We all work on important tasks while we sleep – consolidating memories, building immunity, and managing weight, just for starters – but some of us do a whole lot more. From walking and talking to driving and committing crimes, sleep disorders can be disruptive, dangerous, and downright deadly.
British neurologist and sleep expert Guy Leschziner explains how different parts of the brain can be in different stages of sleep at the same time, how the most common sleep disorder is actually several different problems, and why poor sleep may cause hallucinations and out-of-body experiences.
Plus – how some animals sleep with one eye open!
Phil Stieg: Hello I’d like to welcome Dr. Guy Leschziner, Director of the Sleep Disorder Centre at Guys and St. Thomas Hospital in London. He is a renowned neurologist specializing in sleep disorders and presenter of The Mysteries of Sleep on BBC Radio and Senses on BBC World Service. In 2019, he published The Nocturnal Brain; Nightmares, Neuroscience, and The Secret World of Sleep. Guy, thank you for joining us and explaining the story about sleep.
Guy Leschziner: Thanks very much for inviting me, Phil.
Phil Stieg: So let’s start with why do we sleep and what are the importance of the sleep cycles?
Guy Leschziner: So you’re getting the easy questions out of the way first, I guess? Why do we sleep? Well, as you know, there have been plenty of books written about that. And I think the short answer is there probably is no single reason why we sleep.
In fact, sleep is probably of crucial importance for every aspect of our waking lives. So, it’s probably easier to answer why don’t we sleep rather than why we sleep.
We know that sleep is important for restoration, for growth, for regulation of our immune system, for regulation of our hormonal systems. It’s responsible for a lot of the regulatory functions of our brains — so our memory, our mood, our anxiety levels. And it has important functions on a range of cognitive functions as well. So, when I say it is important for every function of our daily lives, I do mean that.
Phil Stieg: Briefly, can you just go through the phases of sleep?
Guy Leschziner: Yeah. So, we tend to cycle through the various stages of sleep about four or five times over the course of the night if we’re adults. And we divide sleep into non-REM sleep, which essentially is when the brain slows down, the brain waves slow down, everything becomes a little bit more quiescent.
And that’s what we sometimes describe as deep sleep, particularly the deep stages of non-REM sleep. And then there’s REM sleep, which is the stage of sleep that we most associate with dreaming, particularly dreams of a narrative structure. And actually, during that stage of sleep, the brain is very active on the EEG. It looks almost like an awake brain.
So, we think that what is perhaps most important about the cycles between non-REM and REM sleep is that they enable a consolidation of our memory. They enable a facilitation of movement of what we’ve kind of experienced during the day from areas of the brain to more longer-term stores of information. And it’s that flipping between REM sleep and non-REM sleep that is important.
Phil Stieg: But it’s also important that we have what, like four cycles or five cycles of REM? If you only get two, meaning you only sleep for 2 hours, that’s problematic also. Right?
Guy Leschziner: I don’t think we know the answer to that. In the olden days, some of the antidepressant drugs used to completely eliminate REM sleep and using the technology that was available to researchers in those days, there were no obvious long-term harms. Now, it’s likely that actually REM sleep is probably fundamentally more important when we’re younger of age, in that when we’re newborn we spend about 8 hours a day in REM sleep. When we are in our sixties and seventies, that’s probably more like an hour. So, it’s clearly got a much more important function when our brains are developing, when we’re learning about the world than it has when we’re approaching our deathbed.
Phil Stieg: As we think about sleep disorders, is it more commonly due to a psychological issue or to a biological issue?
Guy Leschziner: I think that’s a little bit of a difficult question to answer, because where does the psychological begin and end and the physical begin and end? Even with insomnia, (which, by the way, is the most common sleep disorder, apart from probably chronic sleep deprivation due to burning the candle at both ends.) With insomnia, there are psychological factors, but there are also some biological factors. So, as I said, insomnia is probably the commonest sleep disorder. We know that about one in three adults experience insomnia in any one year. That about 10% of the population experience chronic insomnia. So incredibly common.
