PALLIDOTOMY FOR HEMIBALLISMUS - EFFICACY AND CHARACTERISTICS OF NEURONAL-ACTIVITY

A patient with unremitting, medically intractable hemiballismus underw ent a pallidotomy that abolished his involuntary movements. Firing rat es of cells in the internal segment of the globus pallidus (GPi) recor ded during this procedure were significantly lower than those observed during pallidotomy for Parkinson's disease, either ''on'' or ''off'' medication. Firing patterns in hemiballismus were characterized by low -frequency modulation of the firing rate. These results are consistent with the hyperkinetic model, which suggests that hemiballismus. resul ts from decreased inhibition of the pallidal relay nucleus of the thal amus by the GPi. The efficacy of surgery in the case of hemiballismus demonstrates that pallidotomy can be an effective treatment for this c ondition and suggests that patterned neuronal activity in the GPi is i mportant in the mechanism of hyperkinetic disorders.