Spinal Stimulation Restores Leg Movement & Sensory Feedback After Injury
The landscape of spinal cord injury treatment is shifting, with a recent clinical trial demonstrating a significant step forward in restoring both movement and sensation. Researchers have successfully used spinal cord stimulation – applying electrical impulses to the spinal cord – both above and below the site of injury to enable participants to regain some control over leg movements and, crucially, to perceive where their legs are in space. This dual approach, detailed in a study published in Nature Biomedical Engineering, offers a latest avenue for improving functional independence for individuals living with paralysis.
The study, a collaboration between Brown University, Rhode Island Hospital, and VA Providence Healthcare, involved three participants who had experienced complete spinal cord injuries, resulting in paralysis from the waist down. Surgeons implanted electrode arrays both above and below the injury site. These arrays delivered patterned electrical stimulation designed to mimic the natural signals that travel through a healthy spinal cord. Prior research, including work highlighted in Medical Xpress, had already shown the potential of spinal stimulation to restore muscle control in animal models, but this trial marks the first time both motor stimulation and sensory feedback have been demonstrated simultaneously in humans.
Bridging the Communication Gap
Spinal cord injuries disrupt the complex communication pathways between the brain and the body. Not only is the ability to move limbs often lost, but so is the crucial sensory feedback that allows for coordinated movement. Without knowing where their limbs are in space, individuals rely heavily on visual cues, which isn’t ideal for natural, fluid motion. The research team aimed to address both of these deficits. Stimulation below the injury site helped partially restore muscle control in the lower extremities, even as stimulation above the injury enabled participants to understand the position of their legs, even while walking on a treadmill with the assistance of physical therapists.
“This is the first time that simultaneous motor stimulation and sensory feedback have been demonstrated in people with complete spinal cord injuries,” explained David Borton, an associate professor of engineering at Brown and a biomedical engineer at the VA Center for Neurorestoration and Neurotechnology. “This is an important step toward the goal of fully bridging the gap created by a spinal lesion. By providing both motor activation and simultaneous sensory feedback, we are making progress toward restoring coordinated movements and functional independence.”
The “DJ Board” and Personalized Stimulation
The process wasn’t simply a matter of applying electrical stimulation. Researchers worked closely with each participant to personalize the stimulation patterns. Participants used a device the team playfully dubbed the “DJ board” – an array of knobs and sliders – to control which parts of their spinal cord received stimulation, as well as the speed and intensity. This allowed them to fine-tune the stimulation to achieve specific leg movements and sensations.
“Participants told us that using the DJ board was actually a lot of fun,” said study lead author Jonathan Calvert, now an assistant professor of neurological surgery at the University of California Davis. “We gave them target leg positions and poses and they navigated the board until they found the correct stimulation patterns to achieve that pose. They really enjoyed being able to see their legs move again and having their own control through the interface.”
Data from these “DJ board” experiments was then fed into a machine learning algorithm developed by researchers at Brown. This algorithm optimized the stimulation patterns, identifying the most precise matches between desired muscle activity and stimulation parameters. Co-author Lakshmi Narasimhan Govindarajan explained that the sheer number of possible stimulation combinations makes manual optimization impractical, and machine learning offers a more efficient approach.
Sensory Replacement: Reinterpreting Sensations
Restoring sensation proved to be a more complex challenge. Because the neural pathways carrying sensory information from the legs to the brain are severed by the spinal cord injury, directly recreating the sensation of touch or pressure in the feet isn’t currently possible. Instead, the researchers employed a “sensory replacement” approach. They focused on stimulating areas of the spinal cord that still connect to sensory networks in the brain, aiming to create sensations in other parts of the body that participants could learn to associate with leg movements.
“We used a sensory replacement approach where specific sensations are associated with specific actions or stimuli to enable participants to reinterpret sensory cues,” Calvert said. “In this case, participants might feel a sensation in their chest or arm or back, but they can learn to associate those sensations with different joint angles in their legs.” Participants used the DJ board to select where on their body they wanted to receive sensory feedback, and the machine learning algorithm correlated the electrical stimulation with different knee joint positions.
Blindfolded, participants were then able to accurately report the angle of their knee based on the intensity of the sensations they received, demonstrating that the stimulation was providing useful sensory feedback. One participant described feeling a sensation in their chest when their foot struck the ground during treadmill walking, providing a proxy for the missing sensation of foot contact.
Coordinated Movement and Future Directions
The final stage of the study involved combining both motor stimulation and sensory feedback while participants walked on a treadmill, supported by a harness and assisted by physical therapists. The results were encouraging: participants were able to engage the appropriate muscles for walking while simultaneously reporting when their feet struck the ground. This suggests that the combined approach has the potential to restore more natural and coordinated movement.
“I could tell when [my foot] hit based on feedback up to here [pointing to chest],” one participant shared. “It wasn’t like I could feel my foot hit the treadmill or anything like that, but it was close.”
The researchers emphasize that this is still early-stage research. The study involved a small number of participants, and the effects observed were achieved under carefully controlled conditions in a hospital setting. However, the findings offer a promising glimpse into the future of spinal cord injury treatment. No device-related adverse effects were reported, paving the way for larger, longer-term studies. The team is now planning to recruit new participants for a study that will test spinal stimulation outside of the hospital environment.
“There’s reason to believe that coordinated stimulation across an injury site could produce positive rehabilitation effects,” Borton said. “That’s not something we were able to fully explore in this study, but that we plan to pursue in future work.” The research, published in Nature Biomedical Engineering, represents a significant step towards restoring function and improving the quality of life for individuals living with spinal cord injuries.
The team acknowledges the generosity of the participants who volunteered for the study, recognizing that their contribution is paving the way for future advancements in neurotechnology. As Borton stated, “We are incredibly grateful to the participants who volunteered for this study without expectation of long-term benefit to themselves. Their generosity paves the way for future research aimed at fully restoring functions lost to devastating spinal cord injuries.”