Clever ‘nerve hacking’ prosthetic tricks your brain to make limbs feel lighter

As technology advances, it also typically shrinks in size. The first video cameras were enormous, bulky devices that felt like you were carrying around a shot put on your shoulder. Today, you can get superior recording quality on a smartphone that’s thinner than a deck of cards, and weighs about as much — or as little.

In some cases, however, there’s a limit to how much you can shrink a piece of technology and still have it be useful. A prosthetic leg for an amputee might be slimmed down to a certain degree, but it still needs to stay at a certain size in order to function as a prosthetic leg. Likewise, reducing the weight of the prosthesis can be achieved by using more lightweight materials, although weight reductions are ultimately limited by the size constraints.

So, how do you make a prosthesis like this more comfortable for the people who need to use them day in and day out? According to scientists at ETH Zurich, a university in Switzerland, the answer is (at least in theory) simple: You use some clever “nerve-hacking” technology to trick wearers’ brains into thinking the prosthesis is lighter than it actually is.

“Many of millions of amputees are not using prostheses because they [find] them too heavy, despite being, in reality, lighter than [a biological] leg,” Stanisa Raspopovic, a professor in the Department of Health Sciences and Technology at ETH Zurich, told Digital Trends. “This is why diminishing the weight would boost the users’ experience, and diminish the prostheses’ abandonment.”

Neuro leg experiment
ETH Zurich

A fascinating proof of concept demonstration

In a proof concept demonstration, the researchers recently implanted electrodes capable of feeding electrical impulses into the residual leg nerves of amputees. This resulted in the participants experiencing the sensation of the prosthesis they were wearing feeling 25% lighter than it actually is.

Approximately 36% of the participants said that they felt more confident as a result, and more than 50% said that it made the prosthesis feel like it was more like an actual part of their body. Impressively, they were also able to carry out other tasks — such as the seemingly unrelated one of spelling words backwards while walking — more efficiently because they weren’t mentally or physically weighed down by the prosthetic leg.

While this is currently just the experimental phase of the project, Raspopovic said that commercialization is definitely planned for the future. “[This] would be a small implantable device under skin that stimulates nerves triggered by external wearable sensors,” he said. “We are working [toward that goal], with a spinoff, SensArs, planning a massive clinical trial in 2022. We hope to produce a certified device within [the] next five years.”

A paper describing the work was recently published in the journal Current Biology.

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