MOVEMENT-RELATED POTENTIALS IN PARKINSONS-DISEASE PRESENCE AND PREDICTABILITY OF TEMPORAL AND SPATIAL CUES

Activity of the supplementary motor area may be inferred from movement -related potentials (MRPs) which are associated with the preparation a nd execution of voluntary, or internally determined movements. Supplem entary motor area activity may be abnormal in Parkinson's disease sinc e its major input from the basal ganglia is disrupted. Investigation o f the abnormalities in supplementary motor area activity associated wi th movement deficits in Parkinson's disease may therefore reveal funct ions of the basal ganglia and the supplementary motor area. Movement-r elated potentials associated with sequential movements were investigat ed under various cueing conditions in Parkinson's disease subjects and age-matched controls. In controls, MRPs revealed involvement of the s upplementary motor area in movements which can be internally determine d (non-cued and externally cued, predictable movements, but not unpred ictable movements). In Parkinson's disease, however; the supplementary motor area was only involved in movements which must be internally de termined (non-erred movements, but not externally cued movements); the refore impaired internal control mechanisms, operating via the supplem entary motor area, are bypassed when external cues are given. As a res ult, Parkinson's disease patients are more reliant on external cues an d are unable to use predictive models to internally guide movement. Su pplementary motor area involvement also relied on the predictability ( in controls) or presence (in Parkinson's disease) of timing cues and n ot spatial cues, indicating a role of the supplementary motor area and basal ganglia in the temporal organization of sequential movement rat her than the programming of specific movements. For non-cued movements , abnormalities in MRPs for Parkinson's disease subjects consisted of delayed MRP onset and peak times, and prolonged cortical activity foll owing movement. These observations led to a proposed model of the inte raction between the basal ganglia and the supplementary motor area, in volving the temporal organization of voluntary and internally determin ed sequential movements.