The results of a new study, part funded by the Wyss Center and published in the journal eLife, have shown that tactile information can be transmitted from an artificial fingertip to the brain via nerves in the upper arm. It is hoped that the findings will accelerate the development of bionic prosthetics with sensory feedback.
In the experiment, amputee Dennis Aabo Sørensen could feel rough or smooth textures in real time when his artificial fingertip was moved over different surfaces.
The study also demonstrated that the nerves of non-amputees can be stimulated to feel roughness, without the need of surgery, meaning that prosthetic touch for amputees can now be developed and safely tested on people with functioning limbs.
The technology for the study was developed by Professor Silvestro Micera and his team from EPFL (Ecole Polytechnique Fédérale de Lausanne) in Switzerland together with Dr Calogero Oddo and his team from SSSA (Scuola Superiore Sant’Anna) in Italy.
“The stimulation felt almost like what I would feel with my hand,” said Dennis Aabo Sørensen about the artificial fingertip connected to his stump.
“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.”
«The stimulation felt almost like what I would feel with my hand, 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.»
Amputee, Dennis Aabo Sørensen
The study is the first in the world in which an amputee has recognized 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 pieces of plastic engraved with either rough or smooth patterns. 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. The same experiment was performed on non-amputees without performing surgery. The tactile information was delivered through fine needles that were temporarily attached to the median nerve of the arm through the skin.
The non-amputees were able to distinguish roughness in textures 77% of the time.
To test whether the sense of touch from the bionic fingertip truly resembled the feeling of touch from a real finger, the scientists compared the brain activity of non-amputees when using the artificial fingertip and then when using their own finger. The brain scans, recorded with an EEG cap on the subject’s head, revealed that activated regions in the brain were similar whether the artificial or the real finger was used.
The research demonstrates that sensory information delivered via needles is similar to that delivered via implanted electrodes, giving scientists new avenues to improve touch resolution in prosthetics.