"The stimulation felt almost like what I would feel with my hand," said amputee Dennis Aabo Sørensen. "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 said to be the first person in the world to recognise texture using the bionic fingertip which is connected to electrodes that were surgically connected to nerves in his upper arm.
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, and then delivered to the nerves.
Sørensen could distinguish between rough and smooth surfaces 96% of the time.
This same experiment testing coarseness was performed on non-amputees, without the need for 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.
The scientists tested whether the touch through the bionic fingertip resembles touch through a real finger by comparing brain-wave activity of the non-amputees, once with the artificial fingertip and then with their own finger. The EEG brain scans 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.
"This study merges fundamental sciences and applied engineering: it provides additional evidence that research in neuroprosthetics can contribute to the neuroscience debate, specifically about the neuronal mechanisms of the human sense of touch," said Oddo. "It will also be translated to other applications such as artificial touch in robotics for surgery, rescue, and manufacturing."
