Observations on physiological and psychological functions of the ventral oral internal nucleus of the human thalamus.

Eight patients underwent VOI thalamotomy for spasmodic torticollis or choreoathetosis. The clinical results were disappointing: at follow-up examination 8 months postoperatively, on average, none of the seven patients with torticollis regarded the effect as good. In two there was some long-lasting improvement, but in five the results was nil. One patient with choreoathetosis did not benefit from surgery. Side-effects were frequent but not serious; they included excessive sleepiness, drowsiness, weight increase, deterioration of memory and loss of general activity. Electrical stimulation of the VOI nucleus caused subjective sensations in the neck and shoulder muscles without movements of the head, and autonomic or emotional reactions. An evoked scalp response was recorded in contralateral frontal area 8. As shown by psychological tests, in visuospatial performances there is a preoperative defect, which seems to be specific to spasmodic torticollis. After left VOI thalamotomy both receptive and expressive verbal efficiency were impaired. Visual perception and memory were almost unaffected by VOI thalamotomy.