Prosthetic third thumb reshapes the body and mind : Short Wave Today on the show, we meet a prosthetic designer and a neuroscientist fascinated with understanding how the brain and body might adapt to something we haven't had before — a third thumb. Dani Clode and Tamar Makin spoke to Short Wave in Washington D.C., at the 2023 annual meeting for the American Association for the Advancement of Science (AAAS).

What could we do with a third thumb?

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EMILY KWONG, BYLINE: You're listening to SHORT WAVE...


KWONG: ...From NPR.


If you've ever read comic books or watched the Marvel movies, it is easy to dream about how cool it would be to have extra mechanical limbs, you know, to soar through the sky with the metal wings of Falcon or to climb a building with the extendable arms of Dr. Octopus. But even if we had that technology, there's a question that fuels the neuroscientist Tamar Makin.

TAMAR MAKIN: Can we handle extra body parts, different body parts from those we were designed to have through evolution?

SCOTT: Tamar runs the plasticity lab at the University of Cambridge. Her research on how the brains of amputees adapt to the loss of a limb and the use of prosthetics led her to ask how our brains might adapt to an additional body part we never had before.

MAKIN: So we were shopping for an augmentation technology that was mature enough to just give participants to take home and try out and kind of just make it part of their routine. But we couldn't find a good enough collaborator because technologies were just failing whenever they would come to our lab. And then one day, someone sent me one of Dani's YouTube videos. And we saw this gorgeous device that looked so functional and so flexible and could do a lot, many more things than all the technologies we were trying in the lab.

SCOTT: Dani is Dani Clode, an augmentation and prosthetics designer. And she and Tamar joined us on stage for one of the live shows we recorded at the big American Association for the Advancement of Science, or AAAS, Conference earlier this year. And Dani showed off the device that she designed called the Third Thumb.

DANI CLODE: So it's got two degrees of freedom. And so it moves across the hand and up towards kind of your pinky finger. It sits on the other side of the hand as your biological thumb. It's completely 3D-printed, and it's controlled with your big toes. There's pressure sensors underneath my big toes. It's proportional controls. So as I press down on my right toe, it flexes across the hand. And as I press on my left toe, it goes up towards the fingers. And those can be moved together. So it's a completely flexible extra thumb.

SCOTT: The third thumb enables two basic types of movements. It can either hold something against the wearer's hand like a jar, and then the wearer can use their fingers and their first thumb to say, unscrew the lid of that jar and dip a spoon in. And the third thumb can also collaborate with nearby fingers to pinch and manipulate things so that your hand could say, pinch two things at once.

And tell me then about how you went about researching using the third thumb to figure out how our brains could respond or control an additional body part.

MAKIN: So by wearing and using Dani's thumb, Dani practically invites you to change the way you use your own body in daily life. And we thought the maybe most important first question for us is to understand how extensive use of an extra body part going to change the way the brain represents and controls your own biological one. So in our very first study together with Dani, we invited people to wear the thumb for about five days and use it as much as they like throughout the day. So they ended up using it for about 4 1/2 hours every day just to show you how useful it is. And before and after that, we scanned their brains. And we wanted to see whether the representation of the biological fingers of the hands are changing, even if they're not using the thumb. And the answer was yes, they're changing.


SCOTT: Today on the show, Tamar Makin and Dani Clode explore how our brains adapt to an extra body part and what something like the Third Thumb could mean for everyone from amputees to surgeons. I'm Aaron Scott, and you're listening to SHORT WAVE from NPR.


SCOTT: Tamar And Dani's research involved setting folks up with the thumb and testing how well they can learn to do a set of manual tasks. But they also let their subjects take the thumbs home with them to just play around. And I wanted to ask about one person who I saw playing guitar with the Third Thumb in a video.

CLODE: Yeah, he was pressing strings on a guitar. You know, there's so many objects in - that we've - obviously designed in our world that are designed around having two hands or 10 fingers. So it's really interesting to interact with something like an instrument because you can just kind of have this unlimited interaction with it and create these new things that we can't do with our bodies.

SCOTT: And it's not like it's complicated, either. I mean, I understand from your newer research that you conducted this past summer that pretty much anybody can pick this up and do it very, very quickly.

CLODE: Yeah. So we had the amazing opportunity to display the Third Thumb at the Royal Society Summer Science Exhibition in London, which is kind of like their flagship public engagement event. We set up some thumbs - we had an adult-sized thumb and a kid-sized thumb. And we actually got to collect data from almost 600 participants, ranging from about 3 years old to about 97 years old, and do a task with them. And almost 99% of people could do the task successfully. So yeah, I'm pretty impressed with that.

