EFFECTS OF MAGNETIC STIMULATION OVER SUPPLEMENTARY MOTOR AREA ON MOVEMENT IN PARKINSONS-DISEASE

Movement execution can be delayed by transcranial magnetic stimulation delivered over primary motor cortical areas, resulting in transient i nhibition of cortico-motor output. Inhibition or disruption of higher- order motor planning an preparatory processes, such as are thought to occur in the supplementary motor area (SMA), would allow an examinatio n of processes at other stages of the motor control system. In this st udy, six subjects with Parkinson's disease and six healthy control sub jects performed a non-cued sequential finger movement task. At various times relative to movement, high-intensity single-pulse magnetic stim ulation was delivered over the region of the SMA, with minimal current spread to primary motor areas. When magnetic stimulation was given at early stages during the movement for parkinsonian subjects, movements times were significantly increased, indicating disrupted movements. S upplementary motor area stimulation has no effect on movements in thei r later stages when planning may be complete, but may disrupt movement s in their early stages, when preparation for later stages may still b e in progress. Further, possible instability of motor planning/prepara tion processes in Parkinson's disease is suggested, since these proces ses appeared more susceptible to disruption by magnetic stimulation in parkinsonian subjects than controls.