Physically healthy humans often take for granted the amazing mechanisms at work that allow their bodies to function. The fact that we can keep track of where our limbs are without visible confirmation is something we probably never marvel at, but it’s actually the result of incredible connectivity and communication between muscles and the mind.
When we put our arms and legs in motion, the movement is the result of the combination of two joined muscles called agonist-antagonist pairs. For example, when someone bends their elbow, the bicep muscle contracts while the triceps muscle stretches. The motion of stretching sends sensory feedback to the brain, which helps it determine which position the limb is in.
In general, conventional limb amputations sever the agonist-antagonist muscle pairs. Once a prosthesis is attached to the body, the muscles aren’t able to communicate well with one another. This sends confusing signals to the brain, which means most amputees must watch their prosthesis which provides visual feedback to the brain, ultimately facilitating its movement.
Fortunately, this may be improved with the development of a new procedure called agonist-antagonist myoneural interface (AMI). This procedure joins the severed ends of the paired muscles once the amputation itself takes place. This allows the muscles to reconnect their communication system, which gives the brain a better idea of where the missing part of the limb would be if it were still attached.
Around 25 patients have had AMI surgery performed at the Harvard University-affiliated Brigham and Women’s Hospital. Scientists assessed 15 of these individuals, all of whom had a single below-the-knee amputation.
In comparison to those who had undergone conventional amputations, the AMI amputees had better control over their phantom limb. As an added benefit, the AMI group reported experiencing less pain than the control group.
There is still a lot more research that has to be done to more accurately assess the benefits of AMI surgery, but it is worth noting that there is also a version of this type of amputation called “regenerative AMI”. This allows the agonist-antagonist muscle that has already been severed in traditional amputations to reconnect and improve the communication between muscles and mind.
If you want to know more about this exciting new technology, check out this paper published in Science Translational Medicine.
