How Does The Brain Control Your Every Move?

JOHN DANKOSKY: This is Science Friday. I’m John Dankosky. I want you to now become hyper aware of what you’re doing right now. Are you driving? Are you washing the dishes? Are you going for a walk?

Odds are you weren’t really thinking about what you were doing until I just asked you. Every little action that your body takes has to be dictated by your brain from your eyes scanning the space in front of you to your legs moving one in front of the other. And this all usually happens without really thinking much about it at all.

So this is a very complicated process in the brain and one that still has a lot of mysteries to it. We’ll try to unpack some of those mysteries with two researchers today. Dr. Evan Gordon is assistant professor of radiology at Washington University School of Medicine in Saint Louis. And Dr. Michael Graziano is professor of psychology and neuroscience at the Princeton Neuroscience Institute in Princeton, New Jersey. I’d like to welcome you both to Science Friday.

MICHAEL GRAZIANO: Hello.

EVAN GORDON: Hello. Thank you very much for having me on, John.

JOHN DANKOSKY: Of course. Thank you for being here. And we’re going to take some of your listener questions as well. What do you want to know about how the connections are made between our brain and our body? If you have questions, give us a call. Our number is 844-724-8255. That’s 844-SCI-TALK. Or you can always tweet us @SciFri.

So Michael, I want to start with you. And maybe we should start with an explanation of a really important part of the brain. This is the motor cortex. Give us a basic idea of what exactly it is and what it does.

MICHAEL GRAZIANO: Right. So there is a part of the cortex. The cortex is this all important outer layer of the brain. And it’s a part of the cortex that controls movement. And it was really the first part of the cortex that was understood in any way at all. It’s kind of the beginning of modern neuroscience. A little more than 100 years ago in 1870, it was discovered.

And what happens is there’s a kind of a strip of tissue. And the traditional view is that each spot in it connects to a part of the body and controls movement, controls muscles in that part. So it’s kind of a map, if you will, that controls movement. That’s the general idea of the motor cortex.

JOHN DANKOSKY: And how big is the motor cortex area of the brain?

MICHAEL GRAZIANO: It’s not as big as you might expect. In humans especially where we have so much of the rest of the brain taken up by high level cognitive functions, it squeezed up a bit. It’s a narrow strip. It’s only a couple centimeters wide and maybe five times as long.

JOHN DANKOSKY: OK. So not very big. Maybe you could just walk us through this, Michael, so we understand. If I’m reaching for a cup of coffee or I’ve got some water in front of me and I’m reaching for this cup, what exactly is happening in my brain? Maybe you can just map this out for us a little bit so we get an understanding of how this works.

MICHAEL GRAZIANO: Right. So we know certainly there’s a whole pattern of muscle activity that allows you to do that. That muscle activity ultimately is coordinated in your spinal cord, which has enormously rich, complicated networks in it. Many people don’t realize the spinal cord is smarter than most animals out there. It’s a very computation heavy part of the body. Then the spinal cord is under direct control by the motor cortex.

And so the motor cortex, in effect, is controlling this set of simpler algorithms in the spinal cord and giving somewhat higher level commands that allow your limbs to move. And exactly how the motor cortex works has been in some contention the simpler, traditional ideas are clearly not 100% right. And so that’s been the topic of very exciting ongoing research.

JOHN DANKOSKY: Yeah. And we’re going to talk about some of that research now. I want to turn to you, Evan. We’ve known about the motor cortex for a while. As a radiologist, what you do is you do scans and you look at people’s brains. And you’ve found something interesting in some scans having to do with a motor cortex. Why don’t you tell us about these findings?

EVAN GORDON: That’s right, John. We found that the motor cortex, which Michael has so eloquently described, has somewhat of a different organization than what science and medicine have believed for 90 years. We see that the motor cortex in addition to containing these different areas controlling different parts of your body, it also seems to control this previously unknown set of areas, networked areas, strongly interconnected that looks like it allows complex planning areas of your brain to influence whole body actions.

So as Michael described, for a long time we believed that in the motor cortex, there’s this smooth progression as you get from the top middle part of the motor cortex to the bottom lateral side part of the motor cortex that controls one part of your body, then the other, then the next, then the next moving from your toes and your feet to your arms and your hands to your face and your tongue. And that each of these regions acts kind of in isolation to control the movement of its particular body part that it cares about.

