The proverbial story of overcoming paralysis tends to start with the legs: Superman vows to walk again; a soap opera character steps out of their wheelchair. “I think society has a tendency to focus solely on the walking aspect of disability,” says Ian Ruder, a magazine editor with the United Spinal Association, a nonprofit advocacy group for people with spinal cord injuries and disorders. But Ruder, who has used a wheelchair following an injury 23 years ago, says even restoring just a fraction of his hand function would improve his quality of life more than walking. “The difference between being able to pinch with my thumb and not be able to pinch with my thumb is hard to understand for most people,” Ruder says. “That would unlock a whole new level of independence.”
Ruder isn’t alone in feeling that way. Surveys of people with quadriplegia find that they rate regaining hand, bladder, core, and sexual function as higher priorities than walking. Yet effective and accessible technologies for restoring motor function to a person’s own upper limb—rather than via a prosthetic device—have been scarce. Earlier this month, however, researchers from the University of Washington’s departments of rehabilitation medicine and electrical and computer engineering reported that they’d restored some hand function in six people using an electrical current delivered through patches on their necks. The benefits emerged quickly and lasted for several months after the trial without continued stimulation—all without any invasive surgery.
“It's totally exciting,” says Ruder, who was not involved in the study. "The possibility of restoring function with such a noninvasive and simple approach is huge."
The lower body, especially the limbs, get more research attention, in part because arm and hand movement is a more complicated dance of motor neurons, muscles, and joints. Researchers have tried to replace or restore that function with a gamut of technologies, from brain-computer interfaces (BCIs) and prosthetics to electrical stimulation for nerves and muscles. Implanted BCIs show promise, but they require surgery to position a chip that reads brain activity, translates it into usable commands, and is worn long-term—and there are costs and infection risks associated with that. Fatma Inanici, a rehabilitation and neuroscience researcher in the Chet Moritz Lab at the University of Washington and lead author of the study, works on something more accessible. "Instead of doing surgery," she says, "you can put the electrodes over the skin and turn on the device to stimulate the spinal cord."
Inanici’s work, published in IEEE Transactions on Neural Systems and Rehabilitation Engineering, builds on earlier evidence that getting current into the spinal cord improves mobility. Her team’s trial tested whether pairing that stimulation with physical rehabilitation training for the participants' hands would allow them to accomplish activities that they couldn’t achieve with training alone. Six people paralyzed by spinal cord injuries joined the trial, each with a range of different abilities, from nearly no hand function to over 50 percent. For a month, they worked each week with a personal coach, pinching beads, stacking blocks, and tying knots. But rehab only got them so far. “All of these things were frustratingly difficult for me,” says Jessie Owen, a teacher from Washington and one of the participants. “I didn’t make much progress.”
The next month, Inanici and her team stuck two flexible round hydrogel electrodes to the back of each participant’s neck, right above the collar. Each patch was about as flat and wide as a quarter, and wired to a stimulator the size of a chunky old cell phone.
Compared to prosthetics and implanted brain chips, the mechanics of neurostimulation are straightforward. Spinal cord injuries reduce the communication between brain and body to a whisper. The brain sends nerves in the arms or hands a cue to move, but the impulse is dampened; it’s not enough to activate movement. Yet even in severe cases, some of that electrical crosstalk persists. The goal of Inanici's neck patches is to turn up the volume—boosting weak signals from the brain to overcome that threshold. The stimulation doesn’t directly jolt muscles into action. But by delivering a strong electrical current to fibers extending from the spinal nerve, called “dorsal roots,” the team hypothesized that they could enable voluntary motion.
But the trick to sending alternating current through the skin that is powerful enough to reach the spine, yet painless, is disguising it in the right overlapping frequency, or carrier wave. At low frequencies, like the kind that runs through your 60-hertz wall outlet, a 10-milliamp current zaps nerves in the skin that communicate pain—it hurts. But at 10 kilohertz, electricity slips by these nerves unnoticed. Inanici used a tablet to control each stimulator’s current, and found she could crank it up to 120 milliamps and keep it noninvasive. “Most people tolerate it easily,” Inanici says. “It's like a buzzing or tingling sensation.” (For the trial, they kept the level between 40 and 90 milliamps.)
Then, once the researchers had wired up the volunteers, the participants resumed their hand activities. For one person, the effect of that spinal cord tingling was immediate. He could squeeze a ping pong ball between his index finger and thumb and drop it into a bucket—moving his digits for the first time since his injury. “The immediate response in the very first session was really unexpected,” says Inanici. “It was thrilling.”
