Speaker 1: Why do brains dream? And what's going on with the
Speaker 1: bizarreness of dreams? Why doesn't your clock work in your dreams?
Speaker 1: And even though you spend a lot of your day
Speaker 1: working on cell phones and computers, why do those almost
Speaker 1: never make appearances in your dream content? There are so
Speaker 1: many cool questions that we're going to address today. Is
Speaker 1: dream content the same across cultures and across time? Are
Speaker 1: dreams experienced in black and white or in color? Why
Speaker 1: do I think about dreams as this strange love child
Speaker 1: between brain plasticity and the rotation of the planet. What
Speaker 1: is the relationship between schizophrenia and dreaming? And in the
Speaker 1: future will we be able to read out the content
Speaker 1: of somebody's dream? Welcome to Inner Cosmos with me David Eagleman.
Speaker 1: I'm a neuroscientist and author at Stanford and in these
Speaker 1: episodes we sail deeply into our three pound universe to
Speaker 1: understand why and how our lives look the way they
Speaker 1: do and how we experience our life includes our nocturnal life.
Speaker 1: We spend a third of our lives with our eyes closed,
Speaker 1: lying still and horizontal, like a meat robot that's been
Speaker 1: switched off. But why in the last episode, we talked
Speaker 1: all about sleep, why brains do that, and why all
Speaker 1: animals do that, and what is happening in the brain
Speaker 1: during sleep. Today we're going to zoom in on one
Speaker 1: of my favorite subjects, a very strange thing the brain does,
Speaker 1: which we call dreaming. We spend a fraction of our
Speaker 1: sleep time locked in a different reality, swimming around in
Speaker 1: plots which aren't real, and they're often not even realistic,
Speaker 1: but which nonetheless convince us entirely. And today we're going
Speaker 1: to see what that's all about. Humans have been writing
Speaker 1: about dreams and pondering about them for a long time,
Speaker 1: and essentially we have evidence of this from the beginning
Speaker 1: of writing. We see detailed dream reports from ancient Egyptians
Speaker 1: and Romans and Chinese. The Bible is full of dreams.
Speaker 1: Every culture in the world has been fascinated by these
Speaker 1: strange nocturnal journeys that we go on. And as we'll
Speaker 1: see shortly, there's an interesting surprise, which is that dream content,
Speaker 1: in other words, the kind of things that people dream about,
Speaker 1: is essentially the same across cultures and across time, and
Speaker 1: that serves as a clue that will allow us to
Speaker 1: unlock some mysteries about what otherwise feels like a deeply
Speaker 1: mysterious experience that we enjoy or suffer every night of
Speaker 1: our life lives. So strap in for an episode full
Speaker 1: of surprises. So let's start with a poem that Lord
Speaker 1: Byron wrote in eighteen sixteen called The Dream. He wrote,
Speaker 1: sleep hath its own world and a wide realm of
Speaker 1: wild reality. And dreams, in their development have breath and tears,
Speaker 1: and tortures and the touch of joy. They leave a
Speaker 1: weight upon our waking thoughts. So dreams are indeed a
Speaker 1: wild reality. The thing we all find so amazing about
Speaker 1: dreaming is its bizarreness. You're seeing new things, you hold
Speaker 1: strange beliefs, and you fall for it all hook line
Speaker 1: and sinker. Whatever your brain serves up to you, you
Speaker 1: believe it entirely. So we'll talk about all this, But
Speaker 1: let's first zoom in on what's happening inside the brain.
Speaker 1: Dreaming occurs during rapid eye moos movement or rem sleep,
Speaker 1: where your eyes are darting back and forth. There's nothing
Speaker 1: coming in the eyes, of course, they're shut, so all
Speaker 1: the activity is internally generated. For good housekeeping, all just
Speaker 1: note that rem sleep isn't necessarily equivalent to dream sleep,
Speaker 1: but that's when most dreaming occurs. Now, how do we
Speaker 1: know that, Well, it's because if you wait until someone
Speaker 1: enters rems sleep, their eyes are going back and forth,
Speaker 1: and then you shake them awake and you say, hey,
Speaker 1: what were you just experiencing? They'll tell you WHOA, I
Speaker 1: was just panicking because I was at work but realized
Speaker 1: I had forgotten to put on pants, and I was
Speaker 1: hiding behind the plant pots and figuring out how to
Speaker 1: escape before the meeting started. But if you wake them
Speaker 1: up during the rest of the ninety minute sleep cycle,
Speaker 1: during the stages that we call slow wave sleep, and
Speaker 1: you say, hey, what were you just experiencing, they'll generally
Speaker 1: say nothing, I wasn't there. Now, for completeness, I'll mention
Speaker 1: that sometimes people report some form of mental activity during
Speaker 1: slow wave sleep, but when they do, this is usually
Speaker 1: just a thought or making a plan. But it lacks
Speaker 1: the visual vividness and the hallucinatory components of typical dreams.
Speaker 1: So dreaming of the sort we're interested in today happens
Speaker 1: during rem sleep. Now, although dreams seem so untethered and ethereal,
Speaker 1: there are specific things happening under the hood. Dreaming depends
Speaker 1: on the normal functioning of a particular network of brain areas.
Speaker 1: This is primarily in the limbic and paralymbic and association areas.
Speaker 1: Now we know that from brain imaging, but also because
Speaker 1: damage in this network can produce temporary or permanent dream
Speaker 1: loss or impairment like loss of visual dream imagery. Now,
Speaker 1: not all of those areas might sound familiar to you,
Speaker 1: but you've probably heard of the limbic system, which sits
Speaker 1: at the heart of your emotions. So presumably this is
Speaker 1: why dreams are so overloaded with high emotion. And I
Speaker 1: also want to mention a brain era that is suppressed
Speaker 1: during rem sleep, and that is the hippocampus. This is
Speaker 1: an area that's required to convert short term memory into
Speaker 1: long term memory. And this is why when you wake
Speaker 1: up from a dream, you can remember it so clearly,
Speaker 1: but after about fifteen minutes it just slips away from you.