But we found out that when we go and map individual human brains in great detail, this isn’t quite true. So certainly, yes, there are these areas that control the feet and the hands and the face. But in between these three known areas, we found three other unusually strongly interconnected regions. The face area and the hand area, they don’t connect to each other.

They don’t act together very much. But these three other areas we found in between, they seem like they do strongly act together. And they act together not just in response to movements of specific body parts but to many different types of movements and especially to movements of your core body.

And the other really interesting thing about them is they seem to be strongly connected to areas in prefrontal cortex that are responsible for planning and decision making, what we think of as the smartest areas of the brain. These areas that we think of as just dumb motor, move your body part areas, are strongly connected to these smart planning areas. And finally, it seems like these areas correspond to regions that in the monkey brain are known to connect directly to internal organs like your stomach or your adrenal medulla.

So this is sort of a complicated set of findings, but we think that this new system represents a circuit that enables whole body actions, not just isolated movements of your fingers like if you’re playing a piano or even if you’re talking and you need to move your tongue in these very complicated ways. But we think about whole body actions like dancing or like sports.

And this system allows these whole body actions to be strongly influenced by your plans and your goals. And the potential connection to these internal organs might allow changes in your adrenaline or your heart rate even before you start an action, sort of anticipatory changes.

JOHN DANKOSKY: In some ways, that sort of sounds like good news, I suppose, for humans who plan things in advance. I want to ask a little bit more about the scans and what you found. But first of all, Michael, I’m just wondering if you could respond. I mean, how much does this upend what we’ve thought about the motor cortex previously?

MICHAEL GRAZIANO: Well, that’s a really good question. The motor cortex field, because it’s so old, is in a sense fraught with a great deal of tradition. And the tradition is on a regular basis kind of bashed and it seems to be toppling and then it kind of recovers itself. And so every so often, you find studies that show that the traditional view is not correct.

And so for example, a little more than 20 years ago, my own lab found evidence that the traditional map of muscles, so called homunculus, the little body in the brain, is not correct and that there’s a great deal of inter coordination between muscles and a sort of rich holistic approach to movement control. And so there’s that. The traditional map is clearly not correct. Exactly how it’s not correct and exactly what is correct, that’s really up to discovery.

And I think that this recent study is fantastic. It’s amazing and it really begins to show that the motor cortex is not just about controlling what are called skeletal movements or movements of your basic joints but can also be involved in internal organs and internal body states and link to higher cognition. So this is really amazing. It does put a dent in the traditional view. I wish the traditional view had a little more dents in it.

[LAUGHS]

JOHN DANKOSKY: And this may well indeed be a dent. So Evan, talk about some of these involuntary movements, things like breathing, my heart pumping. What do we know about how that’s mapped into the brain as opposed to the things that I’m planning to do or the things that I’m trying to do with my arms and fingers at any one time?

EVAN GORDON: Well, we don’t know that much about how sort of these involuntary movements like breathing and heart rate are regulated. We think that the traditional view has been that we think that these are regulated more by very low level systems, mostly in your brain stem. But it’s always been a question in my mind.

Well, OK, if these are sort of just dumb areas of the brain that are regulating your heart rate and your breathing, how is it that when I’m thinking about things that I’m going to do, when I’m thinking about something that’s going to be difficult or anxiety producing, I have to give a big talk in front of a big crowd tomorrow. It’s not even today. It’s tomorrow. I’m thinking about giving this talk. And my heart rate accelerates, my breathing starts changing, I start sweating.

Why is it that just our thoughts can cause these changes in our autonomic body systems? This is where I think we have to look to cortex. We have to look to these very smart areas of cortex and understand how our planning, not doing actions, but planning might be connected in more direct ways to our autonomic body functions.

JOHN DANKOSKY: And I want to get to some phone calls now. We’ve got a lot of questions from our listeners. 844-724-8255. Let’s go to Jim, who is calling from California. Hi there, Jim, you’re on Science Friday.

AUDIENCE: Oh, OK. Do you hear me OK?

JOHN DANKOSKY: Sure can, Jim.

AUDIENCE: OK, good. I was wondering what the chemistry is there to motivate somebody. When you make the conscious choice to do something, what motivates you to do it? Especially if there’s risk involved or some other challenge of pain that might be that you have to overcome what is that chemistry that motivates you passes all those seemingly barriers there.

