Swiss scientists have helped paralysed monkeys regain control of non-functioning limbs in research that might one day help people.
The scientists treated the monkeys with a neuroprosthetic interface that acted as a wireless bridge between the brain and spine.
They said they had started small feasibility studies in humans to trial some components.
Jocelyne Bloch, a neurosurgeon at the Lausanne University Hospital, surgically placed the brain and spinal cord implants in the monkey experiments.
"The link between the decoding of the brain and the stimulation of the spinal cord - to make this communication exist - is completely new," she said.
"For the first time, I can imagine a completely paralysed patient able to move their legs through this brain-spine interface."
Gregoire Courtine, a neuroscientist at the Swiss Federal Institute of Technology (EPFL), which led the work, cautioned there were major challenges ahead.
"It may take several years before this intervention can become a therapy for humans."
The team published their results in the journal Nature.
They said the interface decoded brain activity linked to walking movements and relayed that to the spinal cord - below the injury - through electrodes that stimulated neural pathways and activated leg muscles.
The scientists successful treated two rhesus monkeys, each with one leg paralysed by a partial spinal cord lesion.
One of the monkeys regained some use of its paralysed leg within the first week after injury, without training, both on a treadmill and on the ground. The other took about two weeks to recover to the same point.
"We developed an implantable, wireless system that operates in real-time and enabled a primate to behave freely, without the constraint of tethered electronics," Courtine said.
The brain and spinal cord can adapt and recover from small injuries, but, until now, could not overcome severe damage.
Other attempts to repair spinal cords have focused on stem cell therapy or combinations of electrical and chemical stimulation.
Independent experts not directly involved in the work said it was a step towards a potential future where paralysed people could walk again.
Simone Di Giovanni, a specialist in restorative neuroscience at Imperial College London, said EPFL's results were "solid, very promising and exciting", but would need to be tested further in more animals and in larger numbers.
"This is still very uncertain."