Philip M. Merikle
Department of Psychology
University of Waterloo
Waterloo, Ontario, Canada N2L 3G1
pmerikle@watarts.uwaterloo.ca
Meredyth Daneman
Department of Psychology
Erindale College
University of Toronto
Mississauga, Ontario, Canada L5L 1C6
daneman@psych.utoronto.ca
Studies investigating memory for events during anesthesia show a confusing pattern of positive and negative results. To establish whether there are any consistent patterns of findings across studies, we conducted a meta-analysis of the data from 2517 patients in 44 studies. The meta-analysis included two measures of the effects of positive suggestions on postoperative recovery: (a) the duration of postoperative hospitalization; and (b) the amount of morphine administered via patient-controlled anesthesia; as well as two measures of memory for specific information presented during anesthesia: (c) direct tests, and (d) indirect tests. The meta-analysis indicated that positive suggestions presented during anesthesia have little or no effect on postoperative recovery. On the other hand, the meta-analysis showed that specific information is remembered following surgery, as long as testing is not delayed longer than 36 hours. Studies of memory for events during anesthesia provide a useful avenue for exploring unconscious cognition.