State regulation and response inhibition in children with ADHD and children with early- and continuously treated phenylketonuria: an event-related potential comparison.

BACKGROUND: The presentation rate of stimuli plays an important role in explaining the performance inefficiency in children with ADHD. In general, children with ADHD have been found to perform more poorly in conditions of relatively slow event rates as compared with fast and moderate event rates. The state regulation hypothesis states that these children have problems in correcting their energetic state necessary to counteract a performance decrement, which requires extra effort allocation. In this study, we investigated state regulation in children with ADHD and used children with early- and continuously treated phenylketonuria (PKU) as a clinical contrast group.
METHOD: We measured the parietal P3 during a Go/No-Go task that incorporated a condition with a fast and a slow presentation rate.
RESULTS: We were able to show that children with ADHD, relative to controls, responded more slowly and more variably in the slow condition only, which was accompanied by a smaller P3, suggesting less effort allocation. In contrast, the children with PKU did not show a state regulation deficit. The PKU group showed prolonged stimulus evaluation processing, as indexed by P3 latency, compared to controls and children with ADHD. In addition, they made more errors of commission than the controls and the ADHD group.
CONCLUSIONS: Our electrophysiological data support the state regulation hypothesis of ADHD. Only the children with PKU had more problems in inhibiting pre-potent responding than controls, which is in accord with the prefrontal dysfunction hypothesis of PKU.