Podcast: Amputees Feel Warmth In Their Missing Hand

author avatar
Podcast: Amputees Feel Warmth In Their Missing Hand

In this episode, we discuss the accidental discovery of how amputees can sense temperature in their phantom limbs and how EPFL researchers have exploited this to develop the first generation of prosthetics that can feel.

In this episode, we discuss the accidental discovery of how amputees can sense temperature in their phantom limbs and how EPFL researchers have exploited this to develop the first generation of prosthetics that can feel. 

(0:50) - Amputees Feel Warmth In Their Missing Hand 


What's up everyone. Today we're talking about the future of prosthetics where they're no longer dysfunctional. This team from EPFL has now made a system that allows amputees to feel temperature in their missing limbs. I think it brings us one step closer to truly replicating the human experience with prosthetics. And it's really interesting. So, let's jump right into it.

I'm Daniel, and I'm Farbod. And this is the NextByte Podcast. Every week, we explore interesting and impactful tech and engineering content from Wevolver.com and deliver it to you in bite sized episodes that are easy to understand, regardless of your background. 

Daniel: Hey folks, like we said, today we're talking all about this transformative area of prosthetics. This team of researchers from EPFL is kind of redefining the possibilities of what we think is possible in terms of prosthetic limbs. The why here or the backstory, so to speak, is amputees, despite having prosthetic limbs, right? You know, all these advancements in robotics and other sorts of technology allow them an increasing degree of control over prosthetic limbs. But despite all that, we still lack the sense of touch. So, folks that have had a limb amputated, even if they've got a replacement limb, it's really, really challenging for them to experience the sense of touch in that prosthetic limb. Um, that meaningfully includes the ability to perceive temperature, which significantly impacts their day-to-day experiences. If you've never missed your limb or never missed the ability to feel the different temperatures of things, you may not realize what you're taking for granted, but it's actually a very significant part of the human experience, I think, is being able to feel temperature in your limbs.

Farbod: Yeah, it definitely lacks the human touch when you can't feel the warmth or the coldness of something. Like, just imagine on a hot summer day, you're grabbing a cold Coca-Cola, right? Like, just feeling that on your hand evokes certain emotions and it kind of makes sense that when you think about prosthetics, you know, you have your Maslow's hierarchy of needs function, beat anything else at the beginning, right? Just being able to use that limb that now you've lost, that was the most important thing. But as time has gone on, it would be nice if we could address that sensing capability as well. And I love like the genesis of this article that we're discussing here because it was totally an accident. I think we should get into it. Do you want to get into the story?

Daniel: Yeah. Well, and just in general, right. We love when technology is discovered on accident. I think it's a, it's a cool testament to how some of the most important discoveries ever, I think of things like the microwave, et cetera, have been made completely on accident, and it's a reminder to all of us working on cool projects to keep our eyes open for unexpected outcomes and the ability for us to pivot that into something else that might change the world, right?

Farbod: What an inspiring shout out there. I totally agree. So, the story, it started off with these EPFL researchers working with patients who had amputated limbs, and they had isolated a region on the, that was still attached on the limb that was amputated to test different temperatures just to get them, the patients to tell them where they are feeling that temperature. I think the main purpose of that initial work was how much of the nerves that are still present in that limb working as expected. And so, they had them close their eyes, so they couldn't see where the temperature was being applied. And what they had anticipated, like, let's say if the patient's arm was amputated at the elbow, and they were providing the temperature effect on the, let's say, upper bicep, they were expecting the patient to be like, “Oh, I'm feeling it on my upper bicep.”, but they actually started describing like, I am feeling it on my index finger or like I'm feeling it on my thumb. And the researchers were so shocked, they were like, can you please elaborate like what you mean by that? That is not connecting at all. And I don't know like if our researchers know this, I didn't know about this until I took out of all classes, psych in high school, but there's a syndrome called phantom limb syndrome where once your limb is amputated, if it's your leg or if it's your arm, the patient still feels like it's there. And sometimes the sensation is so strong, I remember reading about this, that like for example for legs, they would try to stand on the phantom leg that is no longer there because you just feel it, like you feel the foot, you feel everything about it. So, in that same sense, these folks were feeling those temperatures on the limbs that just weren't there and that was really blowing away the researchers that were doing this research.

