That Neuroscience Guy - Whats going on in the brain while you sleep?

Episode Date: March 8, 2021

Your brain does not shut down when you are sleeping. Instead, there is a lot of cool stuff going on - and I am not even talking about your dreams! In this episode, I talk about the neuroscience of sleep.

Hi, my name is Olof Kurgolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. We all sleep. But why do we sleep? Obviously, a key reason is to recharge our body. We get tired throughout the day and we need to sleep to regain energy and be able to do it all over again. But what about the brain? What's happening in the brain when we sleep? And specifically, what's the role of sleep in memory? Today, I'm going to talk about the neuroscience of sleep and specifically its impact on human memory. To understand the importance of sleep in its relationship with human memory, we have to first discuss the concept of consolidation.

So when we want to remember something, we hear it, and that information is brought into working memory or short-term memory. And that's where that information is held for, you know, a short period of time, call it 30 to 60 seconds. Imagine someone tells you their name at a party, it goes into short-term memory. And if you forget it, it's because it's being displaced from short-term memory. However, if you it, it's because it's being displaced from short-term memory. However, if you hang on to it, something interesting starts to occur. From short-term memory, what we're trying to do is get that information

into long-term memory. And if it's in long-term memory, that's where it's stored. And like the name says, we can access it for long periods of time. I'm sure all of us can recall memories from our childhood, for instance. These are the things that are stored in long-term memory. And of course, there's the information that was in memory for a short period of time that we've now lost.

But how does information get from short-term memory to long-term memory? The key process is called consolidation. Now, what is consolidation? Let's think of a specific example. Imagine you go out for dinner and that memory is going to stay in your memory for some period of time. That memory is comprised of a whole bunch of pieces of information. For instance, where you were, what music was playing, what you ate, what you were wearing, who you're with. And all of those pieces of information exist throughout

the brain. And what you're trying to do is link those pieces of information together. You're trying to build bridges between them. In the early stages of memory, a part of the brain called the hippocampus does this. It's a midbrain structure and it's very crucial for memory formation and consolidation. The hippocampus builds the bridges between all of these disparate pieces of information and holds them together. Consolidation is the process where the hippocampus is no longer needed. So the brain works to build networks between the pieces of information that can be accessed in the future when you want to remember what happened. This is also true for factual information. When someone explains a new concept to you, for the most part you know most of the words and most of the ideas. You're just

linking them together into a new pattern. And again, the hippocampus does this. It initially holds that pattern together, but through consolidation, that memory solidifies and the hippocampus is no longer needed. And when you want to remember that, prefrontal parts of the brain activate that pattern, and you can access it again and use that information. So now let's talk a little bit about sleep. Typically with sleep, we think about five stages. There's REM sleep, when we dream, which we're all familiar with. And then there's non-REM sleep, which is typically divided into four stages. Stage one non-REM sleep, for instance,

is light sleep, and stage four non-REM sleep is deep sleep. Typically throughout the night, we cycle through these stages. In the early stages, we're in light sleep, and then we drop down to stage two, stage three, and stage four, and we spend a lot of the early part of the night in stage three and stage four sleep. This is when that rest and recharge occurs. But we do cycle through it. For instance, you might pop back up to stage two and then stage one, and you might even wake up and then go back to light sleep and back down. But as the night progresses, you spend less time in stage three and stage four sleep, and you spend more time in stage one and stage two sleep. And I want you to remember that stage two sleep piece.

It turns out to be very important. Interestingly, as a side note, if you measure EEG or brainwaves while people sleep, as you move from stage one to stage four, you see an increase in delta power, or what we call slow wave sleep. This is how sleep clinics, for instance, diagnose problems. They look at the changes in the EEG signal across the night. We can talk about that more in another podcast. Let's get back to the idea of consolidation, stage two sleep, Let's get back to the idea of consolidation, stage two sleep, and the neuroscience behind it. Now, what I'm going to do is talk about a couple of research studies performed by Dr. Matthew Walker.

