Relation of Gamma Oscillations in Scalp Recordings to Muscular Activity
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We recorded scalp electrical activity before and after full neuro-muscular paralysis in 5 volunteers and determined differences due to elimination of muscular activity on several standard applications of EEG. Due to paralysis, there were reductions in ‘noisiness’ of the standard scalp recordings which were maximal over the peripheral scalp, not explained by abolition of movement artefact, and best accounted for by sustained EMG activity in resting individuals. There was a corresponding reduction in spectral power in the gamma range. In central leads, the extent of gamma frequency coherence during a non-time-locked mental task (1 s epochs) was reduced by paralysis, likely due to a reduction in gamma-frequency coherence in widely arising EMG signals. In a time-locked mental task (auditory oddball), evoked responses were qualitatively unaffected by paralysis but 3 of 4 induced gamma responses were obscured by EMG.
KeywordsGamma EEG EMG Paralysis
The EEG Research Unit was funded by an equipment grant from The Wellcome Trust, London, UK. Project support has been provided by the National Health and Medical Research Council and Flinders Medical Centre Foundation. Dr Whitham was supported by a Pfizer Neuroscience Research Fellowship and an Epilepsy Society of Australia Fellowship from UCB Pharma. We also thank our colleagues Mr Dylan DeLosAngeles (Flinders University), Dr Bry Wyman (University of Wisconsin), Dr Arduino Mangoni (Flinders University) and Dr Rob Wilcox (Flinders Medical Centre), for their participation as subjects in the paralysis experiments, as well as Dr Peter Lillie and Dr Andrew Hardy (Flinders Medical Centre) for anaesthetic expertise.
- Whitham EM, Pope KJ, Fitzgibbon SP, Lewis T, Clark CR, Loveless S, Broberg M, Wallace A, DeLosAngeles D, Lillie P, Hardy A, Fronsko R, Pulbrook A, Willoughby JO (2007) Scalp electrical recording during paralysis: quantitative evidence that EEG frequencies above 20 Hz are contaminated by EMG. Clin Neurophysiol 118:1877–1888PubMedCrossRefGoogle Scholar