THE MOVEMENT-RELATED CORTICAL POTENTIAL IS ABNORMAL IN PATIENTS WITH IDIOPATHIC TORSION DYSTONIA

Voluntary movements, such as the self-paced finger extension task used in the present experiments, are preceded by a slowly rising negative electroencephalographic potential [the movement-related cortical poten tial (MRCP)]. The early NS1 component of the potential was no differen t in patients with primary dystonia affecting the arm (n = 6) compared with matched controls, In contrast, the peak amplitude of the MRCP wa s smaller in the patients, despite the fact that the movements made by the two groups were very similar; it was of equal size over both left and right hemispheres, rather than being larger on the side contralat eral to the movement. These results are similar to those observed by o thers in patients with symptomatic dystonia secondary to lesions of th e basal ganglia or their output pathways and may reflect abnormal basa l ganglia input to motor areas of cortex before the onset of a self-pa ced movement.