Instant Genius - Better Sleep: The deep connection between sleep and memory

Episode Date: June 8, 2025

We humans spend roughly one third of our time sleeping. For the average person this adds up to around 26 years over our lifetimes. And though to the outside observer it may seem that there’s little going on, several processes are being carried out by our bodies and brains that are vital for our health and wellbeing. In this episode, part of our four-part Better Sleep miniseries, we speak to Dr Alessio Delogu, a neurobiologist based at King’s College, London, about the intimate link between sleep our memory. He tells how memories are encoded in our brains during sleep, how sleep deprivation hampers our ability to learn new skills, and shares some tips to help us keep our memory systems working in tiptop condition. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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a bite-sized master class in podcast form. Every Monday and Friday, you'll hear world-leading scientists and experts talking about the most fascinating ideas in science and technology today. I'm Jason Goodyear, commissioning editor at BBC Science Focus. We humans spend roughly

one third of our time sleeping. For the average person, this adds up to around 26 years over our lifetimes. And though to the outside observer, it may seem that there's little going on, several processes are being carried out by our bodies and brains that are vital for our health and well-being.

In this episode, part of our four-part Better Sleep miniseries, we speak to Dr. Alessio Delugu, a neurobiologist based at King's College London, about the intimate link between sleep and our memory. He tells us how memories are encoded in our brains during sleep, how sleep deprivation hampers our ability to learn new skills, and shares some tips to help us keep our memory systems working in tip-top condition. So welcome to the podcast. Thanks very much for joining us.

Thank you very much. Pleasure to be here. So today we're talking all about sleep and memory. memory. So let's start with the memory bit. So which areas of the brain are involved in the formation of memories? Yeah, that's a very interesting question and one that is being heavily investigated actually by neuroscientists. So I would say many parts of the brain are involved in learning and memory, but some parts may be more than others. We are all familiar with the shape of the brain and what we see in terms of brain and that tends to be the cortex of the brain. And so the cortex, the surrounding layers of the brain are the most important ones when it comes to memory, learning and memory.

However, there are other components of the brain, which you wouldn't really see them from the outside. They are in the middle of the brain. That are also very important because actually they provide the signals to the cortex, the surrounding layers of the brain, to operate in the way that is then conductive to memory. So overall, in terms of the whole organ, the brain, many different parts. work together in order to encode information and retrieve information, which is really what memory is about. However, I think more interestingly, think that memory happens at a very small scale, not at the level of the entire brain, but actually at the level of small structures that appear in cells,

and cells are the building blocks of the brain. So how are memories encoded in our brains? What do we know about that? Again, so that's an area that is sort of subject of heavy investigation. And it relates a little bit to what I just said before in the sense that we need to think about the brain as an organ of the body like any other organ. And so it is made of the same building blocks. These building blocks are cells. In the brain, in particular, and in the context of memory, the cells that we look at are called neurons. They are very specialized cells.

they are highly polarized, which means they are not really symmetrical. You can pick up a front and a back and a left and the right, and these neurons have appendages. So very, very tiny structures known as synapses. Synapses essentially is where a neuron contact another neuron and transfer some information from that neuron to the next neuron. So those point of contact are known as synapses. And the leading theory about memory is really placing the focus

on these synapses. So memories may be encoded at the level of these synapses. Of course, there's billions of these synapses. It's an enormous amount of this synapses. And what is important is that they are not fixed structures. They are very plastic. They can change.

They can get stronger. They can get weaker. They can form new. They can disappear. That's really critical. The plasticity of these synapses is critical for the process of memory. So we have different types memory, what can we say about that?

Yeah, true. So we tend to classify memories according to very structured criteria. To some instances are artificial classifications, but they are important, especially when we want to investigate mechanisms for memory. I think is important to have these classifications. I think possibly we can divide the main types of memories are episodic memory, semantic memory, procedural memory. And I think it's easy to give examples of these type of memories in the sense that

if you start from procedural memory, for example, you know, learning to ride the bike. So that's a learning process which involves also remembering how to operate the bike and so that's procedural memory or to play a musical instrument. Episotic memory instead is the ability

to recall places and events that happen in particular place at a particular time. Semantic memory, again, is the ability to recall and present concepts, maybe more abstract concepts that we have learned. These three are the main types of memories, and of course, then you can start, you know, divided them into subfields. Interestingly, it seems that different parts of the brain are actually responsible for the encoding and the retrieval of this type of different types of memories. So when we go back to where are memories encoded and where in the brain are these.

