An electromyographic analysis of the effect of levodopa on the response time of healthy subjects

Rationale: Recently, we have shown that oral absorption of levodopa shortens reaction time (RT), measured as the interval between the response signal and the onset of voluntary electromyographic (EMG) activity. The motor time (MT) interval that elapses from the EMG activity to the mechanical response was not analysed. Objective: The purpose of the present study was to analyse the effect of the dose of levodopa administrated in our previous study on the MT. Eight healthy adults (aged 21-28, mean=25), performed a two-choice visual RT task after oral absorption of a single dose of levodopa (200 mg) or a placebo (randomized, double-blind, cross-over design). Results: Like RT, MT was shorter under levodopa than under placebo. Statistical analyses demonstrated that this effect was present for all deciles of the RT and MT distributions. Conclusion: Levodopa shortens not only RT but also MT, which points at the implication of the dopaminergic system in both premotor and motor processes.