Rat Neuroprosthetics Get Closer to Mimicking Natural Leg Movement

The new technology could one day help make rehabilitation easier for patients with partial spinal cord injuries.
 
The new neuroprosthetic system allowed mice with spinal cord injuries to walk further without leg fatigue. | Science Translational Medicine/AAAS

Researchers have fine-tuned a neuroprosthetic technology that electrically stimulates the spinal cord in rats, and may one day help paralyzed patients walk more naturally. The new technology is designed to anticipate changes in the animals' gait and doesn't need constant adjustments to operate smoothly.

The study published in the 24 September issue of the journal Science Translational Medicine is based on a technique called epidural electrical stimulation (EES), which uses implanted electrodes to feed electrical currents to the brain and spinal cord.

"We believe that our method provides a new tool to improve the rehabilitation of people with incomplete spinal cord damage," said Grégoire Courtine, a researcher at the Swiss Federal Institute of Technology (EPFL) in Lausanne, Switzerland and senior author of the study.

Earlier this year, four paralyzed men were able to recover leg movement after receiving EES implants, and Courtine and colleagues demonstrated the technique's potential in paralyzed rats in a 2012 paper published in Science.

Although this technology has the potential to dramatically improve quality of life, it requires constant, specific adjustment. Factors such as the width, amplitude and frequency of the electrical pulses to the spinal cord have to be adjusted manually and can't change quickly to adjust to a new walking challenge. This makes it difficult to send new nerve signals to the legs as they move in more complicated ways, such as lifting to climb a step.

Courtine and colleagues have now developed an EES computational system that is self-adjusting, or "closed-loop." The system allows for continuous control of leg movement without constant monitoring or manually adjusting the electrical pulses.

The researchers show that closed-loop EES can precisely control leg movement in rats with complete spinal cord injury. Treated animals walked over 1000 successive steps without failure, and were able to climb staircases of various heights and lengths with precise, fluid movement.

The animals were assisted by a robotic body-weight system designed to support paralyzed patients against gravity without facilitating movement, much like an adult would hold a young child learning to walk.

The researchers are currently planning a clinical trial testing the closed-loop stimulation and robot-assisted locomotion approach in paralyzed patients. Once patients are strapped into the system, they say, the robot will apply closed-loop EES and assist with re-learning complex walking skills.

"Closed-loop adjustment of the stimulation may allow patients with implants on their spinal cords to perform many exercises with less effort. In turn, increasing the duration and intensity of the exercise plays a significant role in the outcome of the rehabilitation," Courtine said.