Daniel: Yeah. So, in this specific case, right there, they were looking at folks who had had their hand amputated and they were applying temperatures directly to the forearm. So, the way they describe it is if you place something hot or cold onto the forearm of an individual with an intact hand, you know, assuming their nervous system is working properly, that person will feel that object's temperature locally directly on their forearm, you know, around where you're applying the temperature. But in these specific amputees with phantom limbs that they were experiencing this neurological, I don't know, phenomenon where they still experience feeling in that phantom limb, the limb that's been cut off, they were applying temperature to the residual arm, so what's left of the arm, but they could feel the sensation in their phantom limb. If you were using a very concentrated area of the forearm, they could feel temperature in their missing hand. So, I'm not quite sure how that all happens in the brain but you know, my broscience version of that is I think like the brain is trying to compensate or trying to understand the fact that limb is no longer there and that you're no longer receiving neural impulses from the, like the nerve endings in that phantom limb. And it's like, it's almost like cross talk. It's feeling nerve stimulation in a certain part of the forearm. And it's recognizing that as though it were in the phantom limb that's been amputated. Am I on the right track?

Farbod: I'm going to try to follow up on your broscience with my own broscience. I think you're on the right track. And I think it might have to do something with like, you know, when that portion of the limb was amputated, the nerve endings also went with it, but they were connected to like the central nervous system. And they were connected via the nerves that are still remaining in that residual portion of the limb. What these researchers noted is that the locations on the residual limb that could, I don't know, augment those sensations are very specific. Like you can't just put it anywhere and get that feeling. You have to put it in very specific spots to get that sensation going. So, my hunch is like a very similar to yours, is that the brain is kind of like getting tricked into thinking that, hey, once that sensation's there, I am still picking up that phantom index finger or thumb or whatever.

Daniel: So, they stumble upon this accidental discovery, right? Oh, my goodness. And a very, very concentrated part of the forearm, this patient can feel temperature in their limb that's missing. Instead of just writing a paper about it and saying, wow, this is interesting and stopping there, this team from EPFL took it a step further. And what they did is they started to, mimic the rest of the, the missing, let's say like neural architecture that would allow this person to sense temperature and then use that as a method of granted accrued method at this point, but a method of replacing the ability to feel temperature. So, what they did is they, included a heat sensor on the prosthetic limb. So, on the prosthetic hand, let's say they would include heat sensors that would allow them to allow the person with the prosthetic hand to feel the temperature that was locally occurring on the hand. Remember they can't actually feel their hand because their hand's been cut off. It's an artificial hand. They've got a heat sensor on that hand. And this heat sensor detects changes in temperature, similarly to the way that your skin might. So, they're trying to mimic the way that the skin might have, you know, started to comprehend temperature changes if that hand were there and it were a human hand. This heat sensor is then connected to a thermode, which again, uses electricity to produce different temperatures. And these thermodes are pressed against the residual limb in that very specific section that stimulates phantom limb sensation. So, what they're doing is they're sensing the temperature on the prosthetic limb and then stimulating somewhere on the forearm that makes someone feel in the phantom limb that same temperature so that the person can feel in their phantom limb the same temperature that's being locally sensed on the prosthetic hand.

Farbod: Right, right. And that's like a three-part of that you got to think about, right? You have stage one where it was the epiphany of, oh my God, people can feel stuff on their fingertips. Then there's stage two, which is like, well, now that we have that knowledge, how do we integrate it into something? And they were like, great, we can put these thermal resistors on the fingertips that tell us what that temperature is, then translated with another device onto the arm where we can emulate that entire like sensation. So, there's discovery and the realization of like what you can do with this discovery to make something useful.

