The effects of methylphenidate on partial information transmission in a go/no go task: Task performance and lateralized readiness potentials

Considerable research has addressed whether the speeding of reaction time by stimulants involves early stages of processing such as stimulus identification. Inconsistencies among these studies has prompted research focused on response related processes like response preparation. The present study was aimed at clarifying the effects of methylphenidate on normal young adults' Lateralized Readiness Potential (LRP) in a response inhibition paradigm. In addition, this was a reasonable preliminary approach before studying comparable processes in AD/HD patients.;Twenty healthy young adults participated in an initial drug free practice session. In two subsequent test sessions subjects received either methylphenidate or placebo, administered double blindly and in a randomized order. LRPs and electromyographic (EMG) activity were measured in a Go/No Go discrimination task involving easy and difficult discriminations. The side of the display in which the stimulus was presented conveyed information about the appropriate hand for responding, and the type of stimulus (letter vs. number) provided information about whether a response should be made or inhibited. It was assumed that side information was processed earlier than Go/No Go information.;Accuracy was greater and reaction time less variable for easy than difficult stimuli. In addition, subjects responded faster and more forcefully to easy stimuli. As expected, LRPs developed on No Go trials screened for EMG activity, substantiating the presence of partial response preparation. Furthermore, greater preparation, as indexed by greater LRP amplitude, was observed under Go as opposed to No Go stimuli.;Methylphenidate enhanced performance, autonomic arousal, and subjective mood. In contrast to declining LRP amplitude over the course of the placebo session, under methylphenidate there was a consistent pattern for LRP amplitude to increase or remain steady over time. The findings for LRP combined with those for mood and autonomic measures may reflect increases in tonic arousal.