Proprioception is a process that we encounter every day and most likely take for granted. It is the ability to sense the position, speed and motion of our own body parts. For example, even if a person has their eyes closed, they are still able to sense if their arm is above their head or hanging by the side of their body. This process allows us to precisely control our body movements without even thinking about it.
Despite significant technological advancements, researchers have previously been unable to provide this sensation to those with a prosthetic limb. ‘Seeing is believing’ is not always the case for amputees; they often report feeling disconnected from their prosthetic limb, describing that they can see it but cannot feel it, and do not believe it belongs to their body. As a result, they find themselves constantly watching their prosthetic limb to use it correctly and accurately.
However, recent research has shown promising results that proprioception could be provided by implementing an agonist-antagonist myoneural interface (AMI); this is two muscles that are mechanically connected. Following a patient’s below-knee amputation, researchers at the Center for Extreme Bionics at the MIT Media Lab in Cambridge, Massachusetts, surgically constructed two AMI’s within the patient’s limb and developed an advanced prosthetic that is electrically linked to the patient’s nervous system, allowing the brain to interpret it as the body’s natural joint proprioception. This allows the nervous system to send commands to the prosthetic limb, as well as relaying the proprioceptive feedback; so, when movement occurs, this electrical message is sent to the brain and allows the patient to feel the movement. The study compared the AMI patient against four patients who had undergone a traditional below-knee amputation. As a result, it was found that the AMI patient experienced a connection with the prosthetic limb, as well as improved control over the device. Furthermore, the AMI patient also quickly displayed natural, reflexive behaviours such as extending the toes toward the next step when walking down a set of stairs; this natural behaviour was absent in all four patients who had undergone the traditional amputation.
Overall, these results certainly seem promising and provide evidence that ongoing research is important to develop prosthetics that are not only more accurate and effective, but also address the missing link between human physiology and bionic systems.
Megan Kelly (Graduate Trainee, HealthCare21)