How Feets Of Dexterity Change The Brain

9:58 minutes

someone grasping a small card between their big and index toe to paint on a canvas on the ground
Credit: Tom Yendell

For people born with hands, there’s a map in the brain that corresponds to each one. And that map is detailed, including a dedicated region for each finger. When a finger touches something, those regions light up. The fingers are also laid out in an order that corresponds to the order of the fingers themselves.

For the same people, touching their toes does no such thing. The foot “map” is a region that doesn’t distinguish between individual toes. But what happens when you look at people born without hands, who spend their entire lives manipulating tools, driving, and even painting with their feet and toes? It turns out that their brains are different.

In a new study published in Cell Reports, MRI images taken of toe-painting artists’ brains found a much clearer “map” of the foot. There are individual brain regions for each toe that respond when a toe is touched, similar to the finger regions of people born with hands, and they also line up neatly in the same order that the toes are on the foot.

Ira talks to Daan Wesselink, a co-author on the study, about what the brains of these painters say about how all our brains are wired, and the brain’s capability to adapt to the different ways we use our bodies.

Further Reading

Segment Guests

Daan Wesselink

Daan Wesselink is a PhD candidate in Clinical Neurosciences at the University College of London in London, England.

Segment Transcript

IRA FLATOW: If you’re able, go ahead and touch something near you. Maybe your radio, maybe your nose with your index finger. Go on, great, right? Now do the same thing with your pinky finger. According to decades of work in neuroscience, a slightly different area of your brain was activated for each of those actions because your brain contains a map of your hand with individual regions in it for each finger.

But if you perform the same actions with two different toes, your brain might just light up a generic foot region, the same place each time, unless you’re a person who happens to use your feet for everything. New research from Cell Reports last week studied people born without arms and who paint with their feet. And that research found that their brain’s maps of their bodies place a much higher emphasis on their feet and individual toes, which says something interesting about our brain’s capacity for rewiring in response to how we use our bodies.

Here to talk about it is Dan Vesselink, a PhD candidate in clinical Neuroscience at the University College of London, co-author on the new research. And he joins us by Skype. Welcome, Dan.

DAN VESSELINK: Thanks for having me. Hi.

IRA FLATOW: Please explain this mapping that the brain does of our hands, of our feet. Why do we have it, how is a different?

DAN VESSELINK: Yeah, so what we have, we have basically in our brain a big map of our body to know where we’re being touched when we have to use a different body part, right? And as you explained when you touch individual fingers of the hand that activates just slight different place on that map. And yeah. For the feet, normally that doesn’t exist. So different body parts have different resolution, right? So a place where you’re touching a lot, which is your hand, you need that fine detail, you have very detailed regions for parts of our hand. But an area that isn’t touched very much, your lower back maybe, you just don’t have. You just have this generic somewhere around in my back.

IRA FLATOW: Well, that’s why it’s so hard if you tell somebody just to move one of your little toes or toes, you can hardly do that. You move all the toes at the same time.

DAN VESSELINK: Yeah. Yeah, very few people can, indeed.

IRA FLATOW: And so what did you see when you looked at the brains of people who do everything with their feet and who were they?

DAN VESSELINK: Right. So we got in contact with two people who have this amazing dexterity with their feet so that they can paint with their toes and actually make a living doing so. And what we did is we put them in an MRI scanner which is if we touch your body part, we can see exactly which part of the brain is activated when that happens. And what we found is that actually for individual toes, you could see as well of a separation as normally you would see for hands.

IRA FLATOW: Hm. And so it turns out their feet are mapped the way other people’s hands are mapped?

DAN VESSELINK: Yeah. So it really shows that they have this fine dexterity and this fine sense of touch knowing where parts of their feet are, that that has an impact on how the brain represents it as well.

IRA FLATOW: So what happens when people don’t have this map or some part of their body isn’t very well mapped? Would I notice if my brain didn’t have really precise finger map, for example?

DAN VESSELINK: Yeah, yeah you would. So I would touch your lower back, right? And I could possibly even touch you with two fingers in different places of your lower back and you wouldn’t be able to tell the difference whether I’m touching you with two fingers or just one.

