Date: 29 May 2008
Source: New York Times


Monkeys Control a Robot Arm With Their Thoughts

By BENEDICT CAREY

Two monkeys with tiny sensors in their brains have learned to control a prosthetic arm with only their thoughts, using it to reach for and grab food and even to adjust for the size and stickiness of morsels when necessary, scientists reported Wednesday.

The report, released online by the journal Nature, is the most striking demonstration to date of brain-machine interface technology, which scientists expect will eventually allow people with spinal cord injuries and other paralyzing conditions to gain more control over their lives. The findings suggest that brain-controlled prosthetics, while not yet practical, are at least technically within reach.

In previous studies, researchers showed that humans who had been paralyzed for years could learn to control a cursor on a computer screen with their brain waves; and that thoughts could move a mechanical arm, and even a robot on a treadmill.

Yet the new experiment demonstrates how quickly the brain can adopt a mechanical appendage as its own, refining movement as it interacts with real objects in real time. The monkeys in the experiment had their own arms gently restrained while they were learning to use the prosthetic one.

“In the real world things don’t work as expected, the marshmallow sticks to your hand or the food slips, and you can’t program a computer to anticipate all of that,” said the paper’s senior author, Dr. Andrew Schwartz, a professor of neurobiology at the University of Pittsburgh. “But the monkeys’ brains adjusted; they were licking the marshmallow off the prosthetic gripper, pushing food into their mouth, as if it were their own hand.”

Dr. John P. Donoghue, director of the Institute of Brain Science at Brown University, said that the new report “is important because it’s the most comprehensive study showing how an animal interacts with complex objects, using only brain activity.” Dr. Donoghue was not involved in the research.

The researchers, from the University of Pittsburgh and Carnegie Mellon University, first had the two macaque monkeys use a joystick to get a feel for the prosthetic arm, which had shoulder joints, an elbow, and a grasping claw with two mechanical fingers.

Then, inside the monkeys’ skulls, the scientists implanted a small grid, about the size of a large freckle. The grid sat on the monkeys’ motor cortex, over a patch of cells known to signal arm and hand movements. It held 100 tiny electrodes, each connecting to a single neuron, its wires running out of the brain and to a computer.

The computer was programmed to analyze the collective firing of these 100 motor neurons, translate this sum into an electronic command and send it instantaneously to the arm, which was mounted flush with the monkeys’ left shoulder. The scientists used the computer to help the monkeys move the arm at first, essentially teaching them with biofeedback.

After several days, the monkeys needed no help. They sat stationary in a chair, repeatedly manipulating the arm with their brain to reach out and grab grapes, marshmallows and other tasty nuggets dangled in front of them. The snacks reached their mouths about two-thirds of the time — an impressive rate, compared with earlier work. The monkeys learned to hold the grip open on approaching the food, close it just enough to hold the food and gradually loosen the grip when feeding.

On several occasions a monkey kept its claw open on the way back, with the food stuck to one finger. It had apparently learned through experience that it was not always necessary to close the grip, “illustrating the importance of working within a physical environment” as opposed to a virtual one, the researchers concluded. Dr. Schwartz’s co-authors were Meel Velliste, Sagi Perel, M. Chance Spalding and Andrew Whitford.

Scientists must clear several hurdles before this technology becomes practical, experts say. Implantable electrode grids do not generally last more than a period of months, for reasons that are still unclear. The equipment needed to read and transmit the signal is cumbersome, and in need of continual monitoring and recalibrating by technicians. And no one has yet demonstrated a workable wireless system, which would eliminate the need for connections coming through the scalp.

Yet Dr. Schwartz’s team, Dr. Donoghue’s group and others are working on all of these problems, and the two macaque monkeys’ rapid learning curve in taking ownership of a foreign limb gives scientists confidence that the main obstacles are technical and thus negotiable.

In an editorial accompanying the Nature study, Dr. John F. Kalaska, a neuroscientist at the University of Montreal, argues that once such bugs are worked out, scientists may even discover areas of the cortex that allow more intimate, subtle control of prosthetic devices.

Such systems, Dr. Kalaska wrote, “would allow patients with severe motor deficits to interact and communicate with the world not only by the moment-to-moment control of the motion of robotic devices, but also in a more natural and intuitive manner that reflects their overall goals, needs and preferences.”



Refs
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