Article Text

Download PDFPDF

Abnormal refractoriness in patients with Parkinson's disease after brief withdrawal of levodopa treatment.
  1. J Harrison,
  2. L Henderson,
  3. C Kennard
  1. Academic Unit of Neuroscience, Charing Cross and Westminster Medical School, London, UK.


    Two pairwise matched groups of patients with mild to moderate Parkinson's disease and a group of normal age matched controls were used to investigate the effects on simple and choice reaction time (RT) of brief withdrawal of levodopa therapy. Comparisons within and across these groups disclosed a selective effect of levodopa withdrawal. After about 12 hours of levodopa deprivation, patients exhibited an exaggeration of normal refractoriness, the well established tendency for RT to increase progressively as the delay between a response and the next imperative signal is reduced below 0.5 s. Increased refractoriness was at least as great for simple as choice RT. Choice RT on trials involving repetition (as opposed to alternation) of the previous response, however, showed no tendency towards greater impairment by brevity of the recovery period or by withdrawal of medication, eliminating an effector based account. With longer recovery periods, RT was unaffected by medication; indeed, unmedicated patients were as fast as normal subjects under these conditions. Even at the briefest delays, fully medicated patients did not differ from normal controls. The paper concludes with a critical review of chronometric studies of medication effects in Parkinson's disease.

    Statistics from

    Request Permissions

    If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.