Is there postoperative evidence of implicit learning following aural stimuli at moderate hypnotic BIS levels during...

Patients may develop behavioral changes after the administration of a general anesthetic without a triggering stimulus. This phenomenon, referred to as implicit learning, continues to be debated. Some researchers have denied the phenomenon takes place, while others have demonstrated behavioral changes not related to recall. In previous studies it was difficult to determine the effects of taped messages or suggestions, as anesthesia techniques were not standardized, and true depth of anesthesia was impossible to determine. The development of bispectral index (BIS) monitoring allows practitioners to determine the depth of anesthesia based on neuronal activity. In the present study, we compared 2 randomized groups of patients from a convenience sample of patients scheduled to undergo elective spinal surgery at a Department of Veterans Affairs Medical Center. All patients were screened for normal hearing acuity. The control group listened to tapes of white noise, while the experimental group listened to a word list and short story selection. Both groups listened to the tapes at similar BIS levels. A posttest was administered to determine explicit recall, as well as implicit memory formation. No patients had explicit recall. There was no difference in the implicit memory scores between patients in the experimental group and the control group.