That Neuroscience Guy - The Neuroscience of Going for a Walk

Episode Date: August 14, 2024

In today's episode of That Neuroscience Guy, we discuss what's going on in your brain when you take a break and go for a walk. 

Hi, my name is Olof Kregolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. Throughout the time course of this podcast, it's hard to believe we've been running for three and a half years now. It seems like just yesterday that we pushed the first episode. We've talked a lot about, you know, different aspects of neuroscience or brain function in isolation. You know, we talk about memory, but we don't tie it to anything else. We talk about learning and we don't tie it to anything else. We talk about grabbing an apple, but we don't tie it to anything else. So for this last episode of our summer series or our summer season, I guess, I thought I'd try to tie it all

together and just take you for a walk. I go for a walk every morning and I just want to, let's just look at what's going on in the brain as we do something as simple as this. And let's try to tie together some of the bits and pieces I've told you about. So I'm sitting on the couch and I look outside and I see it's nice out. So my sensory system is processing this. My visual system looks outside. All right, my eyes look outside. This information comes in. And what happens to that information? Well, it flows to the back of the brain, to the primary visual cortex. And then it flows through the ventral stream. And again, we have episodes on all of this. I'm just putting it all into one. And as it flows through the ventral stream,

we work with bottom-up processing and top-down processing, and we recognize what we see outside as nice weather. And how do we do that? Well, we take that visual image, the sun shining, no clouds in the sky, maybe we have some perception of temperature, and we search our memory system. So we go through and we index our long-term memory systems and we basically sort through memories and we go, huh. And through experience, we were able to match this as nice weather. So that information then is fired up to the prefrontal cortex. The prefrontal cortex goes, okay, we've looked outside. We see it's nice weather. Now imagine another scenario. Both of them will get us outside for a walk, but you're

sitting on the couch and you look at your watch. I do this all the time. And I look at my step counter and I think, oh gosh, all right, I've got 5,000 steps to go to my daily goal of 12,000. I've got 5,000 steps to go to my daily goal of 12,000. So what's happening there? Well, it's similar in the visual story. You look at your watch, sensory information comes in, it goes to the primary visual cortex, it goes through the ventral stream. And at some point, you translate those numbers into meaning. All right. You know from experience that that number 7,111 is not the number it needs to be, which is 12,000. How do we learn that? Well, we've talked a lot about learning. You know, we learn to add and subtract. We're not born with this knowledge. We acquire this knowledge through learning. And that goes back to prediction errors and all that stuff. So see, it all does fit together, but we see these numbers and we say, okay, those numbers aren't my

goal. So that's again, a check with the prefrontal cortex. If you just recently, I talked about executive control and you've got this sort of, Hey, all right, I have a goal of 12,000 steps a day. So when that information reaches the prefrontal cortex that you only have 7,111 steps, the prefrontal cortex knows you haven't achieved your goal. So whether it's because it's nice outside or whether it's because you haven't achieved your goal, the prefrontal cortex makes a decision. Now it's looking at the available options. There is a value for going for a walk. You would achieve your goal. You would enjoy the weather outside. There's a value for staying on the couch. You might just feel lazy and not want to get up. And there might be a value. You might be thinking to yourself, oh man, I got some work to do.

All right. But your prefrontal cortex weighs these values and the highest value wins. Remember our talks about decision-making? We tend to always choose the highest value option. And of course, these values might be skewed by, you guessed it, the amygdala. We talked about emotional decision-making. As much as you might need to do work, the fact that it's nice outside might add value. The amygdala might add value saying, oh man, I'm going to enjoy this. Or the prefrontal cortex might override the comfort of the couch because your amygdala is saying, you know, I'm happy here. And the prefrontal cortex might override that emotional response and say, no, we need to

achieve this goal we've set for ourselves, 12,000 steps. So the prefrontal cortex makes a decision. All right, we're going to go for a walk. That's the high level part. The lower level of that decision is the anterior cingulate cortex. It receives this input from the prefrontal cortex, and it says, okay, we're going for a walk. And one of the things the anterior singlet cortex does is action selection. So the anterior singlet cortex is basically going, what do I need to achieve this goal of going for a walk? And we actually call this a special name. We talk about hierarchical reinforcement learning, where we actually learn a series of actions.

All right. So to achieve the goal of going for a walk, what actions do we have to put together? So the anterior cingulate cortex sorts through its list of possible actions, and it realizes that standing up is the first thing it needs to do. So the anterior cingulate cortex then sends a message to the motor system and it basically says, stand up. Now we talked a lot about the motor system. So the supplementary motor area and the lateral premotor area or the premotor cortex, they put together a motor plan. What do we need to do to stand up? What muscles do we need to fire and in what order? And then

once that motor plan is generated, it's sent to the primary motor cortex, which fires actual muscles. The whole time, the sensory system is taking in sensory information about the position of the body in space. All right. It's determining that you're in a seated position. And as you begin to stand, it's going to send information to this primary sensory cortex, which will end up informing the motor system about what's actually happening. So the motor system is saying, we're trying to stand up and the sensory system is affirming whether that's happening or not. And eventually you stand up. Now we're back to the anterior cingulate cortex. All right, the goal is to go for a walk. What is the next action in the

sequence? Well, in the case of my house, it would be walk towards the front door. So the motor system engages the walking movement. Now, if you remember, we talked a bit about central pattern generators. All right. So with the central pattern generator, if you remember, that's that circuit within your spinal cord, right? It's a circuit where one neuron activates another, one neuron activates another, and it's a pattern that goes around and around and around. How does that relate to walking? Well, if you remember, this is your ability for your legs to go left, right, left, right, and keep the swing cycle and gait going continuously. And you don't think.

