That Neuroscience Guy - The Neuroscience of Dreaming

Episode Date: April 24, 2022

During sleep, we can replay a combination of memories and images that we seemingly imagined out of nowhere. Dreaming can be different for everyone. But why do we dream, and why can our dreams be so different? In today's episode of That Neuroscience Guy, we discuss the neuroscience behind why we dream and, as a bonus, sleepwalking. 

Hi, my name is Olof Kergolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. I'm sure that all of you dream, but what's going on in your head when you dream? And why does our brain even create dreams? As an add-on, I'm also going to answer a Lister question and talk a little bit about sleepwalking and why we sleepwalk. So on today's podcast, the neuroscience of dreams and sleepwalking. Now we've already done an episode on sleep and how sleep works and learning in sleep. But just for a quick review, basically when you sleep, your brain cycles through five different stages. These are classified typically as non-rapid eye movement sleep stage one, non-rapid eye movement stage two, non-rapid eye movement stage three, and non-rapid eye movement stage four.

And then, of course, REM sleep, which is rapid eye movement stage three and non-rapid eye movement stage four. And then of course REM sleep, which is rapid eye movement sleep. And as you go through the night, you cycle through these. So you start with non-REM one, which is light sleep. You drop down to stage two, then to stage three, then to stage four, and then you might go up to three and then to two and then back down to three and then back down to four, then up to three and back to the four and then up to three, then up to two, up to one. And you might even wake up or you might go up from four to three to two to one and then slip into REM sleep. So in terms of the order to visualize this, there's awake, then there's REM sleep, and then there's one, two, three, four non-REM sleep. And your brain cycles through this all night long, going through these different stages. Just to note,

things have changed since we did the sleep podcast. And now there's a bit of debate as to whether non-REM three and non-REM four are actually different stages of sleep, or whether you could group them together and just call it deep sleep. The jury's out, the science is ongoing, and typically, just in case you want to know how this is done, typically what you do is you use EEG brainwaves, and you can see differences in the EEG signal that are characteristic of the different stages of sleep. Now, dreaming. Dreaming most typically occurs during REM sleep, but it can also occur during stage four deep sleep. Indeed, there's research out there that suggests that the stage of sleep that a dream occurs in can impact what

the dream is about. Now, with that said, the majority of dreaming occurs during REM sleep. So what's the theory behind this? Well, the most prominent theory about why we dream ties it to memory consolidation. So what's consolidation? Again, we talked about this back when we talked about memory. But if you recall from our podcast on memory, this is where the memory firms up, if you will. So if a memory fails to consolidate, then it's something that you don't remember. But if it does consolidate, then that's something that you do keep in long-term memory and is relatively permanent. The nature of dreaming is tied to your

brain trying to organize and code memories during this consolidation process. And it's impacted by emotions that you might be experiencing, you know, stuff that's happening during the day that's carrying on and impacting while you sleep, and the activation of different brain regions. So let's dive into this a little deeper. During the day, our episodic memories, and if you remember, our episodic memories are things that have happened in your life. So what you had for dinner last night, you know, going downtown to see a movie or going out for a walk. And when an episodic memory is forming, a part of the brain called the hippocampus basically ties the memory together. And during consolidation, that's basically the hippocampus successfully tying the memory together. And then you don't need the hippocampus anymore.

Once the hippocampus has tied the memory together, you have a consolidated memory and it's there. So let's just work through a quick example of this so you understand where I'm coming from. Imagine you went down and went for a walk on the beach. Well, there's a whole bunch of different brain regions that are involved in this memory. Now, there'll be a region that's processing what you saw, right? The visual experience, what you smelled, what it felt like emotionally, what you heard, and all of that needs to get tied together in a single memory. Again, thinking back to the memory episode, your memory for, say, going for a walk on the beach isn't just in one specific brain region. It's distributed across the brain in all of the neural regions that are needed to process the event. Now, studies in animal models have found that during sleep,

basically what's happening is that the hippocampus is replaying the events of the day. It's sort of reliving them over and over and over again. And it's been shown that this replay happens faster than real time. And sometimes it even happens backwards. Isn't that kind of crazy? It's like you're going down to the beach and you're seeing it happen from back to front, if you will, like just putting a movie in reverse. And that activity replay is correlated with activity in the other parts of the brain. So the visual cortex for the visual experience, the prefrontal cortex, if you're thinking about things, your goals and planning. And this memory replay occurs during REM sleep and while you're dreaming. And this is where your dreams come from. They're largely based on the events of your life. So a classic dream is just about something that

happened to you recently. And that's because your mind is replaying the event, trying to get it stored or consolidated into memory. And that becomes your dream, if you will. But of course, lots of things happen during a given day. So a dream can also come from a combination of replays. So you're borrowing elements from the different things that happened in the day. Now, it gets even bigger than that. So you're borrowing elements from the different things that happened in the day. Now, it gets even bigger than that. But let's just walk through very carefully.

