From Insomnia To Sexsomnia, Unlocking The 'Secret World' Of Sleep

TERRY GROSS, HOST:

This is FRESH AIR. I'm Terry Gross. Our guest Dr. Guy Leschziner writes that you can survive longer without food than without sleep. As a sleep disorder specialist, he's seen plenty of patients with insomnia and just about every other kind of nocturnal problem - night terrors, narcolepsy, sleep apnea, sleepwalking, sleep-eating, sleep-driving and something called sexsomnia. In his new book, he describes some of his more challenging cases and the growing body of research into sleep and sleep problems.

Guy Leschziner is a neurologist and head of the Sleep Disorders Centre at Guy's Hospital in London. He spoke to FRESH AIR'S Dave Davies about his new book "The Nocturnal Brain: Nightmares, Neuroscience, And The Secret World of Sleep."

DAVE DAVIES, BYLINE: Dr. Guy Leschziner, welcome to FRESH AIR. You've got some fascinating cases in this book. But before we get to them, I want to just cover a couple of basics. A lot of us have heard of rapid eye movement sleep, you know, REM sleep, where our eyeballs are darting rapidly. And then there's non-rapid eye movement sleep, non-REM sleep. You want to just explain the differences between these two kinds of sleep?

GUY LESCHZINER: Well, if one looks at the brain during sleep, we now know that actually, sleep is not a static state. It's not a simple, binary state whereby we're either awake or asleep. What we now know is that actually, there are a number of different brain states that occur while we sleep. And we tend to divide those brain states, those sleep states, into, as you say, REM, or rapid eye movement sleep, and non-REM sleep.

In REM sleep, actually when we look at the brain, the brain from an electrical point of view looks to be very, very active. In fact, the brainwaves look very much like the brainwaves of an awake brain. And it's during this stage of sleep that we associate dreaming to occur, particularly those dreams of a narrative structure, plots evolving overnight. And during that stage of sleep, when the brain is very active, actually, it's probably when we are most separated from our bodies. In fact, although in this stage of sleep the eyes dart back and forward, pretty much every single muscle in our bodies apart from the muscles that control our eyes are completely paralyzed.

Whereas in non-REM sleep, when we look at the brainwaves, the brainwaves are slow. They're large. This is less associated with dreaming, although we do a dream of sorts in non-REM sleep. And it seems that these two different types of sleep probably have rather different functions.

DAVIES: Yeah, what are the different functions?

LESCHZINER: Well, I think the short answer to that is that we don't fully know. We think that REM sleep is particularly important, depending on the stage of life, in the development of consciousness, in learning, in creativity, in emotional processing, whereas non-REM sleep is perhaps the stage of sleep during which those restorative functions that impact the brain and also impact the body occur - so things like cleansing out toxic metabolites from the brain, regulation of the immune system and a variety of other functions.

DAVIES: So it's the non-REM sleep that people refer to as deep sleep, right?

LESCHZINER: Well, non-REM sleep encompasses this slightly different stage of sleep where the eye movements don't dial back and forward. But within non-REM sleep, there exists what we term Stage 1, Stage 2 and Stage 3 sleep. And Stage 3 sleep is the very deep sleep that we associate with waking up feeling restored, feeling refreshed.

DAVIES: OK, let's talk about some of the disorders that confront you in the clinic. Sleepwalking is one. And you've had some patients with some pretty strange episodes. You want to share a couple of them?

LESCHZINER: Yes, so the one that always comes to mind first of all is the 70-year-old woman that I saw a few years ago who would be found to be driving up and down the seafront in her local town in the middle of the night. In fact, in earlier life, she had had a motorbike and had been seen riding her motorbike apparently in her sleep. And even at an earlier stage, she was brought up in Canada, and she would often go into the wilderness with the guides on camp and would wake up her tentmates growling very loudly in the middle of the night. Of course, they thought that they were being attacked by a grizzly bear. And so she was soon sent back home because of the terror that she triggered in all her colleagues.

So that's one example. But you - sleepwalking or conditions associated with sleepwalking can really manifest in a number of ways, and these include sleep terrors, where people wake up in the middle of the night absolutely terrified, screaming and shouting and then go back to sleep often with very little recall.

