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Stimulating a spine to stand

Spinal column lit up on a skeleton

Andrew Meas was driving his car down a 4-lane highway when another driver suddenly cut across in front of him. In the crash that followed he was thrown out of the car and across onto the other carriageway. The accident damaged his spinal cord leaving him paralysed from the neck down. You don't recover from spinal injuries like that. You are left a paraplegic for life: stuck in a wheelchair and dependent on others for everything. Andrew, though, just stood unaided, and it was thanks to an electrical implant intended to relieve back pain.

Wiggle your toes. What just happened is your brain caused an electrical signal to run down the nerves in your spine and then on down your legs. You felt your toes wiggling because electrical signals ran in the opposite direction back to your brain. Andrew Meas had some sensation of feeling in his legs after the accident meaning that some electrical signal was still travelling up his spine. His spinal cord was not completely severed. The paralysis means though that the signals travelling down from the brain don't cross the break.

To be able to just stand without moving seems easy but it's actually quite complicated. That's why it takes babies so long to learn. It involves maintaining balance and for that you actually use information flowing in both directions: up and down your spine - you need information about the position of your body and about how much effort is going in to your muscles, to make the constant fine adjustments that are needed. You do it without thinking.

In fact, your spinal cord isn't just a wire transmitting information to and from the brain. It consists of 'brain' cells - neurons - itself. You really can stand and even walk without thinking: without any help from your brain at all. Once your brain has sent the signal to do so, your spinal cord can just get on with controlling your limbs.

The team of electrical engineers, neuroscientists and medics looking after Andrew and other similar paraplegics - there are over a million just in the US - decided to test an idea that had been tried on animals. They implanted an array of electrodes into their spinal cords. An electrode is just a conductor of electricity that is used to connect between the metal wires of a circuit and non-metallic things - in this case the nerves of Andrew's spinal cord. It gives a way for the doctors to send electrical signals up and down the nerves, just as the brain does. The idea was that stimulating the spinal cord using the electrodes might give it the boost it needed to make it trigger the fine control of the leg muscles that would allow the patients to remain standing without toppling over.

You can stand and even walk without any help from your brain once it has sent the signal to do so!

The medical implant they used is very simple and intended just to relieve back pain - the only kind allowed to be used in humans at the moment. Despite that it worked. The patients could stand. Then one of them decided to try and wiggle his toes...and to everyone's surprise he could do it. After that the other patients with implants found they could force their paralysed limbs to move while the implant was switched on and stimulating their spinal cord. It isn't entirely clear how it happens yet. The most likely idea is that a faint signal is managing to get across the damaged part of their spinal cord and the extra stimulation boosts it to a high enough level that the brain gains control again. The researchers were in for another surprise though, this time from Andrew. After using the implant for several months he found he could actually move his legs even when the implant was switched off! Somehow the stimulation had built up the connections across the damaged area of his spine, reforming the link. He can't walk yet but it's still an amazing thing to have happened.

Better still, now that the team have shown idea works with a really simple array, they think they can do more, with a more complicated array that better mimics the natural signals in the spinal cord. Of course it's hard to experiment on humans. To speed up the work they are combining experiments with results from using computer models of the way the spinal cord works, as well as using special artificial intelligence programs called 'machine-learning algorithms' that can pick out patterns from data. Together this gives them a way of narrowing down the best pattern of signals to use in the electrodes to allow the patients' brains to fully gain control once more. In time they hope that paraplegics with some sense of feeling, as Andrew Maes had, may eventually not only be able to stand and move their legs but actually take steps again too.

Next time you are standing waiting for a bus or train, don't take the fact that you can stand for granted. It's an amazing thing to be able to do, and perhaps seems even more miraculous that it's your spinal cord in immediate control, not your brain. Hopefully in the future more paraplegics will regain that miracle.