Executive functions and methylphenidate response in subtypes of attention-deficit/hyperactivity disorder

Abstract

Background: Oculomotor tasks are a well-established means of studying executive functions and frontal-striatal functioning in both nonhuman primates and humans. Attention-deficit/hyperactivity disorder (ADHD) is thought to implicate frontal-striatal circuitry. We used oculomotor tests to investigate executive functions and methylphenidate response in two subtypes of ADHD.

Methods: Subjects were boys, aged 11.5-14 years, with ADHD-combined (n = 10), ADHD-inattentive (n = 12), and control subjects (n = 10). Executive functions assessed were motor planning (tapped with predictive saccades), response inhibition (antisaccades), and task switching (saccades-antisaccades mixed).

Results: The ADHD-combined boys were impaired relative to control subjects in motor planning (p < .003) and response inhibition (p < .007) but not in task switching (p > .92). They were also significantly impaired relative to ADHD-inattentive boys, making fewer predictive saccades (p < .03) and having more subjects with antisaccade performance in the impaired range (p < .04). Methylphenidate significantly improved motor planning and response inhibition in both subtypes.

Conclusions: ADHD-combined but not ADHD-inattentive boys showed impairments on motor planning and response inhibition. These deficits might be mediated by brain structures implicated specifically in the hyperactive/impulsive symptoms. Methylphenidate improved oculomotor performance in both subtypes; thus, it was effective even when initial performance was not impaired.