By Brooke B., Computer Science/Design ’22
Author’s Note: As a computer science major, I have always been interested in the concept of an algorithm that can communicate with the brain through manufactured nerve signals. I read about this research in the news and I thought it was a great example of the marriage of biology and computer science, as well as how the two together can improve lives. I wrote this news article in hopes to reach more of the general public to shed light on the strides we’re making in prosthetic technology.
New research was published early October 2019 in Science Translational Medicine with the first prosthesis augmented by sensory feedback for above-the-knee amputees.¹ The findings have helped amputees achieve greater control over their prosthetic limbs. One participant in the clinical study reported feeling as if their prosthesis was their real leg again: “After all of these years, I could feel my leg and foot again, as if it were my own leg,” Djurica Resanovic said, “You don’t need to look at where your leg is to avoid falling.”
Swiss companies ETH Zurich and SensArs Neuroprosthetics developed the sensory feedback technology to improve prosthetic devices. Seven sensors detect signals along the foot of the artificial leg prototype, and one sensor detects the angle of flexion from the knee. These communicate via Bluetooth to an electric conductor, called an electrode, surgically implanted into the stump’s tibial nerve. Co-author of the publication and SensArs Neuroprosthetics co-founder Silvestro Micera has found the approach of piercing an electrode through the nerve rather than wrapping around it to be efficient in other studies performed for bionic hands. The sensors on the limb receive spatial information when moved, which are translated into biosignals by the team’s new algorithm. The electrode implanted to the neuron receives the signals and sends the information through the nervous system to be received at the brain for processing. The better integration of the prosthesis to the body depends on the accuracy of these electrical signals, and how closely they resemble those a real leg would have produced.
Three amputees participated in a clinical trial over a period of three months to test the new technology. “We showed that less mental effort is needed to control the bionic leg because the amputee feels as though their prosthetic limb belongs to their own body,” explained Stanisa Raspopovic, an ETH professor who led the study. “…the feedback is crucial for relieving the mental burden of wearing a prosthetic limb which, in turn, leads to improved performance and ease of use.”
Even blindfolded and wearing earplugs, participants were able to feel their prosthetic prototype. With the improved awareness of the limb in space, navigating through obstacles required less effort and as a result, subjects fell less. With no stimulation in the limb, the average ratio of falls to obstacles was 39 percent, as opposed to the ratio of eight percent with the stimulated prosthesis. On a test with stairs where subjects were tasked with completing laps, the average amount completed with the new technology was 2.28, as opposed to an average of 1.67 laps without it. Additionally, the brain appeared to be less burdened by the prosthesis, exhibiting lower amplitudes in acoustic event-related potentials tests.² These tests pick up small voltages the brain gives off in response to stimuli, thus a lower reading would indicate less mental stimulation involved in maneuvering with the prosthesis.³ Consequently, more focus can be devoted towards other tasks within the amputee’s life.
Silvestro Micera believes the intraneural electrodes implemented in this research hold vast prospects in neuroprosthetic applications. “We believe [they] are key for delivering bio-compatible information to the nervous system… Translation to the market is just around the corner.”
References
- Ecole Polytechnique Fédérale de Lausanne. “Amputees merge with their bionic leg.” ScienceDaily. ScienceDaily, 2 October 2019. <www.sciencedaily.com/releases/2019/10/191002144243.htm>.
- Francesco Maria Petrini, Giacomo Valle, Marko Bumbasirevic, Federica Barberi, Dario Bortolotti, Paul Cvancara, Arthur Hiairrassary, Pavle Mijovic, Atli Örn Sverrisson, Alessandra Pedrocchi, Jean-Louis Divoux, Igor Popovic, Knut Lechler, Bogdan Mijovic, David Guiraud, Thomas Stieglitz, Asgeir Alexandersson, Silvestro Micera, Aleksandar Lesic and Stanisa Raspopovic. Enhancing functional abilities and cognitive integration of the lower limb prosthesis. Science Translational Medicine, 2019 DOI: 10.1126/scitranslmed.aav8939
- Sur, S., & Sinha, V. K. (2009). Event-related potential: An overview. Industrial psychiatry journal, 18(1), 70–73. doi:10.4103/0972-6748.57865