In 2003, the man, who is now 29, sustained a severe traumatic brain injury in a road traffic accident. He remained physically unresponsive and was presumed to be in a vegetative state for five years, according to the researchers in Belgium and Britain.

Using functional magnetic resonance imaging (fMRI), the patient's brain activity was mapped while he was asked to answer yes and no questions such as "Is your father's name Thomas?" according to the study results published in the authoritative New England Journal of Medicine.

"We were astonished when we saw the results of the patient's scan. He was able to correctly answer the questions that were asked by simply changing his thoughts, which we then decoded using our fMRI technique," explained Dr Adrian Owen who headed the team from the Wolfson Brain Imaging Centre in Cambridge, England.

The new technique can decode the brain's answers to such questions in healthy, non-vegetative, participants with 100 percent accuracy. But it has never before been tried in a patient who cannot move or speak.

In a three-year study, 23 patients diagnosed as vegetative were scanned in Cambridge and Liege. The new technique was able to detect signs of awareness in four of these cases.

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However the researchers only managed to communicate, in the yes, no fashion, with one of the patients.

"It's early days, but in future we hope to develop this technique to allow some patients to express their feelings and thoughts, control their environment and increase their quality of life," said Dr Steven Laureys of Liege university, who leads the Belgium team.

"For example, patients who are aware, but cannot move or speak, could be asked if they are feeling any pain, allowing doctors to decide when painkillers should be administered," said Liege neuropsychologist Audrey Vanhaudenhuyse.

"This is far-reaching research," Laureys told AFP, while stressing that wider research and more tests on the unresponsive patients was required.

"Now we need to sit down with the multi-disciplinary medical community and legal experts to consider what we are going to do with this," new information which could have ramifications for such areas as assisted suicide.

The findings recall another case involving Dr Laureys which came to light in November.

Rom Houben, a Belgian man who was wrongly diagnosed as comatose for 23 years, is now planning to write a book about his extraordinary story, after Laureys rescued him from isolation.

Since 2006, when his true condition was correctly diagnosed, Houben has regained enough coordination to allow him to use a finger, when aided, to tap out messages on a special computer keyboard.