In one of the most intriguing nerve-related breakthroughs, one that’s already assisted some mobile amputees, surgeons have moved nerve endings to help power the prosthetic arm. Armiger describes how a procedure at Johns Hopkins helped a West Virginia man who had lost his lower arm and part of his upper arm to cancer. In that man’s case, key nerves were transferred just above the amputation to the muscles that controlled the biceps and triceps, Armiger says.
Then, by using electrodes situated over those muscles, the nerve signals were amplified and sent to a small, computerized device at the socket of the amputated arm. “It’s the computer that turns muscle signals into movement,” Armiger explains. The surgical technique, first pioneered by a Chicago physician, even can assist veterans using simpler prostheses, such as the gripper devices. “It means you can just naturally open and close that gripper in the same way that you think about opening and closing your hand,” he says.
According to Columbia University’s Greisberg, as more advances are achieved, it’s possible that those nerve signals could be more directly captured. In one scenario, he says, a cufflike device might be located near the amputation site to read the nerve signals and transmit that information to and from the robotic arm. “That’s not where the research is now, but that’s certainly not crazy to think about,” he says.
THE EVENTUAL GOAL is to pair these sorts of nerve connections with the more sophisticated arm the researchers at the Johns Hopkins lab have built. That arm has potential for 26 degrees of freedom, including notable finger dexterity. Scheuermann’s early 2012 surgery, during which the two electrode arrays were implanted, opens the door for this robotic-limb technology to be used one day by individuals with quadriplegia related to traumatic injury or diseases such as muscular dystrophy.
During the four-hour procedure, the arrays were situated near the brain regions responsible for hand and shoulder movement, says Dr. Elizabeth Tyler-Kabara, Scheuermann’s neurosurgeon at the University of Pittsburgh School of Medicine. (Prior MRI scans had pinpointed both the anatomy of Scheuermann’s brain as well as which areas were active when she imagined specific movements.) The two square arrays, each no larger than a pencil eraser, contain 96 functional minielectrodes, which penetrate slightly into the motor cortex, according to Tyler-Kabara.
“We are recording the responses from single neurons,” she explains. “And so in order to pick up the responses from single neurons, you actually need the electrodes to be next to a neuron.”
Following the surgery, Scheuermann recalls being connected to the computer for the first time and a researcher asking her to imagine moving a finger. “And I did,” she says. “And the neurons started popping.”