It seems that for episodic and semantic memories, actually there's a structure that is known as the hippocampus. And this seems to be very important, at least for the encoding of this type of information, which will then become episodic and semantic memories. Procedural memory could be different, actually, and the motor cortex may be more important, perhaps the cerebellum. So these are different parts of the brain.

So let's have a look at sleep then. So when we fall asleep, it proceeds in different phases, doesn't it? So what are the different phases? Sleep is absolutely fascinating, and it's actually a complex process. So it's not just a single state of the brain. It's a cyclical process. The brain goes through a number of different processes that repeat over the course of the night. So the best way to measure these days is to use EEG, which stands for electroenceilogram.

Now, what is the EEG doing? The EEG essentially is picking up electrical activity from the brain, particularly from the surrounding layers of the brain, the cortex. And those patterns of electrical activity change through the different sleep stages. So thanks to that and other measures that we can also apply, we define something called non-rapid eye movement sleep. That's the first stage of sleep that we get into when we fall asleep. And this is then followed by rapid eye movement sleep or REM.

So in short, the sleep cycle is formed by an N-R-R-R-R-M phase, followed by a RAM phase. And altogether, in humans, it's a very generic approximation, but this should last about 90 minutes. But of course, it's changed through the course of the night as well. At the very least, we can define these two different types of sleep, non-R-R-Sleep, RAM sleep. But actually, when you start looking more precisely within these different two different types of sleep, you see that there are different patterns of electrical activity. And in particular, non-REM sleep can be subdivided into different stages. Again, the main way that we can say in which stage of sleep the brain is, is to look at electrical activity.

And this electrical activity, we can link it back to those synapses, those neurons, those building blocks of the brain. because ultimately really are the neurons that generate those patterns of electrical activity. So by measuring an EEG during sleep, we learn something about what the brain is doing and what the components of the brain, those neurons and those synapses, what they are doing, what kind of processes they are engaging in. So which stages are involved in the consolidation of memories? Yeah, so consolidation of memories is obviously very important. And it seems really that sleep is essential.

It's very, very important to improve consolidation or enable consolidation. Information has been acquired recently. It's quite possible that both types of sleep are important for memory consolidation. Probably in recent years it's fair to say there has been more experimental evidence pointing to non-REM sleep

has been very important for consolidation in particular. But it's quite likely that both components will have a role. Interestingly, when we look at what type of activity goes on in the brain, during sleep and during non-REM sleep, there's something very peculiar that happens. And this is summarized by the concept of active replay of information. Basically, the idea there is that those neurons that were involved in the acquisition of the information, and this is something that would have happened during the wake state, are then again active during non-REM sleep. And this can be measured, actually.

So if provided that the right type of techniques are used, it is possible to identify the very same neurons that were active during the learning phase, during the wake phase. Is it possible to see them then becoming active in that very same pattern during non-REM sleep? So this replay seems to be really very, very important for memory consolidation. So let's have a look at what sort of things can affect memory consolidation.

So first off, how about... sleep deprivation, a lot of us suffer from this. And you think, from personal experience, your memory does seem to suffer. Yeah. So there's something interesting, actually, that has been measured now in many different studies. And that's the fact that the brain experience something like a need for sleep. And this need for sleep increases the longer we are awake. It's probably something physical.

It's probably the accumulation of a certain molecule or a certain signaling factor in the brain that then when it reaches a certain threshold, it will then induce the process of falling asleep. So the brain knows how long it has been awake. And so it goes by itself then that if this period of wake is prolonged for a long time, and that's what we call sleep deprivation, then probably the brain will sense that and will be affected by that. And there is experimental evidence that really shows what happens in terms of our ability to learn and memorize things or simply to perform well in a task when we are sleep deprived. And the outcome of these experiments is very obvious.

