"It's an awesome feeling", says David Mzee, whose left leg was paralyzed in 2010. A team at the University of Louisville reported in September that stimulating the spinal cord-known as neurostimulation-allowed two people to stand independently and walk with assistive devices, like a walker.
The technique is called spinal cord electrical stimulation and, thanks to it, the volunteers who took part in the study could recover some their walking ability, even if not totally. The results, published in Nature and Nature Neuroscience, are dramatic.
Another patient, Sebastian Tobler, said he can now walk a few steps hands-free in the lab with the aid of electrical stimulation. When it's on, he's able to walk more than half a mile.
The difference lies in how constant the electrical stimulation is.
"Selected configurations of electrodes are activating specific regions of the spinal cord, mimicking the signals that the brain would deliver to produce walking", she said.
In rodents, cats, and even monkeys, EES has allowed "standing, walking in various directions, and even running", write Courtine and his colleagues. Physiological differences between humans and rats-including just the difference in body size-could explain why this affects humans and not rats, they suggest.
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"If we can stimulate the central nervous system and peripheral nervous system at the same time, the additive effects could restart touch perception and movement in some people". Then the pattern of electrical signals was calibrated for each individual. In ongoing tests of the system, the patients were able to adjust the length and speed of their strides and to walk on a treadmill for an hour-traveling the equivalent of up to one kilometer.
The University of Technology Sydney will have a research centre capable of administering this treatment in trials within the next year, according to Professor Vissel.
"The participants are constantly challenged to voluntarily generate the appropriate leg movements", says co-author Karen Minassian. This could be due to the fact that the precisely targeted and timed bursts of electrical stimulation aided the patients' movement without getting in the way of sensory signals coming from their legs, the researchers theorised. Also the movement seen is in controlled laboratory conditions.
When the electric device is switched off, Mzee can still walk up to eight paces, the first-ever recording of this in a chronic spinal cord injury.
The study also focused only on patients who had retained some feeling in their lower body. "Now I can walk short distances with the help of electrical stimulation and even without electrical stimulation", he says. "I was like, should we enroll this participant?" But for now, the stimulators are only being used in a small number of patients in research settings. All the participants continued to improve during the five-month course of the study, Courtine says. Understanding the results in a larger population is a crucial next step. Courtine says that if they could use the implant early after the injury, the results may be more encouraging.
And essential, they add, is ensuring that the treatment translates outside of the hospital. Moreover, they exhibited no leg-muscle fatigue, and so there was no deterioration in stepping quality. The real life procedures are not almost as extreme, but they have helped three patients get back on their feet through what it called patterned stimulation.