Readiness potential of cortical area 6 preceding self paced movement in Parkinson's disease.

The vertex Readiness Potential (RP) (Bereitschaftspotential) preceding self paced voluntary movements is reduced in duration and amplitude in patients with Parkinsonism. It cannot be used as an index for delayed initiation of movement. The negative potential is commonly replaced by a positive slow wave. In hemi-Parkinsonism, the abnormal RP is more apparent on moving the affected limb. The abnormal RP is related to the severity but not to the duration of Parkinsonism. Short-term fluctuations of akinesia and rigidity, spontaneous or caused by levodopa are associated with changes of RP duration and amplitude. The abnormality does not correlate with reaction or movement times. It is suggested that the Readiness Potential is a diffuse response of area 6 cortex (especially Supplementary Motor Area) evoked by pallido-thalamo-cortical afferents under dopaminergic control. It is not obligatory for pre-programming of voluntary movement. The authors postulate a dendritic potential of basket cells associated with a pallidal activated gate control of postural set.