A next-generation bionic hand could restore the sense of touch to amputees by replicating the feeling of proprioception – the brain’s capacity to sense the position of limbs.
The new device, developed by researchers from EPFL, the Sant’Anna School of Advanced Studies in Pisa and the A. Gemelli University Polyclinic in Rome, is said to allow patients to reach out for an object on a table and ascertain its consistency, shape, position and size without looking at it.
According EPFL, the prosthesis stimulates nerves in the amputee’s stump, which can then provide sensory feedback to the patients in real time.
The findings are published in Science Robotics and are the result of ten years of research coordinated by Silvestro Micera, a professor of bioengineering at EPFL and the Sant’Anna School of Advanced Studies, plus Paolo Maria Rossini, director of neuroscience at the A. Gemelli University Polyclinic in Rome.
Current myoelectric prosthesics allow amputees to regain voluntary motor control of their artificial limb by exploiting residual muscle function in the forearm, but the lack of sensory feedback means that patients rely heavily on visual cues. This can prevent them from feeling that their artificial limb is part of their body and make it more unnatural to use.
“Our study shows that sensory substitution based on intraneural stimulation can deliver both position feedback and tactile feedback simultaneously and in real time,” said Micera. “The brain has no problem combining this information, and patients can process both types in real time with excellent results.”
Intraneural stimulation re-establishes the flow of external information using electric pulses sent by electrodes inserted directly into the amputee’s stump. Patients then have to undergo training to gradually learn how to translate those pulses into proprioceptive and tactile sensations.
This technique enabled two amputees to regain high proprioceptive acuity, with results said to be comparable to those obtained in healthy subjects. The simultaneous delivery of position information and tactile feedback allowed the two amputees to determine the size and shape of four objects with 75.5 per cent accuracy.
“These results show that amputees can effectively process tactile and position information received simultaneously via intraneural stimulation,” said Edoardo D’Anna, EPFL researcher and lead author of the study.