He's a researcher in the United States who's extremely interested in sleep and its role in memory formation. In one of his early studies, Dr. Walker had a bunch of groups of participants learn a simple motor task, a new skill. And the way it worked is they practiced the task for some period of time. You can imagine learning to putt a golf ball, but that's not quite what they did. Anyway, the participants in this study all practiced the task until they were good at it. And then they were tested to see how well they did. So the key manipulation in the Walker study was sleep. For instance, in one of the groups, they practiced the task, then they were tested on their performance, and then they were tested on their performance again, and then they slept, and then they were tested one time again on their performance.

In another group, they practiced the tasks, and then they were tested for performance, and then they slept, and then they were tested for performance again, and again. The key manipulation was when sleep occurred. Now, the results of this study are interesting. What Dr. Walker found was that performance improvements were only seen on tests after participants in the study had slept. In other words, it was sleep where the performance benefits were solidifying, or as we talked about earlier, consolidating. And the other key finding was that Dr. Walker found that the performance benefits were specifically tied to the amount of time that participants spent in stage two non-REN sleep. So let's review where we're at. at. Performance improvements occur while we sleep, and they specifically are related to the amount of time we spend in non-REM2 sleep. That's when consolidation appears to occur. Now, since then,

the Walker Lab and other researchers have shown this effect in a wide range of skills, not just a simple motor task. The key take-home message is consolidation occurs when we sleep, and it occurs specifically during non-REM2 sleep. And if you remember another thing I said, you spend more time in non-REM2 sleep in the later stages of the evening. So for instance, if you're not getting enough sleep, you're actually impairing your ability to learn because you're not going to be getting enough non-REM2 sleep. So let me say that again. If you're not getting enough sleep and most recommendations for the average person are between seven to nine hours a night, then your learning and memory

systems in your brain are going to be impacted negatively because you won't be getting enough non-REM2 sleep. So let's finish by talking a little bit about how we can optimize our sleep for non-REM2. In other words, how can we optimize our sleep so that we learn better and have better memory? Well, this is where sleep hygiene comes in. And let me tell you the gold standard test before I tell you about what you can do. The gold standard test for sleep hygiene is that you should be able to wake up the same time each day, around sunrise, without an alarm clock, and feel rested and not feel the need for caffeine. I wonder how many of you are actually experiencing that. I know I have trouble with it. What can we do about it?

Well, there's a couple of things and some of them are obvious, but let's go through them. First of all, caffeine. are obvious, but let's go through them. First of all, caffeine. Caffeine actively keeps you awake, so you should restrict caffeine in the evening, and a lot of people say from lunchtime onwards, because if you have too much caffeine, you'll have trouble falling asleep. The use of electronics in the evening has been highlighted in the last couple of years, and it seems pretty clear that if you stick an electronic device in front of your face while you're trying to get ready for sleep, that it's going to help keep you awake and not help you fall asleep. There's an underlying mechanism here, which is

quite interesting. It's tied to how portable electronic devices such as tablets and phones draw information on the screen and the frequency with which they draw that information. And it appears, at least in part, that that awakens us and keeps us alert as opposed to making us drowny. Another thing you can do is establish a regular sleep cycle. A lot of us live in a world where we go to bed early during the week and wake up early for work, but on the weekends we stay up late and then we sleep in. It turns out this is a bad thing to do. Healthy sleep is achieved by having a regular sleep cycle, which means going to a bed at approximately the same time every night and waking up at approximately the same time every day.

And on that note, it also seems clear from the research that oversleeping or sleeping in doesn't make up for sleeping less during the week. You're much better just to have a regular sleep and maintain that pattern. So let's summarize. The neuroscience of sleep. Sleep is important, and in particular stage two non-REM sleep, because this is when memory consolidation takes place. This is when our memories are formed and solidified and move from the sort of initial short-term stage to a long-term stage that can be accessed later. So why don't you get a good night's sleep and sleep on this and think about how that's going

to impact your memory. Thank you for listening to the podcast. My name is Olof Kregolsen and I'm That Neuroscience Guy. You can check out my website at www.olofkregolsen.com or follow me on Twitter at That Neuroscience Guy. See you on the next podcast.