SCOTT: So it seems our brains are particularly plastic when it comes to a little bit of augmentation. But would you just tell us a little bit about how hands and limbs are actually just mapped in the brain?

MAKIN: Yeah. So the way we think about the way the brain supports representation of the body parts is very segregated. So you would have the part of the brain that is responsible for the hand, and that's actually a really massive one. And then you'll have a much smaller one dedicated for the feet. So it basically means that we don't really think about the feet and the hand as interchangeable. But then as Dani points in the way she talks about her choices to use the toes, that there's so many instruments in daily life that take advantage of this ability to collaborate between the feet and the hands. And there seems to be something so incredibly intuitive about Dani's design.

SCOTT: What, I mean, does this say about kind of our brain's plasticity when it comes to really being able to adapt and control extra body parts that were never there before?

MAKIN: This is the big question for us. We want to understand, if you're relying so much on your toes in order to complement and add to your hand function, is that going to take away from your ability to use your toes as toes, for example, for balancing or for walking? So we need to understand whether by kind of, in a very friendly way, hijacking the toes in order to collaborate with the hands, if we are actually changing the order of things. And this is something we wouldn't want to disrupt. So for example, if you think about a factory worker, let's say, in an assembly line who is working with a device like the third thumb for eight, nine hours a day five, six days a week, we want to make sure that once they, you know, get out of the factory and drive home, that they can still drive safely and not confuse what their hands are doing with what their legs are doing.

SCOTT: So a lot of your research is focused on the brain and kind of what this augmentation does to the brain. But you also have both given thought into the practical applications of the thumb. Can you say a little bit about that?

CLODE: Yes. So I've spoken with a surgeon who was really interested in thinking about augmentation in the operating theater. Obviously, his hands are so occupied with specific tools. I think also, surgeons are amazing, I guess, people to work with in terms of something like this that may require a little bit more training when we're getting to this high-level precision. The hundreds of hours that they put into their tool use is really amazing. Also thinking about kids with upper limb difference. So it's really interesting to think about augmentation as an assistive device, as well, as a kind of alternate to a traditional prosthetic because you can collaborate with the hand. And I think Tamar can talk a little bit more about that. Collaborate with the biological hand rather than kind of starting from scratch from a prosthetic. And then third, just thinking about how quickly people can pick up something like this, thinking about temporary immobilization. So, for example, someone who's recently broken an arm - with leg breaks, we give people crutches, but with arm breaks, we don't really have anything. So thinking about, you know, alternatives for helping in that way, as well.

MAKIN: We have wonderful technologies, but they're all really focused on the idea of substituting something that was impaired. And with Dani's thumb, we're thinking about radical alternatives.

SCOTT: So for example, if you have one arm, instead of using a prosthetic to function as a second arm, the third thumb could be attached to the pinky side of your existing hand so that it could basically do the work of two hands.

MAKIN: We want to give you extra abilities with the hand to allow you to do bimanual functions with just one hand.

SCOTT: I have to ask if you both were to hold an extra large crystal ball with that Third Thumb and kind of stare into the future, how do you see humans using robotic and prosthetic augmentation?

MAKIN: We're already there in terms of very specific use in areas. We already know that, you know, people in factories, some patient groups use exoskeletons in order to provide kind of an external case in order to help them with, for example, carrying loads or balance. Technologies are already at the almost available stage. So for specific use scenarios, I believe in the next decade, you will see more and more of these opportunities. From my perspective, maybe because I'm not an engineer and I'm not aware of how hard it is to design these technologies, the bottleneck is not necessarily technological. The bottleneck is our mind, cognition and neural resources. We don't have unlimited resources. And our attention span tends to be already very, very narrow. And this is because we're so terrible at multitasking. So I think the - at the beginning and the end of the day, humans are pretty limited in what they can aim to achieve in terms of productivity. And I think we need to respect that.

SCOTT: So you're saying Dr. Octopus is is not going to happen.


SCOTT: Dani and Tamar, thank you so much for joining us here.

CLODE: Thank you for having us.


SCOTT: Special thanks to the folks of the American Association for the Advancement of Science for inviting us to record live episodes of their conference. We love us a nerdy science fest. This episode was produced by Liz Metzger and Thomas Lu. It was edited by our managing producer, Rebecca Ramirez, as well as Gabriel Spitzer and Audrey Nguyen. It was fact-checked by Susie Cummings. And our audio engineers were Carleigh Strange and Valentina Rodriguez Sanchez. Beth Donovan is our senior director of programming. And Anya Grundmann is our senior vice president of programming. I'm Aaron Scott. Thank you, as always, for listening to SHORT WAVE from NPR.


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