IRA FLATOW: Wow. Does this have implications for people who might want to use prosthetic limbs, for example?

DAN VESSELINK: Yeah. So in general, what we showed is that you have this correspondence between the way learn to use your body parts or your life and how your brain represents it. And we’ve shown that in these two people who have these phenomenal capabilities, the brain sort of stretches its body representation. And just the fact that the brain can stretch this body representation, that it can make room for more resolution as it were, is very positive news for artificial limbs and prosthetics to see whether that potentially the brain would also have space to make room for those kind of tools.

IRA FLATOW: So were the people you studied, the people, the painters you used who painted with their toes, were these people who did not have hands or arms?

DAN VESSELINK: Yeah. So they were born without any hands. And that’s why they use their feet in their everyday life.

IRA FLATOW: And so in doing that, their brain knew that and rewired their toes, basically to be where their hands would be in the brain?

DAN VESSELINK: Right. Yeah. So we saw two things, both that the normal foot area becomes more defined, but we also saw some evidence of the place you typically would use to control your hands and to do touching with your hands now also was used during foot movement.

IRA FLATOW: Do you think this is something that could be taught to people to aid in that rewiring in the brain if you practiced it enough or even if you had full use of your limbs?

DAN VESSELINK: Right. Yeah. So we do think so. I think the fact that they didn’t have hands is not necessarily important for their foot area and the way that developed. So if you were even if you had hands started from a very young age to use your feet to do your writing, to drive your car, to paint indeed, then probably this foot area would develop similarly as well.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios talking with Dan Vesselink, a PhD candidate from University of College of London. Dan, what do these foot and hand maps tell us about how our brains are at birth? I mean, just tell us. I’m not going to try and figure it out myself.

DAN VESSELINK: Yeah. So the big question that we have going on now is we found these foot maps in foot painters, right? But the one question we do not yet know is whether everyone is born with these maps and you just kind of lose it because no one ever pays attention to our feet movement, right? So we wear shoes all day, we are taught to use our hands to reach for things, and so on. So the one question we do have is are we born with these maps and we just lose it or everyone is born with a generic foot area. And because these artists use their feet in very dexterous ways, they develop this special map.

IRA FLATOW: Do you have any ideas which one you prefer as an answer? What do you think?

DAN VESSELINK: I think there’s probably some genetic predisposition for developing these specialized foot maps because if you look at non-human primates, for example, who use their feet often for grasping branches and climbing in trees and also many dexterous ways, they often also show very localized brain areas for each individual digit of their feet.

IRA FLATOW: So what about amputees later in life? Can they be taught, do you think, to reuse those areas?

DAN VESSELINK: Yeah. So this is the actual main focus of our lab with Professor Macon at University College London. And the main thing that we find actually is that when you are born without a hand, you do not represent this hand. So what is in the hand area and people with both hands is no longer activated. But people who are amputees, as you asked, people who lose a hand later in life, they still represent this hand in that area. So there doesn’t seem to be much changing later in life.

IRA FLATOW: Mm-hmm. Now, we keep talking about how the brain is so plastic and adaptable when we’re young. Are we going to be able to unlock greater plasticity in adults, do you think?

DAN VESSELINK: I think, yeah. I mean currently, we think there probably isn’t a lot of opportunity later in life for this plasticity. And there is a general movement that the neuroscience has made where 20 years ago, people were very optimistic. We saw a lot of evidence for the plasticity of the brain. But now much research has come out that actually for changes later in life, the brain isn’t that plastic anymore.

Like early in life as this study showed, there’s a very large scope. But later in life, not so much. But that is actually good news for people who are amputees because when they lose their hand because the brain is not that plastic. it doesn’t lose that information either. So you could potentially design a prostheses which recruits that information again. So because the brain keeps all the information it used to have, if just find a way to wire an artificial limb to that, we should be able to control it that way.

IRA FLATOW: Yeah, they’re making progress on that. We have been following that. I want to thank you very much for staying up and taking time to talk with us today.

DAN VESSELINK: Yeah. No worries. Thank you.

IRA FLATOW: Dan Vesselink is a PhD candidate in clinical neuroscience at the University College of London.

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