title: Simultaneous bicoherence analysis of occipital and frontal electroencephalograms in awake and anesthetized subjects.
abstract: OBJECTIVE
  Occipital 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.
  
  
  METHODS
  Forty 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.
  
  
  RESULTS
  Occipital 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).
  
  
  CONCLUSIONS
  The 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.
  
  
  CONCLUSIONS
  Nonlinear regulation of the occipital EEG is different from the frontal EEG during every stage of anesthesia.
authors.affiliation: 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.
authors.forename: Kazuko
authors.initials: K
authors.lastname: Hayashi
authors.affiliation: Department of Anesthesiology, Nantan General Hospital, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Mukai
authors.affiliation: Department of Anesthesiology, Kyoto Prefectural University of Medicine, Graduate School of Medical Science, Kyoto, Japan.
authors.forename: Teiji
authors.initials: T
authors.lastname: Sawa
mesh_terms: D000328:Adult; D000368:Aged; D000768:Anesthesia, General; D018685:Anesthetics, Inhalation / Q000008:administration & dosage; D018686:Anesthetics, Intravenous / Q000008:administration & dosage; D004569:Electroencephalography; D005260:Female; D005625:Frontal Lobe / Q000502:physiology*; D006801:Humans; D008297:Male; D008738:Methyl Ethers / Q000008:administration & dosage; D008875:Middle Aged; D009778:Occipital Lobe / Q000502:physiology*; D010880:Piperidines / Q000008:administration & dosage; D000077208:Remifentanil; D060685:Sense of Coherence / Q000502:physiology*; D000077149:Sevoflurane; D014851:Wakefulness / Q000502:physiology*
chemical_list: D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D008738:Methyl Ethers; D010880:Piperidines; D000077149:Sevoflurane; D000077208:Remifentanil
keywords: Alpha wave; Anesthesia depth; Bicoherence; Consciousness; Nonlinear analysis; Occipital electroencephalogram; Thalamocortical network