The patients used brain-machine interfaces, including a virtual reality system that used their own brain activity to simulate full control of their legs. Videos accompanying the study illustrate their progress.

The research -- led by Duke University neuroscientist Miguel Nicolelis, M.D., Ph.D., as part of the Walk Again Project in São Paulo, Brazil -- offers promise for people with spinal cord injury, stroke and other conditions to regain strength, mobility and independence.

"We couldn't have predicted this surprising clinical outcome when we began the project," said Nicolelis, co-director of the Duke Center for Neuroengineering who is originally from Brazil.