And then there are some other conditions - things like sexsomnia, which is sexual behavior in sleep. Sometimes these conditions sound very funny, and indeed can be very funny. But on other occasions, they can be really life-changing, resulting in major injury or, as one of the cases that I describe in the book, in a criminal conviction.

DAVIES: Right. And in all - you had another guy - you had a patient named Alex who would get up and order pizzas. And then none of them - do any of them remember any of this after the fact?

LESCHZINER: Well, we used to think that people don't really remember anything that occurs in this stage that seems to relate to the fact that the brain in parts is in very deep sleep, whilst in other parts is awake. What we have learned over the last few years is that actually, quite a lot of people have some sort of limited recall. They don't necessarily remember the details of all the events or, indeed, the entirety of the event. But sometimes they do experience little snippets.

So Alex, who you referred to, would also do things like distribute glasses of water around the house for his sleeping flatmates without any recollection. But those events that were associated with a much stronger emotional content, so natural disasters - on one occasion, he dragged his girlfriend out of bed in the middle of the night because he thought that a tsunami was about to wash them away - and those kinds of events with strong emotional context are often better remembered.

DAVIES: Right. So this category of sleep problem, this is non-REM parasomnia. This is from the sleep where your eyeballs are not darting about.

LESCHZINER: That's right.

DAVIES: What do scientists think is going on when this happens?

LESCHZINER: Well, I talked earlier about the fact that we no longer consider sleep to be a binary state, an on or off state. But what sleepwalking in particular tells us is that sleep is also not a global state. And what I mean by that is that the whole of the brain can - is not necessarily in the same stage of sleep at the same time. So that in individuals who exhibit this group of disorders called the non-REM parasomnias, these unwanted behaviors that arise from non-REM sleep - typically the very deeper stages of non-REM sleep - what we see by either scanning them while they're exhibiting these behaviors or sometimes with electrodes is that certain parts of the brain can remain in very deep sleep.

And the parts of the brain that in particular remain in very deep sleep are the frontal lobes, which are the seats of our rational thinking, our planning, our restricting our normal behaviors, whereas other parts of the brain can exhibit electrical activity that is really akin to being wide awake - so in particular, the parts of the brain that are responsible for emotion, an area of the brain called the limbic system, obviously the parts of the brain that are responsible for movement.

And it's this dissociation, this disconnect between the different parts of the brain in terms of their sleep stages that actually give rise to these sorts of behaviors.

DAVIES: OK, so part of our brain is sleeping soundly, and some other part, for some reason, is aroused and functioning. Do we know why this happens?

LESCHZINER: We know that sleepwalking and these related conditions seem to run very strongly in families. So there seems to be some sort of genetic predisposition to being able to enter into this disconnected brain state. And we know that anything that disrupts your sleep, if you have that genetic predisposition, can give rise to these behaviors.

So for example, I've seen people who have had non-REM parasomnia events triggered by the fact that they sleep in a creaky bed, and their bed partner has rolled over, sometimes a large truck driving past in the street outside the bedroom. But there are also internal manifestations, internal processes that can give rise to these partial awakening. So for example, snoring or, more severe than snoring, sleep apnea, where people stop breathing in their sleep occasionally - other sleep disorders, like a condition called periodic limb movement disorder, where people kick.

And so anything that causes a change in the depth of sleep in people who are predisposed to this phenomenon of being in multiple sleep stages at the same time can give rise to these behaviors. And we think that it's probably a throwback to certain evolutionary mechanisms. So for example, if you look at certain animals, particularly aquatic mammals and certain species of birds, they can sleep with only one half of their brain at the same time because that allows them to swim or to surface for air or to carry on flying whilst they are asleep. And so it's well-established that having different parts of the brain in different stages of sleep occurs in nature.

DAVIES: Right.

LESCHZINER: So it may be that this is a bit of an evolutionary hangover for us.

DAVIES: Right. You mentioned that it manifests in sleepwalking, sleep driving, sleep eating and something you refer to as sexomnia. You want to tell us what that is, what your patients have exhibited?

LESCHZINER: So sexomnia is really a type of non-REM parasomnia that manifests with sexual behavior, and the range of sexual behavior can be quite broad. But at its extremes, it can result in people trying to pursue full-blown sexual intercourse in sleep. We used to think of sexomnia as being a relatively rare phenomenon, but actually, whenever I do anything like this on the radio or write about it, I'm usually inundated by emails or messages saying, oh, yes, I do that.

