Effects of midazolam on explicit vs implicit memory in a pediatric surgery setting

Rationale: Placebo-controlled studies show that midazolam impairs explicit memory in children undergoing surgery (Buffett-Jerrott et al., Psychopharmacology 168: 377-386, 2003; Kain et al., Anesthesiology 93: 676-684, 2000). A recent within-subjects study showed that midazolam impaired explicit memory while leaving implicit memory intact in a sample of older children undergoing painful medical procedures (Pringle et al., Health Psychol 22: 263-269, 2003). Objectives: We attempted to replicate and extend these findings in a randomized, placebo-controlled design with younger children undergoing surgery. Materials and methods: Children aged 3-6 years who were undergoing ear tube (myringotomy) surgery were randomly assigned to receive midazolam (n=12) or placebo (n=11). After surgery, they were tested on explicit (recognition) and implicit (priming) memory for pictures encoded before surgery. Results: Relative to placebo, the midazolam-treated children showed poorer recognition memory on the explicit task but equivalent priming on the implicit task. Conclusions: Overall, it appears that midazolam induces a dissociation between explicit and implicit memory in young children in the pediatric surgery setting. Theoretical and clinical implications of the findings are discussed along with directions for future research.