Movement-related electroencephalographic desynchronization in patients with hand cramps: Evidence for motor cortical involvement in focal dystonia

We studied the dynamic changes in the amplitude of scalp electroencephalogr aphic (EEG) oscillations to self-paced simple index finger abduction moveme nts in patients with writer's cramp and compared them with those of normal aged-matched controls. The changes in EEG oscillations were measured in pre defined frequency bands (8-10, 10-12, 12-20, and 20-30 Hz) by using the eve nt-related desynchronization technique. Movements of the affected and unaff ected hand in patients with writer's cramp showed significantly less reduct ion in 20- to 30-Hz power compared with controls. The differences in moveme nt-related EEG power decline were apparent over the contralateral central a nd midline regions before and after electromyographic onset. Because EEG be ta rhythm in the sensorimotor region likely emanates from the motor cortex and is related to ongoing muscle activity, this abnormality could be a mani festation of the abnormal motor command at the cortical level.