BCIs for Amputations

            One of the first things people do before starting their day is take a shower. It is a relatively simple task that starts with stepping into the shower stall. However, for some, that first step is a hurdle. For reasons like complications from diabetes or cardiovascular disease, around 150,000 Americans undergo lower extremity amputation per year (Molina & Faulk, 2020). According to the National Institutes of Health, lower extremity amputation is a surgical procedure defined by the removal of limbs below the hip (Molina & Faulk, 2020). 

People with limb differences are challenged daily from their first step of the day to their last. Fortunately, research is being conducted to help alleviate their difficulties. Since the late 15^th century, prosthetic limbs have been steadily improving. Prosthetic technology has advanced to the point that healthy individuals with mid-calf amputation can participate in a full range of normal responsibilities (Marks & Michael, 2001).

However, there are still drawbacks. An above-the-knee prosthetic leg requires 60% more metabolic energy to walk with than a normal leg (Murphy et al, 2017). This is due to the prosthetic limb's passive nature. It cannot generate more mechanical energy than its spring structure can store (Murphy et al, 2017). Thus, despite the strong mechanical dexterity of artificial limbs, they are still unable to operate without being physically manipulated.  

Enter BCIs. Brain-computer interfaces (BCIs) decode movement intention from the brain to control movement-evoking stimulation (Samejima et al, 2021). Simply put, BCIs acquire brain signals, analyze them, and then translate them into commands that can be picked up by output devices that carry out the desired actions. This means that with proper integration, a BCI can communicate with a prosthetic limb. This will allow a person with limb difference to mentally control their artificial appendage.

The use of BCIs to restore limb function is not novel. Dr. Soshi Samejima and his colleagues have explored the use of BCIs to restore upper limb function in rats after a debilitating spinal cord injury. Using a local field potential-based BCI, Samejima et al decoded forelimb movement from the sensorimotor cortex, a major brain player in the execution of movement, and triggered spinal stimulation to restore forelimb movement (Samejima et al, 2021). Simply put, the spinal cord injury that paralyzed the rats was overcome.

Now take that idea and implement it on individuals with amputations. With a BCI, the brain can send the movement signal to the prosthetic leg, and the prosthetic leg will interpret the data and execute the movement. This means that instead of the artificial limb reacting passively to the user’s movement, it will be proactively moving with the person! Not only that, further improvements on the BCI could allow for dynamic adjusting of the prosthesis allowing the user to respond effectively to complex environmental situations.

However, more research is needed. Although BCIs hold the potential to open the functionality of prosthetic limbs, BCI-controlled prosthesis still has a long way to go in terms of reliability, dependability, and adaptability. In addition, prosthetic technology is still not up to par with the full range of movement of a human leg. Despite this, there is hope that in the future, individuals with limb differences can start their day without hurdles and take that first step into the shower stall without a second thought.

References

Marks, L. J., & Michael, J. W. (2001). Artificial limbs. BMJ : British Medical Journal, 323(7315), 732–735. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1121287/

 

Molina, C. S., & Faulk, J. (2024). Lower extremity amputation. In StatPearls. StatPearls Publishing. http://www.ncbi.nlm.nih.gov/books/NBK546594/

 

Murphy, D. P., Bai, O., Gorgey, A. S., Fox, J., Lovegreen, W. T., Burkhardt, B. W., Atri, R., Marquez, J. S., Li, Q., & Fei, D.-Y. (2017). Electroencephalogram-based brain–computer interface and lower-limb prosthesis control: A case study. Frontiers in Neurology, 8, 696. https://doi.org/10.3389/fneur.2017.00696

 

Restoring amputees’ natural functionality with brain-controlled interfaces. (2021, July 13). MIT News | Massachusetts Institute of Technology. https://news.mit.edu/2021/restoring-amputees-natural-functionality-brain-controlled-interfaces-0713

 

Samejima, S., Khorasani, A., Ranganathan, V., Nakahara, J., Tolley, N. M., Boissenin, A., Shalchyan, V., Daliri, M. R., Smith, J. R., & Moritz, C. T. (2021). Brain-computer-spinal interface restores upper limb function after spinal cord injury. IEEE Transactions on Neural Systems and Rehabilitation Engineering: A Publication of the IEEE Engineering in Medicine and Biology Society, 29, 1233–1242. https://doi.org/10.1109/TNSRE.2021.3090269