Others, including Owen, improved slowly but noticeably. “It was not a light switch for me, but by the second week, I could stack more blocks,” says Owen. “And I wasn’t fast, I wasn't amazing. But it was a lot better.”
After four months of training—including two with stimulation—every person more than doubled their pinching strength. Several doubled their grasping strength. Inanici says one person regained enough dexterity to drive without an assistive device. Another could handle their catheter well enough to insert it on their own. Owen decided to try painting. At the beginning of the experiment, she recalls, “I was like, ‘I can kind of hold a brush and some paints, and why don't I give this a go?’” So she ordered a paint-by-numbers kit of a portrait of a dog. “It was kind of hard, and I don't think it turned out very well, but I'm still really impressed by it,” she says.
Still, when she brought it to the lab, “that was really an emotional moment for me,” Inanici says. “Even a small contribution to people's well being and quality of life is really so rewarding.”
Why did it work? Inanici thinks it’s because the device made more movement possible, which made rehab easier, which made more movement possible—and so on in a cycle. Renewed activity enticed the neurons to build stronger interconnections, demonstrating neuroplasticity. “By practicing the movement again and again, these activated neural structures become stronger,” says Inanici. “They connect with each other better. So, after a while, they do not need any external stimulation anymore.”
Inanici’s team tracked everyone’s mobility for three to six months after their final training session, hoping that the rehab helped them build back lost function more permanently. They reported that people retained some of their hard-earned gains for up to six months with no stimulation.
“That, I think, is probably the most exciting part about it,” says Peter Grahn, a senior engineer with the Mayo Clinic’s Department of Neurologic Surgery who was not involved in the study. Grahn injured his fifth vertebra in a swimming accident in 2005, resulting in quadriplegia. “To have a potential therapy that can try to recover some of this function is very interesting to me personally, as well as obviously being a researcher in the field,” he says.
Jennifer Collinger is a biomedical engineer at the University of Pittsburgh who develops mobility technology for people with paralysis and has conducted surveys to guide her research. She says that Inanici’s results are convincing and the lasting improvements are encouraging. She notes that researchers in the field know that people with paralysis prefer less cumbersome tech—BCIs and neurostimulation both have ways to go to that end. “We want to make it as easy to use and invisible to people as possible,” she says. “But the best case scenario is that people can just be the way that they were before their injury without any need for daily technology that needs to be put on or calibrated.”
Each emerging approach has its pros and cons. The diversity in the community of people with quadriplegia means there’s not necessarily a single best device for everyone—many disagree over whether surgically-implanted electrodes like BCIs are worth the expense and infection risks, Ruder says.
"The fact that you can stick a couple of electrodes on the back of the neck and generate improvements that seem to be impossible otherwise is intriguing and certainly something exciting, because it's so easy to do, and I'm sure will lead to new studies in the future," says Robert Gaunt, a neural engineer who develops BCIs, prosthetics, and stimulation tech at the University of Pittsburgh. But he points out that the study’s small sample size complicates the math of quantifying average gains. Small improvements are more significant for someone starting with almost no function than someone with partial function. And with the diversity of injuries out there, a six-person trial can’t speak for everyone. "Without further study," he says, "it would be really difficult to predict how much improvement any particular person with a spinal cord injury that might undergo this sort of therapy, how much they might benefit from this sort of thing."
And spinal cord injury is also not the only cause of paralysis. Stroke, infectious disease, and multiple sclerosis silence brain-body communication differently, and so they might not respond to an extra stimulating boost to the spinal cord the same way. Inanici says her team’s future work will include more people and different underlying conditions. Their eventual goals are to test the device’s long-term safety, whether it leads to lasting improvements, and to make it more portable. Right now, the device has wires, a pocket-sized stimulator, and requires a person to control it by tablet. Inanici envisions the tech one day using a smaller stimulator and a phone app.
She is quick to point out that much of restoring mobility remains a puzzle. For example, one of their six volunteers showed results that surprised them. Following a spinal injury 12 years ago, the man’s heart rate often sank to 40 beats per minute, leaving him dizzy and nearly fainting. Four days into stimulation, however, his heart rate began inching up to a more normal 60 beats per minute—an effect on his involuntary movement, not his hand motions. “We didn’t expect it,” says Inanici; in the paper, her team could only speculate as to how that happened.
"There's really good evidence that it is beneficial," Gaunt says of combining physical training with electrical stimulation to the spinal cord. "But boy, for many of these things, we just don't really quite know how they work."
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