Scientists have managed to communicate with a brain-damaged patient who was thought to be in a vegetative state following a road accident seven years ago.
The 29-year-old answered "yes" and "no" to questions during the experiment by communicating via his thoughts.
He conjured up imaginary scenes while undergoing a brain scan as part of the tests by British and Belgian researchers.
The Belgian man has shown no sign of being aware of the outside world after he suffered serious head injuries in a road accident in 2003.
In 2008, doctors presumed he had slipped into a vegetative state after being in a coma.
The researchers now know that the diagnosis was wrong. The man was able to respond to questions about his life as scientists monitored activity in his brain.
Today they admitted to being "astonished" by the result, which has enormous implications for the care and treatment of vegetative patients.
The study was published today in the New England Journal of Medicine.
Commenting on the results, Professor Chris Frith, a leading neuropsychologist from the Wellcome Trust Centre for NeuroImaging at University College London, said: "Adrian Owen and his group have previously used brain imaging measures to show that a patient in a vegetative state was conscious.
"They have now gone a huge step further and shown that a patient previously assumed to be in a vegetative state could use his thoughts, as reflected in brain activity, to give yes or no answers to questions. This is even stronger proof of consciousness."