The unidentified 38-year-old patient had received a traumatic brain injury in an assault that had left him bed-ridden and under 24-hour nursing care, incapable of moving or communicating except with slight movements of the eye or finger.
Reporting in the British journal Nature, the US team used a technique called deep brain stimulation, in which electrodes deliver impulses to the central thalamus, a region that helps adjust brain activity to match cognitive demands.
They used computer-generated maps, image-guided navigation and 3-D mapping of the brain to manoeuvre the electrodes in place with millimetric accuracy and connect them to programmable pacemaker batteries, implanted in the chest.
Sixteen months after the operation, the patient has enjoyed "remarkable and sustained" improvement, said lead author Ali Rezai of the Center for Neurologic Restoration at the Clevic Clinic Foundation, Ohio.
The patient now interacts with family and friends, using words and gestures and responding swiftly to questions.
In addition, he now chews and swallows his food, whereas previously he needed a feeding tube to provide nutrition.
He can also perform some complex movements, including those required for drinking from a cup or brushing hair, although long years of immobility and tendon damage crimp his ability to carry out those tasks, said Joseph Giacino, a neuropsychologist at JFK Johnson Rehabilitation Institute and the New Jersey Neuroscience Institute.
Weill Cornell Medical College in New York, whose physicians also took part in the surgery, quoted the patient's mother as saying that the family had had little hope of any recovery before the operation.
"Now, my son can eat, express himself and let us know if he is in pain. He enjoys a quality of life we never thought possible," she said.
Patients in a so-called minimally conscious state (MCS) may seem comatose but their diagnosis is technically different from people in a coma or persistent vegetative state.
People in MCS show occasional signs of awareness and may even attempt, fleetingly, to communicate using simple sounds or signals.
Such activity points to the existence of a still-functioning brain network in which, in theory, the thalamus would play a key regulatory role.
"Our theory was that electrical impulses targeted to this area would help amplify the existing low level of activity that we thought was already there," said Giacino.
"In other words, we assume that the signals that help drive speech and movement are still present in the brain -- we're just 'bumping up' their efficiency and function, to help get them working better."
Deep brain stimulation is routinely used to improve symptoms among people suffering from Parkinson's disease, and trials are under way in the United States for using it to treat epilepsy, obsessive-compulsive disorder and depression.
This, though, is the first time that it has been used on a patient in MCS. A total of 12 such operations have been authorised by the US Food and Drug Administration in a pilot study.
If the success is replicated, the implants could sweep away conventional ways of perceiving and treating people in MCS, argued Joseph Fins, director of medical ethics at Weill Cornell.
"It will force us to take a second look at each case and -- for appropriate patients -- move away from the therapeutic nihilism that has so plagued this population, most of whom are ignored, receiving what is euphemistically described as 'custodial care'."
In a commentary carried by Nature, US neurologists Michael Shadlen and Roozbeh Kiani cautioned that such intervention could only help those patients who have an undamaged cerebral cortex, which is essential for thought and memory.