Oculomotor abnormalities in attention deficit hyperactivity disorder - A preliminary study

Background: Prevailing hypotheses suggest that attention deficit hyperactiv ity disorder (ADHD) is secondary to dysfunction of motor intentional system s mediated by prefrontal circuitry. Oculomotor paradigms provide a mechanis m for examining and localizing dysfunction at the interface between movemen t and cognition. Objective: Three different saccade tasks (reflexive or pro saccades, antisaccades, and memory-guided saccades) were used to examine fu nctions necessary for the planning and the execution of eye movements, incl uding motor response preparation, response inhibition, and working memory. Methods: The study included 19 children with ADHD, divided into two groups: a group of 8 children on methylphenidate at the time of testing and a grou p of 11 children not taking any psychoactive medication. Results from the t wo groups were compared with those from 25 age- and gender-matched normal c ontrol children. Results: Both groups of children with ADHD made significan tly more directional errors than did controls on the antisaceade task and s ignificantly more anticipatory errors than did controls on the memory-guide d saccade task, findings that are consistent with deficits in response inhi bition. There were no significant differences in prosaccade latency, althou gh unmedicated children with ADHD showed significantly greater variability in latency on the prosaccade task than did controls. On the memory-guided s accade task there were no significant differences in saccade accuracy; howe ver, unmedicated children with ADHD showed longer saccade latency than did either controls or medicated children with ADHD. Conclusions: Oculomotor fi ndings suggest that deficits in prefrontal functions, in particular respons e inhibition, contribute to behavioral abnormalities observed in ADHD. Find ings also suggest that the administration of methylphenidate is associated with improvements in the consistency of motor response. Although there were no observed improvements in response inhibition with methylphenidate, conc lusions await a design in which subjects complete testing both on and off m edication.