Does methylphenidate affect information processing? Findings from two studies on performance and P3b latency.

Abstract

ABSTRACTTwo studies were conducted to assess the impact of methylphenidate on normal young adults in a fixed version of Steinberg's memory scanning task. Both studies yielded characteristic monotonic increases in reaction time (RT) and P3b latency as a function of memory load. Also, in both studies, methylphenidate speeded up RT as and decreased error rates and intra subject RT variability. However, the slope of RT as a function of memory load, i.e. the rate of memory search, was not altered by the stimulant. In Study 1, P3b latency also was not affected by methylphenidate, a result suggesting that the stimulant brought about the decrease in RT by acting after the completion of evaluation, presumably by accelerating response processes. However, in Study 2, the drug significantly shortened P3b latency and the interval between RT and P3b latency. Thus, a speeding of both evaluation as well as motor processes was achieved. A review of procedural differences between the two studies suggests some possible explanations. In combination, the two studies indicate that methylphenidate consistently shortened the timing of motor processes and, under some circumstances, the duration of evaluation processes as well.