Four patients with Parkinson's disease (PD) achieved excellent improvement of their unilateral tremor by chronic deep brain stimulation (DBS) of the contralateral ventral intermediate (Vim) nucleus of the thalamus. Repeated measurements of cerebral blood flow were obtained 14 days apart off and on stimulation using 99mTc-ECD SPECT. Subjects were scanned at rest and the data were compared with those of normal healthy volunteers. During stimulation, there were highly significant deactivations in the motor area and supplementary motor area on the electrode side and in the prefrontal area and the anterior cingulum bilaterally. No cerebellar deactivation was detected. We conclude that the mechanism responsible for suppression of parkinsonian tremor by thalamic stimulation is deactivation of thalamocortical activity.