Speaker 1: You just can't hold on to what happened. This is
Speaker 1: because you have the short term memory just fine, but
Speaker 1: you're not converting it into long term memory, and so
Speaker 1: it simply fades before your eyes. And by the way,
Speaker 1: I think this experience that we have every morning can
Speaker 1: enhance our empathy about what it would be like to
Speaker 1: have something like Alzheimer's disease, because a person with Allsheimers
Speaker 1: says on the phone, Okay, I'll be right down there
Speaker 1: in a moment, and they hang up, and then the
Speaker 1: memory of that just slips away. So even though you
Speaker 1: might tell a relative with Alzheimer's, come on, just try
Speaker 1: harder to remember. Just think about somebody telling that to
Speaker 1: you about your dreams in the morning. So back to
Speaker 1: the Byron poem, the line that I thought was interesting
Speaker 1: was they leave a weight upon our waking thoughts because
Speaker 1: they don't directly interact with our waking thoughts, but instead
Speaker 1: they can just put a spin on our mood, even
Speaker 1: if we don't remember why. Okay, so what do we
Speaker 1: see in the brain when dreaming begins, Well, just before
Speaker 1: the onset of your eyes darting back and forth, you
Speaker 1: have a group of neurons in the brain stem, specifically
Speaker 1: in an area called the ponds, and these crank up,
Speaker 1: and these trigger several consequences. The first is that your
Speaker 1: major muscle groups get paralyzed. This is called atonia. So
Speaker 1: you've got this elaborate neural circuitry that keeps the body
Speaker 1: paralyzed during dreaming. And by the way, the very elaborateness
Speaker 1: of this circuitry emphasizes the biological importance of dream sleep.
Speaker 1: You don't get this kind of complexity by accident. Presumably,
Speaker 1: dreaming would be unlikely to evolve and remain without an
Speaker 1: important function behind it. So why do we get this
Speaker 1: paralysis of the muscles. It allows the possibility for the
Speaker 1: brain to experience things and simulate reality without actually moving
Speaker 1: the body. The second consequence of these neurons in the
Speaker 1: ponds is that they trigger these waves of activity known
Speaker 1: as PGO waves, and these are key to the experience
Speaker 1: of dreaming. These PGO waves travel to a tiny area
Speaker 1: called the geniculate nucleus and from there these waves of
Speaker 1: activity slam into the occipital cortex at the back of
Speaker 1: your head. In other words, they drive activity into the
Speaker 1: visual system. So that's why these are called PGO waves.
Speaker 1: Because they start in the ponds, p move to the
Speaker 1: geniculate g and go to the occipital cortex. Oh pgoh
Speaker 1: I mention all this detail. Because PGO waves are the
Speaker 1: neural correlate of dreaming, the visual areas become alive with
Speaker 1: activity allowing us to see our dreams. You blast activity
Speaker 1: into the visual cortex and you enjoy visual experience even
Speaker 1: though your eyes are closed. Now, interestingly, when you measure
Speaker 1: electrical activity across the brain with EEG, when you do
Speaker 1: this during rem sleep, it looks really similar to that
Speaker 1: during the waking state. You see similar patterns in both states,
Speaker 1: for example, lots of gamma wave frequency, which is generally
Speaker 1: thought to reflect something about cognitive processing, with the exception
Speaker 1: of the paralyzed muscles and the lack of external visual
Speaker 1: input because your eyes are closed, the states of rem
Speaker 1: sleep and of wakefulness they kind of resemble one another.
Speaker 1: And this is what we might expect from a state
Speaker 1: of consciousness that's altered. But it's some sort of consciousness nonetheless. Okay,
Speaker 1: so that's what's happening in the brain when we dream.
Speaker 1: But why do we dream? Well, there are various hypotheses
Speaker 1: about this, and I mentioned one last week, which is
Speaker 1: that maybe dreams allow us to simulate rare situations. In
Speaker 1: other words, these nocturnal neural simulations might allow us and
Speaker 1: all animals to test out activities without the danger and
Speaker 1: risk of doing so in the real world. So you
Speaker 1: can practice through different scenarios with your muscles all shut down.
Speaker 1: So people who advocate this theory suggest that the periodic
Speaker 1: stimulation of the cortex in this semi random and non
Speaker 1: specific manner this can maintain circuits that are really important
Speaker 1: for survival, but they rarely get activated because you don't
Speaker 1: run into emergencies that often. So the idea is that
Speaker 1: you're just sending in random activity, keeping the engine oiled
Speaker 1: in case you need one of these programs sometime, and
Speaker 1: some researchers suggest that it's even more specific than that.
Speaker 1: A version of this framework called threat simulation theory, suggests
Speaker 1: that dreams exist to simulate threatening events and to rehearse
Speaker 1: what to do in the face of threat, and that
Speaker 1: seems on its surface at least consistent with the high
Speaker 1: prevalence of violence and aggression in dreams. But I want
Speaker 1: to note that there's no data that directly supports this idea,
Speaker 1: and I mentioned last week that this theory suggests that
Speaker 1: people exposed to more survival threats in waking life might
Speaker 1: have a more common experience of threat dreams at night,
Speaker 1: but the data do not support that. Also, the threat
Speaker 1: perception theory doesn't explain the fact that most dreams are
Speaker 1: totally meaningless and bizarre instead of involving any meaningful threat
Speaker 1: perception or threat avoidance. So back to the question of
Speaker 1: why we dream. A few years ago, my colleague Don
Speaker 1: Vaughan and I proposed a new theory which is the
Speaker 1: only one that makes quantitative predictions across species. And if
Speaker 1: you heard episode eleven you may remember about this. That
Speaker 1: theory has to do with brain plasticity. And here's the idea.
Speaker 1: In a nutshell, we know that if a person goes blind,
Speaker 1: other senses start to take over what was the visual cortex.
Speaker 1: In other words, the territory of the visual system is
Speaker 1: not fixed permanently, but instead the wiring of the brain
Speaker 1: is quite fluid, and there's a takeover that happens. Okay, now,
Speaker 1: it turns out that if you take a normally cited
Speaker 1: person and you blindfold, you can start seeing the beginnings
Speaker 1: of this takeover in neuroimaging starting in about one hour.
Speaker 1: And that really surprised us because of how fast the
Speaker 1: takeover starts to happen. So what does this rapidity of
Speaker 1: the takeover of the cortex have to do with dreaming?
