Speaker 1: Why do we spend one third of our lives asleep?
Speaker 1: What does this have to do with living in an
Speaker 1: underground cave with no light, or whether we can die
Speaker 1: from a lack of sleep, or the length of a
Speaker 1: day on Mars. Why are some people night owls and
Speaker 1: some morning larks? How long is it possible to keep
Speaker 1: yourself awake physically? And why does the Guinness Book of
Speaker 1: World Records no longer track that record? Welcome to Inner
Speaker 1: Cosmos with me David Eagleman. I'm a neuroscientist and author
Speaker 1: at Stanford and in these episodes we sail deeply into
Speaker 1: our three pound universe to understand why and how our
Speaker 1: lives look the way they do. Today's episode is about sleep.
Speaker 1: Why do we do it? Why do we spend so
Speaker 1: much of our lives in this weird doppelganger state? When
Speaker 1: you're asleep, it still looks like you, but you are
Speaker 1: essentially shut off. And even though we're not typically aware
Speaker 1: of being in this state, because we have no sense
Speaker 1: of the passage of time there, we spend so much
Speaker 1: of our lives there, more time than you spend doing
Speaker 1: almost anything else, whether that's eating or showering or being
Speaker 1: with friends. Or listening to podcasts. All of those presumably
Speaker 1: take up a smaller fraction of your life. Sleeping is
Speaker 1: at the top of your list of activities, and certainly
Speaker 1: at the top of the list of activities that you
Speaker 1: do consistently. Other hobbies come and go, sleep remains. So
Speaker 1: in today's episode, we're going to talk about everything you've
Speaker 1: ever wanted to know about sleep, and we're going to
Speaker 1: uncover what the brain is really doing during this time.
Speaker 1: And this is the first part of a three parter.
Speaker 1: Next week we're going to dive into dreams. Why do
Speaker 1: we dream? What's that about? Is it a form of consciousness?
Speaker 1: Do all animals dream? And finally, two weeks from now,
Speaker 1: will dive into lucid dreaming, which is where you become
Speaker 1: consciously aware that you are in a dream state and
Speaker 1: you are able to take control of the plot. So
Speaker 1: join me for those episodes. They build on this one
Speaker 1: about sleep, and I promise you there will be no
Speaker 1: end of mind blowing surprises there. So for today's episode,
Speaker 1: we're going to start in the early morning of May
Speaker 1: twenty fourth, nineteen eighty seven, when a man named Kenneth
Speaker 1: Parks is watching TV on the couch and he fall sleep,
Speaker 1: and he gets up. He drives across the city of
Speaker 1: Toronto where he lives, and he enters his in law's home,
Speaker 1: and there he stabs his mother in law to death
Speaker 1: and attempts to murder his father in law as well,
Speaker 1: and then he drives himself to the police station and
Speaker 1: turns himself in. Now everyone agrees that Kenneth Parks had
Speaker 1: no motive. He loved his in laws and he had
Speaker 1: a close relationship with them, and even more strangely, he
Speaker 1: appears to have been asleep the whole time. Now, that
Speaker 1: claim sounded outrageous to most people, especially as Parks had
Speaker 1: to drive fourteen miles to get to his in law's home.
Speaker 1: But as the case was investigated, the sleepwalking story began
Speaker 1: to take shape. When he arrived at the police station,
Speaker 1: he had looked down in confusion at his bloodied hands
Speaker 1: and he said, quote, I think I may have killed
Speaker 1: some people. He claimed to have no memory of what
Speaker 1: had happened, and he appeared horrified when he learned the details.
Speaker 1: He testified that he wasn't awake and he wasn't conscious
Speaker 1: during the crime, and by the way, his testimony never
Speaker 1: wavered throughout the whole trial. So his legal team argued
Speaker 1: that the case represented homicidal somnambulism, which is just a
Speaker 1: fancy way of saying killing while sleepwalking. So electrode recordings
Speaker 1: in a sleep lab showed that the electrical activity in
Speaker 1: his brain was highly unusual and consistent with sleepwalking. So
Speaker 1: I'll quote the expert testimony given by a psychiatrist named
Speaker 1: Ronald Billings. The lawyer asks, is there any evidence that
Speaker 1: a person could formulate a plan while they were awake
Speaker 1: and and then in some way ensure that they carry
Speaker 1: it out in their sleep, And Billings says no, absolutely not.
Speaker 1: Perhaps the most striking feature of what we know of
Speaker 1: what goes on in the mind during sleep is that
Speaker 1: it's very independent of waking mentation in terms of its
Speaker 1: objectives and so forth. There's a lack of control of
Speaker 1: directing our minds in sleep compared to wakefulness. In the
Speaker 1: waking state, of course, we often voluntarily plan things, what
Speaker 1: we call volition. We decide to do this as opposed
Speaker 1: to that, and there is no evidence that this occurs
Speaker 1: during the sleepwalking episode. So the lawyer asks, and assuming
Speaker 1: he was sleepwalking at the time, would he have the
Speaker 1: capacity to intend and Billing says no, And the lawyer says,
Speaker 1: would he have appreciated what he was doing? And Billing
Speaker 1: says no, he would not, And lawyer says, would he
Speaker 1: have I've understood the consequences of what he was doing,
Speaker 1: And Billing says no, I do not believe that he would.
Speaker 1: I think it would all have been an unconscious activity,
Speaker 1: uncontrolled and unmeditated. So what would your opinion be if
Speaker 1: you were a juror on this case? Does sleepwalking sound
Speaker 1: like an excuse? Is one either asleep or awake? Or
Speaker 1: can a brain be caught between those two states? So
Speaker 1: in today's podcast, we're going to explore the fundamental differences
Speaker 1: between the states of wakefulness and sleep. We'll look at
Speaker 1: the purpose of sleep and the way that transitions between
Speaker 1: sleep and wakefulness can go awry, and then, armed with
Speaker 1: our new knowledge, will return to the Parks case at
Speaker 1: the end of this episode to see what the jury concluded.
Speaker 1: To my mind, one of the most astonishing facts of
Speaker 1: guroscience is that adult humans we spend a third of
Speaker 1: our lives in the strange world of sleep, and by
Speaker 1: the way, newborn babies spend about two thirds. So it's
Speaker 1: insanely difficult to stay awake for more than a full
Speaker 1: day night cycle, and if you somehow manage to stay
Speaker 1: awake for a while, you're gonna be a bit cognitively impaired.
Speaker 1: And in animal studies, if you deprive a rat of
Speaker 1: sleep for weeks, the rat will die. So we can
Speaker 1: see that sleep really matters. It's not just a choice
Speaker 1: we make and we could do otherwise. And the massive
Speaker 1: importance of sleep can also be gathered from the fact
Speaker 1: that sleep is conserved through evolution. All mammals sleep, reptile sleep,
Speaker 1: birds sleep. Even in the fruit fly, you can measure
Speaker 1: sleep wake cycles and three days of sleep deprivation result
Speaker 1: in the fli's death. The fact that all animals sleep
Speaker 1: suggests that sleep is not an accident but something really fundamental. Now,
Speaker 1: the first question we're going to ask is what is
Speaker 1: happening under the hood, Because when you look at somebody
Speaker 1: who's sleeping, it looks like everything is shut down. The
Speaker 1: eyes are closed, the muscles are relaxed, breathing is regular,
Speaker 1: there's no response to sound or light. So a century ago,
Speaker 1: people thought that wakefulness was the natural state of the brain,
Speaker 1: and that sleep represented a phase in which brain activity
Speaker 1: was just decreased or shut down. But in the last century,
Speaker 1: scientists discovered that the brain is not so much naturally
Speaker 1: awake as it is kept awake by a whole system
Speaker 1: of brain areas. For example, if you injure the brain stem,
Speaker 1: that can cause you to fall into a sleep like
Speaker 1: state that we call coma. So you need special machinery
Speaker 1: to run in order to be awake, and as it
Speaker 1: turns out, you also need special machinery to sleep. If
Speaker 1: you damage part of the hypothalamus, you get long lasting
Speaker 1: sleep difficulties. In other words, for both waking and sleeping,
Speaker 1: you need particular networks to run. You need the activity
Speaker 1: of certain cells. Waking is a neurally active state, and
Speaker 1: so is sleeping. Now, people noted these things about sleep
Speaker 1: by observing brain damage, but you can really only tell
Speaker 1: so much from that. So how did the field make
Speaker 1: progress from there? Mostly it was due to a technology
Speaker 1: people had developed some time ago called electro and cephalography
Speaker 1: or EEG, which is a technique where you stick electrodes
Speaker 1: onto the scalp and you try to surface clues about
Speaker 1: what's happening on the inside of the skull. But what's
Speaker 1: fascinating is that the EEG was invented in in nineteen
Speaker 1: twenty four, but researchers only ever measured people who were awake,
Speaker 1: and it wasn't until almost three decades later that anyone
Speaker 1: thought took this up to a person while they were asleep.