And actually, in the sleep lab, if you directly ask people about sexomnia, a lot of people will actually report it, but they don't tend to go to their doctor with it because, for most people, it's not a particular problem. Where it does get to be a major problem is if it results in unwanted sexual behavior, usually when you're sharing a bed with somebody who's not your regular partner. And as I describe in one of the cases, one of my patients ended up convicted of rape as a result of one of these events.

DAVIES: For a lot of people, these non-REM parasomnia, these conditions can create serious problems. So for people like Jackie, who was driving around in her neighborhood, or Alex, who was ordering pizzas, how do you treat them?

LESCHZINER: Well, I think the first question is whether or not they want specific treatment. As I talked about in the book with Jackie, actually, the reason why Jackie came to see me is because she was worried about the fact that she was driving up and down her seafront in the middle of the night and thought that she might be a danger to herself and to other people. And it was when she went to her family practitioner that she was told, well, actually, the only way to manage this might be to get her admitted into an inpatient secure psychiatric unit.

But actually, she had gone through her life seeing this as very much part and parcel of who she was. And she actually hit upon in her own way of trying to manage this, in that she bought herself a time-locked safe where she would deposit her car keys and knew that she could not get her car keys out of the safe until 6 o'clock in the morning, thus treating herself very well.

For people who are putting themselves at risk or putting other people at risk, there are a range of things that we can do. The first thing is to try and optimize sleep, generally, because, in people who are sleep-deprived, that in itself can prime the brain for developing these sorts of behaviors. But for more extreme cases, and if that doesn't work, then dealing with anything else that might be disrupting their sleep, looking at their environment, looking to see whether or not they snore, and treating those issues is often a very successful way of dealing with these sorts of problems.

In very few cases, when people are really putting themselves at risk, then we will resort to certain types of medication to try and treat these sorts of events.

DAVIES: What kinds of medication?

LESCHZINER: Well, the sorts of treatments that have been demonstrated to work include drugs like melatonin in certain instances, benzodiazepines like clonazepam and also a range of antidepressant drugs. Now, all of these drugs have potentially serious short- and long-term side effects. So in any individual, the risks and the benefits of treating them with medication need to be weighed up very carefully.

DAVIES: So you manage it behaviorally if you can?

LESCHZINER: And I think that that's the case for many sleep disorders. If we can avoid medication, then that would be the optimal way of managing these conditions.

DAVIES: Guy Leschziner is a neurologist and sleep disorder specialist. His new book is called "The Nocturnal Brain." We'll talk more after a short break. This is FRESH AIR.

(SOUNDBITE OF THE ACORN'S "LOW GRAVITY")

DAVIES: This is FRESH AIR. And we're speaking with Dr. Guy Leschziner. He is a neurologist and head of the Sleep Disorder Centre at Guy's Hospital in London. His new book is "The Nocturnal Brain: Nightmares, Neuroscience And The Secret World Of Sleep."

Sleep apnea is an issue that really troubles some people. What exactly is it?

LESCHZINER: Sleep apnea describes the phenomenon of our airway collapsing down in sleep. So our airway is essentially a floppy tube that has some rigidity, some structure to it, as a result of multiple muscles. And as we drift off to sleep, those muscles lose some of their tension, and the airway becomes a little bit more floppy. Now, when it's a little bit floppy and it reverberates as we breathe in during sleep, that will result in snoring; the reverberation of the walls of the airway result in the noise. But in certain individuals, the airway can become floppy enough or is narrow enough for it to collapse down and to block airflow as we are sleeping.

It's normal for that to occur every once in a while for everybody. But if it occurs very frequently, then what happens is that sleep can be disrupted sometimes 10, sometimes 20, sometimes even a hundred times an hour because, as we drift off to sleep, the airway collapses down, our oxygen levels drop, our heart rate increases, our brain wakes up again, and our sleep is essentially being disrupted, and then the airway becomes a little stiffer. They then gradually start dozing off into deeper stages of sleep, and that cycle continues.

DAVIES: You say that we're seeing an epidemic of sleep apnea.

