Spinal stimulators repurposed to restore touch in lost limb

Date:
July 21, 2020
Source:
University of Pittsburgh
Summary:
Devices commonly implanted for chronic pain could expand patient
access to prosthetic arms that ''feel.''


FULL STORY ========================================================================== Imagine tying your shoes or taking a sip of coffee or cracking an egg
but without any feeling in your hand. That's life for users of even the
most advanced prosthetic arms.


========================================================================== Although it's possible to simulate touch by stimulating the remaining
nerves in the stump after an amputation, such a surgery is highly complex
and individualized. But according to a new 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 today in eLife, 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," said study senior author Lee Fisher, Ph.D.,
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, 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.



==========================================================================
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 said. "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 said. "If the electrodes are moving around, that's going to change what a person
feels when we stimulate." 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," Fisher said. "Mostly we wanted to demonstrate the
possibility that something like this could work."

========================================================================== Story Source: Materials provided by University_of_Pittsburgh. Note:
Content may be edited for style and length.


========================================================================== Journal Reference:
1. Santosh Chandrasekaran, Ameya C Nanivadekar, Gina McKernan, Eric
R Helm,
Michael L Boninger, Jennifer L Collinger, Robert A Gaunt, Lee
E Fisher.

Sensory restoration by epidural stimulation of the lateral spinal
cord in upper-limb amputees. eLife, 2020; 9 DOI: 10.7554/eLife.54349 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/07/200721084158.htm

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