Treatment effects of methylphenidate on cognitive functioning in children with mental retardation and ADHD.

OBJECTIVE: Cognitive effects of stimulant medication were investigated in children with mental retardation (MR) and attention-deficit/hyperactivity disorder (ADHD). METHOD: Performance on tasks tapping sustained attention, visual and auditory selective attention, inhibition, and immediate memory was assessed for 24 children (mean age 10.9 years) during a placebo-controlled, double-blind, crossover treatment trial with 0.15, 0.30, and 0.60 mg/kg b.i.d. dosages of methylphenidate (MPH). RESULTS: Successively higher MPH doses were associated with consistent gains in cognitive task performance, with optimal performance noted at the highest dose. Analysis of dose-response curves revealed significant linear components of trend on measures tapping sustained attention, visual selective attention, auditory selective attention, as well as two tasks tapping inhibition/impulsivity: delay of gratification and match-to-sample. No evidence of a curvilinear dose-response relationship emerged for any measure. CONCLUSIONS: Inattention and disinhibition/impulsivity decline with MPH treatment in children with ADHD/MR, and consistent with the Multimodal Treatment Study of ADHD, higher MPH doses are most effective. These findings also suggest that cognitive testing, together with behavioral and medical assessment, can be an effective tool in assessing stimulant response in children with ADHD/MR.

Effects of methylphenidate treatment in children with mental retardation and ADHD: individual variation in medication response.

OBJECTIVE: Individual variation in cognitive and behavioral response to methylphenidate (MPH) was investigated in children with mental retardation and attention-deficit/hyperactivity disorder. METHOD: Twenty-four children (mean age 10.9 years, SD = 2.4) participated in a placebo-controlled, double-blind, crossover trial with 0.15-, 0.30-, and 0.60-mg/kg b.i.d. doses of MPH. Parent and teacher behavioral ratings, as well as cognitive task performance, were assessed at each dose. RESULTS: Relative to placebo, most children with attention-deficit/hyperactivity disorder and mental retardation showed some degree of behavioral and cognitive improvement with MPH treatment. However, fewer of these children made substantial gains (>30% improvement, relative to placebo) with MPH treatment. At the highest dose, 55% of the children showed substantial behavioral gains and 46% made substantial gains in cognitive task performance. However, there was substantial independence between changes in behavior and changes in cognitive performance. CONCLUSIONS: At the 0.60-mg/kg MPH dose, more children showed substantial cognitive and behavioral gains than those who showed substantial declines in a ratio of more than 5:1. However, it may be prudent to assess cognitive change as well as behavioral effects because improvements in the former do not necessarily forecast improvements in the latter in children with attention-deficit/hyperactivity disorder and mental retardation.