Event- and Motor-Related Potentials During the Continuous Performance Task in Attention- Deficit/Hyperactivity Disorder

Contingent negative variation (CNV) and evoked potentials were recorded during the continuous performance test in 20 children (aged 7 to 12) with attention deficit/hyperactivity disorder (ADHD) and in 19 age-matched healthy children. A series of letters were displayed every 2.1 s and a button had to be pressed whenever the letter O was followed by an X. Children were also given neuropsychological tests and questionnaires assessing anxiety and depression. Unlike ADHD children, healthy children showed a more pronounced CNV after the cue - the letter O - than after the distractors. At Fz, CNV negativity was significantly correlated with IQ and executive function. Control children also exhibited a higher parietal N375 post S1 - likely to be associated with letter processing - and a higher N550 amplitude at Fz than ADHD children post S1 and S2; both groups showed a higher N550 amplitude whenever X followed non-O or O was followed by non-X. This component appears to be involved in decision-making processes regarding the initiation or inhibition of movement. ADHD children had a faster reaction time but made more errors of omission and commission. Results suggest that ADHD children show deficits in both stimulus processing and response execution.