title: EEG entropy measures indicate decrease of cortical information processing in Disorders of Consciousness.
abstract: OBJECTIVE
  Clinical assessments that rely on behavioral responses to differentiate Disorders of Consciousness are at times inapt because of some patients' motor disabilities. To objectify patients' conditions of reduced consciousness the present study evaluated the use of electroencephalography to measure residual brain activity.
  
  
  METHODS
  We analyzed entropy values of 18 scalp EEG channels of 15 severely brain-damaged patients with clinically diagnosed Minimally-Conscious-State (MCS) or Unresponsive-Wakefulness-Syndrome (UWS) and compared the results to a sample of 24 control subjects. Permutation entropy (PeEn) and symbolic transfer entropy (STEn), reflecting information processes in the EEG, were calculated for all subjects. Participants were tested on a modified active own-name paradigm to identify correlates of active instruction following.
  
  
  RESULTS
  PeEn showed reduced local information content in the EEG in patients, that was most pronounced in UWS. STEn analysis revealed altered directed information flow in the EEG of patients, indicating impaired feed-backward connectivity. Responses to auditory stimulation yielded differences in entropy measures, indicating reduced information processing in MCS and UWS.
  
  
  CONCLUSIONS
  Local EEG information content and information flow are affected in Disorders of Consciousness. This suggests local cortical information capacity and feedback information transfer as neural correlates of consciousness.
  
  
  CONCLUSIONS
  The utilized EEG entropy analyses were able to relate to patient groups with different Disorders of Consciousness.
authors.affiliation: Department of Neurology, Klinikum rechts der Isar, Technische Universität München, Germany; Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, Germany. Electronic address: alexander.thul@mytum.de.
authors.forename: Alexander
authors.initials: A
authors.lastname: Thul
authors.affiliation: Department of Psychology, Laboratory for Sleep, Cognition and Consciousness Research, University of Salzburg, Austria.
authors.forename: Julia
authors.initials: J
authors.lastname: Lechinger
authors.affiliation: Apallic Care Unit, Neurological Division, Geriatriezentrum am Wienerwald, Vienna, Austria.
authors.forename: Johann
authors.initials: J
authors.lastname: Donis
authors.affiliation: Apallic Care Unit, Neurological Division, Geriatriezentrum am Wienerwald, Vienna, Austria.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Michitsch
authors.affiliation: Apallic Care Unit, Neurological Division, Albert-Schweitzer-Klinik, Graz, Austria.
authors.forename: Gerald
authors.initials: G
authors.lastname: Pichler
authors.affiliation: Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, Germany.
authors.forename: Eberhard F
authors.initials: EF
authors.lastname: Kochs
authors.affiliation: Department of Anesthesiology, Klinikum rechts der Isar, Technische Universität München, Germany.
authors.forename: Denis
authors.initials: D
authors.lastname: Jordan
authors.affiliation: Department of Neurology, Klinikum rechts der Isar, Technische Universität München, Germany.
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Ilg
authors.affiliation: Department of Psychology, Laboratory for Sleep, Cognition and Consciousness Research, University of Salzburg, Austria; Centre for Cognitive Neuroscience Salzburg (CCNS), Salzburg, Austria.
authors.forename: Manuel
authors.initials: M
authors.lastname: Schabus
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000328:Adult; D000368:Aged; D002540:Cerebral Cortex / Q000502:physiology*; D003243:Consciousness / Q000502:physiology; D003244:Consciousness Disorders / Q000175:diagnosis* / Q000503:physiopathology; D004569:Electroencephalography / Q000379:methods*; D019277:Entropy; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008606:Mental Processes / Q000502:physiology*; D008875:Middle Aged; D018458:Persistent Vegetative State / Q000175:diagnosis / Q000503:physiopathology; D055815:Young Adult
keywords: Disorders of consciousness; Electroencephalography; Information theory; Non-linear analysis; Own-name paradigm; Permutation entropy; Symbolic transfer entropy