Research News

Biomedical engineers in Cleveland and Italy were working toward the same goal: creating robotic arm prostheses that users can perceive as naturally as biological limbs. Both needed an interface between the brain and machine that restored kinesthesia, the body's sense of movement. 

The teams separately developed bionic arms that worked in very different ways to provide movement sensation. As the only two labs in the field, they have a “competitive, but friendly” relationship working toward the same goal. This unique international collaboration helped the two groups studying separate solutions compare notes and recognize patterns.  

The teams looked at the strange results they'd been seeing in their bionic arms and found the same unexpected pattern was appearing across two very different systems. Together, their findings helped redefine a fundamental principle in neuroscience. 

What is kinesthesia? 

Kinesthesia (sometimes called “kinesthesis”) is our body's nonconscious ability to sense where its different parts are moving in physical space without looking at them. Kinesthesia is essential for natural movement, even though we don't think about it. Amputees working with prosthetic limbs don't have kinesthesia, because the prosthetics aren't connected to their brains the way our biological limbs are.  

Cleveland Clinic biomedical engineer Paul Marasco, PhD, and his team invented a bionic arm that restores kinesthesia with a combination of robotic engineering and surgical nerve manipulation. In Pisa, Italy, researchers at the Sant'Anna School of Advanced Studies invented a bionic arm with restored kinesthesia using a different approach: they implanted tiny magnets in the patients' muscles.  

Both groups initially expected that study participants would report feeling each finger move individually. Instead, when individuals with arm amputations volunteered to test their technologies, they reported feeling the same types of coordinated movements across their hands. 

Global conversations drive discovery 

The teams’ combined results meant that our brains interpret hand movements as their intended simultaneous coordinated actions, like pinching or giving a thumbs up, as opposed to a sequence of signals to each finger that directs each movement in the process. The distinction seems small, but it makes a big difference in how scientists design prostheses and implants. 

"For years we've been told that our interface is useless because it doesn't give you individual fingers, even though everyone who tested it had strong functional outcomes," Dr. Marasco says. "[Christian Cipriani]'s team was initially pretty disappointed with their results for the same reason. But we all had it. We just needed to talk to each other to realize we had it." 

Dr. Marasco is already applying what he's learned about kinesthesia beyond robotic arm prostheses, expanding into rehabilitation and sensory restoration after neurological events. He says that sharing and building on his Italian colleagues' work helped turn his team's interesting observation into a fundamental truth. 

"It's one thing to say how a system should work. It's another thing entirely to say how a system does work," he says. "In this case, scientists working together helped bring us one step closer to understanding the truth."