AMPUTEES DISCERN FAMILIAR SENSATIONS ACROSS PROSTHETIC HAND
Even before he lost
his right hand to an industrial accident 4 years ago, Igor Spetic had family
open his medicine bottles. Cotton balls give him goose bumps.
Now, blindfolded
during an experiment, he feels his arm hairs rise when a researcher brushes the
back of his prosthetic hand with a cotton ball.
Spetic, of course,
can't feel the ball. But patterns of electric signals are sent by a computer
into nerves in his arm and to his brain, which tells him different. "I
knew immediately it was cotton," he said.
That's one of several
types of sensation Spetic, of Madison, Ohio, can feel with the prosthetic
system being developed by Case Western Reserve University and the Louis Stokes
Cleveland Veterans Affairs Medical Center.
Spetic was excited
just to "feel" again, and quickly received an unexpected benefit. The
phantom pain he'd suffered, which he's described as a vice crushing his closed
fist, subsided almost completely. A second patient, who had less phantom pain
after losing his right hand and much of his forearm in an accident, said his,
too, is nearly gone.
Despite having phantom
pain, both men said that the first time they were connected to the system and
received the electrical stimulation, was the first time they'd felt their hands
since their accidents. In the ensuing months, they began feeling sensations
that were familiar and were able to control their prosthetic hands with more --
well -- dexterity.
To watch a video of
the research, click here: http://youtu.be/l7jht5vvzR4.
"The sense of
touch is one of the ways we interact with objects around us," said Dustin
Tyler, an associate professor of biomedical engineering at Case Western Reserve
and director of the research. "Our goal is not just to restore function,
but to build a reconnection to the world. This is long-lasting, chronic
restoration of sensation over multiple points across the hand."
"The work
reactivates areas of the brain that produce the sense of touch, said Tyler, who
is also associate director of the Advanced Platform Technology Center at the
Cleveland VA. "When the hand is lost, the inputs that switched on these
areas were lost."
How the system works
and the results will be published online in the journal Science
Translational Medicine Oct. 8.
"The sense of
touch actually gets better," said Keith Vonderhuevel, of Sidney, Ohio, who
lost his hand in 2005 and had the system implanted in January 2013. "They
change things on the computer to change the sensation.
"One time,"
he said, "it felt like water running across the back of my hand."
The system, which is
limited to the lab at this point, uses electrical stimulation to give the sense
of feeling. But there are key differences from other reported efforts.
First, the nerves that
used to relay the sense of touch to the brain are stimulated by contact points
on cuffs that encircle major nerve bundles in the arm, not by electrodes
inserted through the protective nerve membranes.
Surgeons Michael W
Keith, MD and J. Robert Anderson, MD, from Case Western Reserve School of Medicine
and Cleveland VA, implanted three electrode cuffs in Spetic's forearm, enabling
him to feel 19 distinct points; and two cuffs in Vonderhuevel's upper arm,
enabling him to feel 16 distinct locations.
Second, when they
began the study, the sensation Spetic felt when a sensor was touched was a
tingle. To provide more natural sensations, the research team has developed
algorithms that convert the input from sensors taped to a patient's hand into
varying patterns and intensities of electrical signals. The sensors themselves
aren't sophisticated enough to discern textures, they detect only pressure.
The different signal
patterns, passed through the cuffs, are read as different stimuli by the brain.
The scientists continue to fine-tune the patterns, and Spetic and Vonderhuevel
appear to be becoming more attuned to them.
Third, the system has
worked for 2 ½ years in Spetic and 1½ in Vonderhueval. Other research has
reported sensation lasting one month and, in some cases, the ability to feel
began to fade over weeks.
A blindfolded
Vonderhuevel has held grapes or cherries in his prosthetic hand -- the signals
enabling him to gauge how tightly he's squeezing -- and pulled out the stems.
"When the
sensation's on, it's not too hard," he said. "When it's off, you make
a lot of grape juice."
Different signal
patterns interpreted as sandpaper, a smooth surface and a ridged surface
enabled a blindfolded Spetic to discern each as they were applied to his hand.
And when researchers touched two different locations with two different
textures at the same time, he could discern the type and location of each.
Tyler believes that
everyone creates a map of sensations from their life history that enables them
to correlate an input to a given sensation.
"I don't presume
the stimuli we're giving is hitting the spots on the map exactly, but they're
familiar enough that the brain identifies what it is," he said.
Because of
Vonderheuval's and Spetic's continuing progress, Tyler is hopeful the method
can lead to a lifetime of use. He's optimistic his team can develop a system a
patient could use at home, within five years.
In addition to hand
prosthetics, Tyler believes the technology can be used to help those using
prosthetic legs receive input from the ground and adjust to gravel or uneven
surfaces. Beyond that, the neural interfacing and new stimulation techniques
may be useful in controlling tremors, deep brain stimulation and more.
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