Life, Death, and the Middle Ground: What the New Neuroscience Tells Us About Who We Are
The last thing you feel is the brute force of a head-on collision. The paramedics arrive at the scene to find you unconscious, a victim of massive head trauma in a devastating car accident. They rush you to the nearest emergency room, where doctors do everything they can to stem the bleeding and limit the damage to your brain.
Your loved ones arrive at the hospital, and they are told to prepare for the worst. Only time and a battery of neurological tests will reveal the true nature and severity of your injuries. You spend several days in a coma, and then, to the great relief of your family and friends, you open your eyes. Everyone close to you rejoices. They take this development as a sign of recovery—that you can see them, hear them, know that they love you. But the doctors caution that it is too early to know if you will ever recover awareness of your surroundings. Their bedside tests indicate that so far, you have not.
You wake up and fall asleep just like a healthy person. This encourages the people who love you, but it does not prove awareness. Sleep cycles are controlled by your brain stem—the most primitive part of your brain—not by regions involved in conscious perception or thought. Over the next several months, you consistently fail standard neurological tests designed to establish whether you are a thinking, feeling, and aware person. You show no overt behaviors that could be read as willed, voluntary, or responsive. Your doctors see no reason for hope. After five months, they diagnose you as persistently vegetative.
Your case, it turns out, is extraordinary, and—quite harrowingly—you are the only person who knows it. You are, in fact, fully aware of yourself and your surroundings, but you are incapable of making any purposeful movements at all. You cannot even blink your eyes on command. It is the stuff of nightmares—trapped inside a body that you cannot control. Without tools to communicate your thoughts or feelings to loved ones, doctors, or nurses, you feel utterly terrified and alone, cut off from the world. You have no way of knowing whether anyone will ever detect that your mind is still alive, feeling the pain of total isolation.
Can such a catastrophic fate exist? It can, and it has in rare cases, say researchers who are working to scan the brains of patients diagnosed as vegetative.
In July 2005, a 23-year-old English woman was critically injured in a car accident. For a full five months she failed clinical tests of consciousness and her doctors declared her vegetative. Not until half a year after her accident—when researchers in Cambridge, England selected her to take part in a study of brain activity in vegetative patients using state-of-the-art functional magnetic resonance imaging (fMRI)—was her surprising brain activity discovered.
MRI technology uses an extraordinarily powerful magnetic field (often up to 30,000 times stronger than the earth's magnetic field) to align excited water molecules with—or against—the direction of the force. The water molecules absorb or transmit radio waves, producing a pattern detected and analyzed by a computer. Structural MRIs have been producing high-resolution, two- and three-dimensional images of the brain since the 1980s.
Functional MRI scanning, first developed in the early 1990s, has been refined and applied at an astonishing pace. The technology uses an MR signal to measure blood-flow changes by recording shifts in blood-oxygen levels. When activity in a certain part of the brain increases, so does the need for fresh oxygen. Blood rushes in, causing the MR signal to increase. In this way, fMRI technology can reveal which parts of the brain are working and under what circumstances.
The young English patient was placed inside an fMRI scanner, and something remarkable happened. When she heard spoken sentences, and then acoustically matched but meaningless noise sequences, her brain was able to tell them apart, lighting up in telltale language-processing patterns in response to the meaningful sentences.
Lead investigator Adrian M. Owen and the rest of the British and Belgian researchers studying her case were careful to point out that these patterns by themselves were not indisputable evidence of awareness. Studies of "implicit learning and priming," they emphasized in their report, "as well as studies of learning during anesthesia and sleep, have demonstrated that aspects of human cognition, including speech perception and semantic processing, can go on in the absence of conscious awareness."1
But then the truly startling result: Asked to respond to mental imagery commands—first, imagining herself playing tennis, and then picturing herself walking through the rooms of her home—her brain responded instantly and sustained the mental "work" for a full 30 seconds. On screen, her patterns of mental activity were measured by blood traffic to movement and imagery centers in her brain and looked just like a healthy person's.
This extraordinary result led the neuroscientists studying her case to conclude that she was "beyond any doubt...consciously aware of herself and her surroundings." Next to brain scans of 12 healthy volunteers, reported Dr. Owen, "you cannot tell which is the patient's."2 And six months later—one year post-accident—she was able to follow a mirror intermittently to one side, thus joining a relatively new category of patients described as "minimally conscious."
Dr. Owen and his co-investigators have faced intense criticism from fellow neuroscientists who believe that the findings were overstated—that the fMRI results cannot be deemed clear evidence of purposeful mental activity. The crux of detractors' arguments is the idea that words presented to the patient in the imagery tasks—words like "tennis" and "house"—could have triggered her mental response even in the absence of awareness.
Not so, said Owen and colleagues in their spring 2007 response in the journal Science. Such automatic changes in the absence of conscious awareness "are typically transient (i.e., lasting for a few seconds) and, unsurprisingly, occur in regions of the brain that are associated with word processing. In our patient, the observed activity was not transient but persisted for the full 30 [seconds] of each imagery task.... In fact, these task-specific changes persisted until the patient was cued with another stimulus indicating that she should rest. Such responses are impossible to explain in terms of automatic brain processes." What is more, her responses were observed not in the word-processing centers—as would be expected in an unconscious patient—but in "regions that are known to be involved in the two imagery tasks that she was asked to carry out."3
Psychologist Daniel Greenberg proposed the following test of whether the patient had made a conscious decision to cooperate: What would happen, he asked, if investigators "presented a similar noninstructive sentence such as 'Sharleen was playing tennis?'"4 Owen and colleagues addressed Greenberg's question by prompting a healthy volunteer with these sorts of noninstructive statements, and the results were persuasive: No activity was observed in any of the brain regions that had been triggered in the patient or healthy volunteers when they were performing the mental imagery tasks. This result, the researchers argued, reaffirmed their original conclusion that the patient was knowingly following instructions, despite her diagnosis to the contrary.