Modern neuroscience posits that central pattern generators govern simple actions like walking. So walking is controlled at the spinal level. It's not controlled from the brain. The primary motor cortex isn't sending down messages left, right, left, right. What happens is it just sends down a high-level message of walk. And then what it does is the motor system just guides you. So it allows you to dodge around furniture. Well, how does that happen?

We're back to vision. As we're moving, as we do anything, you always have to remember your sensory system, even when you feel like you're daydreaming, it's constantly pulling in information. In this case, what matters? It's the dorsal stream. Visual information flows to the primary visual cortex, but in this case, it goes up through the dorsal stream, which allows you to build your representation of visual space. That's the part of the visual system that tells you where the table is, it tells you where the corners are, and your visual system interacts with the motor system.

And it's basically saying, here is the way that visual, here is the space you're in, and then the motor system navigates through that space. You get to the front door. The anterior cingulate cortex, hmm, what's the next action in the sequence? Now, the prefrontal cortex isn't governing this. Once the plan is executed, the prefrontal cortex is just sitting back and it's just making sure that the plan is being followed. All right. So it's not like the prefrontal cortex is doing this high-level selection at every step. Lower-level brain systems govern this once we're ongoing.

We talk about being on autopilot, and this is kind of what I mean. When you walk down a hallway, your brain is just doing it. Your decision has been made to walk through to the front door. The prefrontal cortex just keeps an eye on it. It's not monitoring it at a very high level. It's just sort of passively sitting there, keeping an eye sort it. It's not monitoring it at a very high level. It's just sort of passively sitting there, keeping an eye sort of semi-open on what's going on. You get to the front door and the anterior cingulate cortex, what's the next thing you

need for a walk? Put on shoes. So guess what? That engages a motor plan, premotor cortex, supplementary motor cortex. They take in sensory information, the visual system, that ventral stream that we use to tell it was nice outside. Guess what? Where are my shoes? Hey, those are my shoes. Motor system, grab shoes. Shoes are on. Back to the anterior cingulate cortex.

What's next in the action sequence? Open the door. All right, motor system's re-engaged. Sensory system helps, keeps an eye on things, makes sure what's happening is happening. You step outside. You close the door. This might be where a higher level system kicks in. The prefrontal cortex raises its ire a little bit more and goes, hey, remember to lock the door. All right. Ah, yes.

So then another motor plan is engaged and you lock the door. You walk down the driveway and you get to the bottom. And in my case, you would walk a little bit further to the bottom of the street. And then you have a choice. Do I turn left and walk for the beach or do I turn right and walk towards the park? And this is where the prefrontal cortex comes fully awake. It goes, okay, we're achieving this goal of going for a walk, but you've put me in this high level decision. And it reviews again, the values. What's nice about the beach? Ah, yes, the waves, the ocean, the sand,

but the forest is quiet and cool and the prefrontal cortex will evaluate this. It's going to think about and it's going to search and engage memory systems. Now there might be, again, the amygdala might be chiming in going beach, beach, beach, it's the summer, go to the beach. What is that doing? It's biasing values. All right. It's going to bias the value in my case to turn left, but maybe it's a really hot day, like really hot. So the emotional system might be biasing you the other way. The forest is cool. The forest is cool. Meanwhile, the prefrontal cortex is doing the logical part of this. It's trying to think about what's most beneficial for you,

keeping in mind this overarching goal of going for a walk. Now, depending on your mood, the day, and what's happened recently, again, memory and emotion, you decide to walk to the beach. It's what I tend to do every morning. Anyway, I hope you got something out of that. I was just thinking a lot about how we talk about these things in isolation. And I really wanted to try and stitch it all together. And I definitely left some things out, but I tied in a lot of concepts we've talked about over the past couple of seasons. And with that, we're done our summer season.

Matt and I are going to be off until September. But what we need from you, please, please, please, we really need to know what you want to know about the neuroscience of daily life. Take five minutes and email us, thatneuroscienceguy at gmail.com. Heck, we're so desperate for ideas, you can email me, Craig Olson at uvic.ca or craigolson at gmail.com. We really want to know what you want to know about the neuroscience of daily life threads and X at that neuroscience guy,

please send us ideas. We are going to get back on track in September. We're planning to push a solid through till Christmas and drop an episode every week. We need to get back in. I'll apologize again. It's been a busy summer and we've been a bit off our game, but we've tried to get you as much content as we can. The simple truth is I am

a full-time research professor and Matt is desperately trying to finish his PhD. We just do this for fun. But of course you can support graduate students in the Craig Olson Lab through Etsy and Patreon. I know we need t-shirt designs. If you have ideas, send those in too. And on Patreon, we appreciate, we truly appreciate the people that have supported us. Matt gets the money. It helps pay tuition for him and it helps pay rent while he's struggling to also be a full-time PhD student. And finally the the podcast itself. We just pushed through 800,000 downloads. I can't believe that. When I launched the podcast back in February of 2021, I honestly thought we'd have five listeners, which would be five of my friends. For those of you that do listen, thank you so much.

We truly appreciate it and it keeps us going. So if you haven't subscribed, please do. And thank you again for listening. Like I said, we're going to take a break for a couple of weeks, but we'll be back in September for more of That Neuroscience Guy. And on that note, my name is Olaf Kregolsen and I am That Neuroscience Guy. I'll see you soon.