Todd Kuiken: Can A Prosthetic Limb Feel? Physiatrist and engineer Todd Kuiken is building a prosthetic arm that connects with the human nervous system — improving motion, control and even feeling.
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Can A Prosthetic Limb Feel?

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Can A Prosthetic Limb Feel?

Can A Prosthetic Limb Feel?

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It's the TED Radio Hour from NPR. I'm Guy Raz. And on the show today, extrasensory - how technology and even human behavior can actually stretch our senses. Hello. Is that Todd?

TODD KUIKEN: Yes it is. Hi there.

RAZ: So this is Todd Kuiken. He's a doctor and researcher who runs the Center for Bionic Medicine. So I'm sure you've been asked this question before like, a hundred times, but I have to ask you this question 'cause the first time I saw your TED talk, I'm thinking - I'm thinking of Steve Austin.


UNIDENTIFIED SPEAKER: He's alive. He lost an arm, two legs and one eye, but he's alive.

RAZ: I'm thinking, gentlemen, we can rebuild him.


SPEAKER: We have the capability to make the world's first bionic man.

RAZ: Do you remember what they said about him? I mean, they said Steve Austin will be that man, better than he was before.

KUIKEN: Well, you know, I loved that show as a kid. And I think it's inspiring, and Lord knows we would love to get there.

RAZ: I mean, we are kind of at this sort of bionic human place.

KUIKEN: Yes, we have, I believe, crossed a big hurdle by developing a way for a person to control their prosthetic limb that's not just, you know, goofy movements, unintuitive things. We've developed a system where a person thinks about what they want to do and it happens.

RAZ: A system where someone with an artificial hand or arm just thinks about moving it and it happens. And Todd isn't actually focused on the robotic arm or hand alone, but his big idea is to literally rewire the human body, to make those arms and hands work better.

KUIKEN: Instead of just making a machine for the human, we've changed the human to be able to use the machine better.

RAZ: Well, what really amazed me was this - I'm moving my - like, when I want to close my hand or bend my elbow, it's just intuitive, right. Like, we don't - we're not thinking about that. You just do it, but these patients are literally thinking in their brains bend elbow, move hand, and that happens. How does that happen?

KUIKEN: Well, think of the brain as where thoughts start, right? That's where you first decide you want to move your hand. And even though you're not thinking about it, you send signals down your neck, and you make the nerve fire. It has little electrical signals that hops down your nerve all the way to the end of the nerve, where little chemicals go across to the muscle and make the muscle have a little electrical spark that hops down the muscle fibers telling them to contract.

RAZ: And then your hand just closes, like, without even thinking about it.

KUIKEN: Yes. But what happens when you lose your arm above the elbow?

RAZ: Right, you don't have those muscles to move your hand anymore.

KUIKEN: That's right. You've lost not only the muscles and bones, but the controller.

RAZ: OK, so here's where the rewiring comes in, right, because you've lost those critical muscles that control your arm and your hand, but the nerve endings, they're still there.

KUIKEN: I could tap the end of a nerve of a World War II amputee and they'd still feel their missing hand. So they're alive and they work. They're like the data cables.

RAZ: So the nerve endings and the nerve signals are still there, right, but without those muscles, it's really hard to figure out what those nerve signals are actually saying.

KUIKEN: The signals are really, really, really tiny, and you have to listen to it a single nerve fiber at a time. Can't we plug them in someplace better?

RAZ: A place that might be able to amplify those nerve signals, and then rewire those nerves to other muscles. Todd explains how this can be done on the TED stage.


KUIKEN: We're using a biological amplifier to amplify these nerve signals - muscles. Muscles will amplify the nerve signals about 1,000 fold so that we can record them from on top of the skin. So our approach is something we call targeted reinnervation. Imagine with somebody who's lost their whole arm, we still have four major nerves that go down your arm.

And we take the nerve away from your chest muscle, and let these nerves grow into it. Now you think close hand, and a little section of your chest contracts. You think bend elbow, a different section contracts. And we can use electrodes or antennas to pick that up and tell the arm to move. That's the idea.

RAZ: That's just unbelievable. I mean, you can go into the body and basically say, like, we're going to attach this nerve to that nerve and that nerve to this muscle. It's like you're tricking the brain into, like, thinking a hand is there.

KUIKEN: Well, you know, frankly, I'm an engineer and they wouldn't let me rewire people. It's really sad. So my colleague Greg Dumanian at Northwestern is a talented surgeon, and he goes in there and finds the right nerves and the ends of them, and then we redirect them to where we have spare muscle. I guess the analogy I use is that the nerve is a wire, and we've lost the phone at one end, and so we just take the wire and hook it up to a different phone so that we can talk.

