Evidence of brain activity raises issues for neurologists.

'Vegetative' patient shows signs of conscious thought

The question of whether outwardly unresponsive patients may in fact be aware of their surroundings is one of the most heated debates in clinical neuroscience, with huge implications for the way such patients are diagnosed and treated. In a remarkable study published last week, researchers report that a patient who meets all the criteria of being in a 'vegetative state' can perform mental tasks on request. But the case highlights the difficulty of probing the mental state of an individual who cannot communicate, and of drawing any general conclusions about his or her condition.

Adrian Owen of the Medical Research Council's Cognition and Brain Sciences Unit in Cambridge, UK, and his colleagues used functional magnetic resonance imaging (fMRI) to scan the brain of a 23-year-old woman left in a vegetative state after a car accident in July 2005. Such patients do not respond to their surroundings, and doctors have always assumed that they are completely unaware of them. Previous brain-scanning studies have failed to detect more than reflex reactions to stimuli such as sound or pain.