Proceedings of The Physiological Society

University College London December 2005 (2006) Proc Physiol Soc 1, PC6

Poster Communications

Globus pallidus field potentials in patients with primary dystonia

Wang, Shouyan; Yianni, John; Peden, Robert; Bergen, Olivia Van; Heinzen, Jamie; Bain, Peter; Aziz, Tipu; Liu, Xuguang; Stein, John;

1. University Laboratory of Physiology, University of Oxford, Oxford, United Kingdom. 2. Nuffield Department of Surgery, University of Oxford, Oxford, United Kingdom. 3. Division of Neuroscience and Mental Health, Imperial College London, London, United Kingdom.

Dystonia is thought to result from disorders of basal ganglia function, hence the globus pallidus is the preferred target for its functional surgical treatment by high frequency electrical stimulation. To explore the role of abnormal neuronal activity of the globus pallidus in the generation of dystonia in man, local field potentials (LFPs) were recorded from the globus pallidus internus (GPi) in 13 patients undergoing deep brain surgery for primary dystonia and compared with EMGs recorded from the affected muscles. Their frequency composition was analysed before and during dystonic phases, and during voluntary movements. As is often seen, in 5 patients with rhythmic bursting involuntary movements, the muscle EMG bursts were phase locked with oscillations in the contralateral pallidal LFPs at the burst frequency. But in patients with tonic dystonia without rhythmic components no significant coherence between EMGs and LFPs was seen. The most interesting features emerged, however, when the patients involuntary dystonic movements were compared with their voluntary movements. During both, power in the GPi LFPs increased at the movement frequencies (0.15 Hz), as one might expect. However, during voluntary movements power in the higher beta (25-35 Hz) and gamma (45-85 Hz) frequency bands also increased, whereas that between 8 and 20 Hz decreased. In contrast during involuntary dystonic episodes power at 8-12 Hz increased, whereas there was no increase in power at any of the higher beta and gamma frequencies. Since these higher frequencies are thought to be responsible for helping to bind together and time accurately the elements of a complex movement, their absence during dystonia may help to explain its uncontrolled character. In addition the pathological increase in GPi LFP power at 8-12 Hz during dystonic episodes may contribute directly to them. Such frequencies may be projected to excite the muscles, but since the muscles + limb act as low pass filters, this rate may be too high to appear as tremor, but instead it may contort the limb into its dystonic postures.

Where applicable, experiments conform with Society ethical requirements