Deep-brain stimulation offers hope for minimally conscious patients.
Brain function has been improved in a patient who was in a minimally conscious state, by electrically stimulating a specific brain region with implanted electrodes. The achievement raises questions about the treatment of other patients who have been in this condition for years, the researchers say.
Patients in a minimally conscious state, often the result of severe brain trauma, show only intermittent evidence of awareness of the world around them. Typically, they are assumed to have little chance of further recovery if they show no improvement during their initial 12-month rehabilitation programme.
In the latest case study, neuroscientists describe how they implanted electrodes in the brain of a 38-year-old man who had been in a minimally conscious state for more than six years following a serious assault. By electrically stimulating a brain region called the central thalamus, they were able to help him name objects on request, make precise hand gestures, and chew food without the aid of a feeding tube (see page 600). The thalamus is involved in motor control, arousal and in relaying sensory signals — from the visual systems, for example — to the cerebral cortex, the part of the brain involved in consciousness.
Nicholas Schiff of Weill Cornell Medical College in New York, and his colleagues chose the patient because they believed his condititon was due to impairment of the arousal system, and that despite considerable damage to his cerebral cortex, many essential areas were preserved.
There will be a subset of patients who are responsive to this approach.
“There will be a subset of patients who are responsive to this approach,” says Schiff. But he adds that patients with different brain injuries may not benefit from electrostimulation. “Not every patient in a minimally conscious state will fit this profile,” Schiff says, and it is difficult for neurologists to identify those patients who will show recovery.
Nevertheless, the case shows that many patients currently seen as beyond hope of rehabilitation might benefit from the results of further research. “Severe brain injury is not an uncommon problem, and the number of people doing research on this is shockingly small,” Schiff says. “It's very rare to find a programme that will take a patient in a minimally conscious state even straight out of acute care. If they don't respond in a lively enough way and can't communicate and interact with people at the bedside, they go to a nursing home directly.”
“The report does not suggest that deep-brain stimulation [DBS] 'cures' the minimally conscious state,” says Paul Matthews, a clinical neuroscientist at Imperial College, London. “Although based on a study of only a single patient, it suggests that DBS may be adapted to benefit at least some patients in the minimally conscious state. And it emphasizes that improvements can be made by patients even long after an injury.
“Although we do not know precisely which brain connections are important, we may expect that some specific connections must be intact for DBS to have a beneficial effect.”
See also News & Views, page 539 .
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Hopkin, M. Implant boosts activity in injured brain. Nature 448, 522 (2007). https://doi.org/10.1038/448522a