Speaker 1: While in the incessant competition for territory in the brain,
Speaker 1: the visual system has a special challenge because of the
Speaker 1: planet's rotation, we experience darkness for about twelve out of
Speaker 1: every twenty four hours. And obviously I'm talking about our
Speaker 1: evolutionary history, not the recently electrically blessed times. In other words,
Speaker 1: our ancestors all spent their lives as inadvertent participants in
Speaker 1: a blindfold experiment every single night. So how did their
Speaker 1: visual cortex defend its territory when you've got no data
Speaker 1: coming in through the eyes. So our proposal is that
Speaker 1: the visual corret tex preserves its territory by finding a
Speaker 1: way to remain active at night. And we call this
Speaker 1: the defensive activation theory. And the purpose of dreaming here
Speaker 1: is to keep cells in the visual cortex active, and
Speaker 1: that's how it resists conquest by the territories of the
Speaker 1: other senses. Vision is the only one of the senses
Speaker 1: that's disadvantaged by darkness. You can still touch and smell,
Speaker 1: and taste and hear in the dark, and so it's
Speaker 1: the only sense that needs internally generated activity to maintain
Speaker 1: its borders during the long night. So, as a result,
Speaker 1: about every ninety minutes you get this internally generated activity
Speaker 1: that blasts exclusively into the visual cortex, and so dreams
Speaker 1: are experienced as primarily visual. So several predictions immediately fall
Speaker 1: out of the defensive activation theory. First, because brain plasticity
Speaker 1: diminishes with age, this would suggest that the amount of
Speaker 1: time spent in REM sleep should also decrease as one
Speaker 1: moves through the lifespan, and that turns out to be
Speaker 1: exactly what happens. REM sleep in humans accounts for half
Speaker 1: of an infant's sleep time, but as a person grows older,
Speaker 1: the percentage of remsleep decreases steadily. In other words, diminishing
Speaker 1: plasticity of the brain correlates with less REM sleep. But
Speaker 1: more importantly, we made a more quantified prediction. We said, hey,
Speaker 1: maybe the more flexible and animal's brain is the more
Speaker 1: REM sleep it requires to defend its visual cortex. So
Speaker 1: Don and I studied the plasticity in twenty five species
Speaker 1: of primates and we found that the species with more
Speaker 1: plastic brains spend more time in REMS sleep every night.
Speaker 1: So you'd think that these two measures REM sleep and
Speaker 1: brain plasticity they would be totally unconnected, So it was
Speaker 1: very surprising to find that they are tightly linked. So
Speaker 1: dreaming defends the visual cortex. Now, the circuitry that underpins dreaming.
Speaker 1: This is so ancient and deeply wired that even people
Speaker 1: who are blind have it. But note that blind people
Speaker 1: don't have visual dreams. Instead, their nighttime hallucinations involve the
Speaker 1: other senses, like feeling their way around an oddly arranged
Speaker 1: kitchen or hearing strangers speaking. Why because other sensory errors
Speaker 1: have annexed the underused visual cortex. So think about it
Speaker 1: this way. People who can see and those with visual impairments,
Speaker 1: they both have activity shooting into their occipital lobe during dreaming,
Speaker 1: but the senses processed by that territory are different. The
Speaker 1: defensive activation theory also makes more general predictions. If dream
Speaker 1: sleep is triggered by the absence of visual input during
Speaker 1: the night, we might presume that a person deprived of
Speaker 1: vision while awake could similarly experience dreamlike visual hallucinations. And
Speaker 1: that is exactly what happens when people have degenerating vision,
Speaker 1: or they end up in solitary confinement or even just
Speaker 1: in a dark float tank. Any situation in which vision
Speaker 1: gets deprived, the brain starts fighting back and having hallucinations.
Speaker 1: So that's the idea. Dreams are a screensaver. The brain
Speaker 1: puts activity into the visual cortex to prevent it from
Speaker 1: getting ruined during the night. Okay, so you might say, fine,
Speaker 1: your hypothesis seems plausible, But why do dreams seem to
Speaker 1: be stories? After all, we don't just see random snow
Speaker 1: like on an old television. We experience stories, and in fact,
Speaker 1: there are various stories of someone discovering something in dreams,
Speaker 1: like Kurkule thinking of the structure of the Benzene ring
Speaker 1: based on a dream he had of two snakes biting
Speaker 1: each other's tails, or Paul McCartney dreaming the melody for
Speaker 1: the song Yesterday. So what's up with dream content? The
Speaker 1: key is that the brain is a storytelling machine. Your
Speaker 1: brain is deeply carved with roadways that represent your experience
Speaker 1: in the world, and these are stored in what are
Speaker 1: called associative neural networks, which means that everything connects to
Speaker 1: other things based on how they relate. So if I
Speaker 1: ask you to think of a mouse that's physically connected
Speaker 1: in your brain's networks to your concept of cheese or
Speaker 1: exterminators or mickey mouse or mazes, or running wheels, or
Speaker 1: mouse traps or pet stores everything else you've ever associated
Speaker 1: with a mouse. So all concepts are related and linked
Speaker 1: physically to what happens during sleep and dreaming. Well, the
Speaker 1: synapses that are used during the day tend to be
Speaker 1: slightly more chemically active, say, they're more hot from the
Speaker 1: activity of the day, and so your dreams usually involve
Speaker 1: something from the day or something that's on your mind.
Speaker 1: They often involve the memories and desires and fears and
Speaker 1: hopes that are brewing in your inner life. But the
Speaker 1: associations are much looser. So maybe you have something about
Speaker 1: your boss or something that happened in a class or whatever,
Speaker 1: but the dream quickly goes off in some weird direction.
Speaker 1: The associations are looser, and so we end up dreaming
Speaker 1: stories with looser associations, following paths along the associative neural
Speaker 1: network that we might not otherwise take. But things make sense,
Speaker 1: at least in the light of dream logic. So even
Speaker 1: if the visual cortex is just getting volleys of random activity,
Speaker 1: you get meaning out of it. You get some sort
Speaker 1: of story. Now people often wake up and say, no, way,
Speaker 1: that wasn't random, That was a metaphor. I'm trying to
Speaker 1: decide if I should quit this job, and I had
Speaker 1: a dream that I went into the office and the
Speaker 1: floor was tilted at forty five degrees and no matter
Speaker 1: what I did, I kept slipping back down. And that
Speaker 1: was a metaphor about the impossibility of my advancement. There,
Speaker 1: that was a sign from my unconscious. Okay, so maybe
Speaker 1: the interesting thing about interpreting the content of dreams is
Speaker 1: that they might be one hundred percent random, but they
Speaker 1: act like a Rorshack blot, which is to say, you
Speaker 1: can assign any sort of meaning to them. You remember
Speaker 1: a Rorshack blot, which is where you squish some ink
Speaker 1: between two pages, and then you pull the pages apart
Speaker 1: and you get some random shape, and you ask people
Speaker 1: to interpret what they're seeing to assign meaning to it.
