National Geographic’s January cover story is all about the future of bionics — arms, eyes, skin, eventually brains. Forget prosthetic hands and cables. Remember RoboCop?In October 2006 Kuiken set about rewiring Amanda Kitts. The first step was to salvage major nerves that once went all the way down her arm. “These are the same nerves that work the arm and hand, but we had to create four different muscle areas to lead them to,” Kuiken says. The nerves started in Kitts’s brain, in the motor cortex, which holds a rough map of the body, but they stopped at the end of her stump—the disconnected telephone wires. In an intricate operation, a surgeon rerouted those nerves to different regions of Kitts’s upper-arm muscles. For months the nerves grew, millimeter by milli meter, moving deeper into their new homes.
“At three months I started feeling little tingles and twitches,” says Kitts. “By four months I could actually feel different parts of my hand when I touched my upper arm. I could touch it in different places and feel different fingers.” What she was feeling were parts of the phantom arm that were mapped into her brain, now recon nected to flesh. When Kitts thought about moving those phantom fingers, her real upper-arm muscles contracted.
A month later she was fitted with her first bionic arm, which had electrodes in the cup around the stump to pick up the signals from the muscles. Now the challenge was to convert those signals into commands to move the elbow and hand. A storm of electrical noise was coming from the small region on Kitts’s arm. Somewhere in there was the signal that meant “straighten the elbow” or “turn the wrist.” A microprocessor housed in the prosthesis had to be programmed to fish out the right signal and send it to the right motor.
Finding these signals has been possible because of Kitts’s phantom arm. In a lab at the RIC Blair Lock, a research engineer, fine-tunes the programming. He has Kitts slide off the artificial arm so that he can cover her stump with electrodes. She stands in front of a large flat-panel TV screen that displays a disembodied, flesh-colored arm floating in blue space—a visualization of her phantom. Lock’s electrodes pick up commands from Kitts’s brain radiating down to her stump, and the virtual arm moves.
In a hushed voice, so as not to break her concentration, Lock asks Kitts to turn her hand, palm in. On-screen, the hand turns, palm in. “Now extend your wrist, palm up,” he says. The screen hand moves. “Is that better than last time?” she asks. “Oh yeah. Strong signals.” Kitts laughs. Now Lock asks her to line up her thumb along side her fingers. The screen hand obliges. Kitts opens her eyes wide. “Wow. I didn’t even know I could do that!” Once the muscle signals asso ciated with a particular movement are identified, the computer in the arm is programmed to look for them and respond by activating the correct motor.
p. There’s also a great interactive illustration.