Bionic Arm Taps New Part of Brain for Natural Moves

Patient Erik G. Sorto operates a prosthetic arm that interfaces with his brain signals. — Erik G. Sorto wanted to be able to drink a beer at his own pace. Here, Sorto issues stop and go brain signals for a sequence of actions programmed by the computer system. He controls the neurons need to signal the action with his brain, and the prosthetic arm carries out the actions. In this work, researchers at Caltech collaborated with colleagues at Johns Hopkins University.

(Image credit: Caltech, Keck USC, Rancho Los Amigos Team)

Mind-controlled prosthetic limbs have been a reality for a few years, but researchers have not found ways to give the people who use them the same, smooth motor control that people have over their natural limbs.

"The [posterior parietal cortex] forms the initial plans to make movements," said Richard Andersen, a professor of neuroscience at the California Institute of Technology and one of the researchers who developed the new prosthesis. For example, when a person decides to grab a coffee cup, the posterior parietal cortex outlines the steps in movement, then, the motor cortexes translate that plan into actual signals that are sent to specific parts of the arm.

In a report published in the May 22 issue of the journal Science, the researchers explain how they connected the posterior parietal cortex of one patient, Erik G. Sorto, to a computer that acted as a kind of artificial motor cortex. The computer used specific signals from the parietal cortex to detect what kind of movement Sorto intended to make, and then translated that into signals for the robotic arm. [Video: Tetraplegic Patient Controls Robotic Limb With His Brain]

Sorto's ability to sip a brew came from the fact that the signals from the parietal cortex told the computer the general trajectory of the movement Sorto wanted to make, and the computer could smooth out the movements of the artificial arm so that they resembled those of a real arm. Other brain-connected bionic arms have aimed at decoding the motor signals involved with individual movements, such as trying to raise an arm by imagining an individual muscle contracting, but in the new prosthesis, the computer looked at the whole picture of what Sorto intended to do — just "get the beer," Andersen said.

Andersen is working with two other patients in the United States who also have prostheses that include neural implants. One even gets some feedback from the arm — a sense of touch, Andersen said. For the new prosthesis, it isn't clear yet what such perception could "feel" like for a user, because there are many components that go into a person's perception of his or her own body. But it is important to have such feedback for bionic limbs to work properly. "If you anaesthetize your fingers, you find fine motor control difficult," he said.

Krishna Shenoy, a professor of electrical engineering who studies neural prostheses at Stanford, was enthusiastic about the new prosthesis. "This is clearly the very first recordings from [the] posterior parietal cortex in humans in the context of qualifying the signals for use in prostheses," he said. "It is important to investigate many brain areas for potential use in prostheses, as different areas may well have different advantages."

Jesse Emspak is a contributing writer for Live Science, Space.com and Toms Guide. He focuses on physics, human health and general science. Jesse has a Master of Arts from the University of California, Berkeley School of Journalism, and a Bachelor of Arts from the University of Rochester. Jesse spent years covering finance and cut his teeth at local newspapers, working local politics and police beats. Jesse likes to stay active and holds a third degree black belt in Karate, which just means he now knows how much he has to learn.