Rats with a spinal cord injury that left their hind legs completely paralyzed learned to walk again on their own after an intensive training course that included electrical stimulation of the brain and the spine, scientists reported on Thursday.


Researchers have known for some time that stimulation and training can improve muscle control somewhat after such injuries in animals. And last year, an international team of scientists reported the case of a 23-year-old paraplegic who regained the ability to stand for a few minutes at a time after a similar program.


But the new study is the most comprehensive and rigorous presentation to date of what is possible, and the Swiss research team is already working on technology to test the techniques in humans.


The report, published online on Thursday in the journal Science, provides a striking demonstration of what until recently few scientists thought possible: complete rehabilitation after a disabling blow to the spinal cord. After weeks of training, many of the rats could walk as well as before the injury, and some could run.


The findings do not apply to all spinal injuries. The animals’ spinal columns were cut without being completely severed; there were still some nerve connections that extended intact through the injured area. But this is also the case for a substantial proportion — perhaps a quarter to a third — of people whose injuries are severe enough to confine them to a wheelchair.


“This is a very exciting study, and my first thought is that it is a proof of principle for treating spinal cord injuries from a wide variety of conditions, including cancer and even multiple sclerosis,” said Dr. Vineeta Singh, a neurologist at San Francisco General Hospital and the University of California, San Francisco, who was not involved in the study. “There’s a huge potential to refine this model to mimic more humanlike conditions.”


In the study, a research team led by Grégoire Courtine of the Federal Institute of Technology in Lausanne, known as EPFL, gave a group of 10 rats the same surgical injury, cutting all direct nerve connections to the hind legs but stopping short of severing the spinal cord. The rats lost the use of their hind legs, but not their front legs.


The rats then began a daily regimen. Outfitted with tiny vests, held upright on their back legs but left to bear their full weight, the rats tried to move toward a piece of cheese that beckoned nearby. They lurched forward like furry paratroopers, unsteady on their feet after a hard landing. 


The scientists provided stimulation in three places: electrically, in the motor area of the brain and in the spinal cord below the injury, and chemically, infusing the wound area with drugs thought to promote growth.


And growth is what they got. After two to three weeks of 30-minute daily sessions, the rats began to take their first voluntary steps. After six weeks, all of the rats could walk on their own, and some could run and climb stairs.


A comparison group of rats that trained more passively on a treadmill did not recover nearly as well. Voluntary motion — hard work combined with sustained stimulation — was necessary for the brain to re-establish command over the limbs.


“The way I think about it is that there is this little island of spare tissue in the injured area, and the neurons in that island begin to act as a relay center, bypassing the injury,” Dr. Courtine, who is also affiliated with the University of Zurich, said in a telephone interview.


In effect, he said, the training forces the brain to recruit what is left of the neural system to get the job done. Neurons sprout like seedlings on a Chia Pet when they are seeking new connections, and the scientists found increases of 300 percent and more in projections in the brain stem and around the injury — evidence that the nervous system was remapping its connections.


Dr. Courtine’s group has demonstrated such recoveries in some 100 rats and is now developing technology for a human trial.


“This effectively affirms in animal models how active state — the person is trying to move — paired with the spinal cord implant confer plasticity in spared neural connections,” Dr. Singh said in an e-mail.