Neuronal activity in the basal ganglia in patients with generalized dystonia and hemiballismus

Microelectrode recording was performed in the basal ganglia of 3 patients w ith generalized dystonia and 1 patient with hemiballismus secondary to a br ainstem hemorrhage. Neuronal activity was recorded from the internal and ex ternal segments of the globus pallidus and assessed for mean discharge rate and pattern of spontaneous activity. The responses of neurons in the inter nal segment of the globus pallidus to passive and active movements were als o evaluated. Mean discharge rates of neurons in both segments of the pallid um in patients with dystonia and the patient with hemiballismus were consid erably lower than those reported for patients with idiopathic Parkinson's d isease. In addition, the pattern of spontaneous neuronal activity was highl y irregular, occurring in intermittent grouped discharges separated by peri ods of pauses. Although receptive fields in the dystonia patients were wide ned and less specific than those reported in normal monkeys, neuronal respo nses to movement were uncommon in the hemiballismus patient. Before surgery , patients with dystonia experienced abnormal posturing and involuntary mov ements. Coactivation of agonist-antagonist muscle groups was observed both at rest and during the performance of simple movements. After pallidotomy t here was a significant reduction in the involuntary movement associated wit h these disorders and a more normal pattern of electromyographic activity d uring rest and movement. Given the improvement in dystonic and hemiballisti c movements in these patients after ablation of the sensorimotor portion of the internal segment of the globus pallidus, we suggest that pallidotomy c an be an effective treatment for patients with dystonia and also for patien ts with medically intractable hemiballismus. Based on the finding of decrea sed neuronal discharge rates in pallidal neurons, we propose that physiolog ically dystonia most closely resembles a hyperkinetic movement disorder. A model for dystonia is proposed that incorporates the observed changes in th e rate and pattern of neuronal activity in the pallidum with data from neur oimaging with positron emission tomography and 2-deoxyglucose studies.