In contrast, Hemmes' chip sat on the surface of his motor cortex, a less invasive method that records from groups of cells. The size of two postage stamps, it's based on a kind of electrical signal mapping used to track seizures in epilepsy patients.
Both approaches need study, says Daofen Chen of the National Institutes of Health, who oversees neurorehabilitation research. He compares the options to eavesdropping on a party by sending in individual microphones or setting up a recorder at the window.
Boninger adds that scar tissue can blunt the penetrating electrodes over time, and the surface chips may be easier to convert to a wireless system, which is important for commercial use.
Hemmes' operation took two hours. He had practiced imagining arm movements inside brain scanners, to see where the electrical signals concentrated. That's where neurosurgeon Elizabeth Tyler-Kabara cut, attaching the chip through an inch-wide opening on the left side of Hemmes' skull.
Two days later, Hemmes was hooked to a computer, beginning simple cursor movements. The next week, it was time to test if he could trigger real-life movement using the DARPA arm.
Hemmes reclined in his wheelchair, the robot arm bolted to a steel rod nearby. The task: make the arm reach out to grasp a ball mounted on a board.
The arm whirs forward, then stops, then goes again, then suddenly pulls back.
"It's doing the opposite of what I ask it do," Hemmes says in frustration. "When I think about reaching back, it goes forward."
Dr. Wei Wang, a member of the research team, watches Hemmes' brain patterns on a nearby computer screen, trying to match them to the robotic movements. Focus on your elbow, Wang advises.
Hemmes takes a deep breath and tries. The arm whirs forward this time, reaching the ball. The fingers clench around it.
"There's no owner's manual," Hemmes says, thrilled that the back-and-forth pays off. "I'm training my brain to figure how to do all this."
Letting go is harder, the motor growling as the arm tugs backward before the fingers fully release. Hemmes starts imagining his hand relaxing before pulling backward, and the robot hand follows.
Sure, a robotic hand that one day mounts to a wheelchair could be useful. But no matter how well today's prosthetics move, they've got a problem: They don't sense what they touch. Normally, instant messages flash from the skin up to the brain to say "squeeze tighter" so we don't drop that coffee cup, or "tight enough" so we don't hug too hard.
Besides, Hemmes shares the dream of many quadriplegics. He doesn't want a bionic third hand. He wants to move his own hands again.
"These are all scientific goals that are very real," Boninger says.
Recreating sensation means crafting a two-way highway with those brain chips. That's what Duke University, in a study published last week in the journal Nature, did with its two monkeys. When the animals "touched" objects on a computer screen with their video game-like arms, electrical signals flashed back up to implanted electrodes -- different signals for different textures, to tell the objects apart.
Sensors in the DARPA arm's fingertips allow for that same kind of feedback. McLoughlin says the plan is for one of the Pittsburgh study patients to begin testing touch capability next year, with a similar attempt at the California Institute of Technology to follow.
What about moving paralyzed limbs? Duke's plan is to turn its research into a robotic exoskeleton that would help the paralyzed move their bodies.
Hemmes is more intrigued by what's called functional electrical stimulation, zapping muscles with electrical currents to make them move. At Hemmes' request, Boninger's team attempted to fit his hand with a stimulator glove that might be linked to his electrode, but it was unsuccessful. The NIH's Chen says still other researchers are working on that kind of approach.
Hemmes likened moving the DARPA arm to learning to drive a car with a manual transmission. It took practice, but by week four he was moving the arm sideways as well as back and forth.
The fingers still clenched pretty tight, though. So when his girlfriend Katie Schaffer spoke up -- "I want to hold your hand," she said on his last day of testing -- Hemmes didn't dare bend them.
The two met after his accident, so he'd never before reached out to her.
"I was just trying to be gentle. I didn't want to hurt her, and I finally got there," Hemmes says. "Definitely the tears were flowing."
He says he was ready for a break after almost daily scientific testing, so removing the electrode and wires the next day wasn't a disappointment. He's confident the researchers will call him back once the technology advances.
"I believe this is the future," he says. "Just let people know there's hope."
Copyright 2011 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.
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