Restoring a Lost Sense of Touch

As scientists help an industrial worker regain his sense of touch through a prosthetic arm, we learn about the mechanics of human touch and why it’s so essential to our lives.

PETER GWIN (HOST): As a kid growing up in the late seventies, science fiction was all about bionic body parts. There was The Six-Million-Dollar Man (with the whole we can rebuild him, better than he was before…)

And then, most famously, in a galaxy far, far away there was Luke Skywalker who—in the climactic scene of The Empire Strikes Back—loses his right hand in a light saber fight with Darth Vader.

The next time we see Luke, he’s testing out his new bionic hand. A robot pricks each finger, one at a time—showing that it can move and feel just like the original. Good as new.

OK, so real science has not produced a Millennium Falcon, and we still can’t jump to hyperspace, but the bionic arm is slowly moving from science fiction to just regular science.

(Sound of a robotic hand moving)

These are the sounds of an experimental prosthesis at the Cleveland VA Medical Center. A mechanic who lost his hand in an accident 10 years ago sits beside a researcher to test the prosthesis. Wiring travels from the mechanical arm, through the skin of his shoulder, and attaches directly to his nerves.

The researcher gently presses each plastic finger…and he can feel it.

DUSTIN TYLER (BIOMEDICAL ENGINEER, CASE WESTERN RESERVE UNIVERSITY): OK, so let’s see if you feel it in your thumb here.

BRANDON PRESTWOOD (PATIENT): Yes, I do.

TYLER: You tell me if it’s light or hard. Close your eyes.

GWIN: I’m Peter Gwin, editor at large at National Geographic magazine, and you’re listening to Overheard, a show where we eavesdrop on the wild conversations we have here at Nat Geo and follow them to the edges of our big, weird, beautiful world.

This week we’ll dive into the science of touch: how it works, why it matters, and the people who are trying to re-create it.

All that and more, right after the break.

But before that, if you like what you hear, please consider a National Geographic subscription. That’s the best way to support Overheard and to ensure we keep providing you with stories from the edges of our big, weird, beautiful world. Go to natgeo.com/exploremore to subscribe.

GWIN: The man connected to the prosthetic arm was Brandon Prestwood, a maintenance technician from North Carolina.

Maybe we could just start at the beginning. Can you tell me how you lost your arm?

PRESTWOOD: May the 14th, 2012. So I took a local maintenance job doing maintenance work. We had a conveyor belt that we were working on; we were changing the tension roller in the conveyor belt. And the machine got turned on, and it just grabbed my fingers. And before I knew it, it had me all the way up to my head. Conveyor belt, it would haul about two tons of laundry at a time, so it wasn't like I was getting away from it. You know, once it had me in its grip, that was it.

GWIN: Brandon was rushed to the hospital, and doctors did what they could to save his arm. But after 30 days of recovery, things didn’t get better. And Brandon was faced with a choice: try to save his hand, or amputate it.

When you were trying to decide about your treatment, do you remember the conversation you had with your doctor? Like, how did they lay out the options that you were facing?

PRESTWOOD: I do remember him coming in and being like, all right, here’s what we got. He said, I still want to save your arm. And I kind of, I remember I asked him, How much use am I going to have out of my hand after it’s—if it’s—healed? And he said, you’ll probably never make a fist again. You might be able to touch your fingers.

GWIN: The attempt to save his hand would be a lengthy process. In order to heal, his arm would have to be surgically attached to his abdomen where it could get a steady blood supply until it was healthy enough to be reconnected.

PRESTWOOD: And I just kind of looked at Amy, and I was like, I don’t want it to be useless. You know, prosthetics, you can work with them. But I didn’t want to have a useless intact arm.

GWIN: So Brandon decided to amputate.

PRESTWOOD: I didn’t think being an amputee was a bad thing. My dad was an amputee, a lower-leg amputee.

GWIN: Oh really?

PRESTWOOD: So you know, I grew up. He had a wooden leg, and I thought, It can’t be that bad. That kind of helped me make my decision as, you know, I see my dad, and he was able to do things with us anyhow. So I thought, Well, I can make it through that too. Little did I know it’s—you know, it’s a challenge every day.

GWIN: Brandon’s whole life was turned upside down after the amputation. He became dependent on painkillers; he lost his ability to work as a mechanic. Workers’ comp was not enough to support his family, and so his wife, Amy, dropped out of school to help make ends meet.

PRESTWOOD: I went about four years—three and a half, four years—of some deep depression, often thoughts of just ending it and being done with it. The thoughts that went through my mind is how can I do this and not leave a mess for my family to have to clean up?

