The news that a patient in a vegetative state has shown signs of awareness of the outside world, and an ability to perform mental tasks on request (see page 132), marks a turning point in the investigation of these enigmatic medical conditions. It also means that neuroscientists have some serious thinking to do.

The evaluation of vegetative states, in which patients are often 'awake' but show no outward sign that they are aware of themselves or their environment, has always been difficult, simply because of the huge variability in the nature and severity of the brain injuries that underpin them. What is often so heartbreaking for friends and relatives is that the patient's mental quality of life is unknowable.

In the wake of the latest research (A. M. Owens et al. Science 313, 1402; 2006), the inevitable calls for all 'vegetative' patients to be considered internally conscious should not be heeded. This case has little bearing on ethical questions over whether or not the most severe cases should be denied treatment and allowed to die. Clearly, for those with the bleakest prognosis — those who have shown no improvement over a period of at least 12 months and are categorized as being in a 'permanent vegetative state' — the chances of finding any sign of awareness are negligible.

But when considering those at the less severe end of the spectrum, such as the British patient at the heart of the latest research, the new discovery presents a conundrum. Loved ones of similar patients will clamour for a chance to see whether they, too, are capable of similar feats. Clinical neuroscientists should stress that no two vegetative patients are alike, and that this remarkable case may be a one-off.

Unique or not, the discovery blurs the distinction between a vegetative patient and those classed as 'minimally conscious' — showing limited or intermittent interaction with their surroundings. As the patient has reportedly improved since the study was carried out, it is entirely possible that the brain scans simply reflected early signs of her recovery. But with brain scanning of vegetative patients becoming more common (although far from routine), the medical criteria for diagnosing a vegetative condition will have to be scrutinized.

A patient is currently classed as vegetative if there are no outward signs of genuine awareness, rather than simple reflex responses to stimuli such as pain. But although this patient remained inscrutable throughout the study, her brain scans suggested she was picturing herself scampering across a tennis court, or roaming around her home. If such rich internal mental processes are seen in other outwardly vegetative patients, then clinicians should revise their opinion on whether or not these patients are really vegetative at all.

Some clinicians take issue with the use of the word 'vegetative' and the unpleasant imagery it evokes. Replacing it with the term 'outwardly unresponsive' would help to eliminate any confusion over whether internal awareness should be factored into a diagnosis. But the ultimate impact of this discovery will hinge on whether more patients are found to have this sort of inner responsiveness. Then, the issue of what constitutes consciousness in these patients — a question that transcends mere brain imaging — will come alive.