They can't quite walk. Yet. But four wheelchair-bound men who until recently were completely paralysed below the waist can now move their legs and toes and even lift up to 100 kilograms with their legs. Their spinal cords have been reawakened by electrical implants that revive the flow of information between limbs and brain. Such feats would previously have been unthinkable in people with spinal cord injuries.
"We think it's a very large milestone," says Claudia Angeli of the University of Louisville's Kentucky Spinal Cord Injury Research Center. "There's not been anything like this, and no hope previously for the most severely injured patients, so this is a very important step forward for them."

The device ? an array of electrodes ? is implanted not at the point of injury, but in the still intact lumbosacral region of the spinal cord, which is the main information hub linking the brain to the lower limbs. Despite being crushed, Angeli says, the spinal cord and its associated nerve connections retain huge capacity to continue sending messages.
Since New Scientist reported the breakthrough in 2012, the four men have continued to improve their strength, precision and range of movement. "We've not seen a plateau in their performance yet," says Angeli. One of the men, Drew Meas, says he can stand without his stimulator. "I'm going for full walking again, that's my motto," he says.
Angeli is now planning to test the device in a further eight patients. She says that it might be possible to refine the implant so it enables better coordination, possibly leading to walking. With this in mind, she is starting experiments in animals with an implant that has 27 instead of 16 electrodes.
Angeli says the implant restores what in healthy people would be the resting potential of the spinal cord, the baseline electrical activity that keeps the cord alert, but which wanes through lack of use in people who are paralysed.

Once this background electrical impetus is restored artificially, the cord reawakens and can register the brain's "intent" to move from the brain and convert this into fine movement at the motor neuron level. And by modulating the voltage for each individual and for each task, algorithms that optimise delivery of electrical activity for specific movement can be worked out and applied at will by the patients.
But the existing device has limitations, says Angeli. For example, the programs tend to be different for right and left legs or toes, so only one can be moved at a time. The hope is that a more sophisticated device will be able to deliver algorithms simultaneously, and so coordinate movement in both legs to enable standing and walking. Simple as it sounds, this remains a challenge.
Another boost for the men is that to varying degrees they have all recovered bladder, bowel and sexual function. "That really restores dignity," saysRoderic Pettigrew, director of the US National Institute of Biomedical Imaging and Bioengineering in Bethesda, Maryland.