Speaker 1: And it's easy enough to say, yeah, that looks like
Speaker 1: this thing in my life, maybe this issue that's been
Speaker 1: chewing at me. And that's how doctor Rhorshak used this
Speaker 1: to determine what had meaning in a person's mind. But
Speaker 1: you would never say the blob of ink carried meaning.
Speaker 1: It's all about the imposition of meaning by the viewer.
Speaker 1: And this, I suggest could be what happens with dreams
Speaker 1: as well. You interpret the ink blob, and that interpretation
Speaker 1: might have significance to your life, but you imposed that
Speaker 1: meaning instead of it being inherent in the dream. Here's
Speaker 1: an interesting parallel. Pablo Picasso once said, we all know
Speaker 1: that art is not truth. Art is a lie that
Speaker 1: makes us realize the truth, and that could be the
Speaker 1: same thing with dreams. They are a lie that makes
Speaker 1: us realize the truth. So in this sense, it's the
Speaker 1: same thing. If you're thinking about some problem and you
Speaker 1: go to the bookshelf and you pull off any random
Speaker 1: book and turn to a random page and you read
Speaker 1: the sentence. Often it will very tangentially give you some
Speaker 1: push to the thing that you're trying to solve. But
Speaker 1: that doesn't mean the awe of the book cared about
Speaker 1: you and wrote that sentence with that future moment in mind.
Speaker 1: It simply tells us that lots of things in the
Speaker 1: world are like lots of other things and can therefore
Speaker 1: be interpreted. And I do just want to add one
Speaker 1: more word of caution to the game of dream interpretation.
Speaker 1: By the time you turn to the person next to
Speaker 1: you and say, oh my gosh, I just had the
Speaker 1: strangest dream and you tell them, you are forced to
Speaker 1: add another layer of narrative scaffolding so that it makes
Speaker 1: sense as a story that you're telling. So a narrative
Speaker 1: that's very thin can seem to have more flesh after
Speaker 1: you've pushed it through your storytelling machinery. In other words,
Speaker 1: we layer on narrative structure to give our dreams a
Speaker 1: shape that they didn't actually have. And so especially if
Speaker 1: you've had a dream that you've told over and over,
Speaker 1: it usually has more of a scaffolding than it actually
Speaker 1: started with. Nonetheless, the content of dreams has always fascinated humans,
Speaker 1: spurring societies to invent cultural uses for dreams in religious
Speaker 1: ceremonies and medicinal practices, or doomed attempts to predict the future.
Speaker 1: Sigmund Freud, who lived decades before modern brain science, he
Speaker 1: thought that dreams provided an inroad into the underlying functions
Speaker 1: of the brain and especially the subconscious. He suggested, as
Speaker 1: had many before him, that dreams concealed hidden meanings that
Speaker 1: were just at the threshold of breaking through the barrier
Speaker 1: to consciousness. More specifically, he proposed that dreams constitute a
Speaker 1: disguised attempt at wish fulfillment. Similarly, Carl Jung positive that
Speaker 1: dreams may offset features of a character personality that you
Speaker 1: might ignore while you're awake. In general, both those theories
Speaker 1: have been criticized because they can't be proven wrong, and
Speaker 1: critics have pointed out that the wish fulfillment interpretation seems
Speaker 1: improbable in view of the recurring nightmares that attend post
Speaker 1: traumatic stress disorder. So I am, of course not the
Speaker 1: first to propose that dreams might have no inherent meaning.
Speaker 1: The psychiatrists j al And Hobson and Robert McCarley suggest
Speaker 1: that dreams may have no meaning at all, and they
Speaker 1: have a model they call the activation synthesis model, which
Speaker 1: proposes that random activity from the brain stem goes to
Speaker 1: the cortex, which tries to turn it into motor output.
Speaker 1: But given the paralysis of the major muscle groups, the
Speaker 1: brain has to explain the paradox between outgoing motor signals
Speaker 1: and a lack of expected sensory feedback. So in this situation,
Speaker 1: the cortex synthesizes an explanation, essentially weaving a story from
Speaker 1: the random inputs. Now Hobson and McCary faced criticism for
Speaker 1: this aspect of their theory because dreams often do have
Speaker 1: a relation relationship to life experience. So in that light,
Speaker 1: they made modifications to allow that dream content relates to
Speaker 1: memories and fears and desires and hopes and so on,
Speaker 1: but that these provide the background context and not the
Speaker 1: exact content of the cortexas interpretation of the random activity.
Speaker 1: So which is it, Does dream content tell us anything
Speaker 1: at all? Or nothing? Well, here's how we can approach
Speaker 1: the problem. When you look at one person's dreams like
Speaker 1: you think about your own dreams, you may not be
Speaker 1: able to use the content as a key to unlock
Speaker 1: much about the brain. But as you move from considering
Speaker 1: one dreamer to doing the science and looking at thousands
Speaker 1: of dream reports and hundreds of thousands from all over
Speaker 1: the world, you can start to see the fence lines.
Speaker 1: You see that dreams aren't a wild unleashing where anything
Speaker 1: can happen. Instead, dreams have particular rules to the stories,
Speaker 1: and that gives us hints. So what are those rules? Well,
Speaker 1: I recently read a very cool new book by my
Speaker 1: colleague Rahul John day Al called This Is Why You Dream,
Speaker 1: and he outlines a series of studies that demonstrate a
Speaker 1: remarkable consistency of themes. Across cultures and across decades, the
Speaker 1: same kinds of dreams are reported, for example, being unable
Speaker 1: to find one's way or being late for an important event.
