title: Cortical processing of complex auditory stimuli during alterations of consciousness with the general anesthetic propofol.
abstract: BACKGROUND
  The extent to which complex auditory stimuli are processed and differentiated during general anesthesia is unknown. The authors used blood oxygenation level-dependent functional magnetic resonance imaging to examine the processing words (10 per period; compared with scrambled words) and nonspeech human vocal sounds (10 per period; compared with environmental sounds) during propofol anesthesia.
  
  
  METHODS
  Seven healthy subjects were tested. Propofol was given by a computer-controlled pump to obtain stable plasma concentrations. Data were acquired during awake baseline, sedation (propofol concentration in arterial plasma: 0.64 +/- 0.13 microg/ml; mean +/- SD), general anesthesia (4.62 +/- 0.57 microg/ml), and recovery. Subjects were asked to memorize the words.
  
  
  RESULTS
  During all periods including anesthesia, the sounds conditions combined elicited significantly greater activations than silence bilaterally in primary auditory cortices (Heschl gyrus) and adjacent regions within the planum temporale. During sedation and anesthesia, however, the magnitude of the activations was reduced by 40-50% (P < 0.05). Furthermore, anesthesia abolished voice-specific activations seen bilaterally in the superior temporal sulcus during the other periods as well as word-specific activations bilaterally in the Heschl gyrus, planum temporale, and superior temporal gyrus. However, scrambled words paradoxically elicited significantly more activation than normal words bilaterally in planum temporale during anesthesia. Recognition the next day occurred only for words presented during baseline plus recovery and was correlated (P < 0.01) with activity in right and left planum temporale.
  
  
  CONCLUSIONS
  The authors conclude that during anesthesia, the primary and association auditory cortices remain responsive to complex auditory stimuli, but in a nonspecific way such that the ability for higher-level analysis is lost.
authors.affiliation: Department of Anesthesia, McGill University. gilles.plourde@staff.mcgill.ca
authors.forename: Gilles
authors.initials: G
authors.lastname: Plourde
authors.forename: Pascal
authors.initials: P
authors.lastname: Belin
authors.forename: Daniel
authors.initials: D
authors.lastname: Chartrand
authors.forename: Pierre
authors.initials: P
authors.lastname: Fiset
authors.forename: Steven B
authors.initials: SB
authors.lastname: Backman
authors.forename: Guoming
authors.initials: G
authors.lastname: Xie
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Zatorre
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000768:Anesthesia, General; D001303:Auditory Cortex / Q000502:physiology*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D015742:Propofol / Q000494:pharmacology*; D012894:Sleep Stages / Q000502:physiology
chemical_list: D015742:Propofol