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03-06-2010 | Anaesthesiology | Article

Implicit memory formation ‘unlikely’ in pediatric anesthesia


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MedWire News: Children are very unlikely to form implicit memories while under general anesthesia, show randomized trial results.

Implicit memories cannot be consciously recalled, but influence feelings and behavior nonetheless. Implicit memory is thought to be present and stable from the age of 3 years.

Awareness (explicit memories) during anesthesia is believed to be a greater problem among children than adults, so Andrew Davidson (Royal Children’s Hospital, Parkville, Australia) and colleagues aimed to determine if the same was true for implicit memories.

The team enrolled 300 children, aged between 5 and 12 years, who were due to undergo general anesthesia. Before the procedure, the researchers familiarized the children with a “degraded auditory stimulus recognition task.” In this task lasting 60 seconds, white noise gave way to a familiar sound – a cow noise, in this case – and the children identified the sound as soon as they were able.

The children were then randomly assigned to two groups. Children in one group were played white noise while under general anesthesia; children in the other group heard a sheep noise. Variables including the delivery and depth of anesthesia were left to the discretion of the anesthetist.

“The reason for doing this was that we wished to determine whether implicit memory is formed during routine or real-life pediatric anesthesia,” say Davidson et al.

After the operation, the children again performed the degraded auditory stimulus recognition task, with the noise this time being a sheep’s. Both groups took a median of 22 seconds to identify the sheep noise, the researchers report in the journal Anesthesiology.

Children in the sheep group were a nonsignificant 14% more likely to recognize the sheep sound faster than those in the white noise group. This effect was weakened further after accounting for the children’s age, which itself was strongly associated with time taken to identify the sheep noise.

Duration of anesthesia differed significantly between the two groups, but did not affect children’s recognition of the sheep noise.

Twenty-two (14.9%) children reported dreaming while under anesthesia. Six (2%) reported memories that suggested intra-operative awareness.

“Although implicit memory tests are not without limitations, this result does add to the increasing body of evidence suggesting implicit memory formation is unlikely to be relevant to pediatric anesthesia,” conclude the researchers.

MedWire ( is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010

By Eleanor McDermid