LONDON: A man who was paralysed from the waist down has become the first such case to walk again using only his own brain power.
Neurosurgeons achieved the world first by transmitting signals from the 26-year-old American's brain to electrodes placed around both knees.
The man, who had been paralysed five years earlier following a motorcycle accident, is the first to walk without relying on manually operated robotic limbs.
The "neural bypass" procedure generated impulses triggering movement that avoided the torn spinal cord, the University of California study discovered.
After extensive training, the man managed to step falteringly along a 12ft (3.66m) course while a harness and walking frame prevented him from falling.
Dr An Do, from the University of California at Irvine, who co-led the study, said: "Even after years of paralysis the brain can still generate robust brain waves that can be harnessed to enable basic walking.
"We showed that you can restore intuitive, brain-controlled walking after a complete spinal cord injury. This non-invasive system for leg muscle stimulation is a promising method and is an advance of our current brain-controlled systems that use virtual reality or a robotic exoskeleton."
Although the man is still a long way from the freedom of movement he had before his accident, the fact that he was able to walk at all is a major achievement. The nerves of the spinal cord are unable to regenerate and severing them usually results in irreversible life-long paralysis.
British charities said they were excited by the news, which could offer hope to thousands of people who have suffered spinal cord injury. Estimates suggest there are 40,000 such cases in the UK, with 1,200 injuries which result in paralysis each year.
Further work is needed to establish whether the procedure can be used to restore a practical level of walking ability and help other patients.
In future, the electrode cap used in the study to record brain signals is likely to be replaced by hidden implants.
Dr Zoran Nenadic, study co-author also from the University of California at Irvine, said: "We hope that an implant could achieve an even greater level of prosthesis control because brain waves are recorded with higher quality.
In addition, such an implant could deliver sensation back to the brain, enabling the user to feel their legs."
Learning how to walk again involved a 19-week multi-step training programme.
First, the patient was taught to control a virtual reality "avatar" with his brain
waves and given exercises to recondition and strengthen his leg muscles.
Later he practised walking while suspended five centimetres above the ground, so that his legs could move freely without having to be supported.
After 20 sessions he graduated to a body-weight support system to prevent falls.
The system used a bluetooth connection to transmit electroencephalogram (EEG) brainwave signals wirelessly from the patient's cap to a computer.
After decoding the brainwave patterns the computer sent command messages to a belt-mounted microcontroller worn around the man's waist.
This in turn fired the trigger impulses that activated the leg muscles.
The results are reported in the Journal of NeuroEngineering and Rehabilitation.
During the experiment the patient was able to conduct a "light conversation" with the test team while attempting to walk, the scientists said.
They wrote: "This robustness in real-time control, together with a high level of performance sustained across months, indicates that BCI-FES (brain-computer interface functional electrical stimulation) mediated restoration of basic walking function after SCI (spinal cord injury) is feasible."