Spinal Stimulators Repurposed to Restore Touch in Lost Limbs

Although it’s possible to simulate touch by stimulating the remaining nerves in the residual limb after an amputation, such surgery is highly complex and individualized. But according to a study from the University of Pittsburgh’s Rehab Neural Engineering Labs, spinal cord stimulators commonly used to relieve chronic pain could provide a straightforward and universal method for adding sensory feedback to a prosthetic arm.

For this study, published in eLife, four amputees received spinal stimulators, which, when turned on, created the illusion of sensations in the missing arm.

“What’s unique about this work is that we’re using devices that are already implanted in 50,000 people a year for pain—physicians in every major medical center across the country know how to do these surgical procedures—and we get similar results to highly specialized devices and procedures,” said study senior author Lee Fisher, PhD, assistant professor of physical medicine and rehabilitation, University of Pittsburgh School of Medicine.

The strings of implanted spinal electrodes, which Fisher describes as about the size and shape of “fat spaghetti noodles,” run along the spinal cord atop the same nerve roots that would normally transmit sensations from the arm.

Fisher’s team sent electrical pulses through different spots in the implanted electrodes one at a time, and all the participants experienced sensations somewhere on their missing arms or hands. Three participants reported feelings localized to a single finger or part of the palm.

“That’s important because we want to generate sensations only where the prosthetic limb is making contact with objects,” Fisher said.

All four participants reported feeling natural sensations, such as touch and pressure, though these feelings were often mixed with decidedly artificial sensations, such as tingling, buzzing, or prickling.

The next big challenges are to design spinal stimulators that can be fully implanted rather than connecting to a stimulator outside the body and to demonstrate that the sensory feedback can help to improve the control of a prosthetic hand during functional tasks like holding an egg without accidentally crushing it. Shrinking the size of the contacts—the parts of the electrode where current comes out—is another priority. That might allow users to experience even more localized sensations.

To watch a video about this technology, visit bit.ly/318vIli.

This article was adapted from information provided by Health Sciences at the University of Pittsburgh.

IMAGE: Spinal leads exit the back to connect to an external stimulator. UPMC.

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