John Donoghue, senior author of the Nature article and chief scientific officer of Cyberkinetics Neurotechnology Systems Inc., the company that makes BrainGate, acknowledged there was room for improvement.

But the technology has gotten even better since his team wrote the article, he said.

Nagle sometimes moved the cursor in a wobbly fashion and overshot his target on the computer screen. Subsequent patients have performed much better because researchers have refined the computer algorithm, Donoghue said.

Other teams of researchers have experimented with an external system that reads brain signals through the scalp - an approach that has the advantage of not requiring surgery. But patients sometimes need weeks or months to learn to operate the scalp-based system, because the signals are not as precise.

Nagle and others with implants have been able to communicate their thoughts immediately, simply by thinking "left," "right," "up," "down."

Still, translating such signals is tricky because millions of neurons are associated with moving the arm, whereas BrainGate's hair-thin electrodes only pick up signals from dozens.

People with spinal-cord injuries are wary of getting their hopes up for every new discovery, but this field is getting some attention. Mark Chilutti, who was paralyzed from the chest down by a gunshot wound, had a one-word reaction to the latest developments: "Wow!"

"When they're ready and working, we're all going to be getting in line," said Chilutti, who now works at Magee Rehabilitation Hospital in Philadelphia, where he was once a patient.

Alisa Brownlee, a technology specialist with the ALS Association of Greater Philadelphia, said: "For years we've been waiting for this brain-wave technology... . It holds exciting potential."

One hitch is that the array of electrodes implanted in Nagle's brain seemed to have suffered a short-circuit toward the end of the 14-month experiment.

The breakdown was not caused by any adverse reaction in the brain itself, Donoghue said. "The barriers to this seem more technological, but surmountable, rather than anything biological," he said. "I'm very encouraged."

When the team develops a wireless device, it would function somewhat like today's cochlear implants, the implantable devices that bypass the inner ear so deaf people can perceive sound.

While the current system allows patients to move computer cursors and prosthetic devices, the researchers hope someday to transmit electrical signals from the brain to a patient's real hands and arms.

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