It has been an age-old dictum in neurology that nerve tissue once damaged cannot come back to normal. The hope that someone paralysed for years by a severe spinal-cord injury would ever be able to walk again was just that - hope. But recent advances are bringing those hopes closer to reality. Researchers now describe a treatment - a combination of electrical stimulation of the spinal cord and physical therapy - that has enabled three men with spinal-cord injury to walk. And this is not just in controlled laboratory conditions: they have been able to take walks outside again.
It’s an extraordinary development that could have implications for hundreds of thousands of people around the world. And it’s also the result of decades of cross-disciplinary research that has steadily built an evidence base in animal experiments and taken that work carefully into the clinic.
Researchers have long pursued diverse strategies to repair and reactivate the spinal cord after injury. Many approaches are remarkably effective in regenerating and achieving functional recovery in mice and other animals, but fail to translate to human therapies. The advance in the current study was that, rather than delivering a constant electric current the researchers applied patterns of stimulation calculated to activate the correct groups of leg muscles at the correct time during stepping.
In this way, specific locations in the spinal cord could be targeted, to activate the muscles in a coordinated fashion. This patterned stimulation protocol not only allowed the unprecedented restoration of walking ability, but also enabled the individuals to regain control over previously paralysed muscles when electrical stimulation was turned off. This indicates that the brain and spinal cord had re-established functional connections, revealing an unexpected degree of plasticity.
Spinal injuries vary enormously in their location, severity and outcome, and it will take many more studies to understand who will benefit from this technology. The current research is a proof of concept in a small number of participants who had a range of residual leg function at the start of the study. A major challenge is to understand what determines successful recovery. For example, one source of variability might be how much sensory information the damaged spinal cord can still transmit to the brain.
According to the World Health Organization, between 250,000 and 500,000 people around the globe are affected by a spinal-cord injury each year, most caused by road accidents, falls or violence. Spinal stimulation is a complex and expensive medical procedure, and recovery also seems to require intensive rehabilitation. It will not be available to all, at least, any time soon. But it is a first step.
(Nature Neuroscience 31 October 2018).