Gert-Jan Oskam was living in China in 2011 when he was involved in a motorcycle accident that left him paralyzed from the hips down. Now, with a combination of devices, researchers have given him control of his lower body again.

“For 12 years I’ve been trying to get back on my feet,” Oskam said in a press conference on Tuesday. “Now I’ve learned to walk normally, naturally.”

In a study published Wednesday in the journal Nature, researchers in Switzerland described implants that provided a “digital bridge” between Mr. Oskam’s brain and his spinal cord, bypassing damaged sections. The discovery enabled Mr Oskam, 40, to stand, walk and climb a steep ramp using only a walker. More than a year after the implant was inserted, he has retained these abilities and has actually shown signs of neurological recovery, walking with crutches even after the implant was turned off.

“We have captured Gert-Jan’s thoughts and translated those thoughts into a stimulation of the spinal cord to restore voluntary movement,” Grégoire Courtine, a spinal cord specialist at the Swiss Federal Institute of Technology, Lausanne, who helped lead the research, said at the press conference.

Jocelyne Bloch, a neuroscientist at the University of Lausanne who placed the implant in Oskam, added: “It was quite science fiction at first for me, but it became true today.”

There have been a number of advances in the technical treatment of spinal cord injury in recent decades. In 2016, a group of researchers led by Dr. Courtine was able to restore ability to walk in paralyzed monkeys, and another helped a man take back control of his crippled hand. In 2018, another group of researchers, also led by Dr. Courtine, a way to stimulate the brain with electric pulse generators, enabling partially paralyzed people to walk and cycle again. Last year, more advanced Brain stimulation procedures allowed paralyzed subjects to swim, walk and cycle within a single day of treatment.

Mr. Oskam had undergone stimulation procedures in previous years and had even regained some ability to walk, but eventually his improvement plateaued. At the press conference, Oskam said that these stimulation techniques had made him feel that there was something alien about the movement, an alien distance between his mind and body.

The new interface changed this, he said: “The stimulation used to control me, and now I control the stimulation.”

In the new study, the brain-spine interface, as the researchers called it, utilized a artificial intelligence mind decoder to read Mr Oskam’s intentions – detectable as electrical signals in his brain – and match them with muscle movements. The etiology of natural movement, from thought to intention to action, was preserved. The only addition, which Dr. Courtine described it, was the digital bridge spanning the damaged parts of the spine.

Andrew Jackson, a neuroscientist at Newcastle University who was not involved in the study, said: “It raises interesting questions about autonomy and the source of commands. You continue to blur the philosophical line between what is the brain and what is technology.”

Dr. Jackson added that researchers in the field had theorized about connecting the brain to spinal cord stimulators for decades, but that this represented the first time they had achieved such success in a human patient. “It’s easy to say, it’s much harder to do,” he said.

To achieve this result, the researchers first implanted electrodes into Oskam’s skull and spine. The team then used a machine learning program to observe which parts of the brain light up when he tried to move different parts of his body. This thought decoder could match the activity of certain electrodes with specific intentions: One configuration lit up when Oskam tried to move his ankles, another when he tried to move his hips.

Then the researchers used another algorithm to connect the brain implant to the spinal cord implant, which was set to send electrical signals to different parts of his body, triggering movements. The algorithm was able to account for small variations in the direction and speed of each muscle contraction and relaxation. And because the signals between the brain and spine were sent every 300 milliseconds, Oskam could quickly adjust his strategy based on what worked and what didn’t. During the first treatment session, he was able to twist his hip muscles.

Over the next few months, the researchers fine-tuned the interface between the brain and spine to better accommodate basic actions such as walking and standing. Mr. Oskam regained a somewhat healthy-looking gait and was able to walk over steps and ramps relatively easily, even after months without treatment. In addition, after a year in treatment, he began to notice clear improvements in his movement without the aid of the brain-spine interface. The researchers documented these improvements in weight bearing, balancing and walking tests.

Now Mr. Oskam can walk in a limited way around his house, get in and out of a car and stop at a bar for a drink. For the first time, he said, he feels like he’s in control.

The researchers acknowledged limitations in their work. It is difficult to discern subtle intentions in the brain, and while the current brain-back interface is suitable for walking, the same probably cannot be said for restoring upper body movement. The treatment is also invasive and requires multiple surgeries and hours of physical therapy. The current system does not fix all spinal palsy.

But the team was hopeful that further advances would make the treatment more accessible and more systematically effective. “This is our true goal,” said Dr. Courtine, “to make this technology available worldwide to all patients who need it.”