NEWS
01 July 2024

Bionic leg moves like a natural limb — without conscious thought

Computer interface links signals from the brain to an artificial limb, giving the wearer better balance, flexibility and speed.

By Miryam Naddaf



A robotic leg that can be fully controlled by the brain and spinal cord has enabled seven people who had lost a lower leg to walk roughly as fast as people without amputations.

The bionic limb uses a computer interface that amplifies nerve signals from muscles in the remaining part of the leg and allows the wearer to move the prosthesis with their own thoughts and natural reflexes.

In a clinical trial involving 14 people, participants with this interface were able to walk 41% faster than were those with standard robotic legs. They also had better balance and ability to change their speed, climb stairs and step over obstacles. The results were published today in Nature Medicine1.

“This is the first study that demonstrates natural gait patterns with a full neural modulation where the person’s brain is 100% in command of the bionic prosthesis, not a robotic algorithm,” said study co-author Hugh Herr, a biophysicist at the Massachusetts Institute of Technology in Cambridge, at a press conference announcing the findings.

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Article
Open access
Published: 01 July 2024

Continuous neural control of a bionic limb restores biomimetic gait after amputation

Hyungeun Song, Tsung-Han Hsieh, Seong Ho Yeon, Tony Shu, Michael Nawrot, Christian F. Landis, Gabriel N. Friedman, Erica A. Israel, Samantha Gutierrez-Arango, Matthew J. Carty, Lisa E. Freed & Hugh M. Herr

Nature Medicine (2024)

Abstract
For centuries scientists and technologists have sought artificial leg replacements that fully capture the versatility of their intact biological counterparts. However, biological gait requires coordinated volitional and reflexive motor control by complex afferent and efferent neural interplay, making its neuroprosthetic emulation challenging after limb amputation. Here we hypothesize that continuous neural control of a bionic limb can restore biomimetic gait after below-knee amputation when residual muscle afferents are augmented. To test this hypothesis, we present a neuroprosthetic interface consisting of surgically connected, agonist–antagonist muscles including muscle-sensing electrodes. In a cohort of seven leg amputees, the interface is shown to augment residual muscle afferents by 18% of biologically intact values. Compared with a matched amputee cohort without the afferent augmentation, the maximum neuroprosthetic walking speed is increased by 41%, enabling equivalent peak speeds to persons without leg amputation. Further, this level of afferent augmentation enables biomimetic adaptation to various walking speeds and real-world environments, including slopes, stairs and obstructed pathways. Our results suggest that even a small augmentation of residual muscle afferents restores biomimetic gait under continuous neuromodulation in individuals with leg amputation.

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