title: Implicit memory formation during routine anesthesia in children: a double-masked randomized controlled trial.
abstract: BACKGROUND
  Implicit memory cannot be consciously recalled but may be revealed by changes in behavior. There is evidence for implicit memory formation during anesthesia in adults, but several studies in children have found no evidence for implicit memory. This may be due to insensitive testing. Also many of these tests were undertaken under controlled conditions. It remains unknown whether implicit memory is formed during routine pediatric anesthesia. The aim of this study was to determine whether there is evidence of implicit memory formation during routine anesthesia in children, using a degraded auditory stimulus recognition task.
  
  
  METHODS
  Three hundred and twelve children, aged 5-12 yr, were randomly assigned to be played either a sheep sound or white noise continuously through headphones during general anesthesia. No attempt was made to standardize the anesthetic. On recovery, children were played a sheep sound degraded by a white noise mask that progressively decreased over 60 s, with the outcome being the time taken to correctly recognize the sheep sound.
  
  
  RESULTS
  Three hundred children completed the task. A comparison of the distribution of recognition times between the two groups found little evidence that exposure to a sheep sound during anesthesia was associated with postoperative time to recognition of a degraded sheep sound (hazard ratio 1.14, 95% CI of 0.90-1.43, P = 0.28).
  
  
  CONCLUSIONS
  No implicit memory formation during routine anesthesia was demonstrated in children. It is increasingly likely that the potential clinical implications of implicit memory formation are less of a concern for pediatric anesthetists.
authors.affiliation: Department of Paediatrics, University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Xiuzhi
authors.initials: X
authors.lastname: Pham
authors.forename: Katherine R
authors.initials: KR
authors.lastname: Smith
authors.forename: Suzette J
authors.initials: SJ
authors.lastname: Sheppard
authors.forename: Carolyn
authors.initials: C
authors.lastname: Bradshaw
authors.forename: Eric
authors.initials: E
authors.lastname: Lo
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Davidson
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000758:Anesthesia / Q000379:methods*; D002648:Child; D002675:Child, Preschool; D004311:Double-Blind Method; D005072:Evoked Potentials, Auditory / Q000502:physiology; D005260:Female; D006801:Humans; D007432:Intraoperative Period; D008297:Male; D008568:Memory / Q000502:physiology*; D011939:Mental Recall / Q000502:physiology; D013997:Time Factors