McGowan Institute for Regenerative Medicine faculty member Andrew Schwartz, PhD, professor of neurobiology at the University of Pittsburgh, is part of a multi-institute team of researchers working on a $34.5 million Defense Advanced Research Projects Agency (DARPA) contract awarded to the Johns Hopkins University Applied Physics Laboratory (APL) to manage the development and testing of the Modular Prosthetic Limb (pictured), or MPL, on a human subject, using a brain-controlled interface.
APL scientists and engineers developed the underlying technology under DARPA's Revolutionizing Prosthetics 2009 program, an ambitious 4-year effort to create a prosthetic arm that would by far eclipse the World War II era hook-and-cable device used by most amputees. The program has already produced two complex prototypes, each advancing the art of upper-arm prosthetics.
The final design—the MPL—offers 22 degrees of motion, including independent movement of each finger, in a package that weighs about 9 pounds, the weight of a natural limb. Providing nearly as much dexterity as a natural limb, the MPL is capable of unprecedented mechanical agility, and is designed to respond to a user's thoughts.
Along with Dr. Schwartz and his team of scientists at the University of Pittsburgh, APL will be working closely on the project with the California Institute of Technology, also for their experience in brain computer interfaces; the University of Chicago, for its expertise in sensory perception; the University of Utah, for its capabilities in developing implantable devices suitable for interfacing with the human brain; and HDT Engineered Technologies, for its skill in building prosthetic limb systems.
Experts in both Dr. Schwartz's lab in Pittsburgh and laboratories at Caltech have conducted research using chips with hairlike electrodes to record neurological signatures in the brain. Last year, in an independent effort, Pittsburgh showed that a pair of macaque monkeys with tiny chips implanted in their brains could operate a robotic arm just by thinking about it. Wires carried the signals through the skull, and then computer software converted these signals into robotic arm movements.
As part of the new DARPA work, APL aims to begin implanting spinal cord injury patients in 2011, in collaboration with scientists at the University of Pittsburgh and Caltech.
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 Dr. Schwartz. "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 Dr. Schwartz. "This technology will be a big step."
The Pittsburgh team of researchers ultimately aims 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 Dr. Schwartz. His team has developed algorithms that can derive 7 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 Dr. Schwartz.
Illustration: This final prototype of the Modular Prosthetic Limb, successfully demonstrated to the Defense Advanced Research Projects Agency in December 2009, offers 22 degrees of motion, including independent movement of each finger. –Johns Hopkins University Applied Physics Laboratory.