NEW YORK — He was beaten and left for dead in a robbery while walking home one night in 1999. His skull was crushed and his brain severely damaged.

For six years, the man could not speak or feed himself. On occasion he showed signs of awareness, and he moved his eyes or a thumb to communicate. His arms were useless. He was fed through a tube.

But researchers chose him for an experimental attempt to rev up his brain by placing electrodes in it. And here's how his mother describes the change in her son, now 38:

"My son can now eat, speak, watch a movie without falling asleep," she said Wednesday while choking back tears during a telephone news conference. "He can drink from a cup. He can express pain. He can cry and he can laugh.

"The most important part is he can say 'Mommy' and 'Pop.' He can say, 'I love you, Mommy' ... I still cry every time I see my son, but it's tears of joy."

The progress of the patient, who remains unidentified at the family's request, is described more formally in today's issue of the journal Nature.

Experts called the results encouraging but cautioned that the experimental treatment must be tried in more patients before its value can be assessed. The researchers are already proceeding with a larger study.

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 his environment. In a coma or vegetative state, by contrast, patients show no outward signs of awareness.

There are no reliable 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 experimental treatment is called deep brain stimulation. It has been used for years in treating Parkinson's disease, although in this case the electrodes were implanted in slightly different places. The goal of the stimulation was to provide "drive" to areas of the brain that are critical for specific skills such as speaking.

The man described in the Nature paper, despite his improvements, remains severely disabled in a rehabilitation facility for brain injury on the East Coast. (To preserve the man's anonymity, the researchers would not identify the facility or even reveal which state it is in.)

He can't walk. While he has regained the ability to chew and swallow, he must be spoon-fed. He can demonstrate the motion of brushing his teeth, for example, but he can't actually do it. That's because tendons in his arms contracted after years of immobility, said study lead author Dr. Nicholas Schiff of Weill Cornell Medical College in New York.

The man's electrodes are left on for 12 hours a day. He has continued to improve since the experiment formally ended in February 2006, the doctors said.