The effect of withdrawal of dopaminergic medication on simple and choice reaction time and the use of advance information in Parkinson's disease.
Eight patients with Parkinson's disease performed simple reaction time (SRT), uncued, partially and fully cued four choice (CRT) tasks. They were tested on two occasions; on their normal dose of dopaminergic medication and following withdrawal of such medication for an average of 14.4 hours. Disability as rated on the Webster scale was greater in the drug reduced state. Although RTs were generally slower when tested in the drug reduced state than when on medication, few differences emerged. Withdrawal of dopaminergic medication had no effect on unwarned SRT and unwarned and uncued CRT performance. Both on and off medication, the patients benefited from a warning signal presented before the imperative stimulus. In both medication states, the speeding up of RT was greatest with a warning signal presented 200 ms before S2. When the imperative stimulus was unwarned, the temporal predictability of its occurrence speeded RT more when on medication than when off. Advance movement parameter information was used by patients to pre-programme responses both on and off medication. In both medication states, the fully cued CRT was the same as SRT only with the 3200 ms S1-S2 interval. Medication state had no effect on movement time or the number of errors. It is suggested that slowness in motor readiness and motor programming may not be specific to striatal dopamine deficiency but rather a nonspecific concomitant of brain damage.