An unstable regulation of cortical arousal is discussed to play an important role in Attention Deficit/Hyperactivity Disorder (ADHD). We measured tonic pupil size as an indirect marker of the tonic activity of the Locus Coeruleus-Norepinephrine (LC-NE) system and performance during a sustained attention task in children and adolescents with ADHD and healthy controls. Individuals with ADHD showed impaired performance compared to controls. The pupil diameter decreased during the task in controls

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... ut not in the ADHD group. Moreover, spontaneous eye blink rate, that has been discussed to be an index of a dopaminergic component of sustained attention, was significantly increased in ADHD compared to controls. Our main results indicate a tonic hyperactivity of the LC and an insufficient adaptation of arousal to the requirements of the task in ADHD. The pupil dynamic during the sustained attention task specifies the contribution of a dysfunctional LC-NE system to inattention in ADHD.