The AMI Procedure- Gateway to a Cyborg Future

Advances in bioengineering and robotics have delivered incredible devices capable of partially restoring functionality to those who suffer from movement related disabilities. However, this technology is not perfect. Patients still complain of ailments such as joint fatigue, reduced capacity for movement and phantom limb syndrome (perceived sensation or pain emanating from a limb that has been removed). Most of these problems stem from the lack of connection between human and machine due to a failure to integrate bionic circuitry with that of our own. To succeed in such an endeavor would make real the fictional beings of our beloved Sci-Fi films and novels—the cyborg.

What is a Cyborg?

To answer this question, we will turn to Hugh Herr, head of the biomechatronics lab at the Massachusetts Institute of Technology (MIT), who is in the business of creating cyborgs. His story begins with a mountain climbing accident and an extreme case of frostbite, necessitating a below-knee amputation of both of his legs. His love for rock climbing propelled him into the field of bioengineering and prosthetics as he set out to design a pair of legs that not only restored but augmented his ability to climb.

Hugh Herr is a bionic man, but he does not qualify as a cyborg—our popular portmanteau for the term cybernetic organism. His prosthetics include artificial sensors that decode nerve signals from his muscles and transform them into movements that the bionic limbs then perform. This technology allows for a broader range and ease of movement that few devices available to the public offer today. However, despite his technological enhancements, Dr. Herr cannot feel his legs, and therefore, as he describes, they are not a part of him.

In a 2018 Ted Talk, Dr. Herr explains that true cyborg technology must be capable of receiving as well as sending signals to its human counterpart. The difference between a bionic human and a cyborg is the difference between using your bionic hand to pick up a beer versus using your cybernetic hand not only to pick up the beer, but also to feel the cold glass and condensation of the bottle as you pull it from the refrigerator. This bidirectional flow of information dissolves the line between human and machine, enabling a person to experience all the world’s natural sensations.

There is just one problem. Until recently, all patients who required prosthetics due to loss of limb often underwent outdated amputation procedures that injured underlying neural circuitry. Due to the destruction of the residual limb circuitry, there remained no interface for transmitting information to and from the bionic limb, making the bidirectional flow of information impossible. To solve this problem, researchers reexamined the beginning of the human-to-cyborg transition—the amputation process.

Origins of the AMI Procedure

Amputation is one of the oldest procedures that exist to this day. Its history traces back to 5,000 BC as by-products of ancient rituals, punishments, and injuries. Although the standard clinical procedure for amputations has come a long way since a swing of the axe from our ancient past, advancements in amputation surgery have remained mostly unchanged since the Civil War. As it stands now, the standard operating procedure fails to keep up with innovation in the prosthetic field, limiting rehabilitation capacity after trauma.

In a 2018 study, MIT biomechatronics researchers, together with surgeons from the Brigham and Women’s Hospital in Boston, Massachusetts, developed and implemented a new surgical amputation technique named Agonist-Antagonist Myoneural Interface or AMI for short (Clites et al. 2018). This technique preserves neuromuscular circuitry in the remaining or “residual” limb by reconnecting muscle tendons and nerves after removal of the severed “distal” limb. Maintenance of the agonist-antagonist muscle architecture allows for retention of proprioception, the ability to perceive and sense our body’s position and movement—a faculty commonly lost in standard amputation procedure. Furthermore, AMI provides an intact circuit for input and output to and from the bioprosthetic, thereby completing the bidirectional neuronal signaling that comprises cybernetic technology.

Cybernetic and Biological Communication

How, then, does the cybernetic limb communicate with the human nervous system? First, let us look at how the human sends information to the machine. After the AMI procedure, researchers place small artificial myoelectric sensors on each of the AMI muscles designed to record neuromuscular activity in the residual limb. The electrodes transmit the neural activity to small computers in the cybernetic device, which decode the signals into movements that the motors in the appendage perform. Now let us look at how the human receives information from the machine. When the bionic limb moves, it returns myoelectric signals to the AMI muscle sensors, causing one muscle to contract while the other relaxes—reciprocal inhibition reflexes made possible by the AMI amputation procedure. The muscles then relay information to the brain about the cybernetic limb’s location and movement in space, enabling normal sensations of proprioception. The communication loop is complete, and man and machine become one.

