Spinal stimulation may restore movement and sensation in people paralysed by spinal cord injury, a trial suggests.
The clinical trial involved three people who had lost the use of their legs following complete spinal cord injuries.
Participants received electrical stimulation of the spinal cord from electrode arrays implanted above and below their injury sites.
The study found that stimulation below the injury could partly restore muscle control in the lower extremities, while stimulation above the injury enabled participants to understand where their legs were in space as they walked on a treadmill with the assistance of physical therapists.
The research was carried out by a team from Brown University, Rhode Island Hospital and VA Providence Healthcare in the US.
David Borton is associate professor of engineering at Brown and a biomedical engineer at the VA Center for Neurorestoration and Neurotechnology.
He said: “This is the first time that simultaneous motor stimulation and sensory feedback have been demonstrated in people with complete spinal cord injuries.
“This is an important step towards 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 towards restoring coordinated movements and functional independence.”
During the two-week, in-hospital study, surgeons placed small electrode arrays above and below the injury site along the participants’ spinal cords.
Participants then used a control device, dubbed the “DJ board” by the research team, fitted with knobs and sliders that allowed them to adjust which parts of the spinal cord received stimulation, along with the speed and intensity of the stimulation.
This helped them find patterns that generated flexion and relaxation of leg muscles.
Jonathan Calvert, assistant professor of neurological surgery at the University of California Davis, who worked on the project as a postdoctoral researcher at Brown, said: “Participants told us that using the DJ board was actually a lot of fun.
“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.”
The researchers then used data from the DJ board experiments to train a machine learning model, a computer system that identifies patterns in data, to optimise the stimulation patterns and find the most precise matches between desired muscle activity and stimulation parameters.
A similar process was then used to optimise stimulation above the injury site to produce useful sensory feedback.
Because the neural wiring of the sensory pathways to the brain had been severed, the team used a sensory replacement approach, linking sensations in other parts of the body, such as the chest, arm or back, to different positions of the legs.
While blindfolded, participants were able to report the angle of their knees with high accuracy based on the intensity of sensations generated by stimulation.
In a final experiment combining both approaches, participants performed walking movements on a treadmill while supported by a ceiling-mounted harness and aided by physical therapists.
They were able to engage the muscles needed for walking while accurately reporting when their feet struck the ground.
One participant said: “[I] could tell when [my foot] hit based on feedback up to here [pointing to chest]. It wasn’t like I could feel my foot hit the treadmill or anything like that, but it was close.”
Jared Fridley, chief of spinal neurosurgery at the University of Texas at Austin, who contributed to the research while he was a neurosurgeon at Rhode Island Hospital, said: “By simultaneously restoring motor activation and meaningful sensory feedback, we’re moving beyond isolated function toward coordinated, purposeful movement.
“That’s a critical step if neurotechnology is going to translate into real-world independence for people living with severe spinal cord injury.”
No device-related adverse effects from the implanted electrodes or the electrical stimulation protocols were reported. The team plans to recruit new participants in a longer-term study testing spinal stimulation outside the hospital setting.
Borton said: “There’s reason to believe that coordinated stimulation across an injury site could produce positive rehabilitation effects.
“That’s not something we were able to fully explore in this study, but that we plan to pursue in future work.”
