Traumatic brain injuries affect 6 million Americans. Of these, 15,000 exist in a persistent vegetative state (PVS), wholly unaware of anything around them, and 14,250 of them will die within five years. Another 280,000 people with traumatic brain injuries linger in a minimally conscious state (MCS), with wavering awareness and a sporadic ability to respond to stimuli. Unfortunately, the number of MCS cases misdiagnosed as PVS may be as high as 40 percent. Because MCS patients have a far better chance of recovering if given the proper treatment, it is crucial to distinguish between them.
Making an indisputable distinction, however, is challenging. Doctors typically rely on easily misinterpreted responses like blinking and other simple movements. Happily, sophisticated new brain-scanning techniques could one day simplify the diagnosis.
“The two conditions [vegetative and minimally conscious] are often lumped together,” says neuropsychologist Joseph Giacino of the JFK Johnson Rehabilitation Institute and the New Jersey Neuroscience Institute. Giacino made headlines recently for restoring some mental function in a 38-year-old man by surgically implanting electrodes in his brain.
Researchers are examining brain activity by means of functional Magnetic Resonance Imagery (fMRI) and positron emission tomography (PET) to differentiate between patients in the two states. The preserved areas of cognitive function in an MCS patient’s brain will be stimulated when he is shown a family portrait or touched or spoken to, indicating at least some mental process. Measuring glucose metabolism in the brain by PET and scanning for changes in blood flow by fMRI, the technique produces a complete picture of brain activity. “In the future, they will be clinical tools that we use to access a person’s inner consciousness,” Giacino says.
Researchers are also using these scans to peer into the brains of vegetative patients. Adrian Owen, a neuroscientist at the Medical Research Council in Cambridge, England, has employed fMRI as a diagnostic tool, examining real-time snapshots of patients being exposed to speech and testing them to see whether they could perform any complex mental tasks. He reported in Science in 2006 on the brain function of a 23-year-old woman left in a vegetative state by a car crash. When he asked her to think about playing tennis, the fMRI scan showed activity in the supplementary motor area, just as in the brains of healthy volunteers.
“There is reason for optimism, as we have evidence from other groups, such as Owen’s,” Giacino says. “But we have a ways to go: We need more data and we need more subjects. Neuroimaging is changing the way we are thinking about consciousness, making us revisit where the threshold of consciousness lies.”
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