In the current era of functional surgery for movement disorders, deep brain stimulation (DBS) of the globus pallidus internus (GPi) is emerging as the favoured target in the treatment of patients with dystonia. The results of 25 consecutive patients with medically intractable dystonia (12 with generalised dystonia, 7 with spasmodic torticollis, and 6 with other types of dystonia) treated with GPi stimulation are reported. Although comparisons were limited by differences in their respective neurological rating scales, chronic DBS benefited all groups, resulting in clear and progressive improvements in their condition. This study clearly demonstrates that DBS of the GPi provides amelioration of intractable dystonia.

Intellectual, psychological and functional outcomes were evaluated in a consecutive series of 20 Parkinsonian patients who had unilateral (UPVP) or simultaneous bilateral posteroventral pallidotomy (BPVP) using Image Fusion and Stereoplan (Radionics Inc., Boston, Mass., USA) with stimulation for lesion localization. Comprehensive baseline and 3-month postoperative neuropsychological and neurological assessment protocols were administered together with questionnaire measures of functional disability, quality of life and psychological symptomatology. Changes in patients' clinical presentation and scores on psychometric tests, questionnaires and observational rating scales were then examined. We observed no new neuropsychiatric sequelae directly related to pallidotomy. Cognitive sequelae were restricted to selective reductions in categorical verbal fluency following UPVP (P < 0.001) and BPVP (P < 0.01) and a reduction in phonemic verbal fluency following BPVP (P < 0.01); these changes were not reported subjectively. A fall in diadochokinetic rates (P < 0.01) and some subjective reports of a worsening in pre-existing dysarthria, hypophonia and hypersalivation/drooling following BPVP also suggested changes in speech motor apparatus; however, these changes did not have significant functional consequences. There was one case of more generalized cognitive impairment following BPVP. We also observed significant symptomatic improvement on neurological rating scales; following UPVP, Total Unified Parkinson's Disease Rating Scale (UPDRS) scores improved by 27% (P < 0.01) and following BPVP the improvement was 53% (P < 0.05). Patients' perceptions of reduced postoperative functional disability and improvements in 'quality of life' also achieved statistical significance on a number of both physical and psychosocial questionnaire subscales.

The pedunculopontine nucleus is composed of cholinergic and non-cholinergic neurones and is located in the caudal pontomesencephalic tegmentum. Evidence suggests that the nucleus plays a role in the production and control of movement. The nucleus has dense interconnections with the basal ganglia, as well as with other areas of the brain associated with motor control. Electrical stimulation of the pedunculopontine nucleus in the decerebrate cat or rat produces organized locomotor movements. Physiological studies show that the pedunculopontine nucleus modulates its activity in response to locomotion, as well as voluntary arm and eye movements. Degeneration of the pedunculopontine nucleus is seen in post-mortem brains in humans with Parkinson's disease and Parkinsonian syndromes. In animal models of Parkinson's disease, metabolic changes are seen in the pedunculopontine nucleus, and chemical inhibition or mechanical disruption of the nucleus can produce an akinetic state in animals and man. In this paper we review the literature in support of the suggestion that some of the symptoms of Parkinson's disease are caused by dysfunction of the pedunculopontine nucleus. In accordance with this view, direct stimulation of the nucleus can ameliorate some symptoms of the disease, as demonstrated in both experimental animals and man.

In 15 patients with primary dystonia (six cervical and nine generalized dystonias) who were treated with bilateral chronic pallidal stimulation, we investigated the sensorimotor modulation of the oscillatory local field potentials (LFPs) recorded from the pallidal electrodes. We correlated these with the surface electromyograms in the affected muscles. The effects of involuntary, passive and voluntary movement and muscle-tendon vibration on frequency ranges of 0-3 Hz, theta (3-8 Hz), alpha (8-12 Hz), low (12-20 Hz) and high beta (20-30 Hz), and low (30-60 Hz) and high gamma (60-90 Hz) power were recorded and compared between cervical and generalized dystonia groups. Significant decreases in LFP synchronization at 8-20 Hz occurred during the sensory modulation produced by voluntary or passive movement or vibration. Voluntary movement also caused increased gamma band activity (30-90 Hz). Dystonic involuntary muscle spasms were specifically associated with increased theta, alpha and low beta (3-18 Hz). Furthermore, the increase in the frequency range of 3-20 Hz correlated with the strength of the muscle spasms and preceded them by approximately 320 ms. Differences in modulation of pallidal oscillation between cervical and generalized dystonias were also revealed. This study yields new insights into the pathophysiological mechanisms of primary dystonias and their treatment using pallidal deep brain stimulation.