By Matthew Stock
A bionic fingertip has given an amputee the sensation of rough or smooth textures via electrodes implanted into nerves in his upper arm.
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.
"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."