They said yesterday their study showed the woman was conscious despite her coma-like state, although several experts disagreed.
The researchers stressed that the study was unlikely to shed light on issues such as the controversial case of Terri Schiavo, a Florida woman who spent 15 years in a persistent vegetative state and was allowed to die in March 2005 after a long court battle.
Adrian Owen, a neuroscientist at Britain's Cambridge University and colleagues in Britain and Belgium used functional magnetic resonance imaging, or fMRI, to look at the British woman's brain in action.
The 23-year-old woman who was injured in a car accident had been unresponsive, unable to communicate, and met the clinical criteria for a vegetative state, the researchers said.
They looked at her brain function when listening to sentences such as, ''There was milk and sugar in his coffee.'' The brain scan lit up in very similar ways to those seen in healthy volunteers, Owen's team found.
They then asked the woman to imagine certain acts.
''One task involved imagining playing a game of tennis and the other involved imagining visiting all of the rooms of her house, starting from the front door,'' the researchers wrote.
Her scan lit in virtually the same places as the brains of the healthy volunteers asked to do the same thing.
''These results confirm that ... this patient retained the ability to understand spoken commands and to respond to them through her brain activity, rather than through speech or movement,'' the researchers wrote.
She also clearly intended to cooperate, which ''confirmed beyond any doubt that she was consciously aware of herself and her surroundings,'' they wrote.
''This is unlikely the case for all vegetative patients,'' Owen's team cautioned in their report, published in the journal Science.
Experts noted the woman had relatively little brain damage, and said traumatic brain injury often healed better than injury caused by stroke or heart attack such as Schiavo suffered. Schiavo also had been in her state for far longer than the British woman, allowing for severe deterioration of her brain.
RARE CASE? Dr Ross Zafonte, a brain rehabilitation expert at the University of Pittsburgh School of Medicine, said the study showed a unique way of assessing brain function using scans.
''They raise a whole issue regarding consciousness and how we use this term,'' Zafonte said in a telephone interview.
''Is she just a rare bird? Will we see this on a more common basis?'' Other brain experts were skeptical.
''If this patient is actually conscious, why wouldn't she be able to engage in intentional overt motor acts, given that she had not suffered functional or structural lesion of the motor pathways?'' Lionel Naccache of France's INSERM research institute asked in a commentary published with the report.
He said the patient apparently has ''a rich mental life, including auditory language processing and the ability to perform mental imagery tasks''.
The study points to a need to develop better scans to assess a patient's brain status, Naccache said.
Dr Paul Matthews, a neuroscientist at Britain's Imperial College and University of Oxford, said the study did not demonstrate consciousness.
''Response to stimuli, even complex linguistic stimuli, does not provide evidence of a 'decision' to respond -- withdrawal from an unexpected painful pin prick does not represent a 'decision' to respond,'' he said.
Reuters PB GC0924