JOHN DANKOSKY: It’s an interesting question, Jim. Thank you. I’ll put you on hold so you can listen to our experts. I don’t know, Michael or Evan, what do you think about this? I mean, if we’re talking about planning, we’re also talking about all sorts of motivations that people have to do various things.

MICHAEL GRAZIANO: I mean, I could take that. Oh, go ahead. I was going to take a quick stab at it. One of the wonderful things about the brain as people study it further is that there are a very large number of different networks that do different things yet all coordinate with each other. And so when you’re talking about control of movement, that seems to be one network.

You’re talking about deciding, decision making, cognition that allows you to decide what is the right thing to do. That’s perhaps another network. And yet there’s a third system in the brain, which involves motivation, emotional motivated states. And so all three of those need to interact with each other in order to accomplish the kinds of things that the caller is talking about.

JOHN DANKOSKY: Did you have other thoughts?

EVAN GORDON: I think Michael is exactly right here. And in our work, we’ve been thinking about this a lot, because we’ve been trying to map out some of these big brain networks that seem to do these different sorts of things. And one of the things that we’ve observed is that these planning decision areas I’ve been talking about that have this surprising connection to motor cortex, we’ve been trying to look into where they get their inputs from.

And as the caller might have guessed, they seem to have inputs from systems that provide– they have inputs from several different systems. One of them seems to be systems that provide motivation. They get reward information and they decide on the value of that reward. And they project that value judgment backwards into this decision making system. And then another input to this decision making system seems to be some of these networks that do very complicated cognition.

If you need to do math, if you need to think through a series of logical steps, this is the brain network that does that. And this brain network also provides input to this decision making system. And then this decision making system projects right backward into implementing these whole body actions in what we thought of as the motor cortex. So I think that the caller’s instinct is very right, that all of these different inputs are weighed and judged in these certain decision making areas of the brain.

JOHN DANKOSKY: We’re talking about the brain body connection. And this is Science Friday from WNYC Studios. And we’ll get to some more of your phone calls in just a moment at 844-724-8255.

So Michael, in my other life away from radio, I’m a yoga teacher. I’ve practiced yoga for years. And one of the things we talk about a lot in yoga is proprioception, the sense that we can tell how our body’s moving, where it is in space. It’s something that’s really different for everyone.

I guess I’m wondering with what we know about the motor cortex, how it is that people sense where their body is and how their body is moving much differently from person to person. Not everyone knows exactly what it means to hold both arms parallel to the floor, for instance. How exactly does that work out in the motor cortex?

MICHAEL GRAZIANO: Right. Another super good question. The sense of your body configuration and body movement in space is partly involved with the motor cortex. There is a large number of other areas that are involved in that. And what you’re talking about is sometimes called the body schema.

So the body schema is the brain’s essentially simulation or model, a picture that it builds for itself of what your body is doing, where your limbs are. And that body schema is very complex. It’s not just sensors in your joints telling you where your arms are. That’s a very small part of it.

Another part of it is vision. You see where your arms are. So vision has to connect to your joint sense. Another part of it is your motor commands. If you tell your arm to move to the right, well, it’s probably somewhere on the right. And another part of it has to do with just general knowledge that you’ve unconsciously learned about how your body is jointed and put together.

So all of these things come together in this big complex mix in order to allow you to know intuitively where your body parts are, how they’re moving, and that’s something that is trainable, learnable. And so you’re quite right. People who do yoga, people who do dance train up on this and become really good at it, much better than people who aren’t so well trained on it.

JOHN DANKOSKY: And we have a little less than a minute left, but that’s important. This is something that’s trainable this is something that we can make work better in this connection between our brain and our body.

MICHAEL GRAZIANO: Yes. It is trainable.

JOHN DANKOSKY: I want to let our listeners know that we’re talking with Dr. Michael Graziano. He’s a professor of psychology and neuroscience at the Princeton Neuroscience Institute in Princeton, New Jersey. And we’re also talking with Dr. Evan Gordon, assistant professor of radiology at Washington University School of Medicine in St. Louis.

