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

There have been a number of advances in technological spinal cord injury treatment in recent decades. In 2016, a group of scientists led by Dr. Courtine was able to restore the ability to walk in paralyzed monkeys, and another helped a man regain control of his crippled hand. In 2018, a different group of scientists, also led by Dr. Courtine, devised a way to stimulate the brain with electrical-pulse generators, allowing partially paralyzed people to walk and ride bicycles 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 briefing, Mr. Oskam said that these stimulation technologies had left him feeling that there was something foreign about the locomotion, an alien distance between his mind and body.

The new interface changed this, he said: “The stimulation before was controlling me, and now I’m controlling the stimulation.”

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