Speaker 1: In dreams, both men and women usually experience more aggression
Speaker 1: than friendliness, although men in almost all societies have greater
Speaker 1: physical aggression in their dreams than women do. Everyone experiences
Speaker 1: more misfortune than good fortune. People experience more negative emotions
Speaker 1: than positive emotions. So the cross cultural research suggests that
Speaker 1: dreams are similar across a wide range of cultures in
Speaker 1: terms of the subject matter, the level of aggression, familiarity
Speaker 1: with the people in the dreams. For example, let me
Speaker 1: zoom in on this. Jandeal points out that in the
Speaker 1: nineteen fifties there were ques given to college students in
Speaker 1: America and college students in Japan, and the questionnaire asked
Speaker 1: them what they had dreamt about, like showing up somewhere
Speaker 1: with no clothes or flying or trying to do something
Speaker 1: again and again, or being buried alive, or something involving
Speaker 1: school and their teachers or whatever. And as it turns out,
Speaker 1: although American and Japanese students were living pretty different lives,
Speaker 1: their answers were essentially the same. So for the Americans,
Speaker 1: the top five dreams were falling, being attacked or pursued,
Speaker 1: trying again and again to do something, a dream involving
Speaker 1: school or teachers, or studying, and sexual experiences. And when
Speaker 1: you compare this to the Japanese students, it was essentially
Speaker 1: the same. Their dreams were ranked as being attacked or pursued, falling,
Speaker 1: trying again and again to do something, dreams about school
Speaker 1: or teachers or studying, and being frozen with fright, and
Speaker 1: sexual experiences were number six. So halfway across the world,
Speaker 1: very different cultures, same dream content. Now, fifty years after
Speaker 1: that study, similar questions were given to students in China
Speaker 1: and Germany, and they came up with the century the
Speaker 1: same answers. Again, you find people dreaming of being chaste,
Speaker 1: or pursued, or arriving too late, like missing an airplane
Speaker 1: or a final exam. Now you might say, fine, but
Speaker 1: these are all industrialized countries and maybe their lives are
Speaker 1: sort of similar. But in fact people have also studied
Speaker 1: indigenous societies in Brazil and Mexico and Australia and they
Speaker 1: find extremely similar results. The cultures are quite different. But
Speaker 1: the plots of the dreams are not. So there have
Speaker 1: been lots of studies on this sort of thing now,
Speaker 1: and they all conclude that dream content is a century
Speaker 1: same across cultures and across time. As one example, wherever
Speaker 1: you are in the world, men dream more about other men,
Speaker 1: while women dream equally of men and women, and all
Speaker 1: people across cultures are more likely to be victims of
Speaker 1: violence rather than perpetrators. So dreams cover similar themes across
Speaker 1: the world, irrespective of language and culture and time. It
Speaker 1: doesn't seem to matter how rich you are, how poor
Speaker 1: you are. So what does that mean? Well, what's the
Speaker 1: one thing we all have in common? Our organs on
Speaker 1: the inside and specifically the brain. As easy as it
Speaker 1: is to look at different cultures around the world, with
Speaker 1: different governments and different religions and different costumes, this variability
Speaker 1: has cropped up in the last millisecond of human history.
Speaker 1: And if you look just under the skin and the bone,
Speaker 1: you find the same brain in us all. It's the
Speaker 1: same engine under the hood. So whenever we find something
Speaker 1: clear like oh, everyone dreams about the same thing, that
Speaker 1: we are looking at something fundamental and ancient and universal,
Speaker 1: and we find all sorts of other interesting answers by
Speaker 1: looking across thousands of dreams. For example, what if dreams
Speaker 1: are a way to live out fantasies like sexual fantasy.
Speaker 1: That seems consistent with how we talk about dreams a
Speaker 1: way of acting out our desires. But in studies across
Speaker 1: all cultures, it turns out that fewer than ten percent
Speaker 1: of dreams are sexual, which I find fascinating given the
Speaker 1: way we talk about dreams. If a young single person
Speaker 1: says to another single person, oh, I had a dream
Speaker 1: about you last night, then everyone titters, makes assumptions about that,
Speaker 1: and we have terms like dream girl or dream guide,
Speaker 1: But in fact, ninety percent of our dreams have nothing
Speaker 1: to do with that. So the content is remarkably similar
Speaker 1: across the world. But where things get really interesting is
Speaker 1: when we zoom in one more level and really examine
Speaker 1: what dreamscapes look like like in detail. And I'm not
Speaker 1: asking about what's in the dream script here, but if
Speaker 1: you look very closely across thousands of dream reports, you
Speaker 1: can ask what is not in the script. So I
Speaker 1: want to return to a question I posed at the beginning,
Speaker 1: which is that we live in a society where we
Speaker 1: are constantly hunched over our cell phones and our laptops.
Speaker 1: How come these essentially never show up in our dreams?
Speaker 1: Isn't that weird? And even in the era before computers,
Speaker 1: back when people read a lot more books, how come
Speaker 1: no one sits around reading books in their dreams. Why
Speaker 1: can't you even see any text in your dreams? Why
Speaker 1: do you spend so much time writing stuff down in
Speaker 1: real life but you never can write stuff down in
Speaker 1: a dream. How come you never do math in a dream,
Speaker 1: like calculating a tip for a restaurant bill, Even if
Speaker 1: that comes up in a dream plot, it feels totally
Speaker 1: impossible to get the right answer. Well, all of this
Speaker 1: serves as a big clue into the networks that are
Speaker 1: active during a dream, and this is pretty well worked
Speaker 1: out with brain imaging now, although anyone who is being
Speaker 1: very observant probably could have guessed this all even a
Speaker 1: century ago. What reading and writing, and cell phones and
Speaker 1: computers all have in common is that they require the
Speaker 1: use of a network in the brain that we summarize
Speaker 1: as the executive network, which involves a lot of activity
Speaker 1: largely distributed in the frontal lobes and the parietal lobes,
Speaker 1: and you need this for rule based problem solving and
Speaker 1: for making decisions when you've got a particular goal in
Speaker 1: front of you that you're trying to solve. And the
Speaker 1: key is that activity in the executive network is reduced.