GWIN: Were you able to talk to your father at all about—you know, I mean—since he had gone through this, did he, did he give you any sort of advice or counsel about that?

PRESTWOOD: I started not to even talk about my dad. We didn’t have the best relationship. But his advice was to get over it. That was his support, was, get over it. I don’t put this out there much, but I don’t—I mean, I’m open pretty much. He asked for some help building a Quonset hut building—you know, the metal dome buildings. And I could climb up the ladder to get on top. But I wasn’t confident climbing down the ladder, and he left me up there. And finally, Amy had to come out and raise Cain and was like, so they ended up having to get the bucket—tractor and a bucket—and set me down off the roof. It was humiliating. In front of my family and stuff. You know, my family, my son, my wife, that I couldn’t come down the ladder. And it was just fear. I did not trust my prosthetic arm at the time.

GWIN: Hearing you talk about this, I mean, I think that, when people hear about an injury like this, they focus on a specific body part that is affected. It sounds like what you’re telling me, man, it’s a full life experience, from psychological to social to everything.

PRESTWOOD: Social battle was pretty tough. First year or so I didn’t want to go anywhere, I didn’t want to see anybody. You know, I can remember a time we went to eat. You get people looking because I was trying to be independent. Trying to cut a steak with one hand is, I mean, it’s a challenge even to this day. It’s still a challenge. Amy would be my protector. She would—she would, like, take a picture for them and go over to their table and be like, “Here, you know, you want this picture? That way, you don’t have to stare at him while he's eating.”

GWIN: Some of the biggest challenges faced by many amputees have nothing to do with surgeries or pills. For Brandon, the psychological trauma of dealing with a missing part of his body was just as debilitating as the physical trauma.

PRESTWOOD: I used to fish three days a week before the injury. So me and Amy and Jake were on the boat at the lake, and I’m sitting up front and Jake’s catching fish left and right, and I’m used to being able to catch fish left and right, and I can’t. It’s depressing. So I’m sitting up there, and I don’t say a word to anybody. And the thought process went through my head: I’m gonna jump in this water. And I hadn’t been swimming, didn’t know if I could or anything. I said, I’m gonna jump in this water, and I’m gonna swim or drown, one of the two. And I just pitched over out of the boat. Amy and Jake’s freaking out. And you know, I come up and I swim back to the boat, and I was like, “Well, that didn’t work.” They were like, “Why did you do that?” And I was like, “I had to try.”

GWIN: But Brandon was really lucky. His family stood by him and helped him slowly adjust to his new reality.

PRESTWOOD: Amy is as solid as the biggest granite rock there is out there. You won’t break her down as far as she will always be there to support me. Jake’s the same way. And my niece Kaitelin. She was two when I got hurt, and she will not have anything to do with my intact hand. She holds my prosthetic hand. I mean, they all—those three especially—have really impacted how I thought about things.

GWIN: Man, it’s just, I mean—to hear how your family rallied around you is really powerful, Brandon.

PRESTWOOD: I got the best family. I do.

GWIN: About three years after he lost his arm, Brandon’s doctor told him about an experimental surgery. Researchers at Case Western Reserve University were developing a prosthetic arm that could move and feel. Brandon flew to Case Western Reserve to meet with biomedical engineer Dustin Tyler to see if he’d be a good candidate for the procedure that would wire touch sensors directly into his nervous system.

PRESTWOOD: Dr. Tyler said, we could put this system in and it not work. And there was a risk that they could damage it more, you know, during a surgery. You know, mistakes are made sometimes.

GWIN: Only five people had had this surgery before Brandon. So like any experimental procedure, it carried some risk. Brandon had a big decision to make.

PRESTWOOD: I’m flying home and I’m thinking about it, and I was like, Yeah, I’m gonna do this. I want to feel my fingers again.

GWIN: We’ll meet Dustin Tyler and talk about what it takes to create an artificial sense of touch right after the break.

GWIN: About 1 in 200 people in the United States suffers from the loss of a limb. The most common cause of an upper-limb amputation like Brandon’s is a traumatic injury that comes from things like working with heavy machinery or car accidents.

A third major source of amputees comes from the military. In 2019, the Veterans Administration provided care to more 46,000 veterans with a major limb amputation.

That’s why the U.S. Department of Defense has invested heavily in prosthetic limb development. Their research agency, DARPA, and the VA fund the work of Dustin Tyler. At Case Western Reserve University, Dustin studies the sense of touch and how to re-create it.