LESCHZINER: Yeah. So as our girths, as our weights increase, the incidence of obstructive sleep apnea also increases. Sleep apnea is very strongly associated with obesity, in that weight on the throat or on the chest, fat being deposited within the muscles in our throats can often result in our airway becoming narrower or actually losing structural rigidity more easily. So as we as a population get larger, obstructive sleep apnea gets worse.

And the issue is beyond simply that of feeling sleepy because one's had one's sleep disrupted all the way through the night; we are now aware that obstructive sleep apnea has a range of long-term implications on our health, in terms of high blood pressure, in terms of risk of cardiovascular disease, risk of stroke, impact on our cognition - so our mental clarity. And there is now an emerging body of evidence to suggest that actually obstructive sleep apnea may be a factor in the development of conditions like dementia.

DAVIES: Wow. Now, there is this treatment, this, you know, fairly invasive treatment where you wear a mask - the CPAP, right?

LESCHZINER: Yes.

DAVIES: It's called continuous positive airway pressure, where it keeps putting some air pressure into your mouth so that the airway doesn't collapse. That's not the easiest thing to deal with, both for you and your sleep partners, right?

LESCHZINER: It is a challenging piece of kit for many people. I think on the plus side, individuals with sleep apnea often feel transformed by the use of this piece of kit, the CPAP mask. They say that, within a few days, they feel like completely different individuals. They are sleeping through the night. They're full of energy. They feel mentally much clearer.

But we know that in the long term, for many individuals, the use of CPAP can be quite challenging because, essentially, what you're doing is you're taking a mask and you're strapping it to your face to create a seal. And that's attached to a small machine that generates this positive pressure. And so strapping something onto your face in itself every night cannot be particularly easy to handle, but if it's leaking, if it's uncomfortable, then that creates further issues. And so we're constantly looking for alternatives to CPAP in certain individuals.

DAVIES: You do see other sleep aids - you know, mouth guards and the like - for sleep apnea.

LESCHZINER: Yes.

DAVIES: What do you think of those?

LESCHZINER: Yeah. So mouth guards, provided that they are made properly and provided that they're comfortable, can for many individuals be extremely useful. They - essentially, the way that they work is they, first of all, keep your mouth shut whilst you're sleeping. And so that prevents your jaw falling back and narrowing the airway. The second thing that they do is they push the lower jaw forward, and because the tongue is anchored to the lower jaw, it pushes the base of the tongue forward and actually creates a bit more space at the back of the throat.

So for people with mild sleep apnea, or indeed sometimes even simple snorers - so people who snore but don't have sleep apnea - these devices, which we call mandibular advancement devices, can work extremely well. I think there are a whole range of other consumer devices for which the evidence is much less firm. And people will often cycle through many of these things, like nasal strips or little stents that actually are not so helpful.

DAVIES: In a lot of cases, it sounds like the first step might be to lose some weight.

LESCHZINER: Weight loss is a very good way of treating sleep apnea. What we don't know is, for each individual, how much weight they need to lose in order to reverse the sleep apnea that they have. But certainly, it's the one proven long-term way of curing obstructive sleep apnea.

GROSS: We're listening to the interview FRESH AIR's Dave Davies recorded with Dr. Guy Leschziner, a neurologist who heads the Sleep Disorders Centre at Guy's Hospital in London. His new book is called "The Nocturnal Brain: Nightmares, Neuroscience And The Secret World Of Sleep." We'll hear more of the interview after a break, and we'll listen back to an interview with Paul Krassner, founder of the counterculture magazine The Realist, co-founder of the '60s radical group the Yippies. He died Sunday. This is FRESH AIR.

(SOUNDBITE OF DAVE MCKENNA'S "I'LL SEE YOU IN MY DREAMS")

GROSS: This is FRESH AIR. I'm Terry Gross. Let's get back to the interview Dave Davies recorded with doctor Guy Leschziner, a neurologist who heads the Sleep Disorders Center at Guy's Hospital in London. He has a new book about treating a wide variety of sleep problems, including insomnia, sleepwalking, sleep apnea and narcolepsy. The book is called "The Nocturnal Brain: Nightmares, Neuroscience And The Secret World Of Sleep."