Speaker 1: And what did they find. They found that the brain
Speaker 1: was screaming along with activity during sleep in retrospect. By
Speaker 1: the way, just the mere existence of dreams should have
Speaker 1: alerted people that there must be a lot of brain
Speaker 1: activity going on, but as I said, just no one
Speaker 1: had thought of doing that experiment. So they found that
Speaker 1: the brain was active during sleep, and with a little
Speaker 1: bit of study, they soon worked out that there were patterns,
Speaker 1: and these patterns changed, and these changes followed a regular
Speaker 1: cycle during the night. In other words, the EEG pattern
Speaker 1: changes in a predictable way several times during sleep. The
Speaker 1: sleeping brain has these cycles that last about ninety minutes
Speaker 1: and the repeat four or five times during the night.
Speaker 1: Now what immediately became clear is that there are two
Speaker 1: basic stages of sleep. There's this sleep that you have
Speaker 1: where your eyes move rapidly back and forth. This is
Speaker 1: called rem sleep for rapid eye movement. And then everything
Speaker 1: else gets lumped into non REM sleep. So let's begin
Speaker 1: with the non REM stage because that comprises eighty percent
Speaker 1: of your sleep. Now, during non REM sleep, your heart
Speaker 1: rate and breathing becomes slow and regular. The deepest stage
Speaker 1: of this is known as slow wave sleep, and this
Speaker 1: is named that way because the brain's electrical activity oscillates
Speaker 1: at a low frequency and with a high amplitude. Think
Speaker 1: of this like, wooooooo okay. Now, REM sleep is quite different.
Speaker 1: In REM, your heart rate and your breathing beat up,
Speaker 1: and your small muscles twitch like your facial muscles, but
Speaker 1: your major muscle groups are paralyzed by a very elaborate
Speaker 1: neural circuitry. So during REM, brain waves become high frequency
Speaker 1: in low amplitude more like, which reflects more complex cognitive function.
Speaker 1: REM sleep is sometimes called paradoxical sleep because your brain
Speaker 1: is highly active and the EEG signature resembles that of
Speaker 1: the waking state much more so than of deeper stages
Speaker 1: of sleep. Now, REM sleep is the stage that usually
Speaker 1: includes dreaming, and scientists discover this fact very simply by
Speaker 1: waking people up during this stage and saying, Hey, what
Speaker 1: were you just experiencing? So people generally report they had
Speaker 1: story like dreams. During the REM stage. As a side note,
Speaker 1: you can have dreams during non REM sleep, but this
Speaker 1: is much less common and when it does occur, it's
Speaker 1: generally much less visual and more like just having thoughts. Okay,
Speaker 1: so dreaming happens during REM sleep. Now, I just want
Speaker 1: to address the question that comes up a lot. People
Speaker 1: sometimes say to me, I don't think I dream at night. Well,
Speaker 1: everyone dreams. This is apart from a few rare cases
Speaker 1: of patience with specific brain injuries. The thing that happens
Speaker 1: is that some people have more difficulty remembering their dreams,
Speaker 1: and therefore they think that they don't dream. But if
Speaker 1: I awaken you during REM, you will report having just
Speaker 1: been dreaming. Now, we're going to talk more about the
Speaker 1: dreaming phase next week, but for now, what I want
Speaker 1: to make clear is that your sleep cycle follows a
Speaker 1: specific pattern. Non REM sleep proceeds into successive phases of
Speaker 1: depth from stages one to three deeper and deeper, and
Speaker 1: then that reverses in its shallower and shallower until you
Speaker 1: reach REM sleep. And as this cycle continues through the night,
Speaker 1: you tend to experience less deep sleep and more REM. Now,
Speaker 1: although we use a single word sleep for this phenomenon.
Speaker 1: The sleep state emerges from a collaboration of a whole
Speaker 1: bunch of brain areas interacting in a network. These areas
Speaker 1: all work in concert to give rise to this state
Speaker 1: that we experience as sleep. Now, under special conditions, like
Speaker 1: if you're deprived of rem sleep or you don't have
Speaker 1: any light cues, the different areas can get out of
Speaker 1: sync with each other, and that's in large part how
Speaker 1: we can figure out the richness of the underlying mechanisms.
Speaker 1: So let's now look at the most important parts of
Speaker 1: the brain's sleep network. The most important player involved in
Speaker 1: sleeping is an area of the brain called the ventrilateral
Speaker 1: preoptic nucleus. We'll just call this the VLPO. This is
Speaker 1: a collection of neurons in the hypothalamus, and when it
Speaker 1: becomes active, you go to sleep. These neurons inhibit the
Speaker 1: arousal network, which is all about wakefulness. So if there's
Speaker 1: damage to your VLPO, you get insomnia. You can't sleep. Now,
Speaker 1: the arousal network, which it inhibits, also inhibits it right back.
Speaker 1: These two networks are always locked in mutual inhibition. When
Speaker 1: either one is active, it uses inhibitory neurotransmitters to suppress
Speaker 1: the other one. So, as a general principle of brains,
Speaker 1: whenever you have two networks set up with mutual inhibition,
Speaker 1: you get a system that toggles between two stable states,
Speaker 1: in this case being asleep and being awake. You get
Speaker 1: one state or the other, but you can't be in
Speaker 1: both at the same time. Now, the brain doesn't just
Speaker 1: consist of these two networks, but also other networks that
Speaker 1: stabilize or destabilize the balance such that the brain can
Speaker 1: hold onto one state and then make a transition into
Speaker 1: the other state. And we'll talk about this again in
Speaker 1: a minute when we talk about disorders like narcolepsy. So
Speaker 1: the VLPO squelches the arousal system and you sleep. Then
Speaker 1: the arousal system squelches the VLPO and you wake up.
Speaker 1: But as we'll explore more next week, you've also got
Speaker 1: dream sleep. And you get this from a principle that
Speaker 1: puts the brain in a state that shares some qualities
Speaker 1: of both sleeping and waking. Okay, so you have a
Speaker 1: sleep wake cycle, and this determines two things, when you
Speaker 1: sleep and how much you sleep. As for how much
Speaker 1: not everyone needs to leap the same amount seven to
Speaker 1: nine hours is recommended for adults, although a lot of
Speaker 1: people only catch six and a half seven hours of sleep.
Speaker 1: If you look across the whole population, you find a
Speaker 1: really big range between four to eleven hours. Now, how
Speaker 1: much sleep do you need? The suspicion is that that
Speaker 1: has at least some genetic basis to it, but people
Speaker 1: generally find out through experience about how much is required
Speaker 1: for them to feel good. Now, how many hours you
Speaker 1: sleep correlates with what you have done while you were awake.
Speaker 1: If you do a bunch of activity like hiking or
Speaker 1: weightlifting or public speaking, then you tend to sleep longer. Okay,
Speaker 1: so that's about how much you sleep. But now let's
Speaker 1: turn to the other aspect of the sleep wake cycle,
Speaker 1: which is when you sleep. Why is sleep on such
Speaker 1: a regular cycle and what is it synchronized with? The
Speaker 1: answer involves your circadian rhythm, which is a natural internal
Speaker 1: pattern that runs on approximately a twenty four hour cycle.
Speaker 1: Where does the word circadian come from? Circa means about
Speaker 1: and dion is a day. Now our circadian rhythm is
Speaker 1: what times are sleep wake cycles? All animals appear to
Speaker 1: have some form of a circadian cycle that influences not
Speaker 1: just sleep in wakefulness, but also coordination, blood pressure, alertness,
Speaker 1: body temperature, things like that. The circadian rhythm comes from
Speaker 1: preprogrammed mechanisms in our brain, and it persists even when
Speaker 1: there aren't any external cues like the sun going up
Speaker 1: and down. Some animals, like the blind mole rat, maintain
Speaker 1: their rhythms even though they live underground and don't see
Speaker 1: the sun. I'll come back to this in humans in
Speaker 1: just a moment. So the primary clock in mammals is
Speaker 1: a structure called the super chiaismatic nucleus, which is in
Speaker 1: the hypothalamus. So these cells keep a rhythm. And what's
Speaker 1: amazing is if you culture the cells of the super
Speaker 1: chismatic nucleus in a dish, they will maintain their own rhythm. So,
Speaker 1: not surprisingly, when this nucleus gets damaged, that obliterates a
Speaker 1: regular sleepwake rhythm. So the circadian rhythm is generated by
Speaker 1: internal mechanisms and runs on its own machinery, but it
Speaker 1: becomes entrained to cues in the environment. In other words,
Speaker 1: it lines itself up with the environment, and the most
Speaker 1: important cue that it uses is the light dark cycle.
