A brain-to-spine wireless implant uses electrical stimulation of the spinal cord combined with weight therapy to help patients with spinal cord injuries walk.
A pioneering “brain-to-spine” wireless implant that combines targeted stimulation of the spinal cord and weight resistance-assisted therapy has helped three patients with spinal cord injuries learn to walk again with the support of crutches or a walker.
Most individuals with paraplegia, or paralysis of the legs and body caused by spinal cord injury, need wheelchair assistance for the rest of their lives. While physical therapy can help them regain some lost function, restoring meaningful movement to the legs has remained out of reach. The spinal stimulation protocol, known as stimulation movement overground (STIMO), is not the first attempt to use electrical stimulation to try to restore communication between the nerve cells in the spine and brain, said Fabien Wagner, PhD, a post-doctoral fellow in Grégoire Courtine’s laboratory at Switzerland’s Ecole Polytechnique Fédérale de Lausanne (EPFL), which developed the solution.
“People have tried continuous stimulation of the spinal cord in the past. But this has not worked so well,” he said. “Through work on animal models, we learned that the specific timing and location of stimulation is very important. So we have developed specific configurations for specific functionalities.”
The problem with continuous stimulation devices is that they are not always precise in their targeting, resulting in uncoordinated or unwanted movements. In many cases, patients also lose whatever gains they’ve made after the stimulation is powered off.
To compensate for these issues, Courtine’s group developed a series of targeted stimulation patterns. For example, one spatio-temporal pattern of stimulation activates the hip flexors, which lift the leg and control bending. Another pattern activates the leg extensors, which flex the thigh at the hip and extend the leg at the knee. The combination of those two patterns helps the right nerve cells communicate, promoting the kinds of movements that facilitate independent walking.
The STIMO device, made up of an array of electrodes surgically implanted below the area of injury on the spinal cord, connect to a neurostimulation device placed in the abdomen. It sends targeted stimulation to the muscles, creating a facsimile of the brain and spinal cord’s natural communication signals that can be personalized for each patient. The team modified clinically approved technology, using the hardware of a Medtronic neurostimulator while changing the firmware to enable real-time control.
After implantation, patients trained with weight-assisted therapy for six months to help them strengthen muscles that had gone long unused and to “reconnect” the spine to those leg muscles, restoring the critical nervous system signaling that is required for a person to move. Within a week, the three patients were learning how to walk again with the assistance of crutches or a walker. The patients maintained the recovered function even after stimulation was turned off.
“The stimulation activates these muscles in real-time to reproduce the dynamics of motor neuron activation during the act of walking,” Wagner said. “By looking at the dynamics of how humans walk, we tried to replicate it in patients with spinal cord injury, and were able to help them recover some of those motor capabilities.”
José Contreras-Vidal, Ph.D., a biomedical engineer who works on brain-controlled exoskeletons at the University of Houston and was not involved with this study, said the findings are “very powerful.”
“This study shows us the importance of building models of how the muscles work to see what is missing,” he said. “It was far-reaching to think that continuous stimulation would solve the problem. This study shows us why it is so important to look at these patterns of activation in the brain and spinal cord to help restore function after spinal cord injury.”
Wagner said that the results are promising, but that he and his colleagues have a lot of work to do to refine the device and make it ready for real-world use. That will require patients taking the rehabilitation set-up home to continue their training. They also plan to modify the device so a physical therapist can easily customize and optimize it for each patient through an easy-to-use software program.
“We are currently working on developing new technologies that are tailored for this application” Wagner said. “In the future, we would all of our procedures to be automated, and we are working, in parallel, to do that. In the meantime, we are constantly learning by working with our patients on what kind of approaches we can develop for future directions. And, with this, we see that using targeted spatio-temporal stimulation can really bring something meaningful to a large population of patients.”
Kayte Sukel is an independent writer who focuses on technology.