DAVIES: You write about narcolepsy, which is a disease we've heard of. And, you know, we always think of this as people who suddenly fall asleep in the middle of the day. But it's a more wide-ranging problem than that. You write about a guy named Adrian, who had a different manifestation of this. What was going on with him?

LESCHZINER: So Adrian began, in his 40s, experiencing events whereby if he experienced very strong emotion - and it was a very specific emotion. It was an internal feeling of mirth. So if he was telling a joke, or he was the subject of something funny, he would experience something very bizarre in that all of a sudden, he would experience a sudden loss of muscle strength and would collapse to the floor. The first time he experienced this, he was trying to play a trick on his mother. He had driven up outside her house, and he noticed that she was in the garden. And he crept up behind a garden fence and at the last minute jumped out from behind the garden fence and smashed the garden fence in order to make a loud noise, only to find himself lying in the garden face down.

And this was really the first manifestation of this condition, called cataplexy, which is really part and parcel of narcolepsy for a majority of people. So it is the loss of muscle strength associated with strong emotion - usually laughter, actually.

DAVIES: So what's happening here?

LESCHZINER: Well, the answer as to what's happening in narcolepsy has really come from dogs, which is a rather peculiar state of affairs. In the last century, Stanford identified a number of breeds of dogs that had narcolepsy. They bred them for many years before then identifying that these breeds of dogs that had narcolepsy had a mutation, a genetic abnormality, in a very particular gene that coded for a receptor for a chemical called orexin or hypocretin. Now, when this mutation was looked at in humans, it wasn't found. But over the years, we've identified that, actually, this neurotransmitter, this chemical in the very middle of the brain, called orexin or hypocretin, is responsible for regulating multiple aspects of sleep.

In humans, what seems to occur is that there is some sort of immune process that triggers off the attack of a very small number of cells in the depths of the brain in an area called the lateral hypothalamus which are almost entirely or entirely destroyed by our own immune systems. So when that area of the brain is damaged, it disrupts our ability to regulate wake and sleep, but it also damages our ability to regulate switching between dreaming sleep and non-dreaming sleep. And it's these two aspects that really explain most of the features of narcolepsy.

DAVIES: So how have you been able to help people with narcolepsy?

LESCHZINER: Well, narcolepsy, at the moment, is still viewed as a lifelong irreversible condition. Once you have it, you will always have it. But over the last 20 years or so there have been numerous strides in terms of options for treating narcolepsy. And it very much depends on which aspect of narcolepsy you're trying to treat. There are drugs that primarily treat the sleepiness. There are drugs that primarily treat the cataplexy. And there are also other drugs that specifically treat the hallucinations or the sleep paralysis. So it's about trying to find the right drug or the right combination of drugs to treat all the aspects of the condition.

DAVIES: And are there kind of environmental or behavioral things you can do that help?

LESCHZINER: So planned naps are very helpful for people with narcolepsy. So what we often encourage people to do is to work into their school life or their work life the opportunity to have 15 or 20 minutes of a nap at a planned juncture because that's a very good way of preventing sleepiness for the coming few hours. So certainly, there is an aspect of behavior that does help people with narcolepsy.

DAVIES: Well, we haven't talked about insomnia, which is so common. I mean, I didn't get a very good night's (laughter), sleep last night. You say insomnia and sleep deprivation are quite different. In what way?

LESCHZINER: Well, when people have insomnia, they think that they are sleeping very little. And certainly, that's the case for some individuals with insomnia. But we know that insomnia is more than just one condition. So some people, for example, will feel that they've had a very, very poor quality sleep. But actually, when we monitor their brainwaves, their sleep, overnight in a sleep lab, we can actually see that they're getting a pretty decent amount of sleep. And so people can sometimes misperceive the amount of sleep that they have. In other individuals, actually, when one is slightly sleep-restricted as a result of insomnia, the brain tends to compensate for that by increasing the proportion of very deep sleep. So the slight difficulty is that people with insomnia have often read lots of stuff about how disruptive, how bad for every aspect of your health sleep deprivation is.

