Volunteers in this study will get two different cortical chips, each carrying 100 recording electrodes. Scientists hope that doubling the capacity to listen to the brain will provide enough independent signals to enable more complex movements on the sophisticated APL arm. “This is a highly dexterous and anthropomorphic arm,” says Andrew Schwartz, one of the neuroscientists involved in the study. “The information bandwidth you need to control the device is a lot higher.”
The Pittsburgh researchers will also test new chips combined with telemetry systems, which process some of the recorded information on the chip before sending it to a processor implanted in the chest. The processor then wirelessly controls the arm. Current versions in use in humans and monkeys send information via wires coming out of the skull, which increases risk of infection over the long term. While the new setup will be somewhat similar to that used in cardiac pacemakers and deep brain stimulation devices, a prosthetic arm carries out more complex functions than a pacemaker, and therefore more information is needed to control it. “No implantable device has a telemetry system capable of this bandwidth,” says Schwartz. “This technology will be a big step.”
The Pittsburgh researchers ultimately aim to add sensory capability to the arms as well, adding materials that can sense heat and other properties and convey that information to a third chip implanted into part of the brain that processes sensory stimuli.
It’s not yet clear what the highest level of complexity will be in terms of controlling the arm. “We’re hoping to do at least 11 degrees of freedom,” says Schwartz. His team has developed algorithms that can derive seven degrees of freedom of movement in monkeys in real time. “How will we move up to 20 or 30? We don’t know, maybe we’ll need new algorithms, maybe more electrodes,” says Schwartz.
Even if the tests are successful, researchers face a big challenge; they must show that the invasive cortical control system is significantly better than noninvasive approaches. Amputees using the shoe-controlled interface can pick up boxes, operate a drill, and even use chopsticks. “If you were an amputee, and you can do that with shoes, would you have a sensor put in your brain?” asks Donoghue. It may be a matter of personal preference and the level of risk and benefit each person is willing to tolerate. “You might, because it’s more natural and you can walk and do other things.”