Although prosthetic legs usually weigh less than half of a natural limb, their perceived weight remains a point of dissatisfaction among users. Previously, researchers led by Stanisa Raspopovic, PhD, a professor at the ETH Zurich Department of Health Sciences and Technology in Zurich, Switzerland, have shown that connecting the prostheses to the nervous system helps amputees to perceive the prosthesis weight as lower, which is beneficial for their acceptance.
Further, together with an international consortium, Raspopovic has developed prostheses that provide feedback to the user via electrodes implanted in the thigh, which are connected to the leg nerves present there. Information from tactile sensors under the sole of the prosthetic foot and from angle sensors in the electronic prosthetic knee joint are converted into pulses of current and passed into the nerves. By artificially restoring the lost sensory feedback in this manner, Raspopovic and his team showed that wearers of such neurofeedback prostheses can move more safely and with less effort. In a further study, the scientists were able to show that neurofeedback also reduces the perceived weight of the prosthesis.
To determine how heavy a transfemoral amputee perceives the prosthetic leg to be, they had a study participant complete gait exercises with neurofeedback switched on or off. The healthy foot was weighed down with weights and the study participant was asked to rate how heavy he felt the legs were in relation to each other. Neurofeedback was found to reduce the perceived weight of the prosthesis by 23%, or almost 500 grams. The scientists also confirmed a beneficial involvement of the brain by a motor-cognitive task, during which the volunteer had to spell backwards 5-letter words while walking. The sensory feedback allowed both a faster gait as well as higher spelling accuracy.
“Neurofeedback not only enables faster and safer walking and positively influences weight perception. Our results also suggest that, quite fundamentally, it can take the experience of patients with an artificial device closer to that with a natural limb,” said Raspopovic