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.
Subject(s)
Attention Deficit Disorder with Hyperactivity/drug therapy , Attention Deficit Disorder with Hyperactivity/physiopathology , Central Nervous System Stimulants/therapeutic use , Methylphenidate/therapeutic use , Problem Solving/drug effects , Adolescent , Analysis of Variance , Attention Deficit Disorder with Hyperactivity/classification , Child , Demography , Humans , Inhibition, Psychological , Male , Motor Activity/drug effects , Neuropsychological Tests , Predictive Value of Tests , Psychiatric Status Rating Scales , Psychomotor Performance/drug effects , Reaction Time/drug effects , Reproducibility of Results , Saccades/drug effects , Trail Making Test , Visual Acuity/drug effectsABSTRACT
Three experiments were conducted to explore the effects of methylphenidate (MPH), attention-deficit hyperactivity disorder (ADHD) diagnosis, and age on performance on a complex visual-memory search task. Results showed that the effects of MPH varied with information load. On low-processing loads, all doses of MPH helped children with ADHD to improve accuracy with no cost to reaction time (RT), whereas on high loads, higher MPH doses improved error rates while slowing RT. Without medication, children with ADHD showed high error rates and slow RTs across both low and high loads, as did younger, normal control children. Because MPH slowed performance on only the most difficult, high-load conditions, it is argued that the drug improves self-regulatory ability, enabling children with ADHD to adapt differentially to high and low loads.
Subject(s)
Attention Deficit Disorder with Hyperactivity/drug therapy , Central Nervous System Stimulants/therapeutic use , Cognition/drug effects , Methylphenidate/therapeutic use , Psychomotor Performance/drug effects , Adolescent , Age Factors , Central Nervous System Stimulants/pharmacology , Child , Dose-Response Relationship, Drug , Female , Humans , Male , Memory/drug effects , Methylphenidate/pharmacology , Reaction Time/drug effects , Visual Perception/drug effectsABSTRACT
This study examined effects of reward and response costs on the ability of 19 attention-deficit hyperactivity disorder (ADHD) and 17 control children to inhibit responding. Children were tested under 4 reinforcement conditions on a go/no-go learning task developed by J. P. Newman, C. S. Widom, and S. Nathan (1985). Two conditions involved both reward and response costs. 1 response costs only, and 1 reward only. ADHD children made more commission errors than controls across the 4 conditions. Analyses of learning curves indicated that group differences became larger on later trials. Thus, impaired inhibition was more generalized in ADHD children than in the psychopaths and extraverts studied by Newman and colleagues, and it became most evident when the children were required to improve learning across trials.
