20 THE SCIENTIST | the-scientist.com
PAULMARASCO, LABORATORY FORBIONIC INTEGRATIONOhio. “There’s constant and rapid com-
munication that goes on between the
muscles and the brain.” The brain sends
the intent to move the muscle, the musclemoves, and the awareness of that move-
ment is fed back to the brain (see “Pro-
prioception: The Sense Within,” The Sci-
entist, September 2016).Prosthetic technology has advanced
significantly in recent years, but proprio-
ception is one thing that many of these
modern devices still cannot reproduce,
Marasco says. And it’s clear that this is
something that people find important,
he adds, because many individuals with
upper-limb amputations still prefer old-
school body-powered hook prosthetics.
Despite being low tech—the devices
work using a bicycle brake–like cable
system that’s powered by the body’s own
movements—they provide an inherent
sense of proprioception.
To restore this sense for amputees
who use the more modern prosthetics,
Marasco and his colleagues decided to
create a device based on what’s known
as the kinesthetic illusion: the strange
phenomenon in which vibrating a per-
son’s muscle gives her the false sense of
movement. A buzz to the triceps will
make you think your arm is flexing,
while stimulating the biceps will make
you feel that it’s extending (Exp Brain
Res, 47:177–90, 1982). The best illustra-
tion of this effect is the so-called Pinoc-
chio illusion: holding your nose while
someone applies a vibrating device to
your bicep will confuse your brain into
thinking your nose is growing (Brain,
111:281–97, 1988). “Your brain doesn’t
like conflict,” Marasco explains. So if it
thinks “my arm’s moving and I’m hold-
ing onto my nose, that must mean my
nose is extending.”
To test the device, the team applied
vibrations to the reinnervated muscles on
six amputee participants’ chests or upper
arms and asked them to indicate how they
felt their hands were moving. Each ampu-
tee reported feeling various hand, wrist, and
elbow motions, or “percepts,” in their miss-
ing limbs. Kitts, who had met Marasco while
taking part in the studies he was involved in
at the institute in Chicago, was one of the
subjects in the experiment. “The first time
I felt the sense of movement was remark-
able,” she says.
In total, the experimenters docu-
mented 22 different percepts from their
participants. “It’s hard to get this sense
reliably, so I was encouraged to see theNOTEBOOKGOOD VIBRATIONS: The prosthetic
makes use of a kinesthetic phenomenon
whereby vibrating a person’s muscle
provides a false sense of movement.