Phil Stieg: So then what is going on in insomnia and what is insomnia and then how do you go about treating it?
Guy Leschziner: Well, insomnia is actually quite a poorly defined condition in many respects. It basically is described as having difficulty getting to sleep, staying asleep or having stable sleep, or complaining of poor sleep quality associated with daytime symptoms. Probably the most common form of insomnia that we consider used to be termed psychophysiological insomnia, which really recognizes the fact that it’s got a psychological component, it’s got a physical component.
We also know that there is a strong genetic component in that insomnia often runs in families. What we think is going on is that there are some psychological changes as a result of disruption of sleep. So those psychological changes can be conscious or unconscious. The conscious ones, which I think everybody will be very familiar with, is if you’re having a bad night’s sleep or you’re having difficulty getting off to sleep. You may be worried about, “oh God, how am I going to function tomorrow? Is this going to be it for the rest of the night? Is it going to be a really miserable night?” And indeed, if that goes on for a prolonged period of time, maybe you might worry about the long-term health consequences of having very poor sleep.
But there are also some unconscious factors. The fact that we associate particular environments with particular behaviors, and in people who have had ongoing poor sleep, they begin to associate the sleeping environment with being awake rather than being asleep on an unconscious level. And then once you’ve had sleep disrupted for a prolonged period of time, then those physical factors come in. So changes in your cortisol, changes in your adrenaline, which all end up in exacerbating that insomnia, and you end up in this vicious loop.
Phil Stieg: You alluded to the sleepwalking and sleeptalking of that, and I thought that one of the more interesting stories you talked about was Jackie. Was it driving a car, driving a motorcycle, being completely asleep, but doing all these complex tasks? What’s going on?
Guy Leschziner: A lot of people will have experienced sleepwalking in their lives or sleep talking. And particularly when people are young, they will often experience these kinds of behaviors that are termed non-REM parasomnias. So we tend to think of sleep as affecting the whole of the brain – that the whole of our brain is in sleep or in a particular stage of sleep at a time.
But actually, what we are now beginning to understand is that different parts of the brain can exist in different stages of sleep or wake simultaneously. And in individuals who have a propensity to sleepwalking, we understand that there are certain parts of their brain that remain in very deep sleep. So particularly the parts of the brain that are responsible for rational thinking, for planning, or the parts of the brain that are ….
Phil Stieg: Which is the frontal part…
Guy Leschziner: The frontal, yes, frontal part of the brain. And also the parts of the brain that are responsible for memory, like the hippocampus, the temporal lobe. But other parts of the brain are very active, they’re awake, like those areas responsible for movement and those areas responsible for emotion. So when you consider that that’s what this state represents, you begin to understand why people may do things that are out of keeping with their personalities, that are a little bit strange, that perhaps have a very strong emotional content to them, like, for example, sleep terrors.
And depending on the degree to which your brain is asleep or awake or the different parts are asleep or awake, may influence the complexity of the behaviors that you see. So, it may simply be crying out. It may be driving a car or riding a motorbike as in Jackie’s case. It may be as in that famous case from Canada, somebody who drove 25 miles and murdered their mother-in-law and stabbed their father-in-law and then got let off their conviction because they claimed it was sleepwalking.
Phil Stieg: OK, I shouldn’t laugh at that. I mean, it’s a terrible story.
Guy Leschziner: It is a terrible story. But certainly, we’ve seen some extraordinary things happen whilst people are sleepwalking.
Phil Stieg: Narcolepsy probably isn’t that common, but what actually is going on with it? What are the implications, and how does it affect the patient directly?
Guy Leschziner: Narcolepsy is a neurological disorder whereby individuals have great trouble staying awake. They often have sleep attacks during the day, but they also have difficulty staying asleep. So often, people with narcolepsy have very fragmented sleep. And in addition to this failure to control that switch between wake and sleep, they also have a difficulty in controlling the switch between REM sleep and non-REM sleep. And as a result, they will often flick in and out of wake to REM sleep, from REM sleep to wake, which is something that shouldn’t really happen.
