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EEG Detects Signs of Awareness in Vegetative Patients

Researchers develop a simple way to test whether patients who appear unresponsive truly are.
November 10, 2011

Three brain injury patients diagnosed as being in a vegetative state—meaning they do not respond to their environment—may actually be conscious. Using EEG (electroencephalography) to measure their brain activity, researchers found that the patients could follow simple commands.

Mind reading: Using EEG to measure brain activity, researchers found that some patients diagnosed as being in a vegetative state could respond to simple commands. The pattern of electrical activity in these patients (one example is shown above) is identical to patterns seen in healthy people.

This supports previous findings from the same group suggesting that some people who appear outwardly unresponsive may have a relatively high level of cognitive capacity. Researchers aim to ultimately develop the approach into a communication tool.

In the study, researchers examined 16 patients with brain injury—some due to traumatic injury and others due to lack of oxygen—and 12 healthy people, asking both groups to imagine moving either their hands or toes while wearing an EEG monitor. They found that, like the healthy people, three of the brain injury patients could reliably generate two distinct brain activity patterns based on the command. One patient did it more than 200 times, which is even more than the healthy participants managed.

The team had previously used functional MRI, or brain imaging, to show that a patient diagnosed as being in a vegetative state could use a similar system to answer yes or no questions. That startling finding rocked the medical world, begging the question of how many of these patients had cognitive function beyond what their outward function indicated.

MRI machines are, however, expensive and largely limited to hospitals, making them a difficult tool to study brain injury patients, who are often in rehabilitation or nursing homes. In the new study, researchers used a standard EEG device, which is relatively inexpensive and highly portable. “It’s probably about as sensitive as MRI,” says Adrian Owen, a researcher at the University of Western Ontario, who led the study. “That means we have something we can get out into the community and use in hospitals or residential homes.”

The researchers can detect when someone is thinking about moving a hand versus a toe because the brain activity originates in a different part of the motor cortex, the part of the brain that controls movement. Owen’s team spent much of the last year working out how to accurately decode the electrical signals the brain emits when imaging these movements. The findings of the new study were published this week in The Lancet.

The three patients who could respond via EEG did not share any obvious features; they varied in age, in time since the original injury, and in the type of injury suffered. Owen’s team is now using high-resolution functional MRI machines to study these patients’ brains in fine detail in hopes of finding some commonality. “Anything we can do to improve our understanding or to learn more about catastrophic brain injuries can help us understand what’s going on,” says Owen.

They hope to eventually use the EEG setup to ask patients questions, which had been possible with functional MRI. At the moment, researchers can’t read the EEG response in real time, making interaction very difficult. “Our priority now is trying to speed it up; then we’ll move on to communication,” he says. 

What exactly the new findings indicate about the patients’ level of consciousness is still controversial. “I think they were entirely aware and conscious of what’s going on,” says Owen. “For them to do this, they have to have understood the instructions we gave them, to have sustained attention, to keep on task, and to respond. These are all things we associated with consciousness.”

Morten Storm Overgaard, head of the Cognitive Neuroscience Research Unit at Aalborg University in Denmark, disagrees. “I think their study is very interesting, but it’s hard to argue that there is a link between command-following and consciousness. And there’s no independent way of making sure,” says Overgaard, who wrote a commentary accompanying the paper. Overgaard does agree, however, that someone who can reliably answer questions via brain activity is likely conscious.

Both Overgaard and Owen say a new classification system is required to accurately reflect the state these patients are in. “While they do meet all the clinical criteria for the vegetative state, we know they are not actually vegetative,” says Owen. One suggestion that has yet to catch on is “behavioral unresponsiveness syndrome.”

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