Picture of a Cyborg Future

Now that we understand how cyborg technology works, we can consider what this means for our future. In the last few minutes of his TED Talk, Hugh Herr dazzles the audience with colorful graphics of superhuman cyborg exoskeletons capable of enhancing a person’s strength tenfold and bionic wings that connect to our central nervous system flying us to heights only possible in our dreams. While it is fun to imagine ourselves equipped with a pair of wings flying to the grocery store to avoid traffic, it seems we might still be further from that future than Dr. Herr would lead us to believe. So far, only nine patients have received the AMI procedure, and due to its recent innovation in 2018, long term effects of the procedure have yet to be determined. Furthermore, videos shared during the presentation of Jim Ewing, the first man fit with a bionic prosthetic after the AMI procedure, show a bionic foot that, although impressive in its range of motion, does not entirely mimic the fluidity of our anatomical limbs.

Another issue to consider is the biocompatibility of our cybernetic appendages. How will the tissue of the muscles, the brain, or the spinal cord react to implanted electrodes? Can these electrodes successfully facilitate precise signal transmission and integration that mirror our natural neural networks? How would we ensure the protection of our vulnerable nervous system against the malfunction of this cybernetic technology? There are many problems left to solve to predict what this technology might hold for our future, but we have come quite a long way from wooden peg legs and hooks for replacement appendages. In fact, work is currently being done on technology to enhance normal joint and appendage function. One day, this technology may be used to provide amputee patients with bionic limbs stronger, faster, and more efficient than our natural biological arms and legs. Because of the AMI procedure, we now have a chance at a future where full physical capabilities can be restored to amputation patients and a future where physical disability could transform into physical advantage.

Written by Arielle Hogan. Illustrated by Gil Torten.

Edited by Elizabeth Burnette, Sean Noah and Desislava Nesheva.

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References 

Clites, T. R., Herr, H. M., Srinivasan, S. S., Zorzos, A. N., & Carty, M. J. (2018). The Ewing Amputation: The First Human Implementation of the Agonist-Antagonist Myoneural Interface. Plastic and reconstructive surgery. Global open, 6(11), e1997. https://doi.org/10.1097/GOX.0000000000001997 Herr, Hugh M. PhD*; Clites, Tyler R. PhD*;

Herr, H. (2017). On prosthetic control: A regenerative agonist-antagonist myoneural interface. Science Robotics. Vol. 2, Issue 6, eaan2971. http://dx.doi.org/10.1126/scirobotics.aan2971

Herr, Hugh. (2018, April). How We’ll Become Cyborgs and Extend Human Potential. Retrieved from https:// www.ted.com/talks/hugh_herr_how_we_ll_become_cyborgs_and_ extend_human_potential?language=en#t-445392

Herr, Hugh. (2014, March). The New Bionics that Let Us Run, Climb, and Dance.Retrieved from https://www.ted
.com/talks/hugh_herr_the_new_bionics_that_let_us_run_climb_and_dance?language=en

Sellegren, K. R. (1982). An Early History of Lower Limb Amputations and Prostheses. The Iowa Orthopaedic Journal, 2, 13-27.

Srinivasan, Shriya BS*; Talbot, Simon G. MD†; Dumanian, Gregory A. MD, FACS‡; Cederna, Paul S. MD§; Carty, Matthew J. MD*,† Reinventing Extremity Amputation in the Era of Functional Limb Restoration, Annals of Surgery: April 20, 2020 – Volume Publish Ahead of Print – Issue – doi: 10.1097/ SLA.0000000000003895

Wolff, P., Shepard, J. (2013) Psychology of Learning and Motivation. (Volume 58). Retrieved from https:// www.sciencedirect.com/science/article/pii/B9780124072374000050