A crash victim thought to have been in a vegetative state for more than a decade has used the power of thought to tell scientists he is not in pain - by imagining himself playing tennis.
Canadian Scott Routley, from London, Ontario, communicated with researchers via a brain scan, proving that he is conscious and aware.
It is the first time such a severely brain damaged patient has been able to provide clinically relevant information to doctors.
Patients are asked to imagine playing tennis or walking around their home - two thought processes that produce
distinct patterns of activity in different parts of the brain.
By monitoring the activity on an fMRI scanner, the researchers can ask yes or no questions. One type of brain activity is taken as a "yes" and the other as a "no".
British neuroscientist Professor Adrian Owen, who leads the research team at the Brain and Mind Institute of Western Ontario, said: "Scott has been able to show he has a conscious, thinking mind. We have scanned him several times and his pattern of brain activity shows he is clearly choosing to answer our questions. We believe he knows who and where he is."
Prof Owen- who has been dubbed 'the mind reader' - was speaking on a BBC Panorama programme to be broadcast on Tuesday night.
He said the breakthrough could lead to improvements in the treatment of severely brain damaged patients who cannot move or speak.
"Asking a patient something important to them has been our aim for many years," he told the programme.
"In future we could ask what we could do to improve their quality of life. It could be simple things like the entertainment we provide, or the times of day they are washed and fed."
Prof Owen's team uses functional magnetic resonance imaging (fMRI) brain scans to detect hidden awareness in patients and open up channels of communication.
The scans produce images of "active" regions of the brain by tracking the flow of oxygen-rich blood.
Mr Routley suffered traumatic brain injuries when his car was in collision with a police vehicle. Until Prof Owen's intervention, he was assumed to have been in a vegetative state for more than 12 years.
Vegetative state patients are not aware of their surroundings or capable of conscious thought.
Neurologist Professor Bryan Young, from University Hospital in London, Ontario, who has cared for Mr Routley for 10 years, said the scan results overturned all previous assessments of the injured man's condition.
"He had the clinical picture of a typical vegetative patient - no emotional response, no fixation or following with his eyes," said Prof Young.
"He didn't have any spontaneous movements that looked meaningful and I was quite impressed and amazed that he was able to show these cognitive responses with fMRI."
Prof Owen has previously shown that nearly one in five vegetative patients may in fact be conscious.
Another of his patients, road accident victim Steven Graham, was able to answer "yes" when asked if he knew about his two-year-old niece Ceili. Since she born after his car accident, this demonstrated that he was able to create and store memories.
The Panorama team spent more than a year filming several vegetative and minimally conscious patients taking part in pioneering research at the Brain and Mind Institute and Addenbrooke's Hospital in Cambridge.
According to the BBC, in the past two decades, more than 40 vegetative patients have been allowed to die after High Court judges approved the withdrawal of feeding tubes, following a landmark case involving the young Hillsborough victim Tony Bland, who was crushed in the stadium disaster in 1989, suffering terrible brain damage which left him in a vegetative state.
The BBC's Fergus Walsh said in a comment piece for the BBC: "Before any judge decides to sanction the withdrawal of treatment, a thorough behavioural assessment is ordered.
"But they do not ask for brain scans of the type used by neuroscientists in Cambridge and Ontario to search for hidden awareness."
The programme, "The Mind Reader: Unlocking My Voice", airs tonight at 10.35pm on BBC One