Speaker 1: I'll just say it's shut down while you are dreaming,
Speaker 1: so you're not able to read and write and launch
Speaker 1: an app on your cell phone screen and so on,
Speaker 1: because that work requires the executive network, and that network
Speaker 1: is off duty for the night. But what is on
Speaker 1: is an network we summarize as the default mode network,
Speaker 1: which is what kindles to life when you shut your
Speaker 1: eyes and you're not involved in gathering information and acting
Speaker 1: on some other task. So this is called the default
Speaker 1: mode network, but many scientists are renaming this the imagination
Speaker 1: network because this is what lets your storehouse of experiences fly.
Speaker 1: You can piece ideas together and come up with new
Speaker 1: hypotheses and thoughts, and this is what's firing on all
Speaker 1: cylinders when you dream. So the executive network has reduced,
Speaker 1: the imagination network is enhanced, and this is what gives
Speaker 1: dreams their very untethered character. There are other clues you
Speaker 1: can also gather from looking at detailed dream reports, which
Speaker 1: is that sometimes objects will turn into other objects, but
Speaker 1: they're always related in some way. What I mean is
Speaker 1: you might have your bicycle turn into a motorcycle, or
Speaker 1: your small house becomes a mansion, or the cafeteria becomes
Speaker 1: a restaurant, or the hammer becomes a screwdriver, but you
Speaker 1: don't find the bicycle turning into a restaurant or your
Speaker 1: house turning into a hammer. What does that tell us? Well,
Speaker 1: under the hood, we have what are known as semantic maps,
Speaker 1: and more than associations, which I mentioned before, semantic maps
Speaker 1: refer to the way that all the stuff in your
Speaker 1: brain is laid out in terms of relationships between concepts.
Speaker 1: For example, in your semantic map, you have the concept
Speaker 1: of an animal, which might include categories like mammals and
Speaker 1: birds and reptiles and so on, and within one of
Speaker 1: those categories you might have more specific concepts like dog
Speaker 1: and cat and eagle and salmon and snake and frog
Speaker 1: and so on. Things are laid out in your brain
Speaker 1: based on their conceptual meaning. And what we find is
Speaker 1: that dreams follow the semantic maps. In other words, they
Speaker 1: stay local in the little clusters of the maps. So
Speaker 1: this is why you see the bicycle turning into the
Speaker 1: motorcycle because they're both forms of transportation, but not into
Speaker 1: the screwdriver, which is a tool and in a totally
Speaker 1: different category. These things live in different little neighborhoods of
Speaker 1: the semantic map. So again, a careful look at dream
Speaker 1: reports tells us important clues about what is going on
Speaker 1: under the hood, and that tells us that while the
Speaker 1: themes are universal strife and falling and attempting to do
Speaker 1: something over and over, the details are filled in with
Speaker 1: the specifics of your semantic maps. And this all brings
Speaker 1: me back around to a question I had since I
Speaker 1: was a kid about whether dreams are experienced in black
Speaker 1: and white or in color. Now. When I was a child,
Speaker 1: I remember at some point that my parents told me
Speaker 1: that we dream in black and white, and I was
Speaker 1: confused by this because I didn't seem to dream in
Speaker 1: black and white. As far as I could tell, my
Speaker 1: dreams were in color, so I thought I must be
Speaker 1: somehow assessing that incorrectly. Because they were both very smart
Speaker 1: and educated. My mother was a biology teacher, my father
Speaker 1: was a medical doctor, and as I grew older, I
Speaker 1: asked my friends about this, but I couldn't find anyone
Speaker 1: who thought that their dreams were not in color. Now,
Speaker 1: because I genuinely knew that my parents were brilliant, I
Speaker 1: thought maybe there was something they knew that I didn't like.
Speaker 1: Maybe we were dreaming in black and white but didn't
Speaker 1: realize it. And then I found several large scale surveys
Speaker 1: that reported what my parents had said, that most people
Speaker 1: dream in black and white. One study was from nineteen
Speaker 1: fifty eight and they said only nine percent of people
Speaker 1: dream in color, and a paper in nineteen forty two
Speaker 1: reported that only ten percent claimed to frequently or very
Speaker 1: frequently dream in color, and a report in nineteen fifty
Speaker 1: one had the highest percentage. They said that twenty nine
Speaker 1: percent of dreams are in color. But even this didn't
Speaker 1: make things clear what was going on, because dream reports
Speaker 1: from earlier, like Freud's reports of dreams in nineteen hundred,
Speaker 1: often had explicit color descriptions in them. So somehow it
Speaker 1: seemed to be only my parents' generation that dreamed in
Speaker 1: black and white. And it turns out if you run
Speaker 1: the study now, almost everyone says they dream in color.
Speaker 1: As you may have guessed by now. The hypothesis on
Speaker 1: this is that people were influenced by watching black and
Speaker 1: white television and black and white movies and black and
Speaker 1: white photographs, and once the technology changed to color, then
Speaker 1: so did dreams. I'm putting a very nice paper by
Speaker 1: Eric Schwitzkeebel on my site that compiles all these studies
Speaker 1: through the years and the change in the reports. Again,
Speaker 1: this demonstrates that the content of our dreams has to
Speaker 1: do with the experiences that we have now. I'll tell
Speaker 1: you an interesting side note on this. I happened to
Speaker 1: live in California and during COVID, everyone in my neighborhood
Speaker 1: wore masks, and it was a very weird time, and
Speaker 1: so we rarely saw other human beings for a couple
Speaker 1: of years without everyone being in masks. And one of
Speaker 1: the things I remember from that time was that we
Speaker 1: would sometimes watch a movie on TV, and it was
Speaker 1: so shocking that people in the movie would push their
Speaker 1: way through a dense crowd and sit so close to
Speaker 1: their friends and the people they were talking with, and
Speaker 1: they were indoors with such density. And it became in
Speaker 1: twenty twenty so noticeable and so shocking when we were
Speaker 1: in the middle of COVID. Interestingly, it's a little hard
Speaker 1: to remember that now, but I remember it well because
Speaker 1: I was taking careful notes on what was going on
Speaker 1: with my dreams during this time, and specifically, since my
Speaker 1: real life involved the very thinned out crowds and everyone
Speaker 1: in masks, did that show up in my dreams? And
Speaker 1: the answer was is no. The thing that struck me
Speaker 1: the entire time during lockdown is that my dreams were
Speaker 1: totally normal. In my dreams, I was at a big
Speaker 1: party and there were lots of people around, and no
Speaker 1: one ever had masks in my dreams, which struck me
Speaker 1: as weird when I would wake up. Why didn't my
Speaker 1: dreams reflect my daily experience? Now, this is just a
Speaker 1: single person's report, and I didn't think to study this
Speaker 1: carefully at the time by doing a big online survey
Speaker 1: of everyone. But if it's generally true that other people
Speaker 1: were having these very salient daily experiences of lockdown and
Speaker 1: masks and yet it wasn't appearing in their dreams, the
Speaker 1: only interpretation I can make is that our dreams reflect
Speaker 1: pathways that get laid down over our youth when we're young.
