Implanted brain electrodes send signals that bypass damaged spinal cord area, using man’s thoughts to stimulate leg movement
Gert-Jan Oskam lost the ability to walk in 2011 when he injured his spine in a cycling accident in China. Six years later, the Dutch man managed to take a few short steps thanks to a small array of electrodes implanted on top of his spinal cord that delivered nerve-stimulating pulses of electricity. The device allowed him to walk, but the process was stilted and sometimes frustrating.
Today in Nature, an international team of researchers reports giving Oskam a better fix, a way to digitally bridge the communication gap between his brain and lower body. Brain waves signaling Oskam’s desire to walk travel from a device implanted in his skull to the spinal stimulator, rerouting the signal around the damaged tissue and delivering pulses of electricity to the spinal cord to facilitate the movement. Oskam can now walk more fluidly, navigate obstacles, and climb stairs. “The stimulation before was controlling me, and now I am controlling stimulation,” he says.
This new brain-spine interface also seems to foster greater recovery than stimulation alone. Oskam, who retained some intact spinal cord connections after the accident, can also walk using crutches even with both devices turned off, something he had never been able to do before.
Spinal cord stimulation and brain interfaces have both been used in the past, but “they haven’t ever been put together quite this way,” says Keith Tansey, a neurologist at the Methodist Rehabilitation Center. “From a biomedical engineering perspective, it’s a real tour de force.” But he and others, including study authors, stress that it’s important to recognize that the study is a proof of concept with a single participant. Whether the other people with spinal cord injuries will see the same results isn’t yet clear.
Some paralyzing injuries completely sever the spinal cord, but more often, damaged connections between the brain and the lower body remain. For decades, scientists have attempted to find ways to repair these broken nerve highways.
The new study builds on work by Grégoire Courtine, a neuroscientist at the Swiss Federal Institute of Technology in Lausanne, and Jocelyne Bloch, a neurosurgeon at the University of Lausanne. In 2018, the duo and colleagues showed that spinal stimulation combined with intensive training could help people with partial paralysis walk. Oskam was one of the first three participants in that trial, each of whom retained some sensation in the lower body. Last year the researchers reported that stimulation also works in people with more severe injuries who had no sensation or movement in their legs.
But spinal stimulation has some drawbacks. To initiate walking or standing, the user has to manually provoke the signal, say by pushing a button. Oskam could still lift his heel after his injury, and a sensor on his foot could detect this tiny movement, launching the stimulator. After that, the induced movement was robotic and automatic—not under Oskam’s conscious control. On its own, spinal stimulation is “a bit of puppeteering,” says Dennis Bourbeau, a biomedical engineer at the Louis Stokes Cleveland Veterans Affairs Medical Center and researcher at the MetroHealth System.
“I felt with every step a bit stressed,” Oskam says. “I had to be in time with the rhythm otherwise I wouldn’t make a good step.” And many of the movements that would have been useful in daily life—climbing stairs, for example—were out of reach.
The new system aims to make the process more seamless. The brain interface consists of two arrays with 64 electrodes, each embedded in a titanium case. These are surgically embedded in the skull, one on each side of the head, where they sit on top of the motor cortex and capture electrical signals. These signals travel wirelessly to a headset and then to a laptop in a backpack worn by Oskam, where an algorithm decodes his intended movement. The computer then sends these predictions to the stimulator, which delivers different patterns of electrical pulses depending on the desired movement. Combining these devices was not an easy endeavor because “none of these systems are supposed to talk to one another,” says An Do, a neurologist at the University of California, Irvine.
Oskam’s updated system allows him to more precisely control his hip, knee, and ankle joints. After 40 training sessions, he can step, walk, stand, and even climb staircases. And the benefits seem to persist even when the devices are turned off, which suggests the connections between his brain and lower body may have strengthened.
“It’s still very much the early days, but as a proof of concept in a human being, I think it’s a huge step forward,” says Nandan Lad, a neurosurgeon at Duke University.
Michael Fehlings, a neurosurgeon at the University of Toronto, says the results are impressive, but it’s not yet clear which people with spinal cord injuries might benefit and how much function they might regain. “This is an n of 1, and the patient is likely extremely carefully selected.”
And some patients might be turned off by the invasiveness of the therapy. Implanting the devices requires open brain surgery, which comes with risks. In fact, one of the Oskam’s brain implants had to be removed after about 6 months because of a staph infection.
The researchers say their next steps will be to make the technology less bulky. Bloch and Courtine co-founded a company called Onward that plans to develop a streamlined, fully integrated system. The team also plans to test whether the brain-spine interface can help improve or restore upper body movement in patients with higher spinal injuries.
Fehlings is eager to see how the technology advances. “It’s a very interesting case report. It’s a beautiful piece of engineering,” he says. “But the results have to be interpreted with caution.”