A new degraded auditory stimulus test to measure implicit memory during anaesthesia in children

It remains unclear whether children form implicit memories during general anaesthesia. This is partly due to a lack of tests for implicit memory that are appropriate for the anaesthesia setting. The aim of this study was to assess a new implicit memory test that could be more suitable for use with children during anaesthesia. Ninety-three children aged five to 12 years who were undergoing elective surgery were studied. Patients were randomly assigned to one of two groups preoperatively and exposed to a familiar animal sound, followed by a distractor task. Two animal sounds were tested; in one group children were exposed to one animal sound preoperatively, while in the other group they were exposed to the other. After surgery the children were played degraded versions of the animal sounds that had been mixed with white noise and became increasingly clearer over the 60 second recording. Children who explicitly recalled hearing the sound preoperatively were excluded. Response times for recognition were recorded and compared. The analysis revealed evidence for a significant priming effect for one of the two animal sounds tested. The speed and simplicity of administration of this test suggest the degraded auditory stimulus test would be a promising tool to detect implicit memory during anaesthesia in children. However as we found evidence for priming with only one of the sounds, the choice of sound is important.