• Kazuko Hayashi, Nobuhiro Mukai, and Teiji Sawa.
• Department of Anesthesiology, Nantan General Hospital, Japan; Department of Anesthesiology, Kyoto Prefectural University of Medicine, Graduate School of Medical Science, Kyoto, Japan. Electronic address: zukko@koto.kpu-m.ac.jp.
• Clin Neurophysiol. 2014 Jan 1; 125 (1): 194-201.

ObjectiveOccipital electroencephalogram (EEG) activity is known to be different from the frontal EEG during wakefulness and anesthesia. However, less is known about occipital non-linear dynamics analyzed by EEG-bicoherence, which can reflect the oscillatory features that are dependent on thalamocortical modulation.MethodsForty patients were anesthetized using sevoflurane (1% or 3%) combined with remifentanil. Frontal and occipital EEGs were simultaneously collected, and bicoherence was analyzed before and after induction of anesthesia.ResultsOccipital awake EEGs often demonstrate a bicoherence α peak, differing from frontal awake EEGs in the absence of bicoherence growth. With 1% sevoflurane, occipital α bicoherence disappeared and frontal α bicoherence peaks appeared. Although 3% sevoflurane caused an increase in occipital δ-θ normalized power, similar to the frontal region (peak relative δ-θ power, 13.1 ± 2.2% vs. 12.2 ± 2.7%, p>0.05), occipital bicoherence showed no growth in any frequency area, contrasting with the frontal bicoherence spectrum with a conspicuous peak in the δ-θ area (19.8 ± 8.9 vs. 43.6 ± 13.8, p<0.05).ConclusionsThe occipital bicoherence spectrum in the peri-anesthesia period is quite different from the frontal bicoherence spectrum, which is not usually obvious in the power spectrum.SignificanceNonlinear regulation of the occipital EEG is different from the frontal EEG during every stage of anesthesia.Copyright © 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.

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