title: Neurophysiological correlates of sevoflurane-induced unconsciousness.
abstract: BACKGROUND
  Recent studies of anesthetic-induced unconsciousness in humans have focused predominantly on the intravenous drug propofol and have identified anterior dominance of alpha rhythms and frontal phase-amplitude coupling patterns as neurophysiological markers. However, it is unclear whether the correlates of propofol-induced unconsciousness are generalizable to inhaled anesthetics, which have distinct molecular targets and which are used more commonly in clinical practice.
  
  
  METHODS
  The authors recorded 64-channel electroencephalograms in healthy human participants during consciousness, sevoflurane-induced unconsciousness, and recovery (n = 10; n = 7 suitable for analysis). Spectrograms and scalp distributions of low-frequency (1 Hz) and alpha (10 Hz) power were analyzed, and phase-amplitude modulation between these two frequencies was calculated in frontal and parietal regions. Phase lag index was used to assess phase relationships across the cortex.
  
  
  RESULTS
  At concentrations sufficient for unconsciousness, sevoflurane did not result in a consistent anteriorization of alpha power; the relationship between low-frequency phase and alpha amplitude in the frontal cortex did not undergo characteristic transitions. By contrast, there was significant cross-frequency coupling in the parietal region during consciousness that was not observed after loss of consciousness. Furthermore, a reversible disruption of anterior-posterior phase relationships in the alpha bandwidth was identified as a correlate of sevoflurane-induced unconsciousness.
  
  
  CONCLUSIONS
  In humans, sevoflurane-induced unconsciousness is not correlated with anteriorization of alpha and related cross-frequency patterns, but rather by a disruption of phase-amplitude coupling in the parietal region and phase-phase relationships across the cortex.
authors.affiliation: From the Department of Anesthesiology (S.B.-M., V.T., G.V., A.A., D.R., B.S., E.J., G.A.M.) and Neuroscience Graduate Program (G.A.M.), Center for Consciousness Science, University of Michigan Medical School, Ann Arbor, Michigan.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Blain-Moraes
authors.forename: Vijay
authors.initials: V
authors.lastname: Tarnal
authors.forename: Giancarlo
authors.initials: G
authors.lastname: Vanini
authors.forename: Amir
authors.initials: A
authors.lastname: Alexander
authors.forename: Derek
authors.initials: D
authors.lastname: Rosen
authors.forename: Brenna
authors.initials: B
authors.lastname: Shortal
authors.forename: Ellen
authors.initials: E
authors.lastname: Janke
authors.forename: George A
authors.initials: GA
authors.lastname: Mashour
mesh_terms: D000513:Alpha Rhythm / Q000187:drug effects; D018685:Anesthetics, Inhalation / Q000494:pharmacology*; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D001519:Behavior / Q000187:drug effects; D004569:Electroencephalography / Q000187:drug effects; D005260:Female; D006801:Humans; D008297:Male; D008738:Methyl Ethers / Q000494:pharmacology*; D015742:Propofol / Q000494:pharmacology; D000077149:Sevoflurane; D014474:Unconsciousness / Q000139:chemically induced* / Q000523:psychology; D055815:Young Adult
chemical_list: D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D008738:Methyl Ethers; D000077149:Sevoflurane; D015742:Propofol