But the solution for people who are sleep deprived is much easier. Essentially, you just need to increase the amount of time you spend in bed and the amount of time you sleep. Whereas for people with insomnia, that's much more difficult to achieve. It's not a question of how much of an opportunity they have to sleep. It's the very fact that they can't get off to sleep when they want to that is the issue. Or even if they do fall asleep is the fact that they feel that their sleep quality is poor. And so they read all this stuff about how damaging sleep deprivation is and, actually, that increases their anxiety about the fact that they're not getting off to sleep and can result in this vicious cycle.

If you're a good sleeper, you tend to associate being in bed with being that place of comfort, that place where you go and you feel cozy, and you drift off to sleep, and you wake up in the morning feeling wide awake and refreshed. But for people with insomnia, they often associate bed with great difficulty getting off to sleep, with the dread of the night ahead, with the fact that they know that when they wake up in the morning, they will feel horribly unrefreshed and unrested. And so sleep, the environment that we normally would associate with sleep, becomes an instrument of torture for them.

DAVIES: Now, people take pills, like benzodiazepines, like Klonopin, and medicines like, you know, zolpidem. The brand name is Ambien.

LESCHZINER: Yeah.

DAVIES: Good idea?

LESCHZINER: Well, there has been a bit of a sea change in the last few years away from these drugs. We know that these drugs are soporifics. They're sedatives. So the first thing to know is that they do not mimic normal sleep. They're associated with some major problems. So some of these drugs are, for example, associated with an increased risk of road traffic accidents in the morning because of a hangover effect. They're associated with an increased risk of falls in the elderly, for example. And we know that people can develop a dependency on these drugs and can also habituate, by which I mean that they require ever-increasing doses to obtain the same effect.

In the long-term, there are now some signals coming out of the work that is being done around the world that suggests that some of these drugs are actually associated with an increased risk of cognitive decline and dementia. And whilst that story is not completely understood, and it may be that people who have insomnia in themselves are predisposed to dementia or actually that insomnia may be a really early warning sign of dementia certainly gives us cause for concern that perhaps we shouldn't be using these drugs quite as liberally as we have done historically.

And so therefore, the switch to behavioral approaches, approaches like cognitive behavioral therapy for insomnia, has been really driven by some of these concerns.

DAVIES: Guy Leschziner is a neurologist and sleep disorder specialist. His new book is called "The Nocturnal Brain." We'll talk more after a short break. This is FRESH AIR.

(SOUNDBITE OF MUSIC)

DAVIES: This is FRESH AIR, and we're speaking with Dr. Guy Leschziner. He is a neurologist and head of the Sleep Disorders Centre at Guy's Hospital in London. He has a new book. It's called "The Nocturnal Brain: Nightmares, Neuroscience, And The Secret World of Sleep."

You know, I've always been able to function pretty well on five or six hours of sleep at night, or at least so I've thought. Am I deluding myself? Am I harming myself?

LESCHZINER: Well, there are significant genetic influences as to how much sleep we need. So this notion of seven to eight hours being the optimal amount is correct when one looks at a population. But for a particular individual, we know that there are people who get on absolutely fine with less than seven hours or actually need nine or 10 hours to feel fully refreshed.

One of the great difficulties is that we know that there are genetic influences that influence not only our resistance to sleep deprivation in terms of how sleepy we are, but also in terms of the cognitive effects of sleep deprivation. So what I mean by that is that just because you don't necessarily feel sleepy does not imply that the sleep deprivation that you're experiencing is not having any impact on your mental abilities, your performance.

And so perhaps the worst situation to be in is to be one of those individuals who doesn't get particularly sleepy when they're sleep deprived but is very liable to those cognitive effects.

DAVIES: You're a neurologist, and there's a lot of research going on in various aspects of sleep. What are the questions you're most interested in seeing answered in the coming years?

LESCHZINER: Well, I think the question why we sleep still has to be answered. I mean, in a way, you know, we've moved tremendously far in terms of understanding why we sleep. But there is still an awful lot to be learned. You know, we do this thing for eight hours a night. You know, we spend far more time sleeping than doing anything else. And to ask a question why do we eat or why do we drink would be laughable, yet we're still asking the question why do we sleep.

The reality is that sleep probably has a multitude of different functions. But at the moment, we still don't really know the true answer. There's lots of work still to be done.

