Abstract

Background: Oculomotor tasks have been used to investigate executive functions and frontal-striatal functioning in humans, but there are relatively few studies on saccadic eye movements (SEMs) in adults with attention-deficit/ hyperactivity disorder (ADHD). Methylphenidate (MPH) is an effective treatment for ADHD symptoms. We therefore evaluated oculomotor performances of ADHD adults before and after administration of a single MPH dose.

Methods: Forty stimulant drug-naive DSM-5 adult ADHD patients participated in this study. Saccade parameters were measured in the morning at baseline, and two weeks later following a single low dose administration of MPH (10 mg orally). Results were compared with 34 healthy control (HC) subjects. Oculomotor performances were determined in automatic attentional tasks (visually-guided-saccades, i.e. gap and step tasks) and voluntary attentional tasks (overlap and antisaccade tasks).

Results: Compared to HCs, ADHDs at baseline showed increased saccade latency (in the gap and antisaccade tasks), increased directional errors in the antisaccade task, decreased average speed (in all tasks), decreased saccade accuracy (in all tasks), increased percentage of anticipatory saccades (in all tasks) and increased percentage of express saccades (in the overlap task). A single low dose of MPH normalized the saccade latencies and the percentage of errors in the antisaccade task, and improved average speed in automatic attentional tasks.

Conclusions: Medication-naive ADHD adults show impairments on motor planning and response inhibition. A single-dose of MPH improves oculomotor performances in these patients. Thus, impaired SEMs could be potential pathophysiologic markers of deficits in frontal-striatal pathways in adults with ADHD.

Keywords: ADHD; Adults; Oculometry; Saccade; Methylphenidate; Inhibition