More than a decade ago, a 43-year-old woman went to a surgeon for a hysterectomy. She was put under, and everything seemed to be going according to plan, until, for a horrible interval, her anesthesia stopped working. She couldn’t open her eyes or move her fingers. She tried to breathe, but even that most basic reflex didn’t seem to work; a tube was lodged in her throat. She was awake and aware on the operating table, but frozen and unable to tell anyone what was happening.
Studies of anesthesia awareness are full of such horror stories, because administering anesthesia is a tightrope walk. Too much can kill. But too little can leave a patient aware of the procedure and unable to communicate that awareness. For every 1,000 people who undergo general anesthesia, there will be one or two who are not as unconscious as they seem — people who remember their doctors talking, and who are aware of the surgeon’s knife, even while their bodies remain catatonic and passive. For the unlucky 0.13 percent for whom anesthesia goes awry, there’s not really a good preventive. That’s because successful anesthetization requires complete unconsciousness, and consciousness isn’t something we can measure.
There are tools that anesthesiologists use to get a pretty good idea of how well their drugs are working, but these systems are imperfect. For most patients receiving inhaled anesthesia, they’re no better at spotting awareness than dosing metrics developed half a century ago, says George Mashour, a professor of anesthesiology at the University of Michigan Medical School. There are two intertwined mysteries at work, Mashour told me: First, we don’t totally understand how anesthetics work, at least not on a neurological basis. Second, we really don’t understand consciousness — how the brain creates it, or even what, exactly, it is.
Lacking a way to measure consciousness directly, anesthesiologists monitor for proxies of it — the presence of certain types of brain waves, physical responses and sensitivity to pain — and adjust the dosage if they arise. To improve on this method, neuroscientists are searching for what they call neural correlates of consciousness — changes in brain function as a person transitions from being apparently conscious to apparently unconscious. The more they know about these, the better they hope to understand what consciousness is.
Michael Alkire, associate professor of anesthesiology at the University of California, Irvine, was one of the first people involved in the search for neural correlates of consciousness, back in the 1990s. He’s particularly excited now about a study published in August by an international team of researchers based at the University of São Paulo and the University of Wisconsin, Madison. They compared the brain activity of patients from the full spectrum of consciousness — awake, asleep, drugged with anesthetics, in comas or suffering from “locked-in syndrome,” in which the body appears trapped in a comalike state but the brain is active and aware. The researchers stimulated these subjects’ brains with a magnetic field and used EEG to trace the pulse’s path. The brains we might think of as conscious and those we think of as unconscious reacted to the stimulus in distinct ways. “If the patient is awake, the electrical ‘ping’ can travel all around the brain,” Alkire said. “But if they’re unconscious, the ‘ping’ tends to stay localized and just fades away like a sonar blip.”
This finding excites Alkire because it bolsters an existing theory of how consciousness works. Mashour, who also studies neural correlates of consciousness, has repeatedly found evidence that — contrary to conventional wisdom — sensory networks in the brains of unconscious people remain locally functional, but intrabrain communication has broken down. The neighborhood’s lights are on, in other words, but the Internet and phone lines have all been cut.