title: Simultaneous electroencephalographic and functional magnetic resonance imaging indicate impaired cortical top-down processing in association with anesthetic-induced unconsciousness.
abstract: BACKGROUND
  In imaging functional connectivity (FC) analyses of the resting brain, alterations of FC during unconsciousness have been reported. These results are in accordance with recent electroencephalographic studies observing impaired top-down processing during anesthesia. In this study, simultaneous records of functional magnetic resonance imaging (fMRI) and electroencephalogram were performed to investigate the causality of neural mechanisms during propofol-induced loss of consciousness by correlating FC in fMRI and directional connectivity (DC) in electroencephalogram.
  
  
  METHODS
  Resting-state 63-channel electroencephalogram and blood oxygen level-dependent 3-Tesla fMRI of 15 healthy subjects were simultaneously registered during consciousness and propofol-induced loss of consciousness. To indicate DC, electroencephalographic symbolic transfer entropy was applied as a nonlinear measure of mutual interdependencies between underlying physiological processes. The relationship between FC of resting-state networks of the brain (z values) and DC was analyzed by a partial correlation.
  
  
  RESULTS
  Independent component analyses of resting-state fMRI showed decreased FC in frontoparietal default networks during unconsciousness, whereas FC in primary sensory networks increased. DC indicated a decline in frontal-parietal (area under the receiver characteristic curve, 0.92; 95% CI, 0.68-1.00) and frontooccipital (0.82; 0.53-1.00) feedback DC (P<0.05 corrected). The changes of FC in the anterior default network correlated with the changes of DC in frontal-parietal (rpartial=+0.62; P=0.030) and frontal-occipital (+0.63; 0.048) electroencephalographic electrodes (P<0.05 corrected).
  
  
  CONCLUSIONS
  The simultaneous propofol-induced suppression of frontal feedback connectivity in the electroencephalogram and of frontoparietal FC in the fMRI indicates a fundamental role of top-down processing for consciousness.
authors: * Research Fellow, ‖ Resident, # Research Assistant, *** Professor, Director Chair, Department of Anesthesiology, † Associate Professor, § Resident, †† Research Fellow, ## Professor, Director Chair, Department of Neurology, ‡ Research Fellow, ‖‖ Professor, Director Chair, Department of Neuroradiology, Klinikum rechts der Isar, Technische Universität München, Munich, Germany. ‡‡ Research Fellow, Department of Medical Statistics and Epidemiology, Technische Universität München, Munich, Germany. §§ Research Fellow, Max Planck Institute of Psychiatry, Munich, Germany. ** Resident, ††† Professor, Director Chair, Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, and Department of Anesthesiology, Witten/Herdecke University, Helios Clinic Wuppertal, Wuppertal, Germany.
authors: Denis
authors: D
authors: Jordan
authors: Rüdiger
authors: R
authors: Ilg
authors: Valentin
authors: V
authors: Riedl
authors: Anna
authors: A
authors: Schorer
authors: Sabine
authors: S
authors: Grimberg
authors: Susanne
authors: S
authors: Neufang
authors: Adem
authors: A
authors: Omerovic
authors: Sebastian
authors: S
authors: Berger
authors: Gisela
authors: G
authors: Untergehrer
authors: Christine
authors: C
authors: Preibisch
authors: Enrico
authors: E
authors: Schulz
authors: Tibor
authors: T
authors: Schuster
authors: Manuel
authors: M
authors: Schröter
authors: Victor
authors: V
authors: Spoormaker
authors: Claus
authors: C
authors: Zimmer
authors: Bernhard
authors: B
authors: Hemmer
authors: Afra
authors: A
authors: Wohlschläger
authors: Eberhard F
authors: EF
authors: Kochs
authors: Gerhard
authors: G
authors: Schneider
mesh_terms: D000328:Adult; D000465:Algorithms; D000758:Anesthesia; D018686:Anesthetics, Intravenous / Q000494:pharmacology; D002540:Cerebral Cortex / Q000187:drug effects / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods*; D019277:Entropy; D005625:Frontal Lobe / Q000473:pathology / Q000503:physiopathology; D006321:Heart / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008991:Monitoring, Physiologic; D009434:Neural Pathways / Q000187:drug effects; D010100:Oxygen / Q000097:blood; D015742:Propofol / Q000494:pharmacology; D015656:Respiratory Mechanics / Q000187:drug effects; D014474:Unconsciousness / Q000139:chemically induced* / Q000473:pathology* / Q000503:physiopathology; D014851:Wakefulness / Q000502:physiology; D055815:Young Adult
chemical_list: D018686:Anesthetics, Intravenous; D010100:Oxygen; D015742:Propofol