So normally when we go off to sleep, it takes about an hour to enter into REM sleep. But as a result of this flicking between REM and wakefulness very quickly, there are aspects of REM sleep, of dreaming sleep that enter into wakefulness. And this results in a whole range of absolutely fascinating conditions. So it results in hallucinations as they drift off to sleep or wake up, essentially what we consider to be dream intrusion into wakefulness. They will experience something called sleep paralysis, which is when they’re awake, but they feel completely paralyzed.
And that’s because in REM sleep, we are completely paralyzed, that mechanism of paralysis gets switched on inappropriately early while we’re still awake. And when that’s combined with hallucinations, the nature of those hallucinations can be really quite dramatic. Out-of-body experiences. I had a woman say to me yesterday that she drops off to sleep and she has an out-of-body experience where she floats over the hill that’s outside her house, or she’ll be looking down on herself, sleeping in her bed, occasional demons or intruders in the bedroom.
The other thing that they do get is sometimes during wakefulness, that mechanism of paralysis gets switched on inappropriately, often with strong emotion. And so people will experience a phenomenon called cataplexy where they will suddenly lose muscle tone associated with very strong emotions, sometimes spontaneously even.
Phil Stieg: How is it possible for somebody to be both asleep and awake? Finally, does that person, when they wake up, describe a good night’s sleep?
Guy Leschziner: Yeah, well, I think that’s a really good question, Phil. I think we’ve very much moved towards this concept of local sleep, meaning that when the brain sleeps, it’s not a global state. It’s actually a state that exists on much smaller levels. And in fact, we think that even while we’re wide awake, there are constant areas of our brain in the cerebral cortex that are dipping in and out of radio silence, essentially little islands of sleep that are constantly going on. In fact, you might be having little islands of sleep while you’re talking to me.
Phil Stieg: I was just thinking people accuse me of that all the time…l.
Guy Leschziner: As your eyes glaze over. I’m not sure I can see that on zoom. But this perhaps explains why, when we are sleep deprived, our cognitive function, our attention, and various other aspects of our cognitive performance decline, because those little islands get larger, more extensive, and the duration of those areas of local sleep perhaps extends.
But it also relates to a lot of the sleep disorders that we see, which demonstrate clearly that the different areas of the brain can exist in different stages of sleep at the same time. It encompasses sleepwalking, as we’ve discussed. It encompasses various manifestations of narcolepsy that we’ve discussed. It encompasses potentially lucid dreaming, which is this concept of knowing that you’re in a dream while you’re dreaming, or sometimes even being able to control your dream when you’re dreaming.
It probably encompasses conditions like paradoxical insomnia, which is when people say, well, I didn’t sleep a wink last night. But if you monitor their brain waves, it’s very clear that they’ve been asleep for eight and a half hours. Because probably small areas of the brain that are responsible for awareness over our surroundings are awake whilst the rest of the brain is asleep. It encompasses a whole range of these conditions illustrate that very nicely.
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Narrator: It’s surprising to learn that human beings may have “little islands” of sleep going on in their brains at any given moment. But who knew that there are some animals who allow sleep to take over entire continents — or should we say entire hemispheres – of their brains?
Since the 1960’s scientists had theorized that dolphins must have evolved a way to keep swimming while they catch a few ZZZs. How else could they return to the surface to breathe while dozing? But in 1999 researchers in Humboldt, California, determined that dolphins actually allow one hemisphere of their brain to go to sleep while the other stays awake to keep swimming and breathing.
The clue was in the dolphin’s eyes. Mammals’ eyes are connected to the opposite hemisphere of their brains, so when the dolphin’s right hemisphere went to asleep, its left eye would close.
But the right eye would stay open because it was connected to the fully awake Left hemisphere.
Northern fur seals have taken this adaptation to another level. Since they live both on land and in water, fur seals have different strategies for sleep depending on where they are.
