Effects of two doses of methylphenidate on cross-situational and borderline hyperactive children's evoked potentials

This study involved 27 children displaying cross-situational hyperactivity and 14 youngsters with borderline hyperactivity. For all patients, evoked potentials were recorded after receiving 0 (placebo), 0.3 and 0.6 mg/kg methylphenidate. Under each pharmacologic condition, subjects were administered: a photic stimulation procedure; two versions of the Continuous Performance Test (CPT), which varied in difficulty level; and a discrimination ('oddball') test. Under photic stimulation, methylphenidate reduced the impact of increasing brightness levels on the rates of amplitude increment and latency decrease in the P208 component of the visual evoked response. These results are similar to those obtained by Buchsbaum and Wender (1973) for hyperactive patients with a positive clinical response to amphetamine. In CPT and the discrimination test, the two active dosages of methylphenidate brought about a comparable reduction of placebo levels of errors and reaction time. Analogously, in both versions of CPT, the two active dosages resulted in comparable increases in the amplitude of two components of the late positive complex (LPC; P510 and P740). P510 was identified as a classical P300. In the discrimination test, the effect of the stimulant on the response evoked by the visual non-target was to increase the amplitude of a component (P463) previously identified as P300. These pharmacologic results were nearly identical for borderline and cross-situational patients. In general, the results confirmed previous observations that methylphenidate improves hyperactive children's performance and increases the amplitude of their LPC. Further, these findings support previous observations that hyperactive patients' cognitive processing is optimized by a dosage of 0.3 mg/kg methylphenidate. Finally, the similarity between findings for cross-situational and borderline hyperactive patients is consistent with other evidence that stimulant effects are not limited to classically hyperactive children.