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.
Now, a team of researchers says the members have solved part of the problem of smooth motor control by connecting an artificial limb to a different part of the . Previous designs for linked the artificial limb to either the person's motor cortex or the individual's premotor cortex, which both translate signals from the brain to the limbs.
This time, the connections to the were wired into a posterior parietal cortex, which is located on the side of the head near the ear.
The researchers used signals from the posterior parietal cortex "to extract the intent of the subject," Andersen told Live Science. "Instead of 'I want to control muscles,' we can use to work out the fine details" of the movement a person wants to make.
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. [: ]
In a video by the researchers, Sorto used the arm to serve himself a beer.
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 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 . 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.
Eventually, some combination of techniques could make bionic arms a reality for many patients. "[Sorto] was pleasantly surprised at the increase in his ," Andersen said.
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