We’re talking about the connection between the brain and the body. Some new research into the motor cortex, trying to figure out how exactly this stuff works. We’ll even be talking about some mindfulness techniques and taking a lot of your phone calls at 844-724-8255/ that’s 844-SCI-TALK. We’ll be right back in just a minute.

This is Science Friday. I’m John Dankosky in for Ira today. We’re talking this hour about some of the connections between our brain and our body. We’re talking with Dr. Evan Gordon and Dr. Michael Graziano and we’re taking some of your phone calls. Let’s go to Peter, who’s calling from Florida. Go ahead, Peter. You’re on Science Friday.

AUDIENCE: Yeah. Three days ago was the anniversary of Nadia Comaneci getting those perfect tens. So what I’m asking is how long will it be before you can do to my motor cortex make me a great gymnast? You know what I mean? It’s kind of like remember the Six Million Dollar Man or whatever? When can we do that with people?

JOHN DANKOSKY: Yeah. It’s a really good question. I think something that a lot of people are thinking about as they listen to this conversation. Michael, what do you say to our caller?

MICHAEL GRAZIANO: I think that when you’re young, that’s when your brain is most changeable, most learnable, most plastic. And unfortunately, by the time we get older, I think that plasticity is at least reduced. But it’s still there. You can actually– with intense training, you can actually improve skills. As for getting all the way up to the Nadia level of skill, I don’t know. That’s something you start very young.

JOHN DANKOSKY: Well, and maybe, Evan, it’s something that we can’t exactly replicate an Olympic athlete later in our life, but it does speak to the idea. Since we’re talking about this being trainable, it is something that maybe we can all do just a little bit better. Maybe not to get to the Olympics, but maybe just to stand on our two feet a little bit stronger.

EVAN GORDON: I agree. I think that when you start thinking about improving your motor function, improving your motor abilities, there’s no substitute for you have to go out and practice. Because practicing, actually doing it, the act shapes your motor cortex and it refines it. There is a question. Could we help accelerate that shaping? Could we help you learn to do it faster?

There’s amazing new brain stimulation techniques coming out. Transcranial magnetic stimulation where you can activate the brain a little bit by magnetic fields. There’s new techniques coming out where you can use ultrasound, like low intensity sound waves directed at your cortex to increase or decrease the activity of your brain. Could we maybe use some technologies like that to accelerate this learning process? We don’t know how to do it now, but it’s not a crazy idea.

JOHN DANKOSKY: Let’s get to another phone caller here. Valentina is calling from Chicago. Valentina, go ahead. You’re on Science Friday. Oh, Valentina is not there anymore. Michael has a question, actually, that’s not too terribly dissimilar. So let’s go to Michael in Albuquerque. Hi there, Michael.

AUDIENCE: Hey, how are you doing, John?

JOHN DANKOSKY: Doing quite well. What’s your question?

AUDIENCE: My question is this. I am a stroke survivor from February of this year. And of course, I had a ischemic stroke on the right side that affected my left side. And you had the speech, I had the weakness on the left arm and the right leg. And then my question is basically, what does that have to do with the repairing, like restoring your speech and restoring the use of your faculties once you have the stroke? How does the brain or the cortex repair itself to get back to normal?

JOHN DANKOSKY: Great, great question. Evan, what can you tell him?

EVAN GORDON: That’s a wonderful question. We don’t know the exact mechanisms of this repair of how the brain is, the term is plastic. It can change its function a little bit to compensate for large losses in functional areas. What we do know for stroke, motor stroke in particular, is that the way that the brain starts compensating for loss of function mirrors the original organization.

So you may have experienced something where although you have lost, and many people experienced this, although you have lost your hand function, maybe originally you lost the function of your entire arm. The first thing that starts coming back is maybe your shoulder function and then maybe a little after that your elbow function starts coming back. That’s a common experience in people who have strokes and lose arm function. But often the recovery doesn’t get all the way to the hand. They never quite recover hand function.

And we believe that the reason for that is because of the organization of the motor cortex. If you look at how it’s organized, the shoulder is the farthest away from the hand but closest to these new in between areas that we found. It goes shoulder and then elbow and then wrist and the hand.

And if you have a stroke that really destroys your hand function, it may have affected your wrist and your shoulder, but we think it’s possible that these new in between areas in the motor cortex may be able to start progressively taking over the function of the proximal, the nearby lost areas. So they can maybe first take over the function of the shoulder and then take over the function of the elbow. And fortunately, they rarely get to take over the function of the hand.

