Dependence of explicit and implicit memory on hypnotic state in trauma patients

Background: It is still unclear whether memory of intraoperative events res ults entirely from moments of inadequate anesthesia, The current study was designed to determine whether the probability of memory declines with incre asing depth of the hypnotic state. Method: A List of words was played via headphones during surgery to patient s who had suffered acute trauma. Several commonly used indicators of anesth etic effect, including the bispectral index, were recorded during word pres entation. First, these indicators served as predictors of the memory perfor mance in a postoperative word stem completion test. Second, general memory performance observed in the first part was separated into explicit and impl icit memory using the process dissociation procedure, and then two models o f memory were compared: One model assumed that the probability of explicit and implicit memory decreases with increasing depth of hypnotic state (indi vidual differences model), whereas the other assumed equal memory performan ce for all patients regardless of their level of hypnotic state. Results: General memory performance declined with decreasing bispectral ind ex values. None of the other indicators of hypnotic state were related to g eneral memory performance. Memory was still significant at bispectral index levels between GO and 40. A comparison of the two models of memory resulte d in a better fit of the Individual differences model, thus providing evide nce of a dependence of explicit and implicit memory on the hypnotic state. Quantification of explicit and implicit memory revealed a significant impli cit but no reliable explicit memory performance. Conclusions: This study clearly indicates that memory is related to the dep th of hypnosis. The observed memory performance should be interpreted in te rms of implicit memory. Auditory information processing occurred at bispect ral index levels between 60 and 40.