Spinal cord stimulators commonly implanted to help relieve chronic pain could add sensory feedback to a prosthetic arm, according to researchers from the University of Pittsburgh, in an eLife study.

In the study from the University of Pittsburgh’s Rehab Neural Engineering Labs, four amputees received spinal stimulators, which, when turned on, create 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.”

— senior author Lee Fisher, PhD, assistant professor of physical medicine and rehabilitation, University of Pittsburgh School of Medicine

Spaghetti Noodles Along the Arm

The strings of implanted spinal electrodes, which Fisher describes as about the size and shape of “fat spaghetti noodles,” run along the spinal cord, where they sit slightly to one side, atop the same nerve roots that would normally transmit sensations from the arm. Since it’s a spinal cord implant, even a person with a shoulder-level amputation can use this device.

Fisher’s team sent electrical pulses through different spots in the implanted electrodes, one at a time, while participants used a tablet to report what they were feeling and where, a media release from University of Pittsburgh explains.

All the participants experienced sensations somewhere on their missing arm or hand, and they indicated the extent of the area affected by drawing on a blank human form. Three participants reported feelings localized to a single finger or part of the palm.

“I was pretty surprised at how small the area of these sensations were that people were reporting,” Fisher says. “That’s important because we want to generate sensations only where the prosthetic limb is making contact with objects.”

When asked to describe not just where but how the stimulation felt, all four participants reported feeling natural sensations, such as touch and pressure, though these feelings often were mixed with decidedly artificial sensations, such as tingling, buzzing or prickling.

Although some degree of electrode migration is inevitable in the first few days after the leads are implanted, Fisher’s team found that the electrodes, and the sensations they generated, mostly stayed put across the month-long duration of the experiment. That’s important for the ultimate goal of creating a prosthetic arm that provides sensory feedback to the user.

“Stability of these devices is really critical,” Fisher adds. “If the electrodes are moving around, that’s going to change what a person feels when we stimulate.”

Challenges Ahead

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 tying shoes or 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.

“Our goal here wasn’t to develop the final device that someone would use permanently. Mostly we wanted to demonstrate the possibility that something like this could work.”

— Lee Fisher, PhD

[Source(s): University of Pittsburgh, Science Daily]

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