3, both to targets and nontargets, was apparent, as well as a significant increase in percentage of hits. There also wa s a significant increase of an earlier, negative going, wave, the N2, with a frontal maximum, under the influence of MPH. This wave was prob ably a manifestation of an increase in processing negativity for targe t stimuli only, after the intake of the stimulant drug. No effect of M PH was found on the N1 or the P2.