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 Scientists from EPFL (Swiss Federal Institute of Technology) and
SSSA (Sant'Anna School of Advanced Studies, Italy) successfully
allowed amputee Dennis Aabo Sørensen to receive this sophisticated
tactile information in real-time.
The research, published in science journal eLife, says Sørensen is
the first person in the world to recognize texture using a bionic
fingertip connected to electrodes surgically implanted above his
stump.
The nerves in Sørensen's arm were wired to a machine with the
fingertip attached to it. The machine then controlled the movement
of the fingertip over pieces of plastic engraved with different
textures, either rough or smooth. When the fingertip moved across
the plastic, its sensors generated an electrical signal which was
translated into a series of electrical spikes that mimic the
language of the nervous system. This was then delivered to
Sørensen's nerves.
"When the scientists stimulate my nerves I could feel the vibration
and the sense of touch in my phantom index finger," said Sørensen.
"The touching sensations is quite close to when you feel it with
your normal finger; you can feel the coarseness of the plates, and
the different gaps and ribs."
The study states that Sørensen - who was blindfolded during testing
- was able to distinguish between rough and smooth surfaces 96
percent of the time.
Previous tests using a bionic hand allowed Sørensen to recognize
shape and softness. But the bionic fingertip delivers a superior
level of touch resolution.
"We showed that it is possible to deliver to amputees a very
sophisticated part of the sense of touch which is texture
discrimination. It is possible to achieve this thanks to electrodes
surgically implanted into the peripheral nervous system of the
subject," said Prof. Silvestro Micera from EPFL.
The same experiment was repeated with non-amputees, with the tactile
information delivered through electrodes attached to the arm's
median nerve through the skin.
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"We also show that it is possible to deliver the same kind of
sensation to intact [non-amputee] subjects using electrodes
temporarily implanted into the nerves," said Micera, adding that the
non-amputees were able to detect the correct texture 77 percent of
the time.
To determine that touch from the bionic fingertip really resembled
the feeling of touch from a real finger, the scientists monitored
the EEG (electroencephalogram) signals in the brains of the
non-amputee test subjects; once with the artificial fingertip and
then with their own finger. The test showed corresponding parts of
the brain were activated by the sensations.
The research demonstrates that the temporary electrodes relay
information about texture in much the same way as implants, said
Micera. This could eventually enable scientists to accelerate the
development of touch enabled prosthetics.
"This is extremely important because now we know that many of the
things we are testing can in intact (subjects) be used later, if
successful, in amputees," said Micera. "This means we can really
accelerate the translation of (this) different approach."
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