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Modulation of primary orthostatic tremor by magnetic stimulation over the motor cortex

Tsai, C.H., Semmler, J.G., Kimber, T.E., Thickbroom, G., Stell, R., Mastaglia, F.L. and Thompson, P.D. (1998) Modulation of primary orthostatic tremor by magnetic stimulation over the motor cortex. Journal of Neurology, Neurosurgery & Psychiatry, 64 (1). pp. 33-36.

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OBJECTIVES To study the role of corticomotor neuronal pathways in primary orthostatic tremor.

METHODS Transcranial magnetic stimuli at an intensity 10% above the resting motor threshold were delivered over the leg motor cortex in two patients with primary orthostatic tremor while standing still. Electromyographic responses in both tibialis anterior muscles were recorded after 20 stimuli given randomly at intervals of 120 to 180 seconds. Differences between predicted and actual times of occurrence of tremor bursts after the stimuli were used to calculate a resetting index, with a value of 0 representing no resetting and a value of 1 representing complete resetting.

RESULTS Transcranial magnetic stimulation evoked EMG responses in both tibialis anterior muscles, followed by transient suppression of tremor before reappearance of rhythmic EMG activity. Analysis of the timing of tremor bursts from EMG recordings before and after the magnetic stimuli disclosed that the phase of orthostatic tremor could be reset by brain stimulation (mean resetting indices 0.93 and 0.82).

CONCLUSION The results suggest that a central oscillator, involving the motor cortex, has a crucial role in either the generation or modulation of orthostatic tremor.

Item Type: Journal Article
Publisher: BMJ Publishing Group
Copyright: © 1998 by the BMJ Publishing Group Ltd.
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