Speaker 1: In other words, the phase of the circadian rhythm is
Speaker 1: set by the planet's rotation into and out of light
Speaker 1: from the sun. The light information gets from the retina
Speaker 1: to the super chismatic nucleus, which then gets to the
Speaker 1: pineal gland and tells it to make melatonin, which you've
Speaker 1: probably heard of. Melatonin is not directly a sleep hormone,
Speaker 1: as people sometimes think, but instead it's a darkness hormone.
Speaker 1: It gets its darkness information from the super chismatic nucleus,
Speaker 1: and the cycles of melatonin just influence when you get sleepy.
Speaker 1: So what happens if you are not seeing the sun
Speaker 1: go up and down, Well, that's a question you can
Speaker 1: directly explore. In nineteen seventy two, the French underground explorer
Speaker 1: Michael Sifra descended a one hundred foot vertical shaft into
Speaker 1: the Midnight Cave near Del Rio, Texas, and inside he
Speaker 1: had stashed a campsite with food and water and books
Speaker 1: enough to last him the six months of the astounding
Speaker 1: time isolation experiment that he was about to undertake. Because
Speaker 1: the bowels of this cave had no light clues, you
Speaker 1: couldn't tell anything about day from night, and he had
Speaker 1: no time pieces of any sort, he forbade any incoming
Speaker 1: contact from the outside world. His telephone only made outgoing calls,
Speaker 1: and in this self imposed experimental condition, he kept careful
Speaker 1: track of his sleep and wake times by calling his
Speaker 1: support team when he woke up, when he ate, and
Speaker 1: when he went to sleep. He quickly lost a conscious
Speaker 1: sense of time. Just imagine what that would be like
Speaker 1: to have no clues to what time it is. No
Speaker 1: cell phone, no alexa, no wristwatch, nothing, So what happened
Speaker 1: without the ability to see the light and dark cycles
Speaker 1: of the world. The period of his circadian rhythm drifted
Speaker 1: to about twenty five hours, and subsequent experiments verified that
Speaker 1: the circadian rhythm is not an exact twenty four hour clock.
Speaker 1: It's an approximate clock. It gets nudged into rhythm with
Speaker 1: the sun's cycle. Presumably, if we had evolved on a
Speaker 1: different planet with a different light dark period, we would
Speaker 1: have a different approximate period length to our internal rhythms.
Speaker 1: What's cool is that you can use false lighting cues
Speaker 1: to entrain a different cycle, for example, twenty three and
Speaker 1: a half hour cycles, or scientists have done a twenty
Speaker 1: four point sixty five hour cycle and they chose that
Speaker 1: because that happens to be the period of day and
Speaker 1: night on Mars, so we'll have no problem adjusting to
Speaker 1: Martian day night cycles now. Although the period the twenty
Speaker 1: four hours is essentially the same for all of us
Speaker 1: Earth dwellers, the period of this rhythm, in other words,
Speaker 1: when it hits top or bottom, that can vary across
Speaker 1: the population. Some people are night owls, meaning that their
Speaker 1: natural rhythm keeps them up late at night and sleeping
Speaker 1: late into the morning, while other people are mourning larks
Speaker 1: they are early to bed and early to rise. About
Speaker 1: sixty percent of the population is intermediate between the two.
Speaker 1: There's a normal amount of variation in the population between
Speaker 1: night owls and morning larks, but some people on the
Speaker 1: very extremes have to take really drastic measures to adapt
Speaker 1: their lives to societal norms. So consider the case of
Speaker 1: a woman that I'll call Melinda. Every day, Melinda and
Speaker 1: her two children, who are aged thirteen and eleven. They
Speaker 1: go to bed at four in the morning and they
Speaker 1: typically wake up around noon. Now, some of her neighbors
Speaker 1: think she's a bad mother, but Melinda and her children
Speaker 1: suffer from something called delayed sleep phase syndrome, which is
Speaker 1: a disorder of the circadian rhythm, in which a person
Speaker 1: has no trouble maintaining sleep, but can't fall asleep or
Speaker 1: wake up at the same time as the rest of society.
Speaker 1: The family essentially lives with a constant six hours of
Speaker 1: jet lag. Other people have what's called advanced sleep phase syndrome,
Speaker 1: in which you fall asleep and wake up way earlier
Speaker 1: than the rest of society. And remember what I said
Speaker 1: about the circadian rhythm being about twenty four hours. Some
Speaker 1: people have molecular problems which warp this, so it's much
Speaker 1: shorter or longer than twenty four hours, and unfortunately, that
Speaker 1: makes a person incapable of aligning their sleep patterns to
Speaker 1: the societal norm. People with all these disorders typically work
Speaker 1: to adapt their lives and careers around their own rhythms.
Speaker 1: For example, Melinda has a difficult time holding on to
Speaker 1: jobs that require her to be present early in the morning.
Speaker 1: That's not because of a lack of dedication to her job,
Speaker 1: but instead because of her biological clock. So, the way
Speaker 1: she describes it, quote, instead of changing myself to keep
Speaker 1: other people's schedule, I have changed my life so I
Speaker 1: can function on my time. She operates a freight brokerage
Speaker 1: business that she runs from her home. She also homeschools
Speaker 1: her children through the afternoon and evening. Some companies have
Speaker 1: recognized that people have different circadian rhythms and that it's
Speaker 1: not necessary to force everyone into the same time mold.
Speaker 1: So Netflix, for example, doesn't keep track of their employees'
Speaker 1: work hours, just so long as their work produces results.
