Category generation testing in the search for implicit memory during general anaesthesia

Abstract

We gave auditory examples of two semantic categories through headphones to 100 surgical patients anaesthetized with propofol and enflurane. This presentation was made during certain stages of the procedure, potentially associated with arousal, and during steady-state anaesthesia. Postoperative review using category generation tests showed successful priming in a pre-induction group but no evidence of implicit memory in the anaesthetized groups. These results suggest that timing an auditory input to coincide with surgical stimulation does not increase the probability of retrieval of information by this type of testing.

Unconscious learning during surgery with propofol anaesthesia † †This article is accompanied by Editorial II

“…MacRae, Thorp, and Millar presented category examples (e.g.`peach, grape, melon') during different phases of the anaesthetic procedure, including periods associated with arousal, for example immediately after the ®rst incision. 30 Postoperative memory testing revealed no learning during any phase of the anaesthetic procedure. They did not measure depth of anaesthesia, so it is not possible to judge whether the discrepancy between their results and ours is because of deeper anaesthesia in their study.…”