JOHN DANKOSKY: But the discovery of these new in between areas gives us a chance to maybe try new therapies, new ways of actually solving the problems that people have post stroke.

EVAN GORDON: Absolutely.

JOHN DANKOSKY: Very interesting. Let’s go to another phone call. We have Lynn, who is calling from Indiana. Hi there, Lynn. You’re on Science Friday.

AUDIENCE: Hi. My question is my father recently passed away and he suffered from Alzheimer’s at the end of his life. And as I listened to you, one of the things that I’m thinking of is what we noticed was from early on that actually it was his motor things went down as much, but the common therapy right now concentrates on their higher level skills, their memory and things like that.

But I’m wondering that with this knowledge that you have that maybe that’s what we should be looking at. Because I can also tell you that the more active my dad was, the better the rest of his skills of his brain worked. So I’m wondering how this could apply to Alzheimer’s research.

JOHN DANKOSKY: It’s a really good question, Lynn. And I’m sorry to hear about your father. Michael, what can you tell Lynn?

AUDIENCE: Thank you.

MICHAEL GRAZIANO: I think probably actually Evan would know way more about this as a neurologist.

JOHN DANKOSKY: Yeah, Evan?

EVAN GORDON: So absolutely. It is a really good question. And of course, the reason that, you know this, reason that they were focusing so much with your father on focusing on these cognitive skills is that in Alzheimer’s, those are most commonly lost. The areas that are first affected in Alzheimer’s are far away from the motor cortex, especially in areas having to do with memory and the sense of time and the sense of yourself and also the sense of navigation. They’re not very related to motor cortex. They’re not very strongly connected to the motor cortex.

But there is a lot of variability in something like Alzheimer’s. And while most people may have this really primary memory deficit where their motor function is relatively spared for a long time, that’s not the case for everyone. And certainly as you experienced, there are individual cases where motor cortex may be degrading as fast as the cognitive function.

Now, your idea about if we can help recover the motor function, maybe it can help recover the cognitive function, it’s a great idea. It’s something that’s intuitive to us, because I think we all understand how when we are active, it can help us think better. It helps us regulate our emotions better. It helps us concentrate better. This is a well known phenomenon.

And I think that these sets of circuits that we’ve identified here is a potential mechanism how this may be happening. As you engage your body in motion, there may be feedback mechanisms back to these higher level cognitive areas that allow them to activate better, to engage better. And while they probably wouldn’t be slowing the progress of Alzheimer’s, which is a very difficult problem that is not solved, it may very well be that physical activity may help for a little while engage your brain enough that it can overcome the deficits that the disease is causing.

JOHN DANKOSKY: It’s so interesting. And again, Lynn, thank you so much for your question. Michael, I want to get back to something that you talked about earlier. There’s this kind of foundational concept in neuroscience called the homunculus. Maybe you can just describe exactly what this is and why it’s become so prevalent in our understanding of the brain.

MICHAEL GRAZIANO: Right. So the term the homunculus was introduced by the neurosurgeon Penfield in the 1930s. And he’s the one who mapped the motor cortex in humans. He didn’t discover it. It had been discovered 70 years before his time. But he mapped it thoroughly in humans and he noted this apparent map of muscles that if you drew it on a piece of paper looked a bit like a distorted body with really big hands and a really big face. The parts of the body that are controlled in finer detail have greater representation in the cortex.

And so he called it the homunculus. And that was a very clever bit of PR and that term has stuck and now everyone, even non-neuroscientists, have heard of the homunculus. And so that’s kind of the basis of how people have thought about the motor cortex. And of course, it’s a little bit tongue in cheek, because there’s also a widely mocked, let’s say, a straw man view of the brain. The way people function is that there’s a little man in your head that makes you move.

And the reason why that makes so little sense is because then what makes the little man move? Does he have a little man in his head too? And so the homunculus concept is in some sense quite funny. But for the motor cortex, it made a great deal of sense for many, many decades. The homunculus is just much more complicated than a simple map of the body, it turns out.

JOHN DANKOSKY: Yeah, it’s sort of a funny idea to think about. It’s also funny looking. It’s like a little goblin with huge hands if you see it embodied. A big tongue and mouth and big ears. It’s supposed to represent how much brain space is being used for the different body functions. So Michael, is this not true anymore? I mean, do we not believe in this homunculus model at this point?

