Corticomuscular coherence measured between electroencephalography (EEG), magnetoencephalography, or local field potentials and electromyography (EMG) should be helpful in understanding the cortical control of movement. EEG–EMG coherence and phase spectra depend on the types of EEG derivation and current source density function of EEG appears to be the most appropriate for computation of EEG–EMG coherence. A new model for the interpretation of the phase spectra (“constant phase shift plus constant time lag model”) shows that cortical surface negative potentials are phase-locked to EMG firing. There are functional differences of EEG–EMG coherence among the alpha, beta, and gamma bands suggesting differences in their possible generator mechanisms. Since corticomuscular coherence is a noninvasive measure of corticomotoneuronal function in a specific frequency range, clinical application of this method might be very fruitful in tremor research.
Human Motor Control Section, Medical Neurology Branch, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland. U.S.A.
Address correspondence and reprint request to Mark Hallett, M.D., Clinical Director, National Institutes of Neurological Disorders and Stroke, National Institutes of Health, Building 10, Room 5N226, 10 Center Drive, MSC-1428, Bethesda, Maryland 20892-1428, U.S.A.
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