Comparing the effects of stimulation and propofol infusion rate on implicit and explicit memory formation

Doubt remains about the conditions under which learning persists despite an aesthesia. This study investigated the relative importance of dose of anaes thetic and stimulation for learning during propofol infusion before surgery . Thirty-six patients were randomly assigned to three groups. Group 1 recei ved two word lists (category examples and nonsense words) during infusion o f propofol to a target concentration of 2 mug ml(-1). Groups 2 and 3 receiv ed the word lists during infusion of propofol 5 mug ml(-1). Group 2 receive d nonsense words before tracheal intubation and category examples during in tubation; Group 3 heard category examples before and nonsense words during intubation. Bispearal index was recorded as a measure of depth of sedation/ anaesthesia. We assessed explicit memory on recovery using a structured int erview and a recognition test. We assessed implicit memory using a category generation test and a preference rating task. To establish baseline, a con trol group of 12 patients completed the category generation test without re ceiving the category examples during anaesthesia. Overall, there was no evi dence for learning during propofol infusion, though the category generation task showed a trend towards more implicit memory for words presented durin g intubation than during anaesthesia. We conclude that learning does not oc cur during anaesthesia without surgery.