The Bereitschaftspotential, L-DOPA and Parkinson's disease.

Bereitschaftspotentials (BPs) prior to extension movements of the index finger were studied in normal subjects and in patients with Parkinson's disease. In both, BPs were studied before and after L-DOPA therapy; in addition, the normal subjects were studied after dopamine antagonists. In both patients and normal subjects, L-DOPA caused an increase in the amplitude of the early part of the BP and of the point of peak negativity, just prior to EMG onset (N1) but it did not cause an increase of the late lateralized part of the BP (NS' of Shibasaki); in normal subjects dopaminergic antagonists caused a decrease in the amplitude of the N1. Control experiments suggested that the change caused by L-DOPA was not the result of slower movement or poorer triggering when OFF drugs. For patients with Parkinson's disease there was no correlation between the change in their peak BP negativity (N1) after L-DOPA and their change in clinical mobility; in addition, there was no difference in the peak BP negativity of patients OFF therapy and that of age-matched normals, though there was a slight decrease in the amplitude of the early part of the BP for the patients with Parkinson's disease; this was the same part that had been enlarged by L-DOPA therapy. These findings suggest that the N1 is not affected by Parkinson's disease and that the effect of dopaminergic drugs on the N1 is mediated by actions on dopaminergic mechanisms elsewhere than in the striatum, perhaps in the cerebral cortex itself. The effect of L-DOPA will need to be taken into account in subsequent studies of the BP in Parkinson's disease.