Etymology: from bi (as in “life”) + onics (as in “electronics”); the study of mechanical systems that function like living organisms or parts of living organisms
Amanda Kitts is mobbed by four- and five-year-olds as she enters the classroom at the Kiddie Kottage Learning Center near Knoxville, Tennessee. “Hey kids, how’re my babies today?” she says, patting shoulders and ruffling hair. Slender and energetic, she has operated this day-care center and two others for almost 20 years. She crouches down to talk to a small girl, putting her hands on her knees.
“The robot arm!” several kids cry.
“You remember this, huh?” says Kitts, holding out her left arm. She turns her hand palm up. There is a soft whirring sound. If you weren’t paying close attention, you’d miss it. She bends her elbow, accompanied by more whirring.
“Make it do something silly!” one girl says.
“Silly? Remember how I can shake your hand?” Kitts says, extending her arm and rotating her wrist. A boy reaches out, hesitantly, to touch her fingers. What he brushes against is flesh-colored plastic, fingers curved slightly inward. Underneath are three motors, a metal frame, and a network of sophisticated electronics. The assembly is topped by a white plastic cup midway up Kitts’s biceps, encircling a stump that is almost all that remains from the arm she lost in a car accident in 2006.
Almost all, but not quite. Within her brain, below the level of consciousness, lives an intact image of that arm, a phantom. When Kitts thinks about flexing her elbow, the phantom moves. Impulses racing down from her brain are picked up by electrode sensors in the white cup and converted into signals that turn motors, and the artificial elbow bends.
“I don’t really think about it. I just move it,” says the 40-year-old, who uses both this standard model and a more experimental arm with even more control. “After my accident I felt lost, and I didn’t understand why God would do such a terrible thing to me. These days I’m just excited all the time, because they keep on improving the arm. One day I’ll be able to feel things with it and clap my hands together in time to the songs my kids are singing.”
Kitts is living proof that, even though the flesh and bone may be damaged or gone, the nerves and parts of the brain that once controlled it live on. In many patients, they sit there waiting to communicate—dangling telephone wires, severed from a handset. With microscopic electrodes and surgical wizardry, doctors have begun to connect these parts in other patients to devices such as cameras and microphones and motors. As a result, the blind can see, the deaf can hear, and Amanda Kitts can fold her shirts.
Kitts is one of “tomorrow’s people,” a group whose missing or ruined body parts are being replaced by devices embedded in their nervous systems that respond to commands from their brains. The machines they use are called neural prostheses or—as scientists have become more comfortable with a term made popular by science fiction writers—bionics. Eric Schremp, who has been a quadriplegic since he shattered his neck during a swimming pool dive in 1992, now has an electronic device under his skin that lets him move his fingers to grip a fork. Jo Ann Lewis, a blind woman, can see the shapes of trees with the help of a tiny camera that communicates with her optic nerve. And Tammy Kenny can speak to her 18-month-old son, Aiden, and he can reply, because the boy, born deaf, has 22 electrodes inside his ear that change sounds picked up by a microphone into signals his auditory nerve can understand.
The work is extremely delicate, a series of trials filled with many errors. As scientists have learned that it’s possible to link machine and mind, they have also learned how difficult it is to maintain that connection. If the cup atop Kitts’s arm shifts just slightly, for instance, she might not be able to close her fingers. Still, bionics represents a big leap forward, enabling researchers to give people back much more of what they’ve lost than was ever possible before.
“That’s really what this work is about: restoration,” says Joseph Pancrazio, program director for neural engineering at the National Institute of Neurological Disorders and Stroke. “When a person with a spinal-cord injury can be in a restaurant, feeding himself, and no one else notices, that is my definition of success.”
A history of body-restoration attempts, in the form of man-made hands and legs and feet, lines the shelves in Robert Lipschutz’s office at the Rehabilitation Institute of Chicago (RIC). “The basic technology of prosthetic arms hasn’t changed much in the last hundred years,” he says. “Materials are different, so we use plastic instead of leather, but the basic idea has been the same: hooks and hinges moved by cables or motors, controlled by levers. A lot of amputees coming back from Iraq get devices like these. Here, try this on.” Lipschutz drags a plastic shell off one of his shelves.
It turns out to be a left shoulder and arm. The shoulder part is a kind of breastplate, secured across the chest by a harness. The arm, hinged at the shoulder and elbow, ends in a metal pincer. To extend the arm, you twist your head to the left and press a lever with your chin, and use a little body English to swing the limb out. It is as awkward as it sounds. And heavy. After 20 minutes your neck hurts from the odd posture and the effort of pressing the levers. Many amputees end up putting such arms aside.
“It’s hard for me to give people these devices sometimes,” Lipschutz says, “because we just don’t know if they will really help.” What could help more, he and others at RIC think, is the kind of prosthesis Amanda Kitts has volunteered to test—one controlled by the brain, not by body parts that normally have nothing to do with moving the hand. A technique called targeted muscle reinnervation uses nerves remaining after an amputation to control an artificial limb. It was first tried in a patient in 2002. Four years later Tommy Kitts, Amanda’s husband, read about it on the Internet as his wife lay in a hospital bed after her accident. The truck that had crushed her car had also crushed her arm, from just above the elbow down.
“I was angry, sad, depressed. I just couldn’t accept it,” she says. But what Tommy told her about the Chicago arm sounded hopeful. “It seemed like the best option out there, a lot better than motors and switches,” Tommy says. “Amanda actually got excited about it.” Soon they were on a plane to Illinois.
Todd Kuiken, a physician and biomedical engineer at RIC, was the person responsible for what the institute had begun calling the “bionic arm.” He knew that nerves in an amputee’s stump could still carry signals from the brain. And he knew that a computer in a prosthesis could direct electric motors to move the limb. The problem was making the connection. Nerves conduct electricity, but they can’t be spliced together with a computer cable. (Nerve fibers and metal wires don’t get along well. And an open wound where a wire enters the body would be a dangerous avenue for infections.)
Kuiken needed an amplifier to boost the signals from the nerves, avoiding the need for a direct splice. He found one in muscles. When muscles contract, they give off an electrical burst strong enough to be detected by an electrode placed on the skin. He developed a technique to reroute severed nerves from their old, damaged spots to other muscles that could give their signals the proper boost.