Speaker 1: One Netflix executive said that rigid office hours are a
Speaker 1: relic of the industrial age. Now, statistically, you probably have
Speaker 1: a fairly normal circadian rhythm, but you know what it's
Speaker 1: like when you disrupt that rhythm and how tough that
Speaker 1: can be for your brain. When you fly to a
Speaker 1: distant time zone, you've presumably experienced the fatigue and disorientation
Speaker 1: of jet lag, which is just a mismatch of your
Speaker 1: circadian time with the local day night period. You typically
Speaker 1: get irregular sleep patterns and fatigue, maybe headaches, irritability, the
Speaker 1: disorientation as the rhythm struggles to regain alignment. Now, from
Speaker 1: a long term health consequence, there's no problem traveling to
Speaker 1: different time zones once in a while, but long term,
Speaker 1: repeated disturbances of this synchronization can have a negative impact
Speaker 1: on health. One study compared two groups of flight attendants
Speaker 1: who spent the same amount of time in the air,
Speaker 1: but one group did lots of east west flights, which
Speaker 1: means they were always changing time zones, while the other
Speaker 1: group did north south flights, which meant they didn't have
Speaker 1: to change their circadian rhythm. So what the study found
Speaker 1: is that the east west flying tendance had higher stress
Speaker 1: hormone levels and the part of their brain called the
Speaker 1: temporal lobe was physically diminished, which led to demonstrable effects
Speaker 1: on spatial learning and memory. And these sorts of ongoing
Speaker 1: disturbances in the circadian rhythm are also linked to mood
Speaker 1: disorders and obesity. So occasional travel is great, but be
Speaker 1: careful about shifting your rhythm around too often. And since
Speaker 1: we're talking about the rhythm, there's a question that needs
Speaker 1: to be asked about how many times we sleep in
Speaker 1: twenty four hours. Most of us sleep only once in
Speaker 1: the twenty four hour cycle, but having this single long
Speaker 1: period of daytime wakefulness is not necessarily the way our
Speaker 1: natural rhythms evolved. You've probably noticed that you experience a
Speaker 1: dip during the afternoon when you feel less alert. The
Speaker 1: basic circadian rhythm that makes you sleep at nighttime contains
Speaker 1: a bump that nudges you towards a nap in the
Speaker 1: early afternoon. Sleeping only once at nighttime, the way most
Speaker 1: of us do, is not the only way to achieve
Speaker 1: good sleep. As you might guess from watching your cat
Speaker 1: or your dog, Sleeping multiple times a day is the
Speaker 1: norm throughout the animal kingdom. This is known as polyphasic sleep,
Speaker 1: referring to multiple phases, and there are lots of ways
Speaker 1: to do polyphasic sleep. For example, one technique is to
Speaker 1: sleep twice, one for six hours during the night and
Speaker 1: again in the afternoon for ninety minutes. There's another commonly
Speaker 1: used pattern, which is to sleep for half an hour
Speaker 1: every six hours. This was the sleep pattern of Buckminster
Speaker 1: Fuller or other people nap fifteen to thirty minutes every
Speaker 1: four hours, which was allegedly the sleep pattern of Leonardo
Speaker 1: da Vinci. One advantage of polyphasic sleep is that the
Speaker 1: total number of hours can be greatly reduced from the
Speaker 1: usual eight in some cases down to just a few hours,
Speaker 1: apparently without ill effects. Polyphasic sleep is common in historically
Speaker 1: older cultures and in current non industrialized societies, especially during
Speaker 1: the winter months. Even in industrialized countries, many cultures engage
Speaker 1: in a daily post lunch nap. This is known as
Speaker 1: a siesta in Spanish speaking countries, a riposo in Italy,
Speaker 1: and in Japan it's known as an in emuri. And
Speaker 1: you know who naturally goes in for polyphasic sleep. Infants,
Speaker 1: they're up and down all day, and you know who else,
Speaker 1: the elderly. Polyphasic sleep, also, by the way, is often
Speaker 1: adopted in the military, especially when you have a situation
Speaker 1: that doesn't allow for long periods of being down and
Speaker 1: un alert. But as I said, many adults have a
Speaker 1: monophasic sleep schedule. And so one question that's been asked
Speaker 1: is does that indicate that humans have evolved to be
Speaker 1: different than most of our animal cousins. And the answer
Speaker 1: is probably not. It probably just shows that we are
Speaker 1: merely capable of fighting off sleep when we don't want it,
Speaker 1: for example with the help of caffeine, or forcing ourselves
Speaker 1: to sleep when we feel we should be getting it,
Speaker 1: for example with the help of sleeping pills. Okay, so
Speaker 1: we talked about the patterns of sleep, like when you
Speaker 1: sleep and how often in a cycle. Now let's zoom
Speaker 1: out the camera to the really foundational question of why
Speaker 1: brains sleep at all, because the thing to note is
Speaker 1: that sleep entails lost time and reduced defenses. So it's
Speaker 1: striking that across all species in the animal kingdom, everyone's
Speaker 1: doing it. In fact, animals in situations that don't easily
Speaker 1: allow for sleep, they have evolved elaborate mechanisms to get
Speaker 1: that sleep. For example, the bottle nosed dolphin can't just
Speaker 1: go to sleep because it has to periodically come to
Speaker 1: the surface to breathe. So what does it do. It
Speaker 1: has one side of its brain sleep at a time.
Speaker 1: This mechanism has been found in other dolphin and whale species,
Speaker 1: and what it does is allow them to come up
Speaker 1: to the surface to breathe, and it also allows them
Speaker 1: to swim around and avoid predators and even have social
Speaker 1: interaction during sleep when the mammalian brain would other wise
Speaker 1: be in its own world. So all this underscores an
Speaker 1: important clue for us, given the missed opportunities while asleep
Speaker 1: and the dangers of sleeping, as well as the convoluted
Speaker 1: evolutionary adaptations that come about to allow it. Sleep, clearly
Speaker 1: seems to perform some function for the nervous system. But
Speaker 1: what is it. There are lots of theories for why
Speaker 1: we sleep, and these fall essentially into four categories. The
Speaker 1: first is that sleep is restorative. It replenishes our energy stores.
Speaker 1: In other words, sleep may be a metabolic necessity, helping
Speaker 1: the body recover from the work it did while awake.
Speaker 1: And in fact, researchers have long known that the amount
Speaker 1: of slow wave sleep correlates with the amount of exercise
Speaker 1: that you do when you're awake, and if you're deprived
Speaker 1: of slow wave sleep by being woken up every time
Speaker 1: you enter that stage, you're going to be physically pooped out.
Speaker 1: A related idea is that REM sleep allows you to
Speaker 1: replenish the stalks of certain neurotransmitters that you used when
Speaker 1: you were awake. But this sleep as restoration hypothesis is
Speaker 1: not totally clear because you have a lot of activity
Speaker 1: during REM sleep and even during non REM sleep, And
Speaker 1: there's a bigger reason why this hypothesis doesn't seem perfect.
Speaker 1: Although sleep is necessary to all species, there doesn't appear
Speaker 1: to be a fixed amount required, and when you look
Speaker 1: at something like horses, they sleep only about three hours
Speaker 1: per night, whereas koala bears sleep nineteen hours. Now the
Speaker 1: high activity of horses and the low activity of koalas
Speaker 1: doesn't seem to accord with this sleep as restoration hypothesis.
Speaker 1: So it might have something to do with why we sleep,
Speaker 1: but it's certainly not the full answer. Okay, So this
Speaker 1: second theory about why we sleep is that we do
Speaker 1: it because it's a survival advantage. So here's the idea.
Speaker 1: Most animals find the search for food and water to
Speaker 1: be easier during the sunlight hours. At night, it's best
Speaker 1: for these animals to save energy and avoid getting eaten
Speaker 1: and evade dangers such as falling off a cliff. So
Speaker 1: this framework proposes that sleep protects organisms that can't see
Speaker 1: well in the dark and would face greater risks if
Speaker 1: they were active at night. So the idea is, if
Speaker 1: you just curl up in the corner of the cave,
Speaker 1: you stay out of trouble. Now, this framework of sleeping
Speaker 1: to stay out of trouble. This is also imperfect because
Speaker 1: darkness as a survival threat can be addressed by the
Speaker 1: evolution of night vision, and it doesn't apply to nocturnal
Speaker 1: animals which sleep during the day. And also the theory
Speaker 1: doesn't shed any light on the unusual sleep habits of
Speaker 1: for example, the bottle nose dolphin. So onto the third
Speaker 1: theory about why we sleep, which is that sleep allows
Speaker 1: us to simulate rare situations. So let's start with the
Speaker 1: observation that young animals like babies, spend a much larger
Speaker 1: percentage of their sleep time in dream sleep. Now that
Speaker 1: observation has invited these speculations that the nocturnal neural simulations
Speaker 1: may be a really useful or necessary exercise for animals
Speaker 1: to test out activities in the real world. Presumably one
Speaker 1: wants to practice all these programs while your muscles are
Speaker 1: shut down, and according to some versions of this theory,
Speaker 1: the periodic stimulation of the cortex in this sort of
Speaker 1: semi random manner can maintain circuits that you need for survival,
Speaker 1: but they rarely get activated like emergency defense procedures. So
Speaker 1: a specific version of this framework called threat simulation theory,
Speaker 1: suggests that sleep exists to simulate threatening events and rehearse
Speaker 1: threat perception and threat avoidance. The theory suggests that people
Speaker 1: exposed to more survival threats in waking life should more
Speaker 1: commonly experience threat dreams at night. So interestingly, researchers tested
Speaker 1: that idea by comparing participants in a high crime area
Speaker 1: in South Africa to those living in a low crime
Speaker 1: area in Wales, and they obtained detailed dream reports over
Speaker 1: a really long period of time. Now, contrary to the
Speaker 1: predictions of the threat simulation theory, people in the high
Speaker 1: crime area actually reported a lower number of threat dreams
Speaker 1: than those in the low crime area. And in South Africa,
Speaker 1: the percentage of realistic threats and dreams was lower than expected.
Speaker 1: It was only about twenty percent and escape from these
Speaker 1: threats occurred in less than two percent, suggesting that it's
Speaker 1: not really much of a simulation. So tests have so
Speaker 1: far failed to give much support to the threat simulation theory,
Speaker 1: and that leads us to theory number four about why
Speaker 1: we sleep, And this one has the strongest legs, and
Speaker 1: the idea is that sleep plays a role in information processing. Specifically,
Speaker 1: the idea is that sleep allows the brain to cement
Speaker 1: in important memories and to deprogram the miscellaneous events that
Speaker 1: shouldn't get stored. Of all the different theories, the data
Speaker 1: seemed to strongly support this idea that sleep plays an
Speaker 1: informational role. So I'm going to zoom in on this
Speaker 1: for the next few minutes. The first part of the
Speaker 1: idea here is that we sleep to lock in information. So,
Speaker 1: for example, let's say I teach you some new task
Speaker 1: on the computer and you're getting better and better at it.
