A 38-year-old man who spent more than five years in a mute, barely conscious state as a result of a severe head injury is now communicating regularly with family members and recovering his ability to move after having his brain stimulated with pulses of electric current, neuroscientists are reporting.

“I still cry every time I see him, but now it’s tears of joy,” said the man’s mother, in a conference call with reporters on Wednesday; her name was withheld, to protect the patient’s privacy. “He can speak, he can watch movies without falling asleep, he can say ‘Mom’ and ‘Pop,’ and ‘I love you, Mommy.’ ”

He eats without the assistance of a feeding tube. He has regained some movement in his arms. When he speaks, usually with only a word or two, he is engaged in the conversation. He recently recited the first 16 words of the Pledge of Allegiance.

The new report, which appears in the journal Nature, provides the first rigorous evidence that any procedure can initiate and sustain recovery in such a severely disabled person, years after the injury occurred. An estimated 100,000 to 300,000 Americans subsist in states of partial consciousness, and most are written off as beyond help.

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.

“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 the study was based on a single patient, and said 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 Terri 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.

For the new study, researchers chose a patient who was responsive to commands, at least occasionally. After being kicked repeatedly in the head during a mugging in 1999, he was sometimes able to move his thumb in response to yes-or-no questions but do little else. He rarely opened his eyes. Yet tests showed that language circuits in the left side of his brain and running through his prefrontal cortex — the rational, conscious areas — were intact.

Brain injuries from blows to the head often sever nerve connections widely throughout the brain but can leave some circuits intact.

Surgeons at the Cleveland Clinic threaded two wires through the man’s skull and into a subcortical area called the thalamus. The wires were connected to a pacemakerlike unit, implanted under the man’s collarbone.

The central part of the thalamus, in particular, projects widely to areas of the brain known to play a role in supporting consciousness, said Dr. Nicholas Schiff, a neurologist at Cornell, who led the study with Dr. Giacino. “One of the key things the procedure is doing is driving neuronal firing rate in this area, which may be driving systems in the cerebral cortex involved in arousal,” Dr. Schiff said.

Soon after the device was turned on, the man showed some improvements. His eyes opened. He became more reliably responsive. Over a period of months, members of the research team then tracked the man’s abilities during stretches when the current was turned on, and periods when it was off, without knowing when the device was activated.

They found a gradual but consistent improvement in speech and movement when the device was on, and a loss of progress when it was off. The researchers received consent to operate from his parents but said that an ethical framework must be developed to accommodate patients like this, whose mental competency could change by the day. The man now has the device turned on 12 hours a day, and is very much a presence in his room, when he was not before.

“He has regained his personhood, his personal agency,” said Dr. Joseph Fins, chief of medical ethics at Cornell, and a study co-author. The patient has amnesia and cannot yet fully represent his interests, Dr. Fins added, “but now he’s got interests to represent.”