Daniel: And I think, you know, this is all very interesting and definitely the most obvious part of the secret sauce here is the fact that they've figured out this phenomenon that in a very localized area of the residual limb, people can still sense temperature as though, or experience it as though it were in the phantom limb. But I think another interesting part of this, that is a little bit of a departure from different approaches we might see in this space is they're not trying to electrically stimulate the nervous system to simulate the feeling of temperature. What they're doing is they're allowing the brain to fill in the gaps on its own, doing what it has tried to do. You know, in the absence of that limb, which is repurposed a very small section of the nervous system toward feeling sensation in that phantom limb. So again, I think it's a little really interesting. They didn't try to biohack the nervous system, by hooking wires up to it and trying to provide the correct amount of electrical charge to the nervous system so that it might feel a certain sensation or temperature, there are almost certainly research teams doing that to try and replicate the sense of touch for artificial limbs. But with this team from EPFL that was different is they found this tiny little part on the residual limb that can experience temperature. And again, the brain interprets that as though it were in the phantom limb. They're not trying to over-engineer it. They're literally just replicating the temperature that's happening at the heat sensor, again, in that area of the residual limb and letting the brain connect the dots instead of trying to, you know, ground up engineer a new nervous system.

Farbod: And that's an important distinction to make in comparison to the other state-of-the-art approaches for this problem, because it's also non-invasive. So, with all this other stuff where you're trying to bypass the signal from somewhere to your brain or whatever, you have to usually go through surgery. And in this case, you don't. All the heavy lifting is being done for you with external sensors. And your body's natural mechanism is tricking itself into thinking that, that phantom limb is now feeling that sensation, which I think is like, I don't know, one of the better implementations of biohacking that we've seen.

Daniel: Yeah, I agree for sure. And I will say this is still pretty early on in the process, right? They're not ready to roll this out, you know, on the order of millions of people right away. But they have tested this with a set of patients. I think it was 25-30 patients that tested this same setup, right? Heat sensor on the end of an artificial limb, then a local thermode in the residual limb to stimulate what would be the phantom limb with temperature. I think it's 27 patients could all successfully experience temperature in their phantom limb using this prototype system that the team from EPFL developed, which, you know, again, very early stages, if they've only tested a few dozen people, but it is really, really encouraging that it wasn't something that happened just once for one patient. It's something that they were able to replicate with a broad set of patients. And it's encouraging to me because I think that provides them some momentum to start progressing further into different clinical studies and get this out there. To where people without, again, without having to get a really invasive surgery can start to experience, again, what I view to be a really key part of the human experience, which is, you know, being able to feel the temperature of something when you touch it with your hand.

Farbod: Totally agree. And like for me, every so often we talk about some like, new discovery within any given field that might seem very elementary, like in the very early stages, but the reason I find them so fascinating is because I think it's the start of like a paradigm shift. Like we're talking about prosthetics, how the norm has been like just completely focused on function. We've seen prosthetics become lighter and then more higher performance for people that want to do athletics and that's all great. But now you see like maybe potentially the focus can shift to like how do we take them to the next level by adding feel and these folks have proven that you can do that without some like very expensive, very invasive surgery. You can get modern technology to kind of compensate for that in collaboration with just your natural brain chemistry. And that's the exciting part at least for me.

Daniel: And I think definitely for folks who have experienced something as tragic as an amputation, right? I'm really excited that this technology is developing and in a way that, you know, again, it's a remarkable development, but it's developing in a way that it increases the sensory feedback for these users, enhances their overall experience, enhances their quality of life. I view it as, you know, again, thinking of other sorts of sensory enrichment, so to speak. I view it as the difference between, um, maybe watching someone eat a cookie or being able to smell that cookie while you watch someone eat it. And, you know, again, you're, you're just going from having only visual feedback to visual plus one other sense.

Farbod: But that really makes a difference.

Daniel: I imagine that deeply enriches it. And I think that things like that, that feeling the sensation of touch in that phantom limb is probably something that's highly therapeutic for these people. And also, will probably help encourage adoption of these new state of the art prosthetic limbs. If someone's able to actually start to get some sensory stimulation from the use of the technology.

