Several patients who had been paralyzed in their lower limbs for years have now regained some feeling and movement in their limbs, after learning to control a robotic exoskeleton with their brain, a new study says.

The findings were unexpected - researchers had been training the patients to use so-called brain-machine interfaces, including the robotic exoskeleton, with the hope that the patients could one day use the machines to help them walk again.

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But the training appears to have had additional benefits: After a year, the patients experienced improvements in their ability to perceive sensations of touch below their spinal cord injury, and regained some control over muscles in their lower limbs, the study found.

In fact, out of the eight patients in the study, four experienced changes in their muscle control that were significant enough to upgrade their diagnosis from "complete paralysis" (when people have no control over the muscles below their spinal injury) to "partial paralysis" (when people have some control over these affected muscles.)

"We couldn't have predicted this surprising clinical outcome when we began the project," said Dr. Miguel Nicolelis, a neuroscientist at Duke University who conducted the study as part of the Walk Again Project in São Paulo, Brazil.

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The patient with the biggest improvements was a 32-year old woman who had been paralyzed for 13 years. At the start of the study, she was not able to stand using braces at the start of the study, but by the end of the study, she could move her legs on her own while her body weight was supported with a harness.