Vaughan Bell is a clinical and research psychologist based at the Institute of Psychiatry, King’s College London and currently working in Colombia. He’s also working on a book about hallucinations due to be out in 2013.
During surgery, a patient awakes but is unable to move. She sees people dressed in green who talk in strange slowed-down voices. There seem to be tombstones nearby and she assumes she is at her own funeral. Slipping back into oblivion, she awakes later in her hospital bed, troubled by her frightening experiences.
These are genuine memories from a patient who regained awareness during an operation. Her experiences are clearly a distorted version of reality but crucially, none of the medical team was able to tell she was conscious.
This is because medical tests for consciousness are based on your behavior. Essentially, someone talks to you or prods you, and if you don’t respond, you’re assumed to be out cold. Consciousness, however, is not defined as a behavioral response but as a mental experience. If I were completely paralyzed, I could still be conscious and I could still experience the world, even if I was unable to communicate this to anyone else.
This is obviously a pressing medical problem. Doctors don’t want people to regain awareness during surgery because the experiences may be frightening and even traumatic. But on a purely scientific level, these fine-grained alterations in our awareness may help us understand the neural basis of consciousness. If we could understand how these drugs alter the brain and could see when people flicker into consciousness, we could perhaps understand what circuits are important for consciousness itself. Unfortunately, surgical anesthesia is not an ideal way of testing this because several drugs are often used at once and some can affect memory, meaning that the patient could become conscious during surgery but not remember it afterwards, making it difficult to do reliable retrospective comparisons between brain function and awareness.
An attempt to solve this problem was behind an attention-grabbing new study, led by Valdas Noreika from the University of Turku in Finland, that investigated the extent to which common surgical anesthetics can leave us behaviorally unresponsive but subjectively conscious.
Of all the sentences you never want to read from scientists running a study of a promising new medical treatment, high on the list has got to be, “the trial was terminated early for futility.”
Yet there it is, describing what happened when researchers assessed a surgical procedure that had “slam dunk” written all over it. The idea was to take patients who had complete blockages of the internal carotid artery, which carries blood to the brain, with the not-surprising result that they had insufficient blood flow to the brain. The patients had also had at least one transient ischemic attack (TIA), or “mini-stroke,” as a result of blood supply to a part of the brain being temporarily reduced or blocked altogether. Half the patients in the study received standard medical treatment, such as aspirin and other anti-clotting drugs plus anti-hypertension drugs, while the other half got the promising surgery: bypassing the blocked carotid, in the neck, with an artery in the scalp. Surely, went the rationale, steering blood around a blockage would lower the subsequent stroke rate. Expectations were high: leaders of the Carotid Artery Occlusion Surgery Study (COSS) projected that there would be 40 percent fewer strokes on the same side as the blockage in patients who had the surgery.
The experimental surgery was nifty but not effective.
Courtesy of Powers, et al., and JAMA
Not so much. In yet another example of how human biology continues to thwart what seems like compelling medical logic (more on which below), the 97 patients receiving the surgery had no fewer strokes than the 98 receiving standard medical care, the COSS team reports in the Journal of the American Medical Association. Things began to go south early. After one month, 14 of the 97 surgery patients had another stroke, compared to 2 of 98 controls. After 2 years, things merely evened out: 20 patients in each group had had a stroke. (A 1985 trial of the surgery had also shown no benefit, in 808 patients.) At that point, the Data Safety Monitoring Board advised halting the trial, which was done in June 2010. (It seems small comfort that if you survived your first month post-surgery without a stroke, your risk of subsequent stroke fell by about 75 percent.) Bypass, concluded the COSS researchers, “provided no additional benefit over medical therapy for preventing recurrent stroke.”