Speaker 1: If I look at how much better you got, I'll
Speaker 1: see you got a lot better if you slept between
Speaker 1: session one and session two. But if you spent the
Speaker 1: same number of hours awake in between those sessions, you
Speaker 1: didn't get much better. So this started suggesting to neuroscientists
Speaker 1: that sleep had something to do with getting better at
Speaker 1: the task. And in part this is because a nap
Speaker 1: turns out to be as good as getting a night
Speaker 1: of sleep. So if you get even a sixty to
Speaker 1: ninety minute daytime nap, you do just as well as
Speaker 1: someone who slept the whole night. But why does learning improve?
Speaker 1: The evidence generally suggests that you reactivate memories during sleep
Speaker 1: and that on lies locking them in. And this is
Speaker 1: because memories require a consolidation period in which the experience
Speaker 1: becomes part of long term memory, and the consolidation stage
Speaker 1: requires sleep. So let me give you an example. Let's
Speaker 1: imagine that you train a rat to run around a
Speaker 1: track for a food reward. Now there are neurons that
Speaker 1: we call place cells in the hippocampus, and if you
Speaker 1: record their electrical activity, you'll find that this network of
Speaker 1: cells has a distinct pattern, a distinct signature of activity,
Speaker 1: depending on precisely where the rat is in the maze.
Speaker 1: So the rat occupies all these different locations, and each
Speaker 1: of those is represented by a different pattern among the
Speaker 1: place cells. Okay, so now the rat goes to sleep,
Speaker 1: and if you continue recording from these neurons, you'll find
Speaker 1: this same sequence representing this position, then this next position,
Speaker 1: then this next position. You find the same sequence playing
Speaker 1: out while the rat is in rem sleep, the same
Speaker 1: sequence that he ran while he was awake. It's like
Speaker 1: he's rehearsing the trajectory that he learned. It's so closely
Speaker 1: correlated with what he did when he was awake that
Speaker 1: researchers who study this claim that the animal is dreaming
Speaker 1: about running the maze. They can take that activity and
Speaker 1: reconstruct where the rat would be in the maze if
Speaker 1: it were awake, and they can further guess whether the
Speaker 1: animal is dreaming about running from position to position or
Speaker 1: standing still in one spot. Now, this sort of thing
Speaker 1: doesn't just happen in rats. This same kind of rehearsal
Speaker 1: happens in songbirds, whose neural activity during sleep resembles their
Speaker 1: song production activity. So the idea is that this replay
Speaker 1: is part of consolidating events into long term memory. In
Speaker 1: other words, the hypothesis is that the information replayed during
Speaker 1: sleep determines what we later remember. And this idea is
Speaker 1: consistent with human studies in which we see that the
Speaker 1: learning of repetitive tasks relies on REM's sleep to improve
Speaker 1: your performance. In some cases, this offline practice session seems
Speaker 1: to be just as useful as practicing the new task
Speaker 1: when awake, So both rats and humans perform recently learned
Speaker 1: tasks better after a period of sleep. And these dreaming
Speaker 1: rat studies are consistent with a human study in which
Speaker 1: participants learned to play the video game Tetris. That night,
Speaker 1: they dreamt of falling Tetris blocks. Now here's the really
Speaker 1: wacky thing. When subjects with amnesia were trained on the game,
Speaker 1: they reported these same dreams of these colorful falling blocks,
Speaker 1: but they had no idea why they were dreaming about
Speaker 1: such things. So, just as rats dream about repetitive tasks
Speaker 1: performed during the day, the Tetris players dreamed about their
Speaker 1: new video game experience. Now, although a lot of research
Speaker 1: has study the effects of rem sleep on learning, I
Speaker 1: just want to be clear that slow wave sleep is
Speaker 1: also important, and you find the slow wave activity most
Speaker 1: strongly in the brain areas involved in some new task.
Speaker 1: So if I have you do some complex I hand
Speaker 1: coordination task, we'll see enhanced slow wave sleep activity in
Speaker 1: those areas that were involved. That's where we find the
Speaker 1: most action. And what we find is that the more
Speaker 1: slow wave sleep you see in a region, the better
Speaker 1: you get at the task. Okay, Now, if sleep consolidates memories,
Speaker 1: that raises an important question, which experienced events are the
Speaker 1: important ones to cement in and which events should be
Speaker 1: taken out with the neural trash. In other words, if
Speaker 1: your brain is taking in information all the time, are
Speaker 1: you ever at risk of cementing in associations that are accidental?
Speaker 1: Like you shut the refrigerator door and just at that
Speaker 1: moment a dog barks outside, and your brain might say, oh,
Speaker 1: there must be a relationship between those two events. Even
Speaker 1: though it was totally spurious, it was accidental. As it
Speaker 1: turns out, people have been thinking about this question for
Speaker 1: a long time. I found a quotation from seventeen forty
Speaker 1: nine where the English philosopher David Hartley suggested that quote
Speaker 1: the wilderness of our dreams seems to be of singular
Speaker 1: use to us by interrupting and breaking the course of
Speaker 1: our associations. For if we were always awake, some accidental
Speaker 1: associations would be so much cemented by continuance as that
Speaker 1: nothing could afterward disjoin them, which would be madness. End quote.
Speaker 1: Now this idea was taken up by Francis Crick and
Speaker 1: Graham Mitchison, who in nineteen eighty three hypothesized that we
Speaker 1: dream to forget. That is, they suggested that rem sleep
Speaker 1: erases these spurious associations between neurons before they inappropriately lock
Speaker 1: into place. So this theory posits forgetting as an active
Speaker 1: nightly practice, which is quite different from the traditional view
Speaker 1: of forgetting as a slow global degradation of information. Now,
Speaker 1: there are various reasons to take this hypothesis seriously. So
Speaker 1: look at artificial neural networks. They have this tendency to
Speaker 1: turn into memory mud when you expose them to too
Speaker 1: many associations, and Krick and Mitchison were inspired to make
Speaker 1: their proposal not only by the fact that such networks fail,
Speaker 1: but the way in which they fail, because when these
Speaker 1: artificial networks become overloaded, their output can mistakenly associate incorrect inputs,
Speaker 1: or give the same output irrespective of the input, or
Speaker 1: respond to stimuli that wouldn't normally evoke a response. And
Speaker 1: these types of pathological output loosely seem to parallel fantasy
Speaker 1: and obsession and hallucinations, all of which occur in humans
Speaker 1: if they don't get REM sleep. So the idea is
Speaker 1: that daily experience with the world leads to these rich
Speaker 1: changes in your synapses, and sleep goes through and erases
Speaker 1: the spurious associations that could otherwise become fantasies or obsessions
Speaker 1: or hallucinations. In fact, I'll just note that some mammals,
Speaker 1: like the spiny ant eater, don't have REM sleep, and
Speaker 1: they also have larger than normal brains, and that suggests
Speaker 1: the possibility that animals without remsleep require a larger brain
Speaker 1: to prevent overloading. Now, we talked about rehearsal and forgetting,
Speaker 1: and those ideas operate hand in hand, but there's something
Speaker 1: else too, which is that intelligent brains like we find
Speaker 1: in humans also require something else, not just writing down
Speaker 1: precisely what happened, but restructuring memories, thinking through things, and
Speaker 1: that lies at the heart of what we call understanding
Speaker 1: and insight, and sleep appears to be involved in that process,
Speaker 1: so people often claim to have gained insight into a
Speaker 1: problem through sleep. Otto Levy won the Nobel Prize for
Speaker 1: discovering neurotransmission with an experiment he did on the frog's heart.
Speaker 1: Now here's the key thing. He had long believed that
Speaker 1: chemical transmission occurred in the nervous system, but he had
Speaker 1: no idea how to prove that until the night when
Speaker 1: he woke up having dreamt the outline of the experiment.
Speaker 1: He got up and jotted the experiment down, But the
Speaker 1: next morning he discovered that he couldn't read his own handwriting.
Speaker 1: So the next night he had the same dream, and
Speaker 1: in his biography he relates of that second night quote,
Speaker 1: I awoke again at three o'clock and I remembered what
Speaker 1: the experiment was. I got up, immediately, went to the laboratory,
Speaker 1: made the experiment, and at five o'clock the chemical transmission
Speaker 1: of the nervous system was conclusively proved. So he seems
Speaker 1: to have gotten insight from his dream. And in fact,
Speaker 1: this connection between sleeping and insight has been supported by
Speaker 1: the results of careful experiments. So, in one report, people
Speaker 1: practiced some cognitive task in which they learned to respond
Speaker 1: to particular cues with particular responses. Now, practice made them
Speaker 1: better at the task, but although they didn't know it,
Speaker 1: there was a hidden rule underlying the order of the sequences.
