NEW YORK: A brain-damaged man who could communicate only with slight eye or thumb movements for six years can speak again, after stimulating electrodes were placed in his brain, researchers report.

The 38-year-old also regained the ability to chew and swallow, which lets his attendants spoon-feed him rather than providing nourishment through a tube into his belly.

The man suffered brain injury during an assault and spent six years with only occasional signs of consciousness and no useful movement of his limbs. In an experiment, researchers implanted electrodes in his brain for a procedure called deep brain stimulation, which is routinely done for Parkinson's disease and some other illnesses.

They turned the electrodes on and off over six months to test their effect, and report the results in Thursday's issue of the journal Nature. The man, who was not identified at the family's request, now has them turned on throughout the day.

Experts called the report exciting but cautioned that the approach must be tested in more people before its value can be known. The researchers have already begun a study of additional patients.

Before the electrodes were implanted the man was in what doctors call a "minimally conscious state". That means he showed only occasional awareness of himself and the environment. In a coma or vegetative state, by contrast, patients show no outward signs of awareness.

There are no firm statistics on how many Americans are in a minimally conscious state, but one estimate suggests 112,000 to 280,000. Doctors may try medications to improve their condition but no drugs have been firmly established as helpful.

The man described in the Nature study speaks in a breathy but audible voice, said Dr Joseph Giacino, a co-lead author. He does not initiate conversations but can reply to others, typically with one to three words, said Giacino, of the JFK Johnson Rehabilitation Institute in Edison, New Jersey.

Several weeks ago he recited the first half of the Pledge of Allegiance without assistance, Giacino said. The man also recovered some movement. He can demonstrate motions such as brushing his teeth, eating with a fork and drinking from a cup, said study lead author Dr Nicholas Schiff of Weill Cornell Medical College in New York. He can't actually carry out those tasks because the tendons in his arms have contracted after years of immobility.

"He is still totally dependent and severely disabled," Schiff said. But the treatment has helped him, the man's mother said in a statement. "Now, my son can eat, express himself and let us know if he is in pain. He enjoys a qualify of life we never thought possible," she said.