When sleeping on the beach, they can allow both hemispheres of their brains to lapse into a deep, long brain wave sleep.
But fur seals can spend weeks at a time feeding in the ocean. When they’re out in the water, their brains switch to a completely different sleep strategy. They go to sleep floating on their sides – one hemisphere staying awake to hold their nose up above the surface to breathe, while the other hemisphere gets some well-deserved rest.
Interestingly, they always sleep on the side with their closed eye – the sleeping one – facing the sky, and the open eye – the awake one – looking down into the water.
No doubt they do this to better spot orcas, sharks or other potential predators from the deep. We assume that it didn’t take long for fur seals to learn the value of sleeping with one eye open!
Phil Stieg: Given the prevalence of depression in our society, you get a decent night’s sleep, but you wake up and it’s like, “Oh God, I’ve got to go face another day of this world.” Is that different than not getting a good night’s sleep? And how do I, the patient, know the difference?
Guy Leschziner: Well, I think that’s not always so straightforward, actually, because we know that sleep and depression have what we term a bi-directional relationship. If you get terrible sleep, that can make your mood low. If your mood is low, you can get terrible sleep. And that does create some diagnostic issues. I guess the difference between depression and the grumpiness of sleep disturbance becomes evident when you treat the sleep disturbance and you see whether or not that grumpiness goes away.
Phil Stieg: You emphasized a lot of the other factors that can be affected by bad sleep, cardiovascular, inflammatory. Can you go through that for us?
Guy Leschziner: Yeah, sure. So we know that there is an important association between sleep duration and your immune system. And plenty of studies have been done looking at how resistant you are to, for example, acquiring the common cold, depending on how much sleep you have. We know that it affects our hormonal system.
So even a single night’s poor sleep can dramatically influence your glucose tolerance, your insulin resistance. It can certainly put you in a prediabetic state or can exacerbate diabetic control. It can make the regulation of your weight much more difficult because poor sleep influences hormones called leptin and ghrelin that are responsible for appetite and our feelings of satiety.
So poor night’s sleep can increase your caloric intake by about 40% the following day. And I think we’ve all had experience of that when you’re shoving M&Ms in your mouth after sleeping very badly because you think that this is going to give you a bit more energy.
Phil Stieg: You’re describing my life. Come on! (laugh)
Guy Leschziner: But we also know that poor sleep, and in particular conditions like sleep apnea, seem to be very good at changing your cardiovascular health. So they increase your blood pressure. And in fact, sleep apnea is probably a common cause of individuals requiring several antihypertensive drugs to control their blood pressure. We know that it’s associated with heart disease, with the risk of stroke.
One area of particular growing interest is the association between sleep and cognitive decline, particularly dementia. There are channels within our brains called the glymphatic system. And this glymphatic system is thought to be responsible for cleansing toxins or metabolites the breakdown products of simply being alive out of our brains.
And in stage three sleep, in the deepest stages of non-REM sleep, these channels open up significantly and would certainly influence the transport of various proteins, like the protein that is implicated in Alzheimer’s disease be transported out of the brain and back into the rest of the body. So you can begin to understand why poor quality sleep or limited sleep may be a risk factor for conditions like Alzheimer’s disease.
Phil Stieg: You related a story about Vincent getting out of rhythm – what you refer to as the circadian rhythm – then how that just messed up his life. Relate that story, please.
Guy Leschziner: So Vincent was always slightly a late riser and a late sleeper. So he had what we would term a delayed sleep phase. He was an extreme evening owl. In his teens, he underwent a hip operation which put him out of action for a while. And then after that operation began to experience this cycle, this sleep cycle whereby the time that he went to sleep would delay by an hour every day. So, he would go to bed at midnight one day, then 1:00 am, then 2:00 am, and essentially once a month he would be completely out of sync with the world. And this is something called non-24-hour rhythm disorder.