Speaker 1: So if you could figure out that hidden rule, that
Speaker 1: improved your performance. After the initial training on the task,
Speaker 1: one group got eight hours of sleep, another group stayed
Speaker 1: awake during the same hours of the night, and a
Speaker 1: third group was awake for the same number of hours
Speaker 1: during the day. So one group slept and the other
Speaker 1: two did not. Then they were retested and it turns
Speaker 1: out those who had slept for the eight hours were
Speaker 1: twice as likely to gain insight into the hidden rule,
Speaker 1: irrespective of the time of day. So that result suggests
Speaker 1: that sleep facilitated the discovery of the hidden rule, perhaps
Speaker 1: by restructuring memory. So all these are possible reasons why
Speaker 1: we sleep, to rehearse, to forget, and to restructure memory. Now,
Speaker 1: one more thing I want to cover in this episode
Speaker 1: is the issue of sleep deprivation. So while economists worry
Speaker 1: about the national debt, sleep scientists have become concerned about
Speaker 1: the national sleep debt because with the demands of modern life,
Speaker 1: lots of us get less sleep than the demands of
Speaker 1: our brains and bodies would call for. And the effects
Speaker 1: of mild sleep deprivation, for example, losing a few hours
Speaker 1: of sleep for one night, this is surely familiar to you.
Speaker 1: You get irritable, you get muscle aches, you yawn, you
Speaker 1: have trouble maintains attention. With more severe sleep deprivation, say
Speaker 1: lasting two or three days or longer, you can also
Speaker 1: get micro sleeps, which are brief sleep periods in the
Speaker 1: range of seconds or even a fraction of a second,
Speaker 1: and these show up as a short moment of cognitive absence.
Speaker 1: So for drivers on the road this is not uncommon
Speaker 1: and it's very dangerous. Unfortunately, people who experience micro sleeps
Speaker 1: will often be unaware that they were just sleeping. They
Speaker 1: will believe themselves to have been awake, or maybe they
Speaker 1: think they've temporarily spaced out. Many people who operate heavy
Speaker 1: machinery or vehicles will experience these brief moments, and this
Speaker 1: often leads to dire consequences and long term sleep deprivation
Speaker 1: often caused by disorders of sleep and wakefulness. This can
Speaker 1: result in really detrimental health like hypertension or diabetes, or
Speaker 1: heart disease or stroke. The studies performed over the decades
Speaker 1: generally converge on a common theme, which is that the
Speaker 1: effects of sleep deprivation are often more detrimental to the
Speaker 1: mind than to the body. So subjects with sleep deprivation
Speaker 1: often perform fine on physical tasks the next day, although
Speaker 1: their stamina tends to diminish a bit faster, But the
Speaker 1: most striking effects are on cognition and mood. Sleep deprivation
Speaker 1: is a real world problem because you've got medical residents
Speaker 1: and pilots and soldiers and truck drivers and lots of
Speaker 1: others who work long shifts that lead to sleep deprivation,
Speaker 1: and that can lead to poor decision making, which in
Speaker 1: turn leads to avoidable accidents. For example, there have been
Speaker 1: years of research on doctors which make it clear that
Speaker 1: sleep deprivation causes them to make more errors when they
Speaker 1: read charts, and they have lower performance because of a
Speaker 1: distant inclination to apply effort, and they have decreased mood
Speaker 1: and poor attitudes. A review of sleep deprivation studies on
Speaker 1: physicians showed that doctors could still respond without trouble to
Speaker 1: novel situations if they have to learn a new routine,
Speaker 1: but their decreased vigilance led to more mistakes in the
Speaker 1: routine and repetitive tasks that characterize a night in the hospital. Now,
Speaker 1: I just want to say that we always need to
Speaker 1: interpret sleep deprivation studies with an eye towards what else
Speaker 1: could be going on, because often there's lots of other
Speaker 1: stuff too, like stress. So you will feel unwell after
Speaker 1: a night of red used to sleep, but interpret that
Speaker 1: with a little bit of caution, because often the poor
Speaker 1: night of sleep comes from a stress inducer like an
Speaker 1: important exam or a deadline or whatever, and the poor
Speaker 1: physical feelings that you have the next day might be
Speaker 1: caused in part by the effects of distress rather than
Speaker 1: the sleep deprivation itself. Okay, Now, before moving on from
Speaker 1: sleep deprivation, I just want to mention that sometimes people
Speaker 1: can stay awake for remarkably long periods. In nineteen sixty four,
Speaker 1: there was a seventeen year old named Brandy Gardner who
Speaker 1: decided he was going to shoot for the world record
Speaker 1: for sleep deprivation. So, in collaboration with Stanford sleep researcher
Speaker 1: William Dement and physician John Ross, he was continuously monitored
Speaker 1: and he kept himself awake for a record breaking eleven days.
Speaker 1: He then went to sleep, and he woke up feeling
Speaker 1: fine fourteen hours and forty minutes later, and on subsequent
Speaker 1: night he slept a normal eight hours. In other words,
Speaker 1: he didn't require catching up on a sleep debt. He
Speaker 1: merely fell back into his normal rhythm. Now. Dement reported
Speaker 1: that the sleep deprivation's main effect was on Randy's mood,
Speaker 1: involving all the changes that are typical of fatigue, and
Speaker 1: Dement wrote that the deprivation had little effect on Randy's
Speaker 1: cognitive abilities, pointing out that on the tenth day, Randy
Speaker 1: won a game of pinball, and on day eleven he
Speaker 1: gave a press conference in which he appeared healthy and
Speaker 1: his speech was unslurred. But it should be noted that Ross,
Speaker 1: the physician, presented a somewhat different story. Beyond the mood swings,
Speaker 1: He reported extreme problems with Randy's ability to concentrate. For example,
Speaker 1: when Randy was asked to start at one hundred and
Speaker 1: continuously subtract seven. Randy stopped about a third of the
Speaker 1: way through. He stated that he had forgotten what he
Speaker 1: was doing. He also appeared to have paranoia and hallucinations,
Speaker 1: as well as a delusion by the fourth day that
Speaker 1: he was a famous football player. At one point, he
Speaker 1: mistook a street sign for a person, So the effects
Speaker 1: of staying awake that long may not have been as
Speaker 1: harmless as Dement portrayed. In any case, the fact that
Speaker 1: such an extraordinary stretch without sleep is even possible serves
Speaker 1: as an important data point for any theory of sleep.
Speaker 1: Other sleep deprivation records have been set, apparently extending to
Speaker 1: eighteen days and seventeen hours, but these are less documented
Speaker 1: and didn't monitor for micro sleeps. What's interesting is that
Speaker 1: the Guinness Book of World Records no longer maintains a
Speaker 1: sleep deprivation record because they have decided smartly that they
Speaker 1: don't want to encourage people to risk health consequences. By
Speaker 1: the way, I'll just note that many people report sleeping
Speaker 1: poor in being sleep deprived, but measurements taken at home
Speaker 1: or in a sleep lab sometimes reveal that the person
Speaker 1: slept better than they believed they did. Sometimes a period
Speaker 1: of wakefulness in the middle of the night gives the
Speaker 1: lasting impression of a poor night's sleep, when in fact
Speaker 1: it wasn't that long. But in general, there are fewer
Speaker 1: things important than making sure that you are getting a
Speaker 1: good night's sleep. Finally, an episode about sleep wouldn't be
Speaker 1: complete if I didn't talk about sleep disorders. Although lots
Speaker 1: of people get sleep deprivation because of their circumstances and
Speaker 1: stressful work, some people suffer chronic sleep disorders, and this,
Speaker 1: by the way, is the most common medical complaints, second
Speaker 1: only to pain. There are currently about one hundred different
Speaker 1: types of sleep wake disorders. Almost all of these can
Speaker 1: be grouped into four categories. There's insomnia, which is difficulty
Speaker 1: falling asleep or maintaining sleep. There's hypersomnia, which is extreme
Speaker 1: daytime sleepiness, and there's parasomnia's which is complex behaviors performed
Speaker 1: during sleep. And then there's the circadian rhythm disorders, which
Speaker 1: I already discussed before. So I'm going to turn to
Speaker 1: these other three. So let's talk insomnia first. So this
Speaker 1: is the most common sleep problem, and it involves not
Speaker 1: getting enough sleep to feel rested from the brain's point
Speaker 1: of view, insomnia happens when both your sleep and arousal
Speaker 1: systems are simultaneously active. By the way, it's an interesting
Speaker 1: side note, there's often a link between insomnia and psychiatric disorders,
Speaker 1: and the link is bidirectional, meaning either can lead to
Speaker 1: the other. Now, to deal with insomnia, some people take hypnotics,
Speaker 1: which are sleep aids, and although people have used lots
Speaker 1: of compounds as hypnotics over the millennia, such as opium
Speaker 1: and barbituates, these often lead to addiction and sometimes to
Speaker 1: breathing problems. Over the counter hypnotics that are approved by
Speaker 1: the Food and Drug Administration, they're all antihistamines, and these
Speaker 1: can produce next morning sleepiness or several other side effects
Speaker 1: and eventually tolerance to the sedating effects. Now unregulated, over
Speaker 1: the counter sleep aids like valerian or hops or lavender
Speaker 1: or melatonin generally appear to be of no benefit for insomnia.