Speaker 1: And if that's the case, then maybe we could still
Speaker 1: find some black and white dreaming among older people. Now,
Speaker 1: in other words, maybe you'd still see some of that now,
Speaker 1: even though those people have been watching color television for
Speaker 1: sixty years. Now, with all the things on my plate,
Speaker 1: I'm not going to have time to pull off that study.
Speaker 1: But I would love it if listeners could ask their
Speaker 1: oldest living relatives they a parent, or grandparent or great grandparent,
Speaker 1: how they dream and determine if anyone still dreams in
Speaker 1: black and white and what their age is. Okay, so
Speaker 1: that story of black and white dreaming correlated with black
Speaker 1: and white television. That seems like a clean story, But
Speaker 1: there's one thing that still bugs me about it. Although
Speaker 1: television and movies were in black and white, obviously the
Speaker 1: world wasn't. When my parents walked outside, they saw green
Speaker 1: trees and blue skies and red cardinals and yellow sunflowers
Speaker 1: and so on. So why didn't their dreams reflect that? Well,
Speaker 1: there are two things to say here. First, not everyone
Speaker 1: dreamed in black and white. Instead, it was between let's
Speaker 1: say seventy to ninety percent. So had I been alive
Speaker 1: in the nineteen fifties, I would have studied the issue
Speaker 1: of how many hours of television people watched each day,
Speaker 1: and perhaps some measure of how many black and white
Speaker 1: movies they saw on how many newspapers with black and
Speaker 1: white photos and so on, and correlated that to whether
Speaker 1: or not they had black and white dreams. Second, I
Speaker 1: have a totally speculative hypothesis. I don't have any evidence
Speaker 1: for this, but I'm going to say it anyway. What
Speaker 1: if some part of the brain knows, at least in part,
Speaker 1: that dreams are like a fake movie, and in that
Speaker 1: way it takes on the property of fiction, which in
Speaker 1: those days was black and white. Because note that even
Speaker 1: when you're in the middle of a movie, some part
Speaker 1: of your brain still knows you're watching a movie. And
Speaker 1: this is why when the train comes at the camera,
Speaker 1: you don't actually duck and scream. So even though we're
Speaker 1: compelled by fiction, we don't fall for it completely. Could
Speaker 1: it be that to the brain, dreams are more like movies.
Speaker 1: I don't know, because I missed that era, so the
Speaker 1: opportunity seems gone to study that. But I'm wondering if
Speaker 1: we're going to have another shot at studying this question
Speaker 1: once virtual reality becomes ubiquitous and pervasive, and whether a
Speaker 1: big chunk of the population will report dreams that are
Speaker 1: more like synthesized virtual reality worlds than like our daily life.
Speaker 1: To me, this would shed light on the mystery of
Speaker 1: the black and white dreams and the details by which
Speaker 1: your dreams are determined by your experiences in the world. Now,
Speaker 1: there's still lots of stuff that I think we don't understand.
Speaker 1: One is why we can have false, implanted memories inside
Speaker 1: a dream. This is something I've wondered about for years.
Speaker 1: For example, I had a dream many years ago about
Speaker 1: my brother's wedding and he was yelling at me and saying,
Speaker 1: I can't believe you said that to Jenny and ruined
Speaker 1: my wedding, and I felt horrible. I felt as guilty
Speaker 1: as I ever felt. Why did I do that? Why
Speaker 1: was I so insensitive? And then I woke up. As
Speaker 1: it turns out, my brother had a lovely wedding that
Speaker 1: went just perfectly, and I of course never said anything
Speaker 1: bad to his bride, my lovely sister in law Jenny. Ever,
Speaker 1: there was never trouble of any sort there. So why
Speaker 1: did I fall for the false memory? Why couldn't I
Speaker 1: access my real memories of the wedding while I was
Speaker 1: inside the dream? In other words, the issue is that
Speaker 1: not only did I have a false memory. But also
Speaker 1: I had no access to my real memory of the wedding.
Speaker 1: One set of memories was replaced by another. And this
Speaker 1: is what freaks me out, not just about dreams, but
Speaker 1: about our sense of reality. We buy whatever our brains
Speaker 1: serve up to us at every moment. We buy the
Speaker 1: plot of a dream completely. And by the way, this
Speaker 1: is one interpretation of what happened in schizophrenia. The way
Speaker 1: psychiatrists used to describe this about a century ago is
Speaker 1: that psychosis is essentially an intrusion of the dream state
Speaker 1: into the waking state. So the next time you see
Speaker 1: a man talking to himself on the street and having
Speaker 1: an argument with someone who is not there in front
Speaker 1: of him, interpret it through this lens that he is
Speaker 1: having an awake dream, and you might understand what's happening
Speaker 1: in a fresh way. So what we see here, and
Speaker 1: what we've seen in many of these episodes, is that
Speaker 1: we accept whatever reality is served up to us. And
Speaker 1: by the way, I think this is why literature works
Speaker 1: with our species, because we can so easily adopt a
Speaker 1: different reality. We can read a book and we laugh
Speaker 1: and we weep. We are effortlessly deluded. And to understand
Speaker 1: this I think we shouldn't use the term suspension of disbeliefs.
Speaker 1: It's the wrong term because an applies that disbelief is
Speaker 1: the standard disbelief is the normal operating mode. In fact,
Speaker 1: it might be just the opposite. Our brains are perfectly
Speaker 1: willing to accept whatever they are fed. Now, I want
Speaker 1: to hit one more question in today's episode, which is
Speaker 1: where is dreaming headed? Would it be possible to read
Speaker 1: out the content of somebody's dreams? Well, if you happen
Speaker 1: to have heard my episode number twenty seven, you'll know
Speaker 1: that the answer is already yes, at least to some degree.
