title: Reconfiguration of network hub structure after propofol-induced unconsciousness.
abstract: BACKGROUND
  General anesthesia induces unconsciousness along with functional changes in brain networks. Considering the essential role of hub structures for efficient information transmission, the authors hypothesized that anesthetics have an effect on the hub structure of functional brain networks.
  
  
  METHODS
  Graph theoretical network analysis was carried out to study the network properties of 21-channel electroencephalogram data from 10 human volunteers anesthetized on two occasions. The functional brain network was defined by Phase Lag Index, a coherence measure, for three states: wakefulness, loss of consciousness induced by the anesthetic propofol, and recovery of consciousness. The hub nodes were determined by the largest centralities. The correlation between the altered hub organization and the phase relationship between electroencephalographic channels was investigated.
  
  
  RESULTS
  Topology rather than connection strength of functional networks correlated with states of consciousness. The average path length, clustering coefficient, and modularity significantly increased after administration of propofol, which disrupted long-range connections. In particular, the strength of hub nodes significantly decreased. The primary hub location shifted from the parietal to frontal region, in association with propofol-induced unconsciousness. The phase lead of frontal to parietal regions in the α frequency band (8-13 Hz) observed during wakefulness reversed direction after propofol and returned during recovery.
  
  
  CONCLUSIONS
  Propofol reconfigures network hub structure in the brain and reverses the phase relationship between frontal and parietal regions. Changes in network topology are more closely associated with states of consciousness than connectivity and may be the primary mechanism for the observed loss of frontal to parietal feedback during general anesthesia.
authors.affiliation: Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, Michigan; Doctoral Candidate, Department of Physics, POSTECH, Pohang, Korea.
authors.forename: Heonsoo
authors.initials: H
authors.lastname: Lee
authors.affiliation: Faculty, Neuroscience Graduate Program University of Michigan Medical School, Ann Arbor, Michigan.
authors.forename: George A
authors.initials: GA
authors.lastname: Mashour
authors.affiliation: Department of Clinical Pharmacology and Therapeutics, Department of Anesthesiology and Pain Medicine, Asan Medical Center, University of Ulsan College of Medicine, Seoul, Korea.
authors.forename: Gyu-Jeong
authors.initials: GJ
authors.lastname: Noh
authors.affiliation: Asia Pacific Center for Theoretical Physics; Professor, Department of Physics, POSTECH, Pohang, Korea.
authors.forename: Seunghwan
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Anesthesiology, University of Michigan Medical School, Ann Arbor, Michigan.
authors.forename: UnCheol
authors.initials: U
authors.lastname: Lee
mesh_terms: D000328:Adult; D000465:Algorithms; D000771:Anesthesia, Intravenous; D018686:Anesthetics, Intravenous / Q000494:pharmacology*; D004569:Electroencephalography / Q000187:drug effects; D005625:Frontal Lobe / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008297:Male; D009415:Nerve Net / Q000187:drug effects*; D010296:Parietal Lobe / Q000187:drug effects / Q000502:physiology; D015742:Propofol / Q000494:pharmacology*; D009435:Synaptic Transmission / Q000187:drug effects; D014474:Unconsciousness / Q000139:chemically induced* / Q000503:physiopathology; D014851:Wakefulness / Q000187:drug effects; D055815:Young Adult
chemical_list: D018686:Anesthetics, Intravenous; D015742:Propofol