Paul Marasco Ph.D., an Associate Staff Scientist in Biomedical Engineering in Cleveland Clinic Lerner Research Institute and Principle Investigator in the Advanced Platform Technology Center of the Louis Stokes Cleveland VA Medical Center, talks about restoring movement sensation and touch for amputees.
Interview conducted by Ivanhoe Broadcast News in March 2018.
Dr. Marasco: The main finding of the paper is this idea that we can use perceptual illusions to provide individuals with amputation a sense of the movement of their hand its self. Their brain actually perceives that movement as though it was their real hand.
What does this mean for patients?
Dr. Marasco: What it means for patients is this idea that for individuals with amputation we can provide a sense of movement for their hand so that their brain feels like the movement they’re generating belongs to them. Then they can feel where the hand or the robotic hand is in space without actually even having to look at it. These are things that we take for granted as people who are intact.
For someone who has a hand amputation what are some of the limitations? Like they always have to keep track of the hand with their eyes?
Dr. Marasco: Yeah, so when you have an amputation one of the limitations is that you have to constantly watch your hand. To move it to grab anything to even turn a doorknob or to pick anything up you have to watch that device constantly. What it means is you can’t really do anything else other than watch the hand. And that’s very frustrating for people. What this approach does is it provides you with just the basic sense that your hand is moving and where it’s moving to so that you don’t have to watch it constantly. You can actually do other things and look at other things and engage with other things while you’re moving your hand. Much in the way that someone without or someone with a hand actually operates.
If you could quickly say how you did the study, like you hit the nerves or whatever you do, when you vibrated their muscles, that kind of thing.
Dr. Marasco: Sure. The study is based on this idea that we can use vibration of the muscles to generate illusions of movement. And the individuals that we work with are amputees who have had a surgical procedure called targeted reinnervation where their nerves are surgically redirected to new muscle and skin sites. Now what we can do is essentially vibrate the muscles that contain the nerves that used to go to their hands. When we do that, when we vibrate those muscles it generates this illusion of movement. The illusion of movement is kind of an interesting thing because if you vibrate the muscles of an intact person you get the very specific sense that your joints are moving. If you vibrate your arm you feel like your elbow is moving, or if you vibrate your forearm you feel like your wrist is moving and sometimes your hand. What we did was we took those movement illusions and then went to these individuals with the neuromachine interface and we piped that illusionary input in. And what we found which was very surprising was that it generated this very complex sense of their hands moving in to specific grips. Like they could close their hand and do a fist or they can bring their fingers together in a pinch or they could open their hand or they can move their thumb. And these are all very important movements that we use every day when we pick things up and when we move around in our world.
What are the next steps that may be encapsulated in that; what other disease or disorders might this help?
Dr. Marasco: Well we think that this might actually have impact in any kind of situation where people have movement disorders. We’re very curious about how to move these applications in to stroke, we’re really curious about any other type of movement or disorder. We’re looking at the possibility of using these in some way with relationship to spinal cord injury. Any time anybody has an interruption in their sense of movement that’s where I feel like this has implications.
We talked about how this could impact patients. If you wanted to mention how it could possibly impact the scientific world.
Dr. Marasco: The patient impact is pretty clear. That’s one of the exciting parts about this is the movement sensation that we’re able to provide to amputees. We can directly run that in to a system that is on the ground right now. We fit it in to a normal prosthesis and it works within the constraints of all the fitting. And then from a scientific perspective we’re moving in to some really new ground here. We’re providing some knowledge about how the movement sensation system might actually work. What’s the very exciting part of that is that your sense of movement and your sense of where you are in space is actually really quite poorly understood. And so scientifically this adds kind of a new thrust to how we may be thinking about how the brain processes movement information.
Can you talk about a long-term system, how would that function? It would just always be in their prosthesis, this vibration?
