That Neuroscience Guy - The Neuroscience of Why Your Brain Gets Tired

Episode Date: June 7, 2023

Sometimes you wake up and your brain feels foggy. Maybe, halfway through the day you hit a wall and lose the motivation to get things done. But why does our brain get tired? In today's episode of That Neuroscience Guy, we discuss the neuroscience behind why we feel mental fatigue, how it affects the brain, and how to prevent it best. 

Hi, my name is Olaf 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. You know, we've all experienced it, and we try to avoid it, but sometimes it feels like our brains are just tired. Now, I'm not talking about cognitive fatigue or stress and some of the things we've talked about in the past. I just mean our brains just feel tired. They feel sluggish and we just can't get them going. So on today's podcast, why do our brains get tired?

On today's podcast, why do our brains get tired? Well, the simplest way to think of it is that our brain is an energy-hungry organ. It just wants energy and it consumes a lot of energy. The brain on average only takes up about 2% of the body's weight, so relatively it's quite small. But it takes up more than 20% of our daily energy. Just think about that. 2% of our mass, 20% or more of our energy. And because the brain demands such high amounts of energy, and like I mean big amounts of energy, the foods we eat and the way we live our life greatly affect brain function. You know, I mean everything from from decision making to the way we move,

to learning, to memory, even to our emotions. Now, I've talked about this in the past, but at the end of the day, your brain is largely made up of neurons. So let's just think about that for a second. It's largely neurons, at least in terms of the part that's doing the actual work. Now, there's glial cells and other things in there that play a very crucial role, but mostly thinking is all about neurons in the brain and a neuron fires. That's really its only job. If it has sufficient input, a neuron fires and it's that neuronal firing that leads rise to motor output, to our ability to sense things in the world, to all of those high level things like decision making, learning, and memory. But for neurons to fire, they need energy. All right. So they need to get an energy source. Just like if you were going to do something,

you need energy. And basically like most of the other cells in the body, brain cells use a form of sugar to get energy, and we call that sugar glucose, and that glucose is used so that the neuron can effectively recharge and fire again, and glucose comes from the foods we eat, and it's delivered to brain cells, the neurons, right, through the blood system. But what exactly is glucose? We've all heard about it, but what actually is it? Well, basically, the word glucose comes from the Greek word for sweet, and it's a form of sugar, right? And you pull that sugar from the foods that you eat, and you use glucose basically for its energy. And the way it's distributed throughout the body is through your bloodstream.

So the bloodstream carries glucose to your cells. And in this manner, sometimes it's called blood glucose. Now, basically insulin, just to add this to the story, it's a hormone and it moves glucose from your blood into the cells for energy and storage. So that's where insulin fits into the story. So that people with diabetes, for instance, they have higher than normal levels of glucose in their blood. Now, people with diabetes, basically their insulin system is messed up and won't talk about that here, but that's where it fits into the story.

Now, how do you get glucose? So where does it come from? Like we've said, it's from the food you eat and typically foods that are rich in carbohydrates. And later in the podcast, I'll give you some food guidelines, if you will, to promote glucose and good brain health that way. But things like bread, potatoes, and fruit. And basically as you eat, so you consume your food, it travels down into your stomach and their acids break it down, right? Basically the whole point of this stuff in your stomach and all those things you've heard about is to break the food down so it can be digested, not just digested, but transferred into the bloodstream. And when it's broken down, that's where glucose gets released. Now, I was

always bad at organic chemistry, but I'm sure that there's people out there that could give you the formulas for this process. But at the end of the day, you're releasing glucose from this process. And that's where your intestines come in. Basically, your intestines, their whole purpose, in a sense, is to absorb the glucose that's released. And the role of what the intestine does, then it sucks in the glucose that's been broken down what the role of what the intestine does, then it sucks in the glucose that's been broken down and it passes it into the bloodstream. And then once it's in the bloodstream, the blood system, the whole point of it in some sense is to carry glucose around the body to recharge energy sources. And then that goes back to that insulin

piece. Insulin basically takes the glucose from the blood and helps get it into the cells. piece. Insulin basically takes the glucose from the blood and helps get it into the cells. Now, the way your body works with this and your brain, it's all tied to your brain, is your body's trying to keep basically your levels of glucose constant. All right. You don't want to have too much. You don't want to have too little. And basically this is where the pancreas comes in. It monitors your blood sugar levels and people that have pancreatic issues then have problems with blood sugar levels and therefore energy and basically the system works sort of back and forth if if your your glucose levels rise after you eat and then basically there's cells that release insulin and you absorb some and it gets inside but it's then stored right so you you want to store glucose all right and you hold on to it as an energy source and it's the main energy source

for the brain so the the blood system is carrying glucose to the brain so you can use it for energy so if your brain's getting tired, and we'll come back to this, one of the probably the biggest reasons is you're not giving it the right kind of energy or enough energy to function. Now, how much energy does your brain require? Well, like we said, for the average person in a resting state, it's about 20% of the body's energy. But if you're doing a lot of thinking, literally you need more energy. And what does your brain do with that energy? Well, it does exactly what we've been talking about since the first episode of this podcast, right? It's letting you see, it's giving motor output, it's making decisions, it's learning, it's getting memory systems to use. And it's a bit hard to determine the exact way this works out.

