(March 8, 2016) An
amputee feels rough or smooth textures in real-time — in his phantom hand —
using an artificial fingertip connected to nerves in the arm. The advancement
will accelerate the development of touch enabled prosthetics.
An amputee was able to feel smoothness and roughness in
real-time with an artificial fingertip that was surgically connected to nerves
in his upper arm. Moreover, the nerves of non-amputees can also be stimulated
to feel roughness, without the need of surgery, meaning that prosthetic touch
for amputees can now be developed and safely tested on intact individuals.
The technology to deliver this sophisticated tactile
information was developed by Silvestro Micera and his team at EPFL (Ecole
polytechnique fédérale de Lausanne) and SSSA (Scuola Superiore Sant'Anna)
together with Calogero Oddo and his team at SSSA. The results, published today
in eLife, provide new and accelerated avenues for developing bionic prostheses,
enhanced with sensory feedback.
"The stimulation felt almost like what I would feel
with my hand," says amputee Dennis Aabo Sørensen about the artificial
fingertip connected to his stump. He continues, "I still feel my missing
hand, it is always clenched in a fist. I felt the texture sensations at the tip
of the index finger of my phantom hand."
Sørensen is the first person in the world to recognize
texture using a bionic fingertip connected to electrodes that were surgically
implanted above his stump.
Nerves in Sørensen's arm were wired to an artificial
fingertip equipped with sensors. A machine controlled the movement of the
fingertip over different pieces of plastic engraved with different patterns,
smooth or rough. As the fingertip moved across the textured plastic, the
sensors generated an electrical signal. This signal was translated into a
series of electrical spikes, imitating the language of the nervous system, then
delivered to the nerves.
Sørensen could distinguish between rough and smooth surfaces
96% of the time.
In a previous study, Sorensen's implants were connected to a
sensory-enhanced prosthetic hand that allowed him to recognize shape and
softness. In this new publication about texture in the journal eLife, the
bionic fingertip attains a superior level of touch resolution.
Simulating touch in non-amputees
This same experiment testing coarseness was performed on
non-amputees, without the need of surgery. The tactile information was
delivered through fine needles that were temporarily attached to the arm's
median nerve through the skin. The non-amputees were able to distinguish
roughness in textures 77% of the time.
But does this information about touch from the bionic
fingertip really resemble the feeling of touch from a real finger? The
scientists tested this by comparing brain-wave activity of the non-amputees,
once with the artificial fingertip and then with their own finger. The brain
scans collected by an EEG cap on the subject's head revealed that activated
regions in the brain were analogous.
The research demonstrates that the needles relay the information
about texture in much the same way as the implanted electrodes, giving
scientists new protocols to accelerate for improving touch resolution in
prosthetics.