title: Implicit memory for words played during isoflurane- or propofol-based anesthesia: the lexical decision task.
abstract: BACKGROUND
  Unconscious processing of words during general anesthesia has been suggested after surgery with several tests of implicit memory. Patients can neither recall those words nor do they have explicit memories of other intraoperative events. It is unclear to what degree information is processed during general anesthesia and which tests are best suited to detect implicit memory. In the current study, a lexical decision paradigm not previously used to demonstrate implicit memory during anesthesia was used.
  
  
  METHODS
  Sixty patients undergoing lumbar disc surgery were assigned to receive isoflurane infusion- or propofol infusion-based anesthesia combined with alfentanil infusions and a nitrous oxide-oxygen mixture. A control group of 10 medical students listened to tapes without receiving anesthesia. Two tapes, each containing a list of 30 low-frequency German nouns repeated for 15 min, were prepared, with half of the patients listening to tape A and the other half listening to tape B during the operation. Exposure time was 15 min from the time of skin incision onward. In the test phase, approximately 7 h later, words from lists A and B plus 60 nonwords were presented in random order by a computer program. Subjects were asked to indicate, by pressing one of two response buttons, whether the spoken word was or was not a legal German word (lexical decision).
  
  
  RESULTS
  A recognition test revealed chance recognition for words presented during anesthesia. Lexical decision responses, however, were slightly faster to primed (previously presented) words than to unprimed (not previously presented) words when the entire group of patients was tested, suggesting a small implicit memory effect, which barely failed to reach the significance level. When the two medication groups were tested separately, no significant implicit memory effect could be ascertained statistically. The effects of previous exposure were much more pronounced in the control group.
  
  
  CONCLUSIONS
  Balanced anesthesia techniques with isoflurane or propofol lead to only a minimal, statistically borderline implicit memory effect in the lexical decision paradigm.
authors.affiliation: Department of Anaesthesia, Medical School of Hanover, Hanover, Germany. Muente.Sinikka@MH-Hannover.de
authors.forename: Sinikka
authors.initials: S
authors.lastname: Münte
authors.forename: Maren
authors.initials: M
authors.lastname: Schmidt
authors.forename: Maren
authors.initials: M
authors.lastname: Meyer
authors.forename: Wido
authors.initials: W
authors.lastname: Nager
authors.forename: Ekkehard
authors.initials: E
authors.lastname: Lüllwitz
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Münte
authors.forename: Siegfried
authors.initials: S
authors.lastname: Piepenbrock
mesh_terms: D000161:Acoustic Stimulation; D000328:Adult; D015760:Alfentanil; D000769:Anesthesia, Inhalation; D000771:Anesthesia, Intravenous; D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D003071:Cognition / Q000187:drug effects; D005260:Female; D006801:Humans; D007403:Intervertebral Disc / Q000601:surgery; D007432:Intraoperative Period / Q000523:psychology; D008297:Male; D008568:Memory / Q000187:drug effects*; D008606:Mental Processes / Q000187:drug effects; D011939:Mental Recall / Q000187:drug effects / Q000502:physiology; D009609:Nitrous Oxide; D019637:Orthopedic Procedures; D015742:Propofol; D018401:Sample Size
chemical_list: D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D015760:Alfentanil; D009609:Nitrous Oxide; D015742:Propofol