And within regions of the brain, it's very hard to tell which region is drawing more energy than others. But there seems to be evidence from studies in mice in particular that are looking at where the energy goes. It's basically thought that 25% of the energy that's brought in is used just to keep the cells functioning. All right. So basically the basic processes that keep the cells alive, because you have to remember these are little living organisms, right? And the remaining 75% is basically used for signaling. It's the energy you need to fire those neurons, which is how the neurons communicate, which goes back to how the brain functions in general. And where that energy is

actually used is at the synapses themselves. So if you remember previous episodes, we've talked about neuronal firing. Action potential goes down the axon. It gets to the synapse where neurotransmitter is released. and that neurotransmitter crosses the gap and it binds on the postsynaptic neuron and it fires. But this gets a little bit technical, but basically to make this process happen, there's actually a little pump. They're called sodium potassium pumps. It gets really technical and I don't know if I want to go into it. Maybe I will on a future episode with just a warning about, hey, this is going to get really technical. But those sodium potassium pumps basically allow the neurotransmitter to go in and out of the cell. And they also allowed

the receiving cell to bring it out. And that little pump operation, you just think of a pump going up and down. It's not quite how it works, of course, but it turns out that's the most energy intensive process in the brain. So the reason we need glucose in the brain is to keep the neurons alive, but also to keep those little sodium potassium pumps firing, which allows the neurons to signal. Now, are there parts of the brain that require more energy than the others? Typically, the white matter uses less energy than the gray matter. And that's just an estimate. Basically, the white matter is the axons and myelin and things like that. And the gray matter, which is the dendrites, the cell bodies and the site of the synapses uses more energy. And that's because of that synaptic thing we've talked about within the brain itself. There's a lot of debate about this. Hearing is thought,

for instance, to require a lot of energy. And it's because hearing requires really rapid signaling, same with vision. So if you were going to argue which part of the brain uses the most energy surprisingly it's not the prefrontal cortex making those decisions it's probably the sensory systems it's the best estimate and it's just because the timing is needed because if we're going to function in real time you need to have your sensory systems firing you know a question that comes up with energy, and I get this one actually a lot from students, is, you know, does your brain use more energy

when you're thinking hard or completing tasks? Well, yes. The more signaling that occurs, the more energy that's being used. And you can see this in real time. For instance, this is actually how fMRI works. We talked about fMRI, I think, back in season one or season two. But if you scan someone's brain and measure blood flow in real time, as someone thinks more, so the prefrontal cortex gears up, you see more blood flow to the

region. And that's literally what we've been talking about, right? Neurons are firing, those synapses are doing their job, those little sodium potassium pumps are working, and you need glucose and energy to make that happen. So you see more increased blood flow to regions that are more active. In terms of, you know, foods that you should eat, basically the simple lesson for brain health in terms of foods is to avoid simple carbohydrates and eat complex carbohydrates. So this is a dietary thing. You might hear this argument a lot in terms of weight control because we're told to avoid those simple carbohydrates. And simple carbohydrates, the way I always think of it, are the fake ones like chocolate bars and Coca-Cola, and we should eat more complex

carbohydrates. And complex carbohydrates, my son would call them the boring ones, things like brand cereals, apples, oranges, kidney beans, black beans, lentils, wheat tortillas, but whole wheats, skim milk, cashews, peanuts, carrots. And you could go on and look for a list of simple complex carbohydrates to eat and simple carbohydrates to avoid. And the rules that apply for weight control basically apply for brain energy. If you eat lots of complex carbohydrates, your brain will have more energy and therefore it'll function better. And of course, there are the things that I usually mention. I've already talked about diet. So of course, there's exercise, great for brain function.

Why? Increased blood flow, more glucose to the neurons so they can fire and work more efficiently and sleep because your body needs to recharge if you're constantly firing the brain and it fires while you're asleep of course but if you're constantly in active mode if you will you're burning glucose and your brain will get tired so your sleep is where your brain recovers so as usual dr k Craig Olson's advice, sleep, diet, exercise. And the one thing I'll end with here on this is there are no magic brain foods. There aren't. Anything that's said to promote better brain function, basically it's just playing on what's already known.

Stick to complex carbohydrates and your brain will work just fine. All right, that's why your brain gets tired and that's how your brain gets energy. Hopefully you found that interesting. Of course...