Implicit memory formation in children during anesthesia

Abstract

Aim: To determine whether there is implicit memory formation in children during anesthesia.Background: Previous work with adults has found that cognitive processing may persist despite clinically adequate anesthesia, resulting in the formation of implicit memories that cannot be consciously recalled but may be revealed by changes in behavior [1]. Because of methodological limitations in the few pediatric studies that have been conducted, it remains unclear whether this also occurs in children [2,3]. Implicit memories may play a role in postoperative negative behavior changes in children [4].Methods: The ‘degraded auditory stimulus recognition task’ has been validated for the detection of implicit memories in a pediatric anesthetic setting [5]. Three hundred and twelve children, aged 5 to 12 years old, were randomly assigned to be played either a sheep sound or white noise continuously through headphones during general anesthesia. On recovery, children were played a sheep sound degraded by a white noise mask that progressively decreased over 60 s, with the outcome being time taken to correctly recognize the sound.Results: Three hundred children completed the task. A comparison of the distribution of recognition times between the two groups found little evidence that intraoperative exposure to a sheep sound was associated with postoperative time to recognition of a degraded sheep sound (hazard ratio 1.14, 95% confidence interval of 0.90–1.40, P = 0.28).Conclusions: No evidence was found for implicit memory formation in children during anesthesia. It is increasingly likely that the clinical implications of this phenomenon are less of a concern for pediatric anesthetists.References 1 Andrade J, Deeprose C. Unconscious memory formation during anaesthesia. Best Pract Res Clin Anaesthesiol 2007; 21(3):385‐401.2 Andrade J, Deeprose C, Barker I. Awareness and memory function during paediatric anaesthesia. Br J Anaesth 2008; 100(3):389‐96.3 L opez U, Habre W, Laurencon M, Willems SJ, Schmidt C, Van der Linden M et al. Does implicit memory during anaesthesia persist in children? Br J Anaesth 2009; 102(3):379‐84.4 Stargatt R. A cohort study of the incidence and risk factors for negative behavior changes in children after general anesthesia. Paediatr Anaesth 2006; 16(8):846‐59.5 Phelan L, Sheppard SJ, Davidson AJ. A new degraded auditory stimulus test to measure implicit memory during anaesthesia in children. Anaesth Intensive Care 2009; 37(1):60‐5.