You know, performance goes down dramatically. So our ability to learn if we are sleep deprived is compromised, severely compromised. There are some very interesting studies that have been done using laboratory. model systems, typically means laboratory animals. And you can see that some of these changes that should happen at synapsis, you know, these small points of connections between different neurons that I say are very plastic, they can strengthen, they can weaken. Actually, they don't really happen as they should during the period of sleep deprivation.

So sleep deprivation acts at this very microscopic level on these synapses, and it interferes with the ability of synapses. to change. Those changes would be required actually to encode new information. There's also another interesting experiment that has been done on sleep-deprived ruts. It's very indicative, I would say, of what happens during sleep deprivation. So in this particular experiment, using very sensitive technologies, it was possible to look at individual neurons in the cortex of the brain and to monitor their activity. And this activity was monitored during performance of a certain task under normal conditions, but also under sleep deprivation.

And I think it was quite striking to see how individual neurons in a sleep-deprived brain, some of those individual neurons, they seem to actually decide to go into sleep in a sleep mode. Despite the fact at the overall system level, the whole-bock level, that subject was still awake and still performing. actually it was very interesting to see that some neurons, some of these cells in the brain would sort of call themselves off the task and say, well, it's time for me to sleep, now I'm going to sleep anyway. So this was actually called sleep at a single cell level, right? So we don't, maybe it's just not enough to think about sleep, but something that involves

the entire tissue, the entire brain, it can actually happen in one single cell. And so those are signs of what happens during sleep deprivation. And of course, there are many studies that show that performance, as I say, goes down. So our ability to learn to memorize is severely affected by sleep deprivation. No one goes to Hank's for spreadsheets. They go for a darn good pizza. Lately, though, the shop's been quiet. So Hank decides to bring back the $1 slice.

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of scientific discovery was probably one of the first things that people managed to associate to one particular sleep phase, which is the REM sleep. So rapid eye movement sleep is typically when we experience dreams. As I say before, I think it's quite likely that both types of both types of sleep contribute to memory consolidation, non-RAM and RAM. So something will happen during RAM. Historically, RAM was more associated with procedural memories. And as I say, before, procedural memories maybe separated from this structure known as the hippocampus in the brain,

different than the semantic and the episodic memories. But I think that view is changing now, and there's more the appreciation of Rembsley being important regardless of the type of memory. It's interesting also the concept of dreaming, essentially, you know, what is that? And I think that links quite well with this concept of replay of information that I mentioned at the very much. very beginning, right? So memory consolidates because the same networks of neurons, the same patterns of synapses get reactivated during sleep. And so that helps to consolidate, store these memories in a better way. Presumably, dreams are something that reflects that process. However, it would be different than the type of information replay that happens during non-REM sleep. Because, as I say, the

components of the brain that are responsible for that replay are different. Rather than being hippocampus-specific, they may happen somewhere else. And in the end, which part of the brain is active when, I say before, we are measuring activity in the cortex of the brain, but actually that cortex is stimulated by the subcortical brain, by the brainstem, by the hypothalamus, even by hormones. So cortisol is very important actually in REM sleep. and it seems to drive these patterns of cortical activity that may then result in dreaming. There's another important thing that I think is worth saying about

the role of dreaming and REM sleep, in particular in memory consolidation, and is that there seems to be a specific replay of memories that have a strong emotional component during REM sleep. And so, again, trying to link that to the anatomy of the brain, the amygdialize yet another part of the brain that we know is involved in emotion, perhaps negative emotions as well,

that part of the brain is active during REM sleep. So it's possible, again, that REM sleep is specifically consolidating some specific types of memories. So how about aging? Often our ability to remember sort of decreases as we age. And so in some ways does our sleep quality. So are those two things related? Yeah, most likely they are related.

And as you said, it's correct, actually. So the way we sleep changes through our lifetime. And this is without taking into consideration any pathological change to the brain. So even without looking at neurodegeneration or dementia, it is known that if you just measure these different types of sleep, you know, non-dream sleep and dream sleep throughout the duration of the night, you will see a very clear pattern actually coming from a young individual and an elderly person healthy, but the only.

