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Oculomotor abnormalities in attention deficit hyperactivity disorder

A preliminary study

From the Kennedy Krieger Institute (Drs. Mostofsky, Cutting, and Denckla), the Department of Neurology (Drs. Mostofsky, Cutting, Denckla, and Zee and A.G. Lasker), the Department of Psychiatry (Dr. Denckla), and the Department of Pediatrics (Dr. Denckla), Johns Hopkins University School of Medicine, Baltimore, MD.

Address correspondence and reprint requests to Dr. Stewart H. Mostofsky, Developmental Cognitive Neurology, Kennedy Krieger Institute, 707 N. Broadway, Baltimore, MD 21205; e-mail: mostofsky{at}kennedykrieger.org

Background:— Prevailing hypotheses suggest that attention deficit hyperactivity disorder (ADHD) is secondary to dysfunction of motor intentional systems mediated by prefrontal circuitry. Oculomotor paradigms provide a mechanism for examining and localizing dysfunction at the interface between movement and cognition.

Objective:— Three different saccade tasks (reflexive or prosaccades, antisaccades, and memory-guided saccades) were used to examine functions necessary for the planning and the execution of eye movements, including 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 group of 11 children not taking any psychoactive medication. Results from the two groups were compared with those from 25 age- and gender-matched normal control children.

Results:— Both groups of children with ADHD made significantly more directional errors than did controls on the antisaccade task and significantly more anticipatory errors than did controls on the memory-guided saccade task, findings that are consistent with deficits in response inhibition. There were no significant differences in prosaccade latency, although unmedicated children with ADHD showed significantly greater variability in latency on the prosaccade task than did controls. On the memory-guided saccade task there were no significant differences in saccade accuracy; however, unmedicated children with ADHD showed longer saccade latency than did either controls or medicated children with ADHD.

Conclusions:— Oculomotor findings suggest that deficits in prefrontal functions, in particular response inhibition, contribute to behavioral abnormalities observed in ADHD. Findings 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, conclusions await a design in which subjects complete testing both on and off medication.

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