He was able to answer five out of six questions, the researchers reported, adding it was unclear why he was unable to answer the sixth but no brain activity was seen in response to the question.
Outside experts also cautioned against over-interpreting the results.
"The percentage of patients showing a response was low, and longer-term follow up studies are needed to determine whether such fMRI findings by themselves have meaningful predictive value," said Dr. Alan Faden, a neurologist at the University of Maryland School of Medicine in Baltimore. "Use of fMRI is not likely to become standard for evaluation of these subjects but rather probably will be used in selected patients in centers with research interests."
Dr. Steven Flanagan, medical director of the Rusk Institute of Rehabilitation Medicine at the New York University Langone Medical Center, said the legal implications of the study were "a mess," as the study still leaves some key questions about consciousness unanswered.
"It remains impossible to say to families that their loved [ones] are definitively not there; this study certainly supports that we cannot say this," he said. "However, less than 5 percent showed activation, and only those who sustained TBI [traumatic brain injury] had activation. No one with global ischemia or anoxic brain injury did."
And then there is the quality of the awareness, Flanagan said.
"Presuming someone can imagine themselves playing tennis cannot be interpreted as awareness of their condition, prognosis, quality of life, et cetera."
Faden said that the technology may one day have even bigger implications for medical practice. Once it improves, it will likely mean that doctors will have to modify their diagnostic categories for what he called "states of diminished consciousness."
And in an accompanying editorial in the journal, Dr. Allan Ropper of Brigham and Women's Hospital in Boston wrote that such research is "easily subject to over-interpretation and sensationalism."
He cautioned that brain activation was seen only in a few patients and only in those with a traumatic brain injury, rather than global ischemia and anoxia.
Additionally, he wrote, the brain activity seen in the patients is not evidence of such things as memory, self-awareness, anxiety or despair.
"We cannot be certain whether we are interacting with a sentient, much less a competent, person" Ropper wrote.
Still, Dr. Gregory O'Shanick, president and medical director of the Center for Neurorehabilitation Services in Richmond, Va. and national medical director of the Brain Injury Association of America, said that for some patients, the method could offer even more promise. Specifically, for those 12 patients in the study whose vegetative states were caused solely by traumatic brain injury, the fMRI had a 33 percent "hit" rate in finding those who still exhibited responsive brain patterns.
"The use of this fMRI technology with that specific patient population found that one-third of these patients were misdiagnosed," O'Shanick said. "Sadly, in the setting of anoxia, meningitis or stroke, the message from this specific study is less compelling."
Despite such caveats, the research is "critically important," according to Dr. Michael DeGeorgia, director of the Neurocritical Care Unit at University Hospitals Case Medical Center in Cleveland.
It "illustrates both the complexities of this area and the limitations of our bedside clinical examination," he said in an e-mail, adding that more research will be needed to figure out how to use the technology and how to interpret the results.
The research "does raise difficult medical and legal questions," DeGeorgia said.
"We always need to be upfront and honest with families about what we know for certain and what we do not know for certain," he said. "In many of these cases, the honest answer is that we cannot be absolutely 100 percent certain that their loved one isn't 'in there somewhere.'"