Dr. Marasco: Yeah, the key to the long-term system is being able to generate the vibration in to the deep muscles in a way that doesn’t use too much power. We already have smaller tactors or smaller kinesthetic tactors that are on the way that are battery powered. They live on the prosthesis itself and we’re working on shrinking those devices down so that they can be small enough and light enough to be worn every day. From that perspective every time the individual would move their hand or go and do a different type of grip we would provide that illusionary movement that reflected each one of those different hand movements. As a person walked through their day naturally they would feel that their hand was moving in natural ways. As prosthetics become more advanced, many of the functions that they engage with to complete their task are going to be done autonomously. The computing power on the limbs is getting very extensive. The devices are complex enough that just a single amputee can’t control all of those individual pieces on their own. What you don’t want to do is you don’t want to have to think through every single movement in order to be able to operate your device. And interestingly enough that’s how our actual natural limbs operate, is that all of the functionality and all of the movements that we make are done pretty autonomously. When you reach out and grab a glass, your brain just says go get the glass and then your arm works it out. With the prosthetic limbs, we’re trying to start to command them to achieve goals. If you want to reach with a new prosthetic limb or one of the advanced prosthetic limbs, you want to grab a glass much of the movement of the prosthesis itself is controlled onboard the prosthesis and the user doesn’t have much to do with that. This is where it gets really interesting. One of the things that our interface does is that when we provide the illusionary input to the individuals they develop a sense of agency over their movements. Meaning that their brain thinks or their brain understands that they are the author of the movement they make. This concept of agency is key when we interact with different people or if we interact with different machines. And we use the idea that ballroom dancing is a really good example for how cooperation occurs between two autonomous individuals. The amputee is an autonomous person and their arm is an autonomous person. You’re an autonomous person who makes decisions and your arms are relatively autonomous. You just believe that you have control over because you feel like you have agency. With the ballroom dancing analogy, when two people are dancing together they establish a cooperative relationship between each other. And they actually share a sense of agency over the movements even though there’s a leader, someone who’s making the decision who’s driving the dance and there’s a follower as well. The follower is autonomous but together they establish what’s called a cooperative joint agency. They both share the sense that they’re actually the author of their movements even though one person is actually making the commands. A similar thing happens with amputees and a prosthesis. So the amputee and the prosthesis actually have to cooperate with each other in order to complete a task. But the snag is if you don’t have agency over that sense of movement you actually reject the cooperative relationship.
Could you describe the main finding of this research and what it means for patients?
Dr. Marasco: Yes. The main finding of the paper is that we’re able to actually use a perceptual illusion of movement to provide amputees with a sense that their hand is moving in very complex and naturalistic ways. One of the really interesting pieces of this is this idea of agency. When we feel the movements that we generate, our brains believe that we have a sense of authorship over the movement that we just generated. And this has real implications for prosthetics because this sense of agency equates to how you’re able to cooperate either with people or machines and so one of the things that’s very interesting is that when two people are working together they establish a cooperative relationship. One person may be leading but both of these people share. Or one person may be leading the interaction but both individuals share this sense of agency over the movement of the course through this cooperation. Machines are different, when we try to cooperate with machines our brain is really clear that what we’re engaging with is a machine. And the mechanisms that it usually uses to establish this cooperative relationship are inhibited. The way we describe it is with ballroom dancing. With ballroom dancing you have two people who are very skilled at what they’re doing and they’re both autonomous. But they’re in a cooperative joint relationship with each other. What’s interesting about that is one person is leading and one person is following. And so the person who is leading has the agency over the movement. They’re generating the movements and they’re the ones who are saying, I’m the one who did this. But the follower also has a sense of joint agency in that sort of dancing equation. So what’s interesting about machines is that since we inhibit that sense of agency when we’re using or when we don’t have agency over a machine our brains actually inhibit that cooperative relationship between the two. We don’t actually dance in a meaningful way with machines. We can’t cooperate with them we have a leader we have something that’s following but cooperative joint agency isn’t a piece of this. In order to effectively work with someone, if you want to work together with someone you have to have a sense of cooperation. And that sense of cooperation when we engage in that sense of cooperation both of the people that are cooperating together have a sense of agency together. One person may be driving the movement and another person may be feeling or following the movement but together they both have a sense of agency. And this is similar to ballroom dancing. There’s a leader and there’s the follower. Both people who are engaged are autonomous but they share the sense of agency. When the leader makes a decision the follower follows it but then together they both feel like they have agency over that movement. And this is really different with machines, we don’t cooperate effectively with machines. We work together but we don’t cooperate. And one of the key pieces of that is that we don’t share agency with machines at all. And through the approaches that we’re able to use in these amputees or in this no machine interface is we can help people to cooperate more effectively with their prosthetic limbs. Because they feel that the movements that they generate, they feel that they have agency and authorship over those individual movements. Their brain interprets this cooperative relationship with the arm as though it was another human in the loop or as though it was actually the actual human in the loop.
END OF INTERVIEW
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