The research was conducted with collaborators in China, Dr. Courtine said, because Swiss restrictions on animal experiments at the time would not allow the work. Now that the work is proving successful, he has permission to proceed with similar experiments in Switzerland, he said.

Dr. Courtine has written about ethical issues involved in such experiments with primates and emphasized that 10 years of research in rodents was necessary to prepare for the work in monkeys. One of the reasons that only one leg was paralyzed is that four-legged animals can function even without the use of one leg and retain bladder and bowel control, whereas complete severing of the spinal cord can be devastating for an animal’s quality of life.

Further, he said, this kind of work, with all its promise for human beings that have suffered spinal cord damage, cannot be pursued in people without testing in other primates first. The brain recording and the stimulation of the spinal cord involve devices that are already in use in humans for other purposes. Only the brain decoding software has not been used with people.

David Borton, of Brown University, and one of the primary authors of the new report, developed the wireless sensor with colleagues when he was doing doctoral work before he started working with Dr. Courtine. Combined with micro electrodes, it records and transmits impulses in the part of the brain where signals to move the leg originate. He said that one of the reasons the system may be helpful in rehabilitation is that it strengthens remaining connections between parts of the spinal cord and the injured limb. There is a saying in neuroscience, he said, “neurons that fire together, wire together.”

The brain recording device was combined with electrical stimulation to an area just outside the spinal cord that conveyed signals to the reflex system. Walking is only partly under brain control. The spinal cord has its own system for receiving input from the legs and responding. Humans don’t think about walking most of the time, and it’s not that the brain is running the activity below conscious awareness. The spinal cord and reflex system are running much of it.

Dr. Courtine had used electrical stimulation before to train paralyzed rats with spinal cord injuries to walk again.

But that work didn’t involve the brain, and one crucial part of these experiments was timing. “If the brain says it wants that limb to move, it must happen within milliseconds for that connection to strengthen,” Dr. Borton said.