PHOTO CAPTION: Placing sensors on the sole of a prosthesis that are connected to the wearer’s nervous system may help the user perceive the prosthesis as being lighter and aid its acceptance, according to a study conducted by Stanisa Raspopovic at ETH Zurich. (Photo courtesy of ETH Zurich).

Leg amputees are often not satisfied with their prosthesis because they perceive the weight of the prosthesis as too high, despite the fact that prosthetic legs are usually less than half the weight of a natural limb. Connecting the prosthesis to the nervous system may help amputees perceive its weight as lower and aid its acceptance.

Stanisa Raspopovic, a professor at the Department of Health Sciences and Technology at ETH Zurich, together with an international consortium, have developed in recent years prostheses that provide feedback to the wearer’s nervous system. This is done 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 in to the nerves, a media release from ETH Zurich explains.

“To trick an above-knee amputee’s brain into the belief that the prosthetic leg was similar to his own leg, we artificially restored the lost sensory feedback.”

— Stanisa Raspopovic

In a study published last year, he and his team showed that wearers of such neurofeedback prostheses can move more safely and with less effort.

In a further study, published recently in Current Biology, the scientists were now able to show that neurofeedback also reduces the perceived weight of the prosthesis.

How Heavy Is It?

In order to determine how heavy a transfemoral amputee perceives their prosthetic leg to be, they had a voluntary study participant complete gait exercises with either neurofeedback switched on or off. They weighed down the healthy foot with additional weights and asked the study participant to rate how heavy he felt the two 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 five-letter words while walking. The sensory feedback not only allowed him to have a faster gait but also to have a 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.”

— Stanisa Raspopovic

[Source(s): ETH Zurich, EurekAlert]

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