The other areas that I think are going to be of fundamental importance is understanding the association between sleep and some of the major issues from a public health perspective that we face, in particular conditions like dementia. If we are - if we can really truly understand sleep disruption or sleep disorders can increase our risk of developing dementia, then that provides a huge opportunity because sleep is one of the potentially major modifiable risk factors for these sorts of conditions.

DAVIES: And in understanding why we sleep, are there particular hypotheses that you think are promising or areas of research that you think could be particularly revealing?

LESCHZINER: I think that what we're going to find out is that essentially, this pattern of behavior has arisen through evolutionary mechanisms. And as we have - we as organisms have become more complicated, our bodies have developed lots of different functions that have taken the opportunity of this seven or eight hours a night - you know, controlling our blood pressure, controlling our immune systems, regulating various functions of the brain, be it memory, learning, creativity.

And I think that what we're going to end up finding is that basically any waking activity, any physiological activity that we undertake is going to be in some way influenced by sleep. So I think the answer to why we sleep is going to be multiple answers, not just one.

DAVIES: In the interest of us all sleeping a little better, do you have recommendations for what we should do when we go to bed or not do?

LESCHZINER: Using gadgets, in particular, is not very good for our sleep. If you are - and this once again comes down to genes - we know that there is huge variability in terms of the impact of light on sleep in that we have receptors in the back of our eyes called retinal ganglion cells that are not involved in vision at all. But what they essentially are are a direct gateway between environmental light and the part of our brain that regulates our circadian rhythm, our internal body clock.

And so for many individuals, exposure to bright light, particularly blue light, is a very good way of suppressing our own intrinsic melatonin. Melatonin is a hormone that's produced by the brain, and it's really the chemical signal to the brain and the rest of the body that it is time to go to sleep. So what you're potentially doing by, for example, using your tablet or laptop or mobile phone late in the night is you're exposing yourself to large amounts of blue lights, which can really prevent you from drifting off to sleep quite as easily as you otherwise should and can actually have a negative impact on the quality of your sleep. So the first thing that I would say is try and avoid bright light exposure late at night.

The second thing is to make sure that you only go to bed when you're sleepy. The brain likes a rhythm when it comes to sleep. But you should not be slavishly keeping to that rhythm and going to bed when you're not - when you're not sleepy because what that then does is it - if you are in some way predisposed to insomnia, it actually strengthens the association between being in bed and having difficulty getting off to sleep rather than being in bed and drifting off to sleep.

DAVIES: So is reading in bed before you nod off a good idea?

LESCHZINER: Yes, provided you're not reading on a tablet or a laptop. You know, an old-style analog book, I would highly recommend. It's a good way of reducing your light exposure, keeping your mind a little bit active so that you're not concentrating on the prospect of having to drift off to sleep until you're really tired. It's a very good way of keeping your mind occupied.

DAVIES: I'm told there are podcasts that are...

LESCHZINER: Yes.

DAVIES: ...Designed to help you fall - good idea?

LESCHZINER: Well, you know, I've occasionally out of interest listened to one of these podcasts, which was a man in a sort of Deep South accent murmuring gently, telling a very boring story. And the aim of it is to distract you from the process of getting off to sleep, so just providing enough distraction that you're not concentrating on, oh, my God, I've got to go to sleep, I'm going to be awake all night, but not providing enough interest to keep you awake at night.

I think the key thing is to work out what works for you. And if that works for you, great. If a white noise generator or a pink noise generator works for you, then great. And the same thing is the case for caffeine. You know, there are some people for whom having two shots of espresso before they go to bed will have absolutely no impact on their sleep whatsoever. And if that works for you, then go for it. If you know that caffeine is going to disrupt your sleep, then avoid it from lunchtime onwards because caffeine can - depending on how much of it you drink - can hang around for a long, long time.

It's about understanding your own sleep and working out what works for you.

DAVIES: Well, Guy Leschziner, it's been really interesting. Thanks so much for speaking with us.

LESCHZINER: Thanks very much for having me.

GROSS: Dr. Guy Leschziner is a neurologist who heads the Sleep Disorders Centre at Guy's Hospital in London. His new book is called "The Nocturnal Brain: Nightmares, Neuroscience, And The Secret World Of Sleep."

Coming up, we remember Paul Krassner, founder of the counterculture magazine The Realist and co-founder of the 60s radical group the Yippies. He died Sunday. This is FRESH AIR.

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