A mind-controlled prosthetic arm developed by biomedical engineers and physicians from Johns Hopkins Medicine has been able to wiggle “fingers” independently. The technology announced on Feb. 15, 2016, and was described in the online Journal of Neural Engineering.
“We believe this is the first time a person using a mind-controlled prosthesis has immediately performed individual digit movements without extensive training,” says senior author Nathan Crone, M.D., professor of neurology at the Johns Hopkins University School of Medicine. “This technology goes beyond available prostheses, in which the artificial digits, or fingers, moved as a single unit to make a grabbing motion, like one used to grip a tennis ball.”
The young man who was the test subject in this experiment was not missing a hand or arm, but was fitted with a device that used a brain-mapping procedure bypass control of his hand or arm. The participant had epilepsy and was already scheduled for brain mapping at Johns Hopkins Hospital’s Epilepsy Monitoring Unit to identify the origin of his seizures. Before connecting the prosthesis, the scientists mapped and tracked the parts of his brain that were responsible for moving each finger. The device was then programmed to move the finger associated that that section of his brain.
A neurosurgeon first placed an array of 1328 electrode sensors on a credit-card-sized sheet of film and implanted it on the part of the man’s brain that usually controls arm and hand movements. Each sensor measured brain tissue in a circle one mm. in diameter. While the participant moved individual fingers on command, a computer program developed by Johns Hopkins recorded which parts of the brain “lit up” when each sensor detected an electrical signal.
Researchers also measured the electrical brain activity related to tactile sensation. The participant wore a glove with small, vibrating buzzers at the fingertips that went off in each finger. The prosthetic arm was then programmed to move the fingers based on where the brain was active. The prosthetic was then wired to the patient through brain electrodes. The participant was asked to think about moving the thumb, index, middle, ring, and pinkie fingers and did so via electrical activity generated in the brain.
“The electrodes used to measure brain activity in this study gave us better resolution of a large region of cortex than anything we’ve used before and allowed for more precise spatial mapping in the brain,” said Guy Hotson, a graduate student and lead author of the study. “This precision is what allowed us to separate the control of individual fingers.”
The mind-controlled prosthetic was 75 percent accurate at first, and increased accuracy to 88 percent when researchers put the ring and pinkie fingers together. “The part of the brain that controls the pinkie and ring fingers overlaps, and most people move the two fingers together,” Crone said. “It makes sense that coupling these two fingers improved the accuracy.” The researchers reported that no pre-training was required to complete the task and the experiment lasted less than two hours. Crone says, however, that applying this technology to patients that are missing limbs is still years away and will be costly.