The main differences are that some of the stages of non-REM sleep, which are very important for memory consolidation, they are actually now, basically, they are almost not there anymore, or they are there at the beginning of the night, but actually to an extent on a level that is not comparable to a young brain. So this is when this phenomenal replay of information that I mentioned before, that's when it should happen. and if you just look at EEG patterns of elderly people,

you see that those stages are heavily affected. They are not so evident. They are not so dominant as they once used to be. The other thing that happens with aging is that sleep tends to be less consolidated. And the term consolidated refers to the fact that once we fall asleep, we stay asleep continuously for a number of hours. But actually this seems to change during the lifetime, And so elderly people tend to wake up more often.

So this fragmented sleep. Now, perhaps because of this fragmented sleep, then there may be some kind of compensation sleep that tends to happen during the day. And so whilst normally, as a young individual, we sleep during the night, we are alert and awake during the day. Actually, as we age, we may change the world. We tend to be more sleepy during the day, actually, and sleep less during the night or wake up more often.

So yes, there are changes and this may very well have an impact on memory consolidation, perhaps the ability to store new information, yes, which is something that, as we know, happens normally in the process of the university and is, of course, exacerbated in dementia's, such as Alzheimer's disease. Yeah, so sort of one final question then. Are there any sort of tips or techniques that we can use to help us remember things more effectively, you know, consolidate memories as we sleep? Yeah, so I'm not sure if I'm the best person to give tips

because I don't follow them myself. But you can look at all these huge body of information that comes out of research and science and then try to apply that to your daily life. I think one important message, which maybe not everyone is aware of, is the fact that sleep is not a waste of time. this idea that we are asleep one-third of our life

and naively one could say couldn't I actually be doing something more useful than just be there unconscious effectively but the important message is actually that a lot is happening during sleep and it's all very useful things in terms of maintaining the healthy status

of the brain sleep is also seems to be fundamental actually we haven't really said how important sleep is not just to consolidate memories, but actually to prepare you to acquire new information the next day. This is also something where sleep plays

a very important role. So the first message, I think, is not to undervalue the role of sleep, essentially. It's an active process. And so it has to happen. It's beneficial and it happens. The other thing, of course, relates to this concept of sleep hygiene,

which now is commonly used. Sleep hygiene is a more general sort of concept and it covers more than just memory consolidation, but I think it would have also a benefit in terms of memory consolidation. So I think it's very important to ensure that the quality of our sleep is good. Good quality of sleep essentially means that we go through this deep phase of non-REM sleep when information is replayed, is transferred into different areas of the brain of the cortex, is integrated with other information that we have.

So the quality of sleep is very, very important. And in order to have good quality of sleep, I think we should think a little bit about circadian rhythms. So rhythms of our body. The rhythms of our bodies are dominated by the fact that there's an active period, usually when we are exposed to light, to bright light, and there is this period of sleep when there is dark. And so if we can increase that period of wake,

where we are exposed to light, we are very active, you know, we do, we go, we do sports, we run, we engage in intellectual activities, then the consequence of that is that the night that follows will also most likely be a night of good quality sleep. Because again, the brain has been very active and now it requires sleep, requires to go into deep sleep, and that process happens very effectively. Thank you for listening to this episode of Instant Genius, brought to you from the team behind BBC Science Focus. That was Dr. Elisio Delogu. If you liked what you just heard, then please do consider subscribing to Instant Genius on your preferred podcast platform.

If you'd like to see our guests and hosts in person, then please also check out our YouTube channel at ScienceFocus. The current issue of BBC ScienceFocus magazine is out now. Pick up a copy wherever you buy your favourite magazines or download us on your app store of choice. You can also find us on Apple News or online at sciencefocus.com. This podcast is sponsored by name, audio and focal. The texture and emotional depth of music can be lost through digital sources or poor. signal. Name Audio believes you can have digital precision with analog warmth. Alongside French acoustic specialist vocal, name creates high-end audio systems combining innovation with craftsmanship,

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