title: Neural correlates of successful semantic processing during propofol sedation.
abstract: Sedation has a graded effect on brain responses to auditory stimuli: perceptual processing persists at sedation levels that attenuate more complex processing. We used fMRI in healthy volunteers sedated with propofol to assess changes in neural responses to spoken stimuli. Volunteers were scanned awake, sedated, and during recovery, while making perceptual or semantic decisions about nonspeech sounds or spoken words respectively. Sedation caused increased error rates and response times, and differentially affected responses to words in the left inferior frontal gyrus (LIFG) and the left inferior temporal gyrus (LITG). Activity in LIFG regions putatively associated with semantic processing, was significantly reduced by sedation despite sedated volunteers continuing to make accurate semantic decisions. Instead, LITG activity was preserved for words greater than nonspeech sounds and may therefore be associated with persistent semantic processing during the deepest levels of sedation. These results suggest functionally distinct contributions of frontal and temporal regions to semantic decision making. These results have implications for functional imaging studies of language, for understanding mechanisms of impaired speech comprehension in postoperative patients with residual levels of anesthetic, and may contribute to the development of frameworks against which EEG based monitors could be calibrated to detect awareness under anesthesia.
authors.affiliation: Division of Anesthesia, University of Cambridge, Cambridge, CB2 0QQ, United Kingdom.
authors.forename: Ram M
authors.initials: RM
authors.lastname: Adapa
authors.forename: Matthew H
authors.initials: MH
authors.lastname: Davis
authors.forename: Emmanuel A
authors.initials: EA
authors.lastname: Stamatakis
authors.forename: Anthony R
authors.initials: AR
authors.lastname: Absalom
authors.forename: David K
authors.initials: DK
authors.lastname: Menon
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D000704:Analysis of Variance; D001921:Brain / Q000098:blood supply / Q000187:drug effects*; D001931:Brain Mapping; D003657:Decision Making / Q000187:drug effects; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives / Q000097:blood / Q000494:pharmacology*; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010100:Oxygen / Q000097:blood; D015742:Propofol / Q000097:blood / Q000494:pharmacology*; D011930:Reaction Time / Q000187:drug effects; D012660:Semantics; D013223:Statistics as Topic; D014825:Vocabulary; D055815:Young Adult
chemical_list: D006993:Hypnotics and Sedatives; D010100:Oxygen; D015742:Propofol
keywords: functional MRI; inferior frontal gyrus; propofol; sedation; semantic processing