MOVEMENT-RELATED POTENTIAL MEASURES OF DIFFERENT MODES OF MOVEMENT SELECTION IN PARKINSONS-DISEASE

Movement-related potentials were recorded preceding self-paced volunta ry movements in patients with Parkinson's disease and in healthy subje cts of the same age group. We compared the Readiness Potential precedi ng joystick movements in a fixed direction and preceding joystick move ments in freely selected directions. In normal subjects the Readiness Potential amplitude was higher preceding freely selected movements tha n preceding movements in a fixed direction. The Readiness Potential in Parkinson patients failed to be modified by the different modes of mo vement selection. The modulation of the Readiness Potential by differe nt ways of preparing for movement might be due to the supplementary mo tor area (SMA) being more strongly engaged by tasks requiring internal control of movements than by tasks that are externally structured. Th e results suggest that this task-dependent variation of SMA activity i s reduced in Parkinson's disease. A failing capacity to adapt SMA acti vity to different task demands has previously been suggested by eviden ce from positron emission tomography studies using similar tasks.