Speaker 1: There are only a few pharmaceutical treatments for insomnia, and
Speaker 1: most commonly these include drugs that modulate the effect of
Speaker 1: the neurotransmitter called GABA. Now, insomnia can take a heavy
Speaker 1: toll on mood and productivity, and in the most extreme
Speaker 1: and rare cases, it can actually be fatal. I'll tell
Speaker 1: you a case that's really terrifying. Think about what it
Speaker 1: would be like to never sleep again. In nineteen seventy eight,
Speaker 1: there was an Italian woman in her forties who went
Speaker 1: to the doctor with terrible insomnia. Sleeping aids were totally useless.
Speaker 1: She simply couldn't fall asleep anymore, and as the toll
Speaker 1: of the disorder grew over the course of a few months,
Speaker 1: she could no longer walk and could barely speak, and
Speaker 1: within one year of the onset of this insomnia, she
Speaker 1: died with her body exhausted. A year later, the woman's
Speaker 1: sister presented with exactly the same symptoms, and she soon
Speaker 1: died the same death. For both women, their minds remained
Speaker 1: fine as their bodies disintegrated. So there was a physician
Speaker 1: named Ignotio Reuter who was a nephew by marriage to
Speaker 1: these two sisters. He was drawn to this mystery and
Speaker 1: began to plumb his wife's family tree for clues, and
Speaker 1: he discovered that this fatal insomnia had struck down other
Speaker 1: ancestors of theirs, and he suspected he was on the
Speaker 1: trail A rare genetic disorder. So when his wife's uncle, Silvano,
Speaker 1: came to visit, Reuter spotted the early onset of the symptoms,
Speaker 1: and he convinced Silvano to go to an Italian sleep clinic,
Speaker 1: where his worsening insomnia and progressive decline were documented on video,
Speaker 1: and then Silvano died at the age of fifty two.
Speaker 1: Now Silvano's brain was quickly removed and flown to a
Speaker 1: lab at Case Western Reserve University in Cleveland, and there
Speaker 1: a neuropithologist named pure Luigi Gambetti examined the brain and
Speaker 1: noticed that it was shot through with tiny holes, like
Speaker 1: a sponge. This reminded him of something that he'd seen before,
Speaker 1: a brain disease known as kraitzfeld yakub, which is the
Speaker 1: human form of mad cow disease. So Gambetti called Stanley Prusner,
Speaker 1: a scientist who had recently suggested that these brain diseases
Speaker 1: were caused by abnormal proteins called prions. So Prusner performed
Speaker 1: studies and confirmed that this insomniac family had a prion disorder,
Speaker 1: and he won the nineteen ninety seven Nobel Prize for
Speaker 1: his investigation of prions in part for the work on
Speaker 1: this family. Now, in the intervening years, more than thirty
Speaker 1: other families who are carriers of this genetic disorder have
Speaker 1: been discovered, and this is now known as fatal familial insomnia. Thankfully,
Speaker 1: most types of insomnia are typically much milder and more treatable.
Speaker 1: For example, one of the most common forms is restless
Speaker 1: leg syndrome, where upon falling asleep, a person feels unbearable
Speaker 1: discomfort in the legs that calls for relief by stomping
Speaker 1: or rubbing or twitching the legs. And this restless leg
Speaker 1: syndrome is experienced by about five to fifteen percent of
Speaker 1: the population and appears to have a genetic component. But fortunately,
Speaker 1: medications can successfully address restless leg syndrome in most cases. Okay,
Speaker 1: so that's a quick overview of insomnia. But there's also
Speaker 1: the opposite of insomnia, known as hypersomnia. People with hypersomnia
Speaker 1: have excessive sleepiness. Now this is different from being tired
Speaker 1: because of a late night. This exists at such a
Speaker 1: high level that one has no choice but to nap
Speaker 1: frequently during the day, including inappropriate times such as in
Speaker 1: the middle of a conversation or a meeting. Or lunch.
Speaker 1: The naps typically provide little relief from the excessive sleepiness,
Speaker 1: so hypersomnia often comes with anxiety and disorientation upon waking
Speaker 1: and diminished energy and memory problems. As you can imagine,
Speaker 1: hypersomniacs often can't participate in the normal settings of fail family,
Speaker 1: in work life. Sometimes this disorder occurs as a result
Speaker 1: of taking medications for depression or having excess body weight
Speaker 1: or suffering brain damage, and treatment options typically target the
Speaker 1: symptoms because often the cause is unknown. This hypersomnia this
Speaker 1: is the main symptom of narcilepsy, which is something you've
Speaker 1: surely heard of, where people have sudden attacks of sleepiness
Speaker 1: and will fall asleep. Aside from having extreme fatigue and
Speaker 1: frequent naps, narcalptics ironically can also have pretty poor nighttime sleep.
Speaker 1: They have other issues too, like sometimes right when they're
Speaker 1: in between wake and sleep, they'll have hallucinations or they'll
Speaker 1: do automatic behaviors in which they spontaneously produce purposeless sounds
Speaker 1: or acts with no conscious intervention or censorships where sometimes
Speaker 1: in a person with narcilepsy, there muscles will suddenly weaken
Speaker 1: and this can manifest as a slight sagging all the
Speaker 1: way to a complete shutdown of the muscles leading to collapse. No,
Speaker 1: how do we understand this? Note that narcoleptics fall abruptly
Speaker 1: into REM sleep directly from the waking state, whereas normally
Speaker 1: you pass through the stages of non rem sleep first.
Speaker 1: In REM sleep, the major skeletal muscles are shut down,
Speaker 1: and in narcilepsy, this is what happens. The body drops
Speaker 1: straight into REM sleep and causes the major muscle groups
Speaker 1: to just stop functioning. So this mistimed activity to the
Speaker 1: muscles also plays a role in another common symptom of narclepsy,
Speaker 1: which is sleep paralysis, and here the shutdown of the
Speaker 1: muscles lasts longer than it's supposed to, such as the
Speaker 1: brain wakes up but the body is unable to move
Speaker 1: for a short period. Narclepsi appears to be a genetic condition,
Speaker 1: and it results from a lower level of a hormone
Speaker 1: called ourexin, also known as hypocretan. This hormone promotes wakefulness,
Speaker 1: so in the late nineteen nineties, researchers discovered that people
Speaker 1: with narcolepsy have fewer neurons producing this orexin or hypocretin,
Speaker 1: and they realized that narcilepsy can be an autoimmune disorder
Speaker 1: in which the immune system attacks these neurons. Now, remember
Speaker 1: earlier I talked about these two mutually inhibitory networks that
Speaker 1: take care of wake and sleep. The current view is
Speaker 1: that the orexin hypocreting system stabilizes this system in the
Speaker 1: waking state, and if you don't have the proper level
Speaker 1: of these molecules, the flip flop of these networks is
Speaker 1: unstable and can switch states at inappropriate times. Okay, so
Speaker 1: that's what I want to tell you about hypersomnia, where
Speaker 1: the balance is disrupted in the direction of too much
Speaker 1: sleep instead of too little. And there's one more category
Speaker 1: of sleep to that's important. We've been talking about the
Speaker 1: states of sleep and waking as a flip flop system.
