State-of-the-art prosthetic limbs can help amputees achieve a natural walking gait, but they typically rely on mechanical sensors and controllers that move the limb using predefined algorithms, rather than direct neural control. However, researchers at MIT, in collaboration with Brigham and Women’s Hospital, have developed a groundbreaking approach that allows a prosthetic leg to be fully controlled by the body’s own nervous system.
Using a novel surgical technique and a neuroprosthetic interface, the researchers demonstrated that a natural walking gait can be achieved with a prosthetic leg powered by neural signals. This innovative procedure reconnects muscles in the residual limb, enabling patients to receive “proprioceptive” feedback—allowing them to sense the position and movement of their prosthetic limb in space.
In a study involving seven patients who underwent this surgery, the MIT team found that these individuals were able to walk faster, avoid obstacles, and climb stairs more naturally compared to those with traditional amputations.
“This is the first prosthetic study in history to demonstrate a leg prosthesis under full neural control, where a biomimetic gait emerges,” said Hugh Herr, a professor of media arts and sciences, co-director of the K. Lisa Yang Center for Bionics at MIT, and senior author of the study. “No one has previously shown this level of brain control that produces a natural gait—where the human nervous system is directing movement, rather than a mechanical control algorithm.”
Improved Comfort and Reduced Muscle Loss
Beyond enhanced mobility, patients who underwent this surgical approach, known as the agonist-antagonist myoneural interface (AMI), experienced less pain and reduced muscle atrophy. So far, around 60 patients worldwide have received this type of surgery, which can also be performed on individuals with upper limb amputations.
Restoring Neural Feedback
Limb movement is typically controlled by pairs of muscles that work in opposition—one contracting while the other stretches. In a standard below-the-knee amputation, the connections between these paired muscles are disrupted, making it difficult for the nervous system to sense muscle position and contraction speed. This sensory information is critical for the brain to coordinate movement.
Amputees with traditional prosthetics often struggle to control their limbs because they lack accurate feedback about the limb’s position in space. Instead, they rely on built-in mechanical controllers and sensors that adjust to terrain changes.
To address this, Herr and his colleagues developed the AMI procedure, which preserves natural muscle interactions by surgically reconnecting muscle pairs. This allows the residual limb to maintain dynamic communication, helping patients move their phantom limb with natural proprioception. The surgery can be performed during an initial amputation or later as a revision procedure.
“With the AMI amputation technique, we strive to connect native agonists to native antagonists in a physiological way, so that after amputation, a person can move their entire phantom limb with natural proprioception and a full range of motion,” Herr explained.
Enhanced Mobility through Neural Control
In a previous study, Herr’s team found that AMI patients could control their residual limb muscles with greater precision and generate electrical signals similar to those from intact limbs. Building on this, the new study explored whether these neural signals could effectively command a prosthetic limb while simultaneously providing the user with sensory feedback about limb position.
The findings, published in Nature Medicine, show that this neural feedback enables smooth, near-natural walking and improved obstacle navigation.
“Thanks to the AMI neuroprosthetic interface, we were able to amplify neural signaling and preserve as much as possible. This allowed individuals to seamlessly and directly control their full gait across various walking speeds, terrains, and even while stepping over obstacles,” said Hyungeun Song, lead author of the study and a postdoctoral researcher at MIT’s Media Lab.
Natural Walking Patterns
For the study, researchers compared seven AMI patients to seven individuals with conventional below-the-knee amputations. Both groups used the same type of bionic limb—a prosthesis with a powered ankle and electrodes that detect electromyography (EMG) signals from the tibialis anterior and gastrocnemius muscles. These signals were then fed into a controller that determined how much to bend the ankle, apply torque, or generate power.
The participants performed a series of mobility tests, including walking on flat ground, ascending and descending ramps and stairs, and navigating obstacles. Those with AMI prosthetics walked faster—at speeds comparable to non-amputees—and demonstrated more natural movements, such as lifting the prosthetic foot when stepping over obstacles and pushing off the ground with force similar to an intact limb.
“With AMI patients, we saw natural biomimetic behaviors emerge,” Herr said. “In contrast, those without AMI could walk, but their prosthetic movements were less fluid and generally slower.”
Remarkably, these improvements occurred despite AMI patients receiving less than 20% of the sensory feedback that an intact limb would normally provide.
“One of the key findings is that even a small increase in neural feedback from the residual limb can significantly enhance bionic limb control,” Song noted. “This allows individuals to naturally adjust their walking speed, adapt to different terrains, and avoid obstacles—all through direct neural control.”
This research represents a major step toward restoring natural mobility for individuals with limb loss, offering a future where advanced prosthetics seamlessly integrate with the human nervous system.
This news was originally published on the MIT website.