Groundbreaking research, performed at the University of Chicago, provides intriguing insight into the potential future of prosthetic limbs. Current prosthetic limbs provide amputees with the capacity to clutch objects and perform rudimentary tasks, but the absence of sensory feedback restricts what the user is able to realistically achieve. However, the latest research efforts could change all this, providing amputees with that personal touch.
DARPA and the Push on Prosthetics
The study group was led by senior author, Sliman Bensmaia, an assistant professor in the department of Organismal Biology and Anatomy at the University of Chicago, with the results published in the latest online issue of the Proceedings of the National Academy of Sciences (PNAS).
Bensmaia recently explained the necessary requirements to improve the functionality, dexterity and “feel” of prosthetic limbs. Not only do researchers need to establish a means by which the user can move the limb, but they must also ensure such a device can transmit sensory signals back to the central nervous system.
Bensmaia ruminates over what he believes to be the solution to the problem, indicating that reproducing neural patterns within the brain, and applying these findings to the algorithms used in prosthetics, is key to providing amputees with touch.
Most of Bensmaia’s research efforts have been focused on Revolutionizing Prosthetics, a program that was launched by the Defense Advanced Research Projects Agency (DARPA) project. Revolutionizing Prosthetics was commenced in 2006 to advance the technology of upper-limb technology, since it was deemed to be falling far behind the developments witnessed in lower-limb devices.
Following a six year stint, the program produced two anthropomorphic prosthetic arm systems, which were modular in design. These prototype systems offered much greater dexterity, precision and rage of motion. The program saw some of the finest minds in academia, from various government bodies and research institutions, collaborate as a single multi-disciplinary unit.
In the meantime, Bensmaia and his colleagues, in concert with researchers from the John Hopkins University Applied Physics Lab, were hard at work trying to find ways of creating an upper limb that could return both motor control and sensory feedback to amputees.
The Experimental Tests
Specifically, Bensmaia and his fellow researchers elected to use a series of experimental monkey models to investigate the possibility of developing advanced sensory input from these limbs. Monkeys were the perfect choice of animal, since their sensory systems are purported to be analogous to those of humans.
The team looked into electrical patterns of neural activity, whilst the creatures were handling objects. During the first round of experiments, they tried to identify neural patterns that were attributed to sensing points, at which the skin had been touched.
Each of the subjects were then trained to identify particular patterns of physical touch using their fingers. The researchers placed a series of electrodes over the animals’ brains, at locations that corresponded to each individual finger. Then, instead of delivering physical touches to the monkeys, artificial electrical impulses were delivered to the afore-mentioned regions of each brain. Excitingly, the monkeys responded exactly the same way to artificial stimulation as they did with physical touch.
The group then explored the animals’ sensation of pressure. Using algorithms to administer an electrical current that artificially simulated the feeling of pressure, again, the group were able to make the monkeys’ brains interpret both natural and artificial signals in the same way.
The final experiments involved reproducing the sensation that one feels when first grabbing or releasing an object, which sends “bursts” of electrical data to the brain. Likewise, the group were able to mimic these feelings through artificial stimulation.
Ultimately, these experiments cumulatively generated a set of “sensory instructions” that could be used to provide feedback to the brain, possibly through use of a neural interface.
Bensmaia explains how the algorithms for deciphering sensory signals are yet to reach the same level as those used for deciphering motor signals in prosthetic limbs:
“I think there’s a strong argument to be made that they will not be clinically viable until the sensory feedback is incorporated… When it is, the functionality of these limbs will increase substantially.”
Thought-Controlled Bionic Legs
It seems that researchers are making a push in all areas of prosthetics. Only last month, the Rehabilitation Institute of Chicago (RIC) released details of the very first “thought-controlled bionic leg,” with the results published in The New England Journal of Medicine.
Levi Hargrove, the project’s lead scientist, based at the Center for Bionic Medicine, helped to develop a more accurately controlled prosthetic leg. During a recent press release, Hargrove expounds upon the applicability of this groundbreaking technology, describing how their bionic legs allow amputees to shift position easily between “… sitting, walking, ascending and descending.”
The group used a process called targeted muscle reinnervation (TMR) surgery, which provides the patient with the ability to control a bionic leg, after rerouting nerves from the remaining, healthy leg muscle.
This was precisely the technique that was used on Zac Vawter, who was involved in a motorcycle collision during 2009; the accident cost Vawter his lower right leg. Scientists from RIC and Northwestern University incorporated the amputee into their program, rewiring nerves, which originally went down to his ankle, to his hamstring. As a result, when Vawter tried to move his ankle, electrical signals cause his hamstring to contract; electrodes within the bionic leg detect the contraction, which is then translated into movement within the prosthetic limb.
Talking to CNET, Hargrove reiterates some of the same points that Bensmaia reflected upon, explaining that providing their patients with sensory feedback would require “cutting-edge sensors… implanted within the body that could directly interface with the nerve.” He also suggests that this field of research has a long way to go, before real world applications are witnessed.
Although we are a far cry from the Blade Runner-style limbs of Ridley Scott’s classic, the latest research push by DARPA, RIC and private research organizations offers hope to amputees across the globe.
The following video highlights just a small fraction of some of DARPA’s amazing work:
By: James Fenner