Matthew Nagle lost the use of his limbs following a knife wound that severed his spine in 2001. But in 2004 the 25-year-old regained the ability to transform thought into action with the help of a new, implanted sensor. A similar sensor had previously enabled monkeys to move a computer cursor simply by thinking it across the screen but this marks the first time such a device has been demonstrated in humans. Preliminary results from nine months of tests are reported in today's Nature.

Neurologist Leigh Hochberg of Massachusetts General Hospital and his colleagues--including sensor co-inventor John Donoghue of Brown University--placed the tiny sensor containing 100 electrodes, each thinner than a human hair, onto the surface of Nagle's motor cortex, the part of the brain that governs movement. The sensor registered electrical signals from nearby neurons and transmitted them through gold wires to a titanium base on Nagle's skull. Cables connected this base to a set of computers, processors and monitors.

The hardware assessed the firing of the neurons--sometimes as much as 200 times a second--and converted it into action. After personalizing the array by having Nagle track a cursor moved by a technician, the computers generated a neural cursor that he then used over the course of 57 subsequent sessions to open e-mail, draw circles and play a version of Pong. It also enabled him to open and close the fingers of a prosthetic hand as well as use a robotic arm to pick up pieces of hard candy and drop them into a technician's hand. He could even control his television, all while conversing with those around him.

"What's truly exciting is this: the cortical activity of a person with a spinal cord injurycontrolling a device simply by intending to move his own handis similar to the brain activity seen during preclinical studies of monkeys actually using their hands," Hochberg says. "Whether it is real or attempted movement, neurons seem to respond with similar firing patterns."

Numerous hurdles persist, including an inexplicable malfunction after roughly six months and the need for a less bulky system, but the researchers are confident that emerging technologies can overcome them. And another paper in today's Nature shows how the system could be speedier by simply anticipating the desired end result. Extrapolating from results with two macaque monkeys, Krishna Shenoy of Stanford University and his group achieved neural signal processing speeds that would permit typing at 15 words per minute, fast enough for convenient communication. "Though much work remains to be done," Hochberg adds, "hopefully one day I'll be able to say: 'We have a technology that will allow you to move again.'"