MICHAEL GRAZIANO: Well, the basics that you just described are absolutely true. It’s just that in the motor cortex, it was once thought that every muscle had a little spot in cortex. And if you poked that spot, it would make that muscle twitch. And that turns out not to be true. The cortex basically learns really rich, coordinated interconnections between muscles and body parts and helps coordinate movement.

And we have found, for example, you can poke a spot in the motor cortex and cause a behavior as complex as the hand closes into a grip. The grip moves to your mouth and your mouth opens. All of those things happening in coordination because there’s the network in the motor cortex has learned that kind of rich coordination. So what’s in debate is exactly how this is implemented in the motor cortex. But there’s no doubt that different body parts have different amounts of representation in the brain. That basic idea is absolutely correct.

JOHN DANKOSKY: This is Science Friday from WNYC Studios. And we want to get to some more phone calls about the brain body connection. Jennifer is calling from Durham. Go ahead, Jennifer. You’re on Science Friday.

AUDIENCE: Hey, thanks for taking my call. So I am a congenital amputee. I was born with a limb difference. And my husband and I own a small prosthetic company in Durham. And I spent a lot of my time visiting folks that are new to amputation in the hospital following their surgery and just working with people through the rehabilitation process.

And so a lot of people that experience amputation experience something called phantom limb sensation or phantom limb pain, essentially, even though that part of the limb is no longer there, but you are still feeling like it’s there. And it could just be a feeling of twitching in a foot that’s not there or severe pain. And not everybody gets it. Not everybody experiences that. It sort of depends on the circumstances around your limb loss.

And so when I talk to people about that, I usually say, I frame it as in your brain has a map of your body. And now that that part of your body is gone, your brain, it takes a while to really adjust to that and for your brain to understand that and that’s what you are experiencing is a misfiring of your brain. And as you begin the prosthetic rehabilitation, that also helps mapping the new map of your brain.

And right now prosthetics are typically they’re not directly integrated with your nervous system. That’s certainly the future of prosthetics. But all the things that you’re talking about, proprioception, balance, it takes practice. And so people find it’s very difficult at first to use a prosthesis. But throughout the process, that brain is reforming. The map is reforming. And that’s why people eventually progress and feel like, oh, this prosthesis is part of my body now. I just thought it was something to bring up.

JOHN DANKOSKY: I think it’s a very important thing to bring up. I’m so glad you did, Jennifer. And Evan, I don’t know if you want to build a bit on what Jennifer had to say.

EVAN GORDON: I think that Jennifer’s describing it extremely well. This is exactly the right way to think about it. When you have an amputation, you have a part of your sensory cortex, which is organized a lot like the motor cortex, where it has different parts of it that are mapped to different parts of your physical body. That part of your brain has completely lost its input. What is it going to do?

Neurons don’t know what to do when they lose their inputs. They start firing randomly. Everything that they were expecting is messed up. The neurons themselves, they’re organized in a very complex recurrent network. Different neurons are pointing to each other. They’ve all lost their inputs. They’re all pointing randomly at each other. They’re causing random firing all over the place. It’s complete confusion. And that can be easily, easily interpreted as pain.

And that representation of that missing body part needs to be what’s called– it needs to be remapped. And that is exactly what this rehabilitation process that Jennifer is talking about is intended to do. It’s intended to make this remapping process go as fast as possible. You have this part of your brain that was mapped to this missing part of your body. Can we try to remap that part of your brain to something else that is intact that is still getting input and so that this input doesn’t come– that there’s not this lack of input in this crazy activation, which is very unpleasant?

JOHN DANKOSKY: Interesting stuff. There’s so much more to talk about and so many more questions, but we’ve just about run out of time. I want to thank Dr. Evan Gordon, assistant professor of radiology at Washington University School of Medicine in St. Louis. Thank you so much, Evan.

EVAN GORDON: Thank you so much, John. I loved being on here.

JOHN DANKOSKY: And Dr. Michael Graziano, a professor of psychology and neuroscience at the Princeton Neuroscience Institute in Princeton, New Jersey. Thank you so much, Doctor.

MICHAEL GRAZIANO: Thank you.

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