Pupil dilation as a marker of dysfunctional arousal regulation during sustained attention in children and adolescents with ADHD

The pupil size is influenced by attention and arousal enabling the use of pupillometry to explore underlying neurobiological and neurochemical processes. Especially pupil dilation is supposed to be an indirect marker of the activity of the locus coeruleus-norepinephrine (LC-NE) system, that significantly contributes to attention and arousal regulation. The impairment of both functions play an important role in attention deficit/hyperactivity disorder (ADHD) but the underlying neuronal processes and their interplay are not yet sufficiently understood. This study investigates changes in pupil size, spontaneous eye blink rate, and performance in a newly developed sustained attention task in children and adolescents with ADHD and healthy controls (N=65). Individuals with ADHD showed impaired performance compared to controls. The tonic pupil diameter decreased during the task in controls but not in the ADHD group. Moreover, spontaneous eye blink rate 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. Thus, changes in pupil diameter might be a particularly sensitive, non-invasive marker of neuronal mechanisms underlying sustained attention functions that can be easily applied in children and adolescents with ADHD.