Neuroscience

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Paralysis breakthrough: spinal cord damage repaired

I suddenly noticed I could move my pinkie. I was cruising towards the highway when this old guy tried to cross the 4-lane road really fast. He hit me and I ejected over to the opposite lane. Luckily someone found me before the traffic got to me.

Paralysis may no longer mean life in a wheelchair. A man who is paralysed from the trunk down has recovered the ability to stand and move his legs unaided thanks to training with an electrical implant.

Andrew Meas of Louisville, Kentucky, says it has changed his life. The stimulus provided by the implant is thought to have either strengthened persistent “silent” connections across his damaged spinal cord or even created new ones, allowing him to move even when the implant is switched off.

The results are potentially revolutionary, as they indicate that the spinal cord is able to recover its function years after becoming damaged.

Previous studies in animals with lower limb paralysis have shown that continuous electrical stimulation of the spinal cord below the area of damage allows an animal to stand and perform locomotion-like movements. That’s because the stimulation allows information about proprioception – the perception of body position and muscle effort – to be received from the lower limbs by the spinal cord. The spinal cord, in turn, allows lower limb muscles to react and support the body without any information being received from the brain (Journal of Neuroscience, doi.org/czq67d).

Last year, Susan Harkema and Claudia Angeli at the Frazier Rehab Institute and University of Louisville in Kentucky and colleagues tested what had been learned on animals in a man who was paralysed after being hit by a car in 2006. He was diagnosed with a “motor complete” spinal lesion in his neck, which means that no motor activity can be recorded below the lesion.

First, the man had extensive training in which his legs were moved by physiotherapists while his weight was supported by a harness. During this time no improvement was observed.

He then had a 16-electrode array implanted into the lower region of his spinal cord, which stimulated spinal nerves with continuous electrical activity. When the implant was switched on and he was helped into the correct position, he succeeded in holding his own body weight and standing on his first attempt.

Then something unexpected happened. Seven months into training on how to stand using the implant, he tried to move his toe while the stimulation was on. “He just started trying to move his toe,” says Angeli. “He was like, ‘look it’s wiggling!’ Further testing showed that he was able to move his leg and ankle, too – indicating that voluntary signals from the brain were crossing the lesion.

Over time, the volunteer also gained increased bladder control and sexual function, and had better temperature regulation (The Lancet, doi.org/b3spxp). All of these abilities involve input from the brain, confirming information could now be sent across the damaged area of the spine, as long as the stimulation was on.

Reggie Edgerton of the University of California, Los Angeles, who also worked on the study, says that their initial reason for doing the experiment was to utilise proprioception to tell the spinal cord what to do to allow someone to stand. “We had no idea that the stimulation would be working upwards as well, doing something to the connections between the spinal cord and the brain,” he says.

One possible explanation is that new connections grew across the spinal lesion. But since this response to stimulation has never been shown in animals, a more likely explanation is that the stimulation pushed the activity of damaged connections over a threshold needed for them to send information from the brain to the limbs. “There may be ‘silent’ connections that can’t be seen by current imaging techniques, and are too damaged to work by themselves, which can be boosted into crossing a threshold of activation by the stimulation,” says Edgerton.

Another suggestion is that the sensory fibres that allowed this particular patient to retain some feeling in his legs may have been used in motor control. To rule this out, Angeli and her colleagues recruited Meas and another volunteer who had complete motor and sensory paralysis. From the first session with the electrical implant, both were able to move their lower limbs when the stimulation was on.

"We think that the first volunteer may have been able to do it straight away too, but just never tried," says Angeli, who presented the results at the Society for Neuroscience Conference in New Orleans last week.

Over time, all three of the volunteers were able to carry out a variety of movements ranging from whole leg flexion to toe extension. Their coordination also improved and they could generate more force from each movement. And after four months of training, the amount of stimulation needed to create the same amount of movement fell.

However, there was a final surprise in store. At the conference, Angeli showed how, after three months, Meas was able to stand and move his lower limbs without the aid of stimulation. “One day he was training with the stimulation and we shut it off and he was still able to move,” she says. “We didn’t expect to see it happen so quickly.”

We now need to learn how to push these silent connections above their threshold, says Edgerton. He thinks it may simply be a case of improving the implants. “We’re using an implant that was build three decades ago and designed to suppress pain.

We thought it would be good enough to show proof of principle, but our volunteers are going crazy because they know what they need to do but the stimulation device isn’t good enough yet to allow them to do it.”

For now, none of the volunteers can walk without support. “We have a feeling that it’s a question of the technology restricting us, that being able to control stimulation to the left and right legs separately might help,” says Angeli.

Brian Noga, who works on spinal damage research at the University of Miami Health System in Florida, says the work clearly demonstrates that even people with the most severe spinal injuries may have some remaining connections.

"It really makes us open our mind to very new possibilities," says Edgerton. "All those individuals that are considered completely paralysed and know about this experiment, you know they are thinking ‘am I one of those that can do this?’ We just don’t know."

by Helen Thomson, NewScientist

Filed under spinal cord spinal cord injury paralysis implants Neuroscience 2012 electrical stimulation neuroscience science

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