RAZ: And that's exactly how it works. A computerized, prosthetic arm can pick up the nerve signals and then tell the prosthetic hand to open or close. So, for example, Todd did this with a patient of his, Amanda Kitts, who also joined him on the TED stage.


KUIKEN: So, Amanda, would you please tell us how you lost your arm.

AMANDA KITTS: Sure. In 2006, I had a car accident. And I was driving home from work, and a truck was coming the opposite direction, came over into my lane, ran over the top of my car and his axle tore my arm off.

After that, I woke up in the ICU. I didn't know what had happened, and when I realized, you know, that I'd lost my arm, you know, it was completely torn up - I couldn't stop crying for days.

KUIKEN: With Amanda, she lost her arm a couple inches above the elbow. So she had a nice, long, residual limb, if you will.

RAZ: And that is the place where Todd's team rewired Amanda's nerves.

KUIKEN: And we can take the biceps, which has two parts, leave one alone to do the bicep's control of an elbow, but take the other one and put a hand closing nerve into it. And when that nerve grows in, you think close your hand. You aren't thinking bend you're biceps or contract your biceps. You're thinking close my hand, but we've rerouted the nerve, the wire to a different amplifier.

KITTS: And then that's when it was like magic after that. I could just open my hand and the hand would open. I didn't have to use any funny movements to work the arm. So it became like, you know, a natural part of me.

RAZ: And Todd, he was delighted, but he wanted to take it just a step further. So he started to think more about the nerve.

KUIKEN: The nerve actually controls each of your fingers, your thumb, your wrist. Now my colleagues have developed computer decoding algorithms that are a lot like voice recognition. And so we listen to the signals from the muscle, and these computer programs decode it so that we can tell whether you want to close your hand, bend your wrist, turn your wrist or even what type of hand-grasp pattern you want to make.


KITTS: So I have the elbow that goes up and down. I have the wrist rotation that goes...


KITTS: ...And it can go all the way around. And I have the wrist flexion and extension.

RAZ: At this moment when everybody laughs, she's just turned her entire wrist 360 degrees.

KUIKEN: Yeah, well, that's quite a bar trick for you because you give somebody something they can do and they will use it. So sometimes that's functional 'cause you can flip it into a position that isn't even humanoid.

RAZ: And the thing about rewiring those nerves is that when you do that, it means that prosthetic hands are actually getting a lot closer than ever before to a real human hand because the nerves, they can still feel and touch.


KUIKEN: I want you to watch closely.


KUIKEN: That's Claudia and that was the first time she got to feel sensation through a prosthetic. She had a little sensor at the end of her prosthesis that then she rubbed over different services, and she could feel different textures of sand paper, different grits, ribbon cable, as it pushed on her reinnervated hand skin. She said that when she just ran it across the table, it felt like her finger was rocking.

It was one of those scientific surprises. In those nerves to your hand, actually two thirds of them are for sensation. Only one third are for controlling muscles. So there's thousands and thousands of nerves that are trying to grow out into something, and most of them are sensation. And they grew into any little sensory end organ they could.

RAZ: So earlier in the show, we spoke to Neil Harbisson who calls himself a cyborg, right. I mean, his antenna is literally screwed into the bone of his skull. And I wonder if that's sort of the direction we're headed with sort of bionic technology. I mean, could you imagine half-human half-machines who can function normally despite having been born with disabilities or limitations?

KUIKEN: Well, I certainly imagine and we're progressing to having machines help people with disabilities and on even more and more intimate ways. As far as half-human half-machine, I take challenge to that because the essence of human is in our minds and what we think and what we do. And I don't see that ever being replaced. I hope we have things to augment, but I don't ever feel my humanity is going to be integrated with any form of machine.

RAZ: I was thinking about this idea of like, energy that travels through our body. And that energy travels from person to person. Like, when I hold my son's hand, you know, there's that feeling of holding a kid's hand, you know. And I wonder if you could ever replicate that in a prosthetic hand?

KUIKEN: Wow, that's a tough - that's an exciting one. And the question is how much do you get from having it being your own hand? So let me put it this way - something is always better than nothing. So you're holding your son's hand with a very rich, sensory-normal hand, and you get all of these delicate feelings. But for a man with no hands, no arms, if we put a sensor in the prosthesis so that as he touches that child's hand, and it's nothing more than a little squeeze that he feels, but yet it's his squeeze, and it's his kid's hand. So perhaps the fidelity of the feeling is not near as important as the identity of the feeling, and the fact that it's my hand that is touching something, and gosh, that's my kid.

RAZ: Todd Kuiken runs the Center for Bionic Medicine at the Rehabilitation Institute of Chicago. You can watch his amazing, full talk at

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