Researchers used an EEG machine to examine brain waves and found that three of 16 vegetative patients could understand what they heard and follow instructions.
EEG machines are far more common and less expensive than the large functional MRI scanners that have shown awareness in some vegetative patients in previous studies. So they could be set up in a patient's room, avoiding logistical problems that can make it dangerous or impossible to have a vegetative patient scanned at an fMRI facility, researchers said.
"We can take this assessment out into the community, to the patients. … We can go to that bedside and find out what level of awareness they still have," said Damian Cruse, of the University of Western Ontario in Canada, an author of the report.
The technique might also provide a way for some vegetative patients to communicate. That could enable them to participate in their treatment planning, express whether they're in pain, and allow researchers to explore what other mental abilities they have, Cruse and colleague Adrian Owen said in a telephone interview.
But Owen stressed the technique needs further development before it can be used routinely.
The research was published online Wednesday by the journal Lancet.
In a vegetative state, patients are unconscious and unaware of themselves and others, although their eyes are open and they may react reflexively when startled. Nobody knows how many vegetative patients live in hospitals and centers for rehabilitation or long-term care.
The diagnosis is made with tests of patients' behavior, such as whether they can follow a moving object with their eyes, follow commands or show even a rudimentary ability to communicate.
The EEG test involved attaching a tight-fitting cap to each patient's skull with electrodes to monitor brain waves. Patients were told to imagine squeezing their right hand into a fist or wiggling their toes on both feet whenever they heard a tone. Those mental activities were chosen to create a detectable brain wave signal.
Soon after the instructions were given, tones started sounding several seconds apart, and the EEG machine looked for a response to each one. Each patient was asked to imagine both kinds of movement at different times during the assessment.
The researchers noted that three of 12 healthy volunteers failed to produce a detectable brain wave signal in response to the commands. It's not clear why, but that shows that if a vegetative patient doesn't produce such a signal, it doesn't necessarily indicate a lack of awareness, the researchers said.
The positive EEG results with the three patients do show some degree of self-awareness that indicate they weren't truly vegetative, Dr. James Bernat wrote in an email. He's a neurology professor at Dartmouth Medical School and a spokesman for the American Academy of Neurology.
Dr. Joseph Giacino, director of rehabilitation neuropsychology for the Spaulding Rehabilitation Hospital in Boston, who didn't participate in the research, called the results "a really important first step." But he said the EEG technique must prove itself in further research before it can be used routinely.
He also said he saw it as a potential addition to current diagnostic tests rather than a replacement.
A positive result could indicate a need to try rehabilitation, or a longer stay at a rehabilitation hospital than the patient might otherwise get, Giacino said. And it could spur doctors to try to find a way to let the patient communicate, he said.
Dr. Paul Matthews, a professor of clinical neurosciences at Imperial College in London, said in a statement that the study leaves some questions unanswered. It's not clear whether patients who give a positive signal in one testing session will continue to do so later on, he said, nor do scientists know what a positive signal means for likelihood of a substantial recovery.
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