title: Spatial Analytic Phase Difference of EEG activity during anesthetic-induced unconsciousness.
abstract: OBJECTIVE
  A number of studies provide supporting evidence for changes in synchronization during anesthetic-induced unconsciousness. This study investigates how anesthetic administration affects the widespread patterns of phase synchrony.
  
  
  METHODS
  The recently introduced method of Spatial Analytic Phase Difference (SAPD) was used to measure changes in synchrony in the electroencephalogram (EEG) activity of 29 patients undergoing routine surgery. Analysis was performed over 9 frequency bands: (i) δ (1.5-3.5Hz); (ii) θ (3.5-7.5Hz); (iii) α1 (8-10Hz); (iv) α2 (10.5-12Hz); (v) β1 (12.5-18Hz); (vi) β2 (18.5-21Hz); (vii) β3 (21.5-30Hz); (viii) γ1 (30.5-40Hz); and (ix) γ2 (60-80Hz).
  
  
  RESULTS
  Anesthesia was characterized by (a) large and localized synchrony increases in mid-frequency bands (8-12Hz), (b) smaller and widespread synchrony increases in higher frequency bands (30.5-40Hz, 60-80Hz), and (c) both increase and decrease of synchrony in low frequency bands (1.5-7.5Hz).
  
  
  CONCLUSIONS
  This study supports anesthetic-induced changes in synchrony, with the inducement of persistent and reversible widespread γ synchrony being most prominent.
  
  
  CONCLUSIONS
  Our findings have implications in the study of consciousness, support existing literature in the field and contribute towards the theoretical understanding of the mechanisms behind loss of consciousness. Future investigations could result in a synchrony-based measure for monitoring the level of hypnosis of patients during surgery.
authors.affiliation: Holistic Electronics Research Lab, Department of Electrical and Computer Engineering, University of Cyprus, Cyprus; KIOS Research Centre, University of Cyprus, Kallipoleos 75, 1678 Nicosia, Cyprus. Electronic address: nicoletta.n@ucy.ac.cy.
authors.forename: N
authors.initials: N
authors.lastname: Nicolaou
authors.affiliation: Holistic Electronics Research Lab, Department of Electrical and Computer Engineering, University of Cyprus, Cyprus; KIOS Research Centre, University of Cyprus, Kallipoleos 75, 1678 Nicosia, Cyprus.
authors.forename: J
authors.initials: J
authors.lastname: Georgiou
mesh_terms: D000328:Adult; D000758:Anesthesia; D058256:Brain Waves / Q000502:physiology*; D002540:Cerebral Cortex / Q000502:physiology*; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D064795:Intraoperative Neurophysiological Monitoring / Q000379:methods*; D008297:Male; D008875:Middle Aged; D014851:Wakefulness / Q000502:physiology*
keywords: Anesthesia; Awareness; Electroencephalogram; Loss of consciousness; Spatial Analytic Phase Difference; Synchrony