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COLUMBIA-PRESBYTERIAN MEDICAL CENTER
UNCONSCIOUS MEMORIES CAN BE CONDITIONED UNDER GENERAL ANESTHESIA
Raises possibility of improving postoperative outcomes
ORLANDO, FLA., NOVEMBER 11, 1997 -- A Columbia-Presbyterian Medical Center study has demonstrated that patients under general anesthesia are capable of processing certain types of auditory information such as word-pair associations.
The findings, to be presented in a poster session today at the annual meeting of the American Heart Association in Orlando, Fla., raise the possibility that words or music played during surgery can be used to condition patients to respond better during recovery.
In the study, open-heart surgery patients were randomized to hear an audiotape of one of two different lists of 15 highly associated word pairs, such as boy-girl, table-chair, and always-never. The lists were delivered over headphones and repeated continuously throughout surgery.
An average of four days after the operation, the patients were given the first half of each word pair from both lists and asked to free associate, that is, to respond with the first word that came to mind. The patients were also asked a series of questions to determine whether they had any explicit, or conscious, memories of the operation or of the word pairs.
"We found strong evidence of implicit memory," says David C. Adams, MD, Assistant Professor of Anesthesiology at Columbia-Presbyterian and the principal investigator of the study. According to the researcher, during the free-association test, patients made significantly more correct matches with the word pairs that they had heard during surgery than they made with with ones they had not heard. In addition, there was no evidence of explicit memory, suggesting that the unconscious memories of the word pairs were not affected by conscious learning during the operation.
The study is part of a multi-phase investigation into unconscious memory processing. In the first phase, the researchers demonstrated that auditory processing occurs in patients under general anesthesia. In this experiment, patients undergoing open-heart surgery were subjected to auditory stimuli (clicks) while their brainwaves were measured. In all cases, the patients' EEGs responded to the clicks, demonstrating at least some level of cerebral processing during the operation. The response was highest immediately after the patients were put under anesthesia and lowest when they were cooled and placed on cardiopulmonary bypass. The responses grew as the patients were taken off bypass and rewarmed.
In phase two -- the current study -- the researchers demonstrated that this level of processing is sufficient for implicit memory processing.
"In the next phase," says Mehmet C. Oz, MD, Irving Assistant Professor of Surgery at Columbia-Presbyterian and a member of the research team, "we will try to determine whether we can affect the patient's recovery by what we do in the OR. For instance, can we lessen postoperative pain or depression."
The team hopes eventually to test whether involuntary responses, such as heart rhythm or rate of bleeding, can be influenced by intraoperative conditioning. "There are some reasonable studies in which blood loss was reduced, compared to control groups, by playing audiotapes directing the patient to reduce blood flow. It opens an entire array of research," says Dr. Oz.
However, before the researchers get to these phases, they intend to examine whether there might be certain times during anesthesia when patients are more susceptible to conditioning. They will also determine which kinds of audiotapes are most effective: words, music, music with background words, or words with background music.
Other members of the research team are H. John Hilton, PhD, Postdoctoral Research Scientist in Psychology at Columbia University; John D. Madigan, BA, a medical student at Columbia University's College of Physicians & Surgeons; Nicholas J. Szerlip, BA, Research Associate in Psychology at Columbia; Lynn A. Cooper, PhD, Centennial Professor of Psychology at Columbia; and Ronald Emerson, MD, Associate Professor of Clinical Neurology and of Clinical Pediatrics. The surgical team included Craig R. Smith, MD, Chief of Cardiothoracic Surgery; Eric A. Rose, MD, Chairman of Surgery; and Dr. Oz.
Contact: Karin Eskenazi , 212/305-5587
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