Eight paraplegics who used their thoughts to operate a robotic exoskeleton regained partial feeling and control over their legs, according to a study that points to a possible new type of rehabilitation therapy.

The study, published today in Scientific Reports, is a follow-up to a highly publicized spectacle during the 2014 World Cup in Brazil in which a paralyzed patient was shown on television using a brain-controlled robotic exoskeleton to kick a soccer ball.

The Walk Again Project, as it is known, is led by Miguel Nicolelis, a Brazilian-born neuroscientist and longtime professor at Duke University, whose provocative work with brain-computer interfaces has kindled fanfare and skepticism.

A patient moves with the assistance of the brain-controlled robotic exoskeleton.

The eight patients, who all had complete spinal cord injury, meaning they were paralyzed and had no sensation below the lesion, trained twice a week for a year using a brain-computer interface to control either an avatar seen through virtual-reality goggles or a robotic harness.

There’s a growing body of evidence that such biofeedback—like observing an avatar you control—may help people recover from injuries, including strokes. “The approach they are aiming for is enhancing the neurological signals to induce plasticity, the healing of the brain,” says Bolu Ajiboye, a brain-computer interface researcher from Case Western University.

During the study, patients wore caps that recorded their brain waves, or EEG signals, which they used to direct movements of a human figure displayed on an Oculus Rift headset. Patients then graduated to operating a robotic exoskeleton that moved their legs, helping them stand up or walk on a treadmill.

Nicolelis says following the training, patients were able to voluntarily move their legs, however slightly, for the first time in years. They also regained some sensation of feeling in their lower limbs. By the end of the study, half the patients were upgraded from a clinical diagnosis of complete spinal cord injury to “incomplete” paraplegics. In a telephone briefing with journalists, Nicolelis called the results “the first study using long-term brain-machine interface that reports on some kind of partial recovery.”

A patient learns to control an avatar in virtual reality via brain waves.

Exactly why such techniques may help isn’t known. One theory is that when people make repeated efforts to willfully alter their EEG signal, it may help re-establish connections to remaining nerve fibers below the injury area. “We may have rekindled the remaining nerves to be able to send messages from the brain of the patients to the periphery,” says Nicolelis.

Jose Contreras-Vidal, an engineer at the University of Houston who is also researching the use of brain-machine interfaces to power exoskeletons, said it is unclear from Nicolelis’s study which of six different training techniques used might have caused the improvement. That means the technique can’t be applied immediately by rehab centers until it is better understood.

“It is really hard to relate the specific components to the benefits,” said Contreras-Vidal. “Now we need to sit down and tease these effects apart.”