Using Brain Signals to Move Prosthetic Limbs

Sgt. Juan Arredondo's life forever changed on Feb. 28, 2005, when, on a routine patrol between Ramadi and Fallujah, an IED exploded through the door of his vehicle. Arredondo's left arm was severed below the elbow, his hand still clinging to the wheel. Arredondo stuffed it in his pocket. Surgeons at the field hospital tried for five hours to reattach the limb. "I asked the surgeon if I could keep my hand," Arredondo says. " 'No, son,' he told me." Instead, Arredondo got a hook.

Doctors can perform near miracles in reattaching severed limbs, but when these attempts fail, the options have been slim indeed, particularly for patients who lose a hand. Prosthetics researchers have tended to focus on the leg, because legs account for a vast majority of amputations, and because the leg's relatively few muscles and bones and simple network of nerves make it an easier limb to mimic. For decades, hand and arm amputees got either a cosmetic arm with no functional use, a hook or pinchers, which can grab things but has limited flexibility. In recent years, however, a research boom inspired in large part by the wars in Iraq and Afghanistan has begun to offer not only prosthetic legs with active joints but also artificial arms and hands that more accurately mimic the complex movements of the real limb. And now scientists have found ways to connect prosthetic limbs to the patient's nervous system—with an ultimate aim of allowing patients to send signals directly from the brain to the artificial hand or leg.

A few months ago, Arredondo was one of the first patients to receive an experimental bionic hand that allows for more control than anything currently on the market. The $17,000 hand, called the i-LIMB, offers five individually powered articulating fingers and allows for thumb rotation. Doctors attach electrodes on the surface of the skin that pick up signals from nerves. A computer chip in the hand reads the sensors and drives a tiny motor in each finger. It not only looks like a real hand, but it also allows for users to do things like tie their shoelaces, play golf and even fold laundry. Arredondo says it's like something out of "The Terminator." "It really is amazing to see how far technology has come," says Arredondo, 27, who's now retired from the Army and works with an NGO for wounded soldiers. "It's the little things I used to take for granted, like playing with toys with my kids, which I can do again."

Controlling the i-LIMB requires some adaptation on the part of the amputee. The device is programmed for preset grips that cover basic tasks— putting a key in a lock, holding a weight, picking up a pen and pointing. "I flex my forearm muscle one way to open the device and I flex the other way to close it," says Arredondo. "There are sensors on my arm and inside the device so if I want to move my thumb I flex for about two seconds and that activates the device for what I want it to do."

Thanks to such advances in prosthetics, amputees have been returning to active duty in unprecedented numbers. In the U.S. Army, 65 amputee soldiers have gone back to active duty; eight have been deployed back to the theater. Several British soldiers have been fitted for prosthetics and then headed back to the front line. "In the past when you lost a limb you were found unfit for duty," says Chuck Scoville, the amputee-program manager at Walter Reed Army Medical Center. "With the start of this war the philosophy was we are going to do everything we can to return these individuals to their normal function."

The next step is to make limbs that patients control just as they would natural limbs. The U.S. Defense Advanced Research Agency (DARPA) has been building on research—in which scientists have successfully implanted electrodes in the brains of monkeys and then trained them to control a robot arm—to come up with a new generation of prosthetics. "The brain part is very scary, but we are leveraging it against an old DARPA program that did some remarkable work measuring brain activity, getting a computer to figure out what the activity is and then running a peripheral robot arm," says Col. Geoffrey Ling, a U.S. Army doctor and DARPA's program manager. It expects to be ready to test the technology on humans in two years. "Our goal is to make it possible so that if people think about brushing the hair out of their child's eyes, they can do that," says Ling. That wouldn't be better than a natural hand, but it might be a close second.