You know, maybe we could just start with a very basic question.

TYLER: Absolutely.

GWIN: What happens in your finger when you touch something?

TYLER: So there’s 17,000 of these little sensors in your hand—to tell you the complexity of the hand—and every one of them will burst depending on where something touches and how it touches and everything else. Your brain then gets all those little bursts that come from your finger and interprets that to say, “Oh, they just touched the table,” or whatever it is. There are four different types of little sensors that pick up information …

(TYLER’S AUDIO FADES UNDER NARRATION)

…Some of them respond to the moment you touch something that kind of burst and then multiply it and other ones will respond to how hard you’re touching on something. And so these are two different classes of sensors.

GWIN: As Dustin explained how touch signals travel along nerves from the fingertips to the brain, it occurred to me that even though we think of touch as all one sense, it’s really like half a dozen different senses—temperature, pressure, texture, pain.

TYLER: So when you get into the question of what is touch, you’re right. That could be a huge rabbit hole.

GWIN: And the same nerves in the arm which carry touch signals to the brain also send signals in the other direction about how to move the muscles.

TYLER: Let me ask you a question. Like, when you reach out to grab something on your desk, what do you think about?

GWIN: Yeah. Like the shape it is that I need to put my hand around. Is it gonna be hot or cold? Is it gonna be—? Is it gonna hurt me? Is it sharp? Maybe.

TYLER: Do you ever think about how much you’re moving your index finger versus your pinkie? Do you ever think about the muscles internal? So the things that we don’t think about is all that sensory information of what’s expected is coming back and being compared to what the brain is expecting, and then it’s making adjustments to everything that’s going on.

GWIN: Dustin says a sense of touch is essential to human movement. Even simple tasks become clumsy and difficult when you can’t feel what you’re doing. If you’ve ever tried to pick something up after your hand has fallen asleep, you know what that’s like.

TYLER: Simply lighting a match is kind of a classic everybody shows, right? The person’s job is just to light a match. So they come in, full sensation, pick up a match, strike it. Easy, right? And then you totally deaden the surface of the skin. So you give them an anesthetic. The entire sensation of the skin is gone. It is really hard to lift and strike that match because your brain has no information about how hard you’re grabbing the match, if it’s slipping, where it is in your grasp, all these things. So it becomes an incredibly difficult task, even though all of your motor system is still intact. Just because you aren’t getting sensation, it doesn’t know what to do.

GWIN: No matter how sophisticated a robotic hand is, without a sense of touch, it will never be able to do what a human can do. And that’s where Dustin’s research comes in.

TYLER: What we’re doing is we place a device on the person’s nerve. There’s eight to 16 contacts, so individual little points that we can connect to. Each of those individual points has a wire that comes out through his skin.

GWIN: Dustin says to think of the long nerves connecting the hand to the brain as wires that send and receive electrical signals. And his procedure connects actual wires directly to the nerves.

TYLER: I can put a sensor somewhere, anywhere along that wire, and I can apply a tiny amount of current. I can generate those pulses, and then they get transferred to the brain, and the brain interprets them basically as though they came from the hand, even though I put them on the wire.

GWIN: OK. It’s mind-blowing that this works at all: one, that the electricity that powers light bulbs is basically the same stuff that makes human touch; and two, that scientists can directly tap into that system.

TYLER: So, not Brandon but another gentleman—it was our first in. The first time we turn this on, we had no idea what’s going to happen. We just hope it feels OK, doesn’t hurt, blah blah blah. We turned on one of the interconnects that we had. He said—he stopped for a minute, he kind of crinkled his eyes, and he said, “That’s my thumb. I haven’t felt my thumb since the accident.” We tried another one of our interface parts, and he goes, “That’s my finger.” I went through, and he could feel all the parts of his hand. And for him, it was just—it made a difference. And for him, to hear how he talked about, “I have my hand back; I haven’t felt my hand—” was just life changing for me.

GWIN: So I read that you tested the electrical shocks on yourself like these tests to simulate touch. Is that true? What did it feel like?

TYLER: Yeah, I wouldn’t call them electric shocks. The amount of current that we actually use is less than if you touch a doorknob and get that little—chisht—snap feeling. So it’s not a lot of current if we know what we’re doing. To your question, though, when we started working with our first subject, asking him to tell us, “What does it feel like?” And it was hard for him to describe, and at first I was like, “Come on, just tell me what it feels like,” right? But the weird thing is, it’s nothing he has ever felt before.

