Doctors said it was not clear how many such patients would benefit from the treatment, in which two wire electrodes are implanted deep in the brain. The procedure also raises sticky ethical questions about operating on patients who cannot give their consent, they said.

Image Surgeons implanted electrodes deep into the brain of a gravely injured patient in an effort to stimulate new brain activity. Credit... Cleveland Clinic

“We really see this as a first step, but it should open doors that have not been open before for patients like this,” said Joseph T. Giacino, associate director of neuropsychology at the JFK Johnson Rehabilitation Institute and the New Jersey Neuroscience Institute, in Edison. Dr. Giacino performed the study with doctors from the Weill Cornell Medical College and the Cleveland Clinic Foundation.

Other experts familiar with the case have cautioned that study was based on a single patient, and said that the procedure should be seen as experimental. The researchers, who first described the case last October at the annual meeting of the Society for Neuroscience, say they plan to look at the procedure in 11 other patients as part of a larger study.

Doctors have long used the implant surgery, known as deep brain stimulation, to treat Parkinson’s disease. Over the past two decades they have also performed it on a handful of people with brain injuries, including Terry Schiavo, the Florida woman who died in 2005 after her feeding tube was removed amid a national debate over her care.

But in many of those cases, like Ms. Schiavo’s, the brain was so profoundly damaged that the operation made no difference.