Imagine that you woke up and you had breakfast, in my case, with my son. And then I went for a morning walk, which I always do. And then I went into the university and did a couple meetings and talked to a couple of graduate students taught a class and then I came home and I made my son dinner and we decided to go out to a movie and then we came home and you know did the nighttime routine and went to bed well my dream could be a combination of all of those pieces they're just being pierced together in like a weird order so that you think that the dream is unique it It's something you never experienced, but your brain is just stealing bits and pieces from throughout the day. Now, what about the weird things that enter your dreams? The things that you, that you, they're kind of bizarre. Well, this is the impact of your subconscious brain. Basically, the, the bizarreness can come from a couple of sources. Basically, the bizarreness can come from a couple of sources.

There could be conflict between different memories that are trying to consolidate. And when these brain regions are in conflict, you're basically combining things in really weird ways. That's one source of the weirdness of some dreams. But it could also come from something that you've read in a book or seen on TV or in a movie. And it's important to think back to what we said about memory. Again, back in season one, you can't consciously access everything we have seen and experienced. We forgot so much across our life. We remember the big things and the emotional things.

But if you think back to your childhood, there's things that you probably have forgotten that you saw. And so this new content that you think you've never seen before is literally just being pulled in from some previous memory that is in your brain somewhere, but you've just lost the ability to access it. So I'll give you an example of this as well. Recently, I was having a dream and I was playing basketball. And I was playing basketball and I was playing basketball with this strange sort of purple looking, I don't know what to call it. It was a thing. And I totally was going, where did that come from? I woke up and said, what the heck was that all about? And then not long after that, just literally a couple of days later, my son and I were watching television. And there was a show that he used to watch called In the Night Garden. And he flashed up and he laughed and had a quick giggle and said, you know, hey, this show, I remember watching this, Dad.

And there was the purple weird character, Iggle Piggle. And I was going, wow, okay, that's where it came from. Somewhere in my memory, I had stored this thing in my memory, this character, and my brain, for whatever reason, while I was dreaming, just reached out and pulled it back into play, if you will. So what do our dreams mean in terms of the brain? Well, a traditional interpretation of meaning is that they're tied to the ideas and beliefs that you hold in your head. They're stored in the brain. Well, a traditional interpretation of meaning is that they're tied to the ideas and beliefs that you hold in your head. They're stored in the brain. And we talked a couple episodes back

about belief systems and the left brain, right brain. So these things are meaningful to us and our brain knows this. So the memory consolidation process isn't really random, but it's focused on conflicts between past things, but also these sort of biologically determined goals, beliefs, and ideas. So it shouldn't be too surprising that these things impact into our life. You know, my son is the biggest thing in my life, so I definitely have a lot of dreams where he plays a prominent role. You know, let's say a different example. You have a passion for snowboarding. Well, this will influence and bias your dreams because your brain knows that you like it. And as a result, we dream about these things. Now, this is also true for the things that scare us, our nightmares. Our brain also knows what we fear, and this can impact your dreams as well. your dreams as well. Finally, what's the biological basis for our dreams? Well, it's basically the brain is trying to interlink our experiences of the world with our emotional drives. All right,

so the brain during consolidation is trying to just figure out all of this stuff. You know, what have we experienced today? What are we feeling? So dream content isn't really your subconscious trying to send you messages. Basically, your dream content is all about your brain's motivational drives that you have interacting with your day's experiences during consolidation. And it's also pulling in all of this information that you may or may not have forgotten. So it can come together in weird patterns. One other possibility that's being explored with research is that dreams may also allow the brain to explore hypothetical situations and it's basically a way to plan ahead, like what

would I do in this situation? Now, the evidence for that isn't great, but there are studies that show that's true. So when people dream, sometimes you do see patterns of activation that sort of are like a test case scenario. Now quickly a little bit about sleepwalking. Sleepwalking is quite prevalent. It's estimated that between three and a half and four percent of the North American population sleepwalks on a regular basis. So nearly 30 percent of people that have been surveyed said that they'd sleepwalked at some point in their lives. Now sleepwalking doesn't occur during REM sleep when you do most of your dreaming. It does occur during non-REM sleep. Now, this is only a

working theory, but the idea is that if you transition too rapidly through this, it can trigger sleepwalking for some reason. So, for instance, going straight from stage four to stage one, but bypassing stage three and stage two when you cycle through this. It's important to realize that the likelihood of sleepwalking is increased by spending too much time in the deepest stage of sleep, which actually isn't healthy. If you think back to the memory episode,

the sleep episode, stage two Nram Rem sleep is just as important as stage four. So things that lead to sleep deprivation, like excessive tiredness or possibly drinking too much or things that really wear you down can result in an increased incidence of sleepwalking. So there's a bit on the neuroscience of dreaming and a bit on the neuroscience of sleepwalking. Just a tidbit there. Just remember the website's up, thatneuroscienceguy.com. You know, you got links to Patreon where you can support the grad students up, thatneuroscienceguy.com. You know, you've got

links to Patreon where you can support the grad students in the Kregolson Lab and the podcast. We have links to our merch page. I keep promising we're going to have some new shirts up and it's just, it's been a busy end of year, but we're going to get that up. There's also links to our YouTube channel, which is still fledgling, the podcast and my blog, which I update not as frequently as I should. Remember, you can also follow me on Twitter, That Neurosci Guy. I push out cool things about neuroscience that I've seen and neuroscience that occurs in the Kregolson Lab. My name's Olive Kregolson, and I'm That Neuroscience Guy. Thank you so much for listening, and I'll see you on Wednesday for another neuroscience bite.