GWIN: The electrical signals Dustin was sending were not quite the same as the natural signals that come from a human hand. So it was a sensation that was totally outside of human experience. Describing it was like trying to describe a color no one else can see or a flavor no one else can taste.

TYLER: So I started doing that with myself and said, What is this like?

GWIN: Dustin carefully connected the outside of his finger to the same electrical signal he was using with his patients.

TYLER: Yeah, I spent hours in the lab just kind of going through and trying to experience it myself to get a better understanding. I realized, like, I can’t really explain that. It’s like—it’s like pressure, but it’s not pressure.

GWIN: Hmm. I asked Brandon to try to describe what this sensation felt like.

PRESTWOOD: I describe it as, you’ve had your hand asleep before, I know, sometime during your life. And as it’s waking up, not the painful part of when it’s waking up, but right before you get full feeling back, just that if you press, you get that kind of tingling feeling? That’s the sensation that I get.

GWIN: It’s not exactly like feeling through a new hand, but for the first time in years the nerves in Brandon’s arm were back online. Through the biological equivalent of Morse code, they were sending electrical pulses with the message, “Your hand is back! And it’s touching something.”

PRESTWOOD: I was grabbing everything. I mean, it didn’t matter what it was. If it was laying in the lab, I was picking it up. I was just like, as far as the cables would reach, I’d be like, Yeah, I want to see what that feels like. I liked playing with my fingers. I like squeezing these fingers with the prosthetic. I really like doing that because I’m getting sort of two different sensations. But now, like I said, my mind is just adapted to this sensation over here that it’s like, it’s almost like now it’s a challenge. Can I tell the difference?

GWIN: Yeah. Wow. Wow. That’s interesting.

PRESTWOOD: So now it’s like, Well, I’m getting that sensation, but which side’s it coming from, you know? That kind of thing.

GWIN: Right now the system can feel pressure and a little bit of texture, but there is one important sensation the lab hasn’t tried to replicate: pain.

PRESTWOOD: Something I want to do is a pain study. If I’m going to pay X amount of dollars for a prosthetic, if I shut that finger in a door, I should feel some pain from it. Pain is essential. Pain is a part of life. So I mention it to them about every trip I’m over there. Where’s the pain study? They’re like, “You’re not right. Why do you want pain?” And for me it is—it’s an essential part of life.

GWIN: Well, it’s interesting to hear you talk about that because I feel like, you know, there’s part of you when you stub your toe. I think most of us who haven’t gone through an experience like yours, Brandon, you have those moments where, like, why is there pain in the universe? Why can’t we just get rid of pain, you know? And it sounds like you have a very different sort of view of that now.

PRESTWOOD: You know, if you don’t have any pain in your life, how can you file that back into your mind and say, you know, “You don’t hold the nail like that when you hit it with a hammer”? I mean, I do think pain is a teacher.

GWIN: Dustin agrees with Brandon; that if it could be done safely and carefully, a study of pain would be valuable. It would help people avoid breaking their expensive prostheses, for one. And he also thinks pain might help these devices feel more natural—less like a tool and more like their own body.

TYLER: So the idea is how do I make the prosthesis feel like my—how do I embody it, make it my arm? Some of the measures that people look at for this idea of embodiment are things like protection. Do you protect the arm? If it’s being threatened, you protect it. Well, clearly, if it’s gonna hurt, you start to protect it. Right? So I think in an indirect way, pain will actually lead to a greater embodiment of the device.

GWIN: There aren’t any pain studies under way yet. Dustin wants to be very careful about intentionally putting people in pain. But even with the rudimentary sense of pressure, the sense of touch is allowing Dustin’s patients to do all kinds of tasks that used to be impossible for a prosthesis, like plucking the stem off of a cherry or holding a paper cup of water.

These are practical, life-changing applications for this technology. But with a little creativity, it can be used in some jaw-dropping ways. For example, the arm doesn’t have to be connected to the person.

CYNTHIA GORNEY (CONTRIBUTING WRITER): Oh, it was so strange.

GWIN: This is Cynthia Gorney. She’s a contributing writer for National Geographic, and her recent article on the science of touch was how I found out about this technology. In fact, she’s the one who introduced me to Dustin and Brandon. While visiting with Dustin, she had the chance to try the next step of this technology: long-distance touch.

GORNEY: So picture this: In Los Angeles, there’s a laboratory with a robot. This robot—think of a rolling reading lamp on wheels. It’s got a robot brain on its base, and it’s got two little robot arms.

GWIN: The robot was at UCLA in the lab of a scientist named Veronica Santos.

