Bionic Hand

PART 4

Kuiken need an amplifier to boost the signals form the nerves, avoiding the need for a direct splice. He found one in muscle. When muscles contract, they give off an electrical brust strong enough to be detected a technique to reroute severed nerves from their old, damaged spots to other muscles that could give their signals the proper boost.

Bionic woman Kitts imagines a hand movement, and muscle activity in her residual arm-decoded by a computer on her back causes the actual motion. When she straps on the actual motion. When she staps on the experimental Johns Hopkins-developed arm at the Rehabilitation Institute of Chicago, she says, "often it feels like I'm not missing anything."

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 millimeter, 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 places and feel different fingers." What she was feeling were part of the phantom arm that were mapped into her brain, now reconnected to flesh. When Kitts thought about moving those phantom fingers, her real upper-arm 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.

"Now I'm able to see silhouettes of trees again," says Jo Ann Lewis. "That's oneof the last things I remeber seeing naturally. Today I can see limbs sticking out this way and hat."

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.