WASHINGTON -- Scientists in North Carolina have built a brain implant that lets monkeys control a robotic arm with their thoughts, marking the first time that mental intentions have been harnessed to move a mechanical object.
The technology could someday allow people with paralyzing spinal cord injuries to operate machines or tools with their thoughts as naturally as others do with their hands. It might even allow some paralyzed people to move their arms or legs again, by transmitting the brain's directions not to a machine, but to the muscles in those latent limbs.
The brain implants could also allow scientists or soldiers to control, hands-free, small robots that could perform tasks in inhospitable environments or war zones.
In the new experiments, monkeys with wires running from their brains to a robotic arm were able to use their thoughts to make the arm perform tasks. Before long, the scientists said, they will upgrade the monkeys so they can transmit their mental commands to machines wirelessly.
"It's a major advance," University of Washington neuroscientist Eberhard E. Fetz said of the monkey studies. "This bodes well for the success of brain-machine interfaces."
The experiments, led by Miguel A. L. Nicolelis of Duke University in Durham, N.C., and published today in the journal PLoS Biology, are the latest in a progression of increasingly science fictionlike studies in which animals -- and in a few cases people -- have learned to use the brain's subtle electrical signals to operate simple devices.
Until now, those achievements have been limited to "virtual" actions, such as making a cursor move across a computer screen, or to small two-dimensional actions such as flipping a little lever that is wired to the brain.
The new work is the first in which any animal has learned to use its brain to move a robotic device in all directions and to perform interrelated movements, such as reaching for an object, grasping it, and adjusting the grip strength depending on how heavy the object is.
"This is where you want to be," said Karen A. Moxon, a professor of biomedical engineering at Drexel University in Philadelphia. "It's one thing to be able to communicate with a video screen, but to move something in the physical world is a real technological feat. And Nicolelis has taken this work to a new level by quantifying the neuroscience behind it."
The device relies on tiny electrodes, each resembling a wire thinner than a human hair. After removing patches of skull from two monkeys to expose the outer surface of their brains, Nicolelis and his colleagues stuck 96 of those tiny wires about a millimeter deep in one monkey's brain and 320 in the other animal's brain.
The monkeys were unaffected by the 10-hour surgery, Nicolelis said. But now they have tufts of wires protruding from their heads, which can be hooked up to other wires that ran through a computer and on to a large mechanical arm. Then came the training, with the monkeys first learning to move the robot arm with a joystick. The arm was kept in a separate room -- "If you put a 50-kilogram robot in front of them, they get very nervous," Nicolelis said -- but the monkeys could track their progress by watching a schematic representation of the arm and its motions on a video screen.
The monkeys quickly learned how to use the joystick to make the arm reach and grasp for objects and how to adjust their grip on the joystick to vary the robotic hand's grip strength. They could see on the monitor when they missed their target or dropped it from having too light a grip, and were rewarded with sips of juice.
While the monkeys trained, a computer tracked the patterns of bioelectrical activity in the animals' brains. The computer figured out that certain patterns amounted to a command to "reach." Others meant "grasp." Gradually, the computer learned to "read" the monkeys' minds.
Then the researchers did something radical: They unplugged the joystick so the robotic arm's movements depended completely on a monkey's brain activity. In effect, the computer that had been studying the animal's neural firing patterns was now serving as an interpreter, decoding the brain signals according to what it had learned from the joystick games and sending the appropriate instructions to the mechanical arm.
At first, Nicolelis said, the monkey kept moving the joystick, not realizing her brain was now solely in charge of the arm's movements. Then, he said, an amazing thing happened.
"We're looking, and she stops moving her arm," he said, "but the cursor keeps playing the game and the robot arm is moving around."
The animal was controlling the robot with its thoughts.
"We couldn't speak. It was dead silence," Nicolelis said. "No one wanted to verbalize what was happening. And she continued to do that for almost an hour."
At first, the animals' performance declined compared with the joystick sessions. After a day or so, the control was so smooth it seemed the animals had accepted the mechanical arm as their own.
"It's quite plausible that the perception is you're extended into the robot arm or the arm is an extension of you," agreed the University of Washington's Fetz, a pioneer in the field of brain-controlled devices.
John P. Donoghue, a neuroscientist at Brown University developing a similar system, said paralyzed patients would be the first to benefit by gaining an ability to type and communicate on the Internet, but the list of potential applications is endless, he said. The devices might allow quadriplegics to move limbs again by sending signals from the brain to various muscles, leaping over the severed nerves that caused their paralysis.
"Once you have an output signal out of the brain that you can interpret, the possibilities of what you can do with those signals are immense," said Donoghue, who cofounded a Foxborough-based company, Cyberkinetics Inc., to capitalize on the technology.
Both he and Nicolelis hope to get permission from the Food and Drug Administration to begin experiments on people next year. Nicolelis also is developing a system that would transmit signals from each of the hundreds of brain electrodes to a portable receiver, so his monkeys -- or human subjects -- could be free of external wires and move around while they turn their thoughts into mechanical actions.
"It's like multiple cellular phone lines," Nicolelis said. "As my mother said, `You can dial your brain now.' "
Significant challenges remain if the technology is to find widespread application in people. Although earlier experiments suggest the electrodes are safe and continue functioning for three years or more, longer-term safety studies are needed, and implants with far more electrodes might be required to accomplish anything more than the simplest tasks.
"For something basic like grasping a cup of coffee or brushing your teeth, apparently you could do almost all of this with this kind of prosthesis," said Idan Segev, director of the center for neurocomputation at Hebrew University in Jerusalem. "If you were a pianist and had a spinal cord injury and you wanted to play Chopin again, then 500 neurons is not enough." Still, Segev was astonished at how much the monkeys were able to do with signals from only a few hundred of the brain's 100 billion or so nerve cells -- evidence, he said, that "the brain uses a lot of backup and a lot of redundancy."
That may explain one of the more interesting findings of the Duke experiments, he and others said: That neurons not usually involved in body movements, including those usually involved in sensory input rather than motor output, were easily recruited to help operate the robotic arm when electrodes were implanted there.