Farbod: You're absolutely right.

Daniel: Be super interesting to see if they can simulate other parts of touch as well. Right. Can you feel texture? Can you feel pressure? Can you stimulate that in parts of the residual limb or is temperature one of the only things that responds to this phenomenon? And we've got to find another way to solve pressure or to solve texture and other things that we can feel with our sense of touch.

Farbod: Yeah, I'm pretty curious to see that as well. And just a quick note, when you were talking about the difference that one extra sensory input can have, I think one of the first lines in the article is the first patient that they tested this approach with. And he really expressed like, almost like the romantic nature of being able to feel temperature again. So, I don't think you're off the mark there at all. I think that that's a pretty accurate estimation on how this is gonna impact people's lives.

Daniel: I don't think there's a better way to sum this up than to read that quote directly. If you're cool, I do that. Yeah. So, this is Francesca Rossi, one of the people that tested this. She's an amputee from Italy and she tested out, again, tested out this prosthetic system from EPFL. She said, “When I touch the stump with my hand, I feel tingling in my missing hand, my phantom hand. But feeling the temperature variation is a different thing, something important... something beautiful”. I think I don't know. I can't wrap this up any better than that. Right?

Farbod: Yeah. That's perfect. I think it might be worth doing a quick recap though, as we usually try to do. Do you want to do a quick ELI5 of what's happening here?

Daniel: Yeah, I would. I would absolutely love to man. So essentially high level at the problem, people who have lost a limb and use a prosthetic, aka a fake limb, often can't feel temperature. That means they can't feel if things are hot or cold when they touch them with their prosthetic arm. It doesn't feel as real to them if you don't have that sensation of touch. This research team from EPFL developed a new system that allows prosthetics to mimic the feeling of temperature. They found this out on accident by feeling that a certain part of the person's remaining limb, the part that's still there after an amputation, can still feel heat and cold in the phantom limb feeling that that missing limb is still there. So, they made a system with a heat sensor that can detect temperature changes just like skin does. They then connect this to a device called a thermode that's placed on the part of the limb that's still there. That thermode can make that part of the skin feel warmer or cooler. When those skin nerves are stimulated by the thermodes, they send signals back into the brain and the brain interprets these signals as though they were feeling warm or cool in the missing limb. I think it's a really interesting and a really impactful discovery for people who have experienced amputation and are using prosthetic limbs because they can feel things that are more real and it improves their quality of life for the people who are using this technology.

Farbod: Incredible, perfect wrap up. With that said, before we wrap up the episode for real, I wanna quickly shout out the folks of Azerbaijan. Man, you guys, I think it's like what? Two weeks in a row, three weeks in a row? You've been making us trend on your Apple podcast technology charts. Wow. Thank you for the love. I appreciate, we appreciate it. I think one-week you guys made us like top 5 or top 10, which is even, what to do with all this love, you know.

Daniel: I can't believe it.

Farbod: Yeah. So, thank you guys. We hope you guys enjoyed this episode and as always, we will catch you in the next one.

Daniel: Peace.


That's all for today The NextByte Podcast is produced by Wevolver, and to learn more about the topics with discussed today visit Wevolver.com.

If you enjoyed this episode, please review and subscribe, via Apple podcasts Spotify or one of your favorite platforms. I'm Farbod and I'm Daniel. Thank you for listening and we'll see you in the next episode.

As always, you can find these and other interesting & impactful engineering articles on Wevolver.com.

To learn more about this show, please visit our shows page. By following the page, you will get automatic updates by email when a new show is published. Be sure to give us a follow and review on Apple podcasts, Spotify, and most of your favorite podcast platforms!


The Next Byte: We're two engineers on a mission to simplify complex science & technology, making it easy to understand. In each episode of our show, we dive into world-changing tech (such as AI, robotics, 3D printing, IoT, & much more), all while keeping it entertaining & engaging along the way.


The Next Byte Newsletter

Fuel your tech-savvy curiosity with “byte” sized digests of tech breakthroughs.