We all within us have a clock, a circadian clock, which runs on a just over 24 hours cycle and is regulated by a range of things in our environment, like light exposure, when we eat, when we drink, when we exercise. And so that’s constantly being adjusted with the changes in seasons.
But in some individuals that circadian clock, for reasons that we don’t fully understand, doesn’t work properly, or at least it starts running on a rhythm of 25 hours for example, in Vincent. And it’s deeply destructive because essentially, he’s living a nocturnal life for half of his month, impacting his ability to work, his ability to study, his ability to do anything that involves a regular schedule.
Phil Stieg: So, was Vincent’s non-circadian rhythm, is that a form of insomnia or a different way of experiencing insomnia?
Guy Leschziner: It’s not insomnia in that when he feels sleepy, he can sleep, and he can sleep a good amount. And actually, if he were able to cast off all the requirements of modern society and lead his life in the way that he wanted, he would not be tired, he would not have difficulties getting off to sleep, staying asleep, waking up. He would feel refreshed. So that’s not insomnia. It’s what we term a circadian rhythm disorder.
Anybody who’s got teenage kids will know that trying to get them into bed at a decent hour is virtually impossible. And if they could, they would sleep through until one or two pm. So that delay in your circadian clock is actually part and parcel of your brain’s development. It’s also, of course, influenced by a whole range of things that you’re doing. So, if you’re up at night playing on your computer or scrolling doom scrolling on your mobile phone until late in the night, then that exposure to bright light will also have an impact on your own internal body clock.
Phil Stieg: I couldn’t help but think about the emotional and psychological factors that the person with the sleep disorder is going through. I’d like you to characterize that. But in addition to that – what the family goes through, can you characterize that and what are healthy ways to deal with it?
Guy Leschziner: As with all illnesses, as with all serious illnesses, it’s not just the patient who suffers, it’s everybody around the patient as well. For each individual, it is a little bit different. But certainly, if you imagine that many of the conditions that, for example, I see on a regular basis, like extreme sleepwalking or narcolepsy, these are conditions that often come on in teenage years. And you can imagine that the impact of having such a serious condition that really influences every aspect of your life can have, particularly when you’re in those formative years, and how stressful that must be for the parents of those teenagers as well.
You know, ultimately sleep is a consequence of biological factors, of psychological factors, of social factors and environmental factors. In all of these cases, if you sleepwalk and you’re allowed to sleep as much as you want and you don’t necessarily wake up, then you may be completely unscathed by it. Especially if you’re single and you live in a ground floor apartment where you’re not likely to throw yourself out of a window and you have got a good lock on the door.
But somebody who is living on the fifth floor, is sharing a bed with a wife who has insomnia and gets very irate with you when you wake her up in the middle of the night, is going to have a completely different experience of exactly the same condition. And so ultimately, it comes down to all of those factors for that particular individual.
Phil Stieg: And what do you have to say to those of us that leave, have the cell phone light on, the computer light on, or the TV on in the background when we go to sleep? What are we doing?
Guy Leschziner: Horrible!
Phil Stieg: Horrible, Horrible?
Guy Leschziner: Horrible. Horrible. Don’t do it!
I think one of the tendencies of all this information about sleep is that it makes people a little bit anxious about sleep. And if you can sleep with a light on and you get a perfect night’s sleep and you wake up feeling refreshed, then that’s not a problem for you. If you can drink two espressos half an hour before bed, and as soon as your head hits the pillow, you sleep like a log.
Phil Stieg: Have at it!
Guy Leschziner: Don’t worry about it, yeah…
Phil Stieg: Dr. Guy Leschziner, thank you so much for being with us. You have magnified the importance of sleep in our lives and how to go about getting better sleep. But you’ve also made it entertaining to describe some of the unusual aspects of sleep. Thank you so much for being with us today.
Guy Leschziner: Thank you, Phil.
Phil Stieg: Well, I’ve always felt that I have somewhat of a sleep dysfunction because of my sleep deprivation throughout life, so it made me feel better about myself.
Guy Leschziner: Okay, well, at least one happy customer.