Humans can accurately sense the position, speed, and torque of their limbs, even with their eyes shut. This sense, known as proprioception, allows humans to precisely control their body movements.
Researchers at the MIT Media Lab have invented a new neural interface and communication paradigm that is able to send movement commands from the central nervous system to a robotic prosthesis, and relay proprioceptive feedback describing movement of the joint back to the central nervous system in return. This new paradigm, known as the agonist-antagonist myoneural interface (AMI), involves a novel surgical approach to limb amputation in which dynamic muscle relationships are preserved within the amputated limb. The AMI was validated in extensive pre-clinical experimentation at MIT, prior to its surgical implementation in a human patient at Boston’s Brigham and Women’s Faulkner Hospital, and bionic implementation at MIT. In a paper published in Science Translational Medicine (May 30, 2018), the researchers describe the first human implementation of the AMI in a person with below-knee amputation.
The paper represents the first time information on joint position, speed, and torque has been fed from a prosthetic limb into the nervous system. An advanced prosthetic limb was built at the MIT Media Lab, and electrically linked to a patient’s peripheral nervous system using electrodes placed over AMIs subsequent to the amputation surgery. The researchers found that the AMI patient had more stable control over movement of the prosthetic device, and was able to move more efficiently than patients with conventional amputation. They also found that the AMI patient quickly displayed natural, reflexive behaviours such as extending the toes towards the next step when walking down stairs. These behaviors are essential to natural human movement, and were absent in all of the people who had undergone a traditional amputation.
While the patients with conventional amputation report feeling disconnected from their prostheses, the AMI patient quickly described feeling that the bionic ankle and foot had become a part of his own body. “Previously humans have used technology in a tool-like fashion,” senior author and project director Professor Hugh Herr says. “We are now starting to see a new era of human-device interaction, of full neurological embodiment, in which what we design becomes truly part of us, part of our identity.”
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The Science Translational Medicine paper, and other publications related to this research, can be found on the publications page.
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