Speaker 1: Different research groups have been working since at least twenty
Speaker 1: eleven to see if they can measure brain activity in
Speaker 1: the visual cortex to assess what somebody is seeing in
Speaker 1: front of their eyes. In other words, if you're looking
Speaker 1: at a building, there's a different activity in your visual
Speaker 1: cortex than if you're looking at a puppy or a
Speaker 1: cup of coffee and so on, and so the research
Speaker 1: question is can you tell what a person is seeing
Speaker 1: just by measuring the pasterns in their visual cortex? And
Speaker 1: the answer is that you can pretty well tell what
Speaker 1: somebody is seeing this way. After that research came out,
Speaker 1: people realized we might be able to measure dreams because
Speaker 1: dreams are activity in the primary visual cortex. Dreams are
Speaker 1: experienced as visual because it's activity in the visual cortex,
Speaker 1: and your brain understands that as visual experience. So Yuki
Speaker 1: also Comma Tani and his colleagues published a paper a
Speaker 1: few years ago in which he took this same approach.
Speaker 1: He had people look at a bunch of pictures and
Speaker 1: watch a bunch of videos while they were in the
Speaker 1: brain scanner, and then he used machine learning to decode
Speaker 1: how the picture out there corresponds to the activity patterns
Speaker 1: in the brain. And now you let people go to
Speaker 1: sleep in the scanner, and you measure their visual cortex,
Speaker 1: and you use the machine learning model to decode what
Speaker 1: that activity would correspond to, in other words, what they
Speaker 1: were presumably seeing in their dream. And once the machine
Speaker 1: learning model gives an answer, then you can make a
Speaker 1: little video reconstruction of their dream, and you can watch
Speaker 1: what presumably was the experience for the dreamer, albeit with
Speaker 1: very low resolution. Now, when you're decoding pictures or videos,
Speaker 1: it's easier to know if you're getting it right. When
Speaker 1: you're decoding dreaming, it's harder to know for sure that
Speaker 1: you got the right answer. You have to wake up
Speaker 1: your participants and say, hey, what do you remember, and
Speaker 1: then you compare that to what you think you might
Speaker 1: have decoded. But even with those caveats, this gives the
Speaker 1: rough start to a dream decoder that could tell you
Speaker 1: what you were dreaming about. And presumably this will only
Speaker 1: become higher resolution with time. So it maybe that in
Speaker 1: the future we are able to know what you dreamed
Speaker 1: even if you can't remember it. You could keep a
Speaker 1: digitized dream diary that way, or you could share your
Speaker 1: dreams with a girlfriend or boyfriend, or less likely, a
Speaker 1: dream could be used in a court of lossome day.
Speaker 1: Who knows where this will all go, but we can
Speaker 1: imagine that in two hundred years from now, dreams may
Speaker 1: be a very different sort of thing than the entirely
Speaker 1: private experience that we enjoy now. So let's wrap up.
Speaker 1: To my mind, the biggest issue that freaks me out
Speaker 1: about dreams is this issue that we believe patently impossible situations,
Speaker 1: and we accept false memories even when they contradict events
Speaker 1: that we know to be true in waking life. This
Speaker 1: represents a deeper question about why we can be so
Speaker 1: easily fooled, but many other questions about dreams can be answered.
Speaker 1: In the meantime, we're in a moment of using the
Speaker 1: tools of neuroscience to tie specific details of the biology
Speaker 1: to the experience of dreaming. We still have a lot
Speaker 1: long way to go, but some promising leads can come
Speaker 1: from the way that dream content changes with drugs. For example,
Speaker 1: dreams can be made more vivid and frightening by drugs
Speaker 1: that affect the dopamine system or by alkaloids. Antidepressants tend
Speaker 1: to reduce the amount of dream sleep. Medications to reduce
Speaker 1: epileptic seizures also seem to reduce nightmares. So we can
Speaker 1: imagine in the near future having systematic studies to work
Speaker 1: out the effects of different drugs on dream content, and
Speaker 1: to do this in conjunction with brain imaging, and we
Speaker 1: might be able to further nail down the relationships between
Speaker 1: dream content and specific bits of the dream generation network.
Speaker 1: And beyond drugs, we can also look to disease because
Speaker 1: specific problems lead to the loss or impairment of dreaming.
Speaker 1: People can lose dreaming with injuries to the inferior paride
Speaker 1: lobe on either side. Patients with certain forms of dementia
Speaker 1: report bland dreams, involving less aggression and less narrative complexity
Speaker 1: and less emotional content. So by looking at changes to
Speaker 1: the brain and corresponding changes in dreaming, we can better
Speaker 1: map out the landscape of what is involved. And fundamentally,
Speaker 1: studying dreaming may help us to comprehend consciousness. Why because
Speaker 1: there are so many similarities between rem sleep and the
Speaker 1: awake conscious state. Now there are major differences as well,
Speaker 1: but it's important to note that we find both waking
Speaker 1: life and dreaming equally compelling and believable, which tells us
Speaker 1: that all you need to do is strike the right
Speaker 1: notes on the neural piano and you have your totally
Speaker 1: believable experience. But what would be cool is if there
Speaker 1: were something like consciousness during a dream state that was
Speaker 1: even close to our daily, normal conscious experience. And that's
Speaker 1: what we're going to talk about next week. We're going
Speaker 1: to talk about the very rare circumstance when you are
Speaker 1: dreaming and you realize that you are dreaming, and you
Speaker 1: take control of your dream and become an active director
Speaker 1: of the plot. You are essentially conscious but living inside
Speaker 1: the walls of your skull. So join me next week
Speaker 1: as we sail into the very strange and amazing territory
Speaker 1: of lucid dreaming. Go to eagleman dot com slash podcast
Speaker 1: for more information and find further reading. Send me an
Speaker 1: email at podcast at eagleman dot com with questions or discussion,
Speaker 1: and check out and subscribe to Inner Cosmos on YouTube
Speaker 1: for videos of each episode and to leave comments. Until
Speaker 1: next time, I'm David Eagleman, and this is in our
Speaker 1: car is miss