GORNEY: That’s in Los Angeles. In Cleveland, at Case Western Reserve, I’m wearing a virtual headset. And I have on my right hand some electrodes that are just taped to my hand and then a glove over the hand to cover the electrodes.

GWIN: You might be able to see where this is going. Cynthia, in Cleveland, was operating the robotic arm more than 2,000 miles away in Los Angeles. When she moved her wrist in Ohio, the robot wrist moved in California. When she pointed her finger, the robot finger pointed.

GORNEY: So I’m like moving my head around trying to get oriented. What Veronica Santos is seeing in her lab is a robot that looks like it’s drunk. It’s like lurching around from one side to another because it can’t figure out what it’s doing.

GWIN: And with the help of virtual reality goggles, Cynthia could experience reality from the robot’s point of view: sight, sound, and touch.

GORNEY: Whoa. I’m in the UCLA lab. I see the lab furniture I’d seen before. I see legs. I see table legs. I’m like, Oh, I see. OK, I’m looking down. What should I do? Oh, I see feet. Oh, OK. Those are Veronica’s feet. I know those feet because she wears these really odd, kind of single-toed shoes. Oh, I know who that is. I look up, and there’s Veronica’s face, which is startling because it’s right up close. And then in my electrode-taped hand, I feel… How am I going to describe this? In another context, I would have described it as a mild shock. Not as bad as an electric shock, but like a bad static cling shock, right? So it’s startling. In the context, though, I know that Veronica Santos is touching my robot hand. And it amazed me. It really took me aback.

GWIN: Well, how did it compare to actually shaking her hand in person?

GORNEY: So I would say that this experience for me… Did I shake hands with Veronica Santos in Los Angeles? No. A robot that I was embodying shook hands with Veronica. But in that context, with all the information I had been given, did it feel to me like I was touching Veronica Santos from across the country? Yeah, it did.

GWIN: Maybe it is starting to feel like we’re living in a Star Wars universe! In fact, one prosthesis that Brandon uses is called the LUKE arm. It’s easy to get carried away with the potential ways this technology could be used. Dustin gave a few examples like safely defusing bombs or handling rocks on Mars. But what his patients really want is closer to home.

TYLER: You know, when I ask these folks that have limb loss what it is they miss, right, every one of them that I’ve talked to has said, I want to hold my wife’s hands. I want to hold my kid’s hand. So it’s not about the function of the hand overtly right there. They don’t feel whole.

GWIN: Brandon doesn’t normally get to take his touch-enabled hand out of the lab. So he didn’t have a chance to hold and feel his wife’s hand until one occasion when she happened to be in the right place at the right time.

(Audio of conference)

This is cell phone footage from the noisy floor of a conference where Brandon was showing off his LUKE arm. It was the first time Amy, Brandon, and the prosthesis were in the same room together.

PRESTWOOD: Amy comes through the door, and I’m like, Oh shit, this is gonna happen. I mean, I’m gonna get to hold my wife’s hand. And she comes over, and I’m making sure it’s on, you know? All right. Yeah, I’m getting sensation, and we kind of switched positions, because I wanted her on my left side, and I reach out and I hold her hand, and (snap) it was like that. At that point I was complete; I was a whole person again. Even though I can hold her hand all day long with my right hand if I want to, I wasn’t complete. That point, I call it the pinnacle in my healing.

GWIN: For Brandon the project started off as a way to help himself physically recover from the loss of his arm, and it’s doing that. But it’s also helping him with the other stuff.

PRESTWOOD: I have a purpose in life now. I needed something to feel like I was a productive member of society. This program probably done—you know, it’s done great things physical, but even more mental, for me. That’s been my experience. And to know that—you know, again, I don’t like to talk about Dad much, but he was an amputee. I’m an amputee. I have a son that is in the mechanical field. What if he becomes an amputee? Oh, I’m about to cry.

GWIN: You guys talk about that? Do you and your son talk about that?

PRESTWOOD: Yeah. I’m nervous every day he goes to work, you know, because and then he’ll come home and tell me some stupid stuff they’ve done. And I’m like, You just don’t realize how bad that could have went, Son. Come on, use your head. Don’t wind up like your dad. I worry about my son, and I often think about maybe I’ll make a difference where if something was to happen to him, he doesn’t have to go through those thoughts of, Do I want to keep living? or whatever. Yeah, so it’s given me—definitely given me a purpose in life.

GWIN: Thanks to the work of people like Dustin and Brandon, a short time from now in this very galaxy, people using prosthetic arms that move and feel just like biological ones won’t seem like a scene from a science fiction movie.