Speaker 1: But keep in mind that the arousal network or the
Speaker 1: sleep network consists of lots and lots of sub areas,
Speaker 1: and these areas typically work together in a smooth manner
Speaker 1: so that when the networks switch, all the appropriate systems
Speaker 1: come online when the others go offline. But given the
Speaker 1: complexity and size of these networks, the brain sometimes gets
Speaker 1: caught between stages. In other words, some neural areas have
Speaker 1: completed the switchover and others have not, and in these
Speaker 1: cases we find Parasomnia's where you get actions performed during
Speaker 1: sleep that are not under voluntary control, for example, sleep
Speaker 1: walking also known as somnambulism, like we saw in Kenneth
Speaker 1: Parks at the beginning of this episode. Parasomnias used to
Speaker 1: be thought of as a disorder, but they're now understood
Speaker 1: to represent a mixture of the waking state and some
Speaker 1: stage of sleep, either rem or non rem. These parasomnias
Speaker 1: come into being as the brain transitions from one state
Speaker 1: to the next. Now, non rem parasomnias are these disorders
Speaker 1: that happen when a sleeper's brain tries to jump directly
Speaker 1: from a deep sleep into the waking state and it
Speaker 1: becomes caught in between. So you get things like sleepwalking,
Speaker 1: but you also get things like talking in one sleep
Speaker 1: called some niloquy, or sleep eating or teeth grinding, or
Speaker 1: night terrors in which a sleeper will bolt upright in fear,
Speaker 1: often with a scream or a gasp, and have a
Speaker 1: temporary inability to regain consciousness. Now, most of these non
Speaker 1: rem parasomnias exist more commonly in childhood, and they tend
Speaker 1: to diminish in frequency with age. Now you also have
Speaker 1: REM parisomnia's, and the most common of these is REM
Speaker 1: sleep behavior disorder, in which the paralysis of the muscles
Speaker 1: that normally happens during REM is not there, so sleepers
Speaker 1: will act out their dreams, which usually results in injury
Speaker 1: to themselves or others. Ninety percent of patients with this
Speaker 1: disorder are male, and they'll sometimes try to deal with
Speaker 1: this problem by tying themselves directly to the bed or
Speaker 1: constructing fortresses of pillows. Happily, this can typically be dealt
Speaker 1: with with gabba enhancing pharmaceuticals. Now, as the neuroscience of
Speaker 1: sleep progresses, new parasomnias are being identified. For example, there's
Speaker 1: a fairly newly described parisomnia, which is sleep sex or sexomnia,
Speaker 1: in which a person engages in sexual acts while asleep.
Speaker 1: Several defendants in sexual assault trials have been found not
Speaker 1: guilty because of their sex omnia. Now, many people decry
Speaker 1: this plea as an excuse, and possibly sometimes it is,
Speaker 1: but sex omnia is a real thing, and people can
Speaker 1: have full experiences with no conscious awareness or memory of them.
Speaker 1: And when people do become aware. There's typically a lot
Speaker 1: of distress and shame, so people often don't even go
Speaker 1: to the doctor for help, but they should because this
Speaker 1: can often be dealt with with antidepressant and anti anxiety medications.
Speaker 1: So now that you have listened to this episode, you
Speaker 1: understand that there are detectable differences in the activity of
Speaker 1: the sleeping brain in people with parasomnias. Although we tend
Speaker 1: to assume that the brain must be either awake or asleep,
Speaker 1: many well studied phenomenon like the parasomnia's result from the
Speaker 1: brain truly caught in an intermediate state between the two.
Speaker 1: In a network of on hundred billion neurons, there's room
Speaker 1: for a tremendous diversity of different modes of activity, many
Speaker 1: of which were only just beginning to understand. So let's
Speaker 1: wrap up today's episode. It's not clear why we spend
Speaker 1: so much of our live sleeping. Arguments from different angles
Speaker 1: suggest that sleep promotes restoration of the energy you burned
Speaker 1: during the day, or keeps us out of trouble in
Speaker 1: the dark, or allows us to practice neural programs that
Speaker 1: we don't otherwise get the chance to do, and or
Speaker 1: it helps us consolidate memories. These suggestions are not exclusive,
Speaker 1: nor perhaps are they complete, and it remains to be
Speaker 1: understood how sleep restructures memory and inspires insight. Now, at
Speaker 1: the beginning of this episode, I introduced Kenneth Parks, the
Speaker 1: man who killed his mother in law and assaulted his
Speaker 1: father in law during an apparent sleep walking episode. The
Speaker 1: idea of murdering in one sleep tends to challenge the
Speaker 1: belief of the public, and people will typically dig into
Speaker 1: the position that the plea is a fraudulent excuse. But
Speaker 1: whatever the merits of any individual case, we know that
Speaker 1: sleepwalking is a real phenomenon. We saw that transitions between
Speaker 1: waking and sleeping result from these opposing networks, and that
Speaker 1: parasomnia's can result when these networks don't hand off power smoothly. Now,
Speaker 1: a normal sleep cycle moves from very deep sleep into
Speaker 1: more and more shallow sleep and eventually into wakefulness. But
Speaker 1: Kenneth Parks's EEG revealed that he had a parasomnia about
Speaker 1: ten to twenty times each night. His brain networks attempted
Speaker 1: to transition directly from deep slow wave sleep directly into wakefulness.
Speaker 1: The jury came to understand that there was no way
Speaker 1: for him to fake EEG results intentionally, and so those
Speaker 1: measurements proved critical to his defense, and after hours of deliberation,
Speaker 1: the jury found Kenneth Parks not guilty. Now, there are
Speaker 1: other cases that have fared differently. In nineteen ninety seven,
Speaker 1: Scott Fallader was accused of stabbing his wife forty four
Speaker 1: times and holding her head underwater. He pled homicidal somnambulism,
Speaker 1: but he was convicted and sentenced to life in prison.
Speaker 1: In total, there have been dozens of homicidal somnambulism cases
Speaker 1: tried in North America going back to the sixteen hundreds,
Speaker 1: and more recently, parasomnia defenses have been offered in cases
Speaker 1: of sleep sex. Can the legal system assume that some
Speaker 1: of these defenses are fake? Perhaps, but presumably not all
Speaker 1: of them. In many cases, defendants have been a quit
Speaker 1: after careful measurements of their brain activity. So back to
Speaker 1: Kenneth Parks. Most somnambulists are nonviolent. But note that Parks
Speaker 1: had insomnia, and he was depressed, and he was trying
Speaker 1: to overcome a gambling problem, and he had financial and
Speaker 1: marital problems, and he had also been massively sleep deprived
Speaker 1: from not having slept the night before that event. So,
Speaker 1: although it's difficult to know exactly how these factors played
Speaker 1: a role the physiology of his brain as measured in
Speaker 1: an EEG laboratory, this was the clinching piece of evidence
Speaker 1: in convincing the jury that he did, in fact suffer
Speaker 1: from abnormal transitions from slow wave sleep to the waking state,
Speaker 1: transitions that made his actions involuntary. So cases like this
Speaker 1: one highlight the mysterious and poorly understood border lands between
Speaker 1: wakefulness and sleep. So the amazing thing to me is
Speaker 1: that your brain can operate in three very different states.
Speaker 1: There's the waking state, there's rem sleep, and there's non
Speaker 1: rem sleep. And these three states differ fundamentally. They represent
Speaker 1: the same machinery running very different tasks. One of the
Speaker 1: amazing features of the brain is its ability to transition
Speaker 1: between these states, usually without a problem. And although the
Speaker 1: parasomnias represent cases in which the brain has trouble getting
Speaker 1: a state fully locked into place, it's amazing that these
Speaker 1: don't happen more often. So this episode has been an
Speaker 1: introduction to the main landscape about the sleeping brain. Join
Speaker 1: me next week as we zoom in the camera to
Speaker 1: the topic of dreams and the whole wild world of
Speaker 1: what we know and don't know about them. And then
Speaker 1: two weeks from now will come to lucid dream, where
Speaker 1: you become aware that you're in a dream and you
Speaker 1: get to grab a hold of the script. Until then,
Speaker 1: make sure that you're getting sufficient sleep, although you are
Speaker 1: not consciously there for most of it. It is one
Speaker 1: of the most important things that your brain does. Go
Speaker 1: to eagleman dot com slash podcast for more information and
Speaker 1: to find further reading. Send me an email at podcasts
Speaker 1: at eagleman dot com with questions or discussions, and check
Speaker 1: out and subscribe to Inner Cosmos on YouTube for videos
Speaker 1: of each episode and to leave comments. Until next time.
Speaker 1: I'm David Eagleman and this is Inner Cosmos.