METHYLPHENIDATE AND INFORMATION-PROCESSING .1. DIFFERENTIATION BETWEEN RESPONDERS AND NONRESPONDERS .2. EFFICACY IN RESPONDERS

Part 1 of this study attempted to discriminate clinical responders and nonresponders to methylphenidate (MPH) on the basis of neuropsycholog ical deficit profiles. Part 2 addressed the question to what extent MP H might ameliorate these deficits. Hyperactive clinical responders (n = 30) and nonresponders (n = 28) to MPH, were compared to normal contr ols (n = 27) on selective and sustained attention tasks and on convent ional psychological and neurological measures. The responders took par t in a randomized double-blind placebo-controlled crossover study. The y ingested a placebo (PL) or MPH (0.3-0.6 mg/kg/day) during 4 weeks, a nd were then tested. After crossover, another period of 4 weeks was co ncluded by a second test series. Compared to controls, both responders and nonresponders showed attention deficits in encoding, memory searc h, and decision operations, as well as in focused and sustained attent ion, vigilance, and use of feedback. These deficits were the most seve re in the responders. Anamnestic data, IQ scores, and neurological var iables did not discriminate between groups. MPH selectively alleviates attention deficits. MPH did not affect divided attention, except for an increased accuracy of response organization. The drug, however, gre atly improved focused and sustained attention, vigilance, impulsivity, and the behavioral adaptivity to feedback.