Inhibitory control in children with attention-deficit/hyperactivity disorder: event-related potentials identify the processing component and timing of an impaired right-frontal response-inhibition mechanism.

Background: A core deficit in inhibitory control may account for a wide range of dysfunctional behaviors in attention-deficit/hyperactivity disorder (ADHD).
Methods: Event-related potentials were measured in 10 children with ADHD and 10 healthy children during a task specifically involving response inhibition (Stop signal task).
Results: In response to all Stop signals, control participants produced a large negative wave at 200 msec (N200) over right inferior frontal cortex, which was markedly reduced in ADHD children. The N200 amplitude was significantly correlated across subjects with response-inhibition performance. In response to the Go stimuli, ADHD children showed a reduced slow positive wave (250-500 msec) in anticipation of failed inhibitions over right frontal scalp regions.
Conclusions: ADHD children appear to have an abnormality in an early-latency, right inferior frontal processing component critical to the initiation of normal response-inhibition operations. They also appear to have a right frontal abnormality associated to the covert processing of Go stimuli preceding failed inhibitions. By providing timing and processing component specificity, these results extend the findings of recent functional MRI studies of inhibitory control reporting right frontal abnormalities in ADHD.