Bilateral improvement in voluntary movement after unilateral diencephalic lesions for parkinsonism

In 14 patients with parkinsonism a unilateral ablation at the lower border of the ventrolateral thalamus relieved tremor and rigidity in the contralateral arm but not in the ipsilateral arm. Voluntary movement improved in both arms for three single-handed tasks, each involving the proximal and distal parts of the limb. For one task (a ballistic drawing movement) the postoperative change in one arm was correlated with that in the other arm. The lesion also improved repetitive voluntary movement of the fingers, but only in the contralateral hand.