The Joy of Why - Why and How Do We Dream?

Episode Date: August 24, 2022

Dreams are subjective and fleeting, but laboratories have developed ways of getting into the minds of people while they are dreaming. In this episode, Steven Strogatz speaks with sleep researcher Antonio Zadra about how new experimental methods have changed our understanding of dreams.

Daniel and Jorge Explain the Universe is a podcast about, well, everything in the universe. Do you want to understand what science knows about how the universe began and what mysteries remain? Are you curious about what lies inside a black hole and if we'll ever know? Daniel is a physicist working at CERN who actually knows what he's talking about and Jorge asks all the questions that pop up in your mind as you listen to make sure everything is crystal clear. Listen to Daniel and Jorge Explain the Universe on the iHeartRadio app, Apple Podcasts, or wherever you get your podcasts. I'm Steve Strogatz, and this is The Joy of Why, a podcast from Quantum Magazine that takes you into some of the biggest unanswered questions in math and science today.

In this episode, we're going to be talking about dreams. What are dreams exactly? What purpose do they serve? And why are they often so bizarre? We've all had this experience. You're dreaming about something fantastical, some kind of crazy story with a narrative arc that didn't actually happen with people we don't necessarily know in places we may have never even been. Is this just the brain

trying to make sense of random neural firing? Or is there some evolutionary reason for dreaming? Dreams are inherently hard to study. Even with all the advances in science and technology, we still haven't really found a way to record what someone else is dreaming about. Plus, as we all know, it's easy to forget our dreams as soon as we wake up, unless we're really careful to write them down. But even with all these difficulties, little by little, dream researchers are making progress in figuring out how we dream and why we dream. Joining me now to discuss all this is Dr. Antonio Zadra, a professor at the University of Montreal and a researcher at the Center for Advanced Research

in Sleep Medicine. His specialties include the study of nightmares, recurrent dreams, and lucid dreaming. He's also the co-author of the recent book, When Brains Dream, Exploring the Science and Mystery of Sleep. Tony, thank you so much for joining us today. Thank you for having me. I'm very excited to talk to you about this. So let's start with thinking about the science of dreams as you and your colleagues see it today. Why are dreams so hard to study?

One of the biggest difficulties in studying dreams is that we don't study dreams directly. What we study are dream reports, either what people tell us they dreamt about or what they write down. So much of the work is done, if you want, after the fact. Even when dreams are studied in the laboratory, you can look at what's going on in the brain or body while the person is dreaming, for instance, in REM sleep. But what they are dreaming about at that moment, we usually can only know once we wake up the individual and he or she tells us about the dream they were experiencing. So dreams are a private subjective experience, but these challenges in studying dreams aren't unique to dreams. You find them in many other areas. For instance, in the study of pain. When we study pain,

you can't have a machinery that allows you to see the pain. We infer it from, for instance, the adjectives people use to describe their pain. Is it a burning pain, a throbbing pain, a piercing pain? And then where it is localized, people say it's in my lower back, it's in my legs. But again, these are private subjective experiences. And these challenges are true of many subjective states that human beings have. Such an interesting analogy. It never occurred to me to think of it like that. Let me try asking you to define dreams. I know this is going to be a tough one because in any scientific field, giving a definition is often, say, what is life, you know. But let's try. What is a dream? What are the characteristics of dreams? Unfortunately, there's no universally

agreed upon definition of dreams. So for some researchers, dreams are elaborative, narratively driven creations of the brain that are located somewhere, that have temporal dimensions, that involve emotions, often some form of social interaction. And so these are closer to the kinds of dreams people often will recall when they awaken in the morning, typically out of REM sleep. But for other researchers, dreaming refers to any form of thinking or perceptual elements that are experienced during sleep. And so this is often referred to as sleep mentation. And so this is often referred to as sleep mentation. And so depending on how you can define them, dreams can be these relatively isolated images or thought patterns.

They can be geometric images that dance before your eyes as you are falling asleep. Or they can be these rich, narratively driven, immersive experiences. these rich, narratively driven, immersive experiences. And depending on how you define them, you're probably studying various elements or various forms of expressions of dreams. But then again, the same question can arise if we ask, how do you define consciousness? What constitutes consciousness? And so there are minimal forms of consciousness, like when you're sort of groggy and just who are blind, deaf, or have restricted sensory modalities, paralyzed, they also have consciousness. But again, the range of their subjective experiences vary tremendously. And I think the same holds true for dreams. Do we know how our brains create the images associated with dreams?

The short answer is no. And the more nuanced answer would be we're slowly getting there. Because dreams can occur across different stages of sleep and that what brain areas are activated across these different sleep stages vary greatly. And as does the general neurochemistry of the brain, it leads to sort of conflicting views. But we know, for instance, if we take the most vivid dreams, those that tend to occur in REM sleep, well, we know that the secondary visual areas are activated. And that makes sense because dreams are highly visual experiences. So the primary visual areas aren't activated for the

simple reason that your eyes are closed. There's no visual input entering through your retina. So your brain is creating this. We also know that your motor cortex, the part of your brain that controls motor movement, is activated. And that probably is one of the things that helps give us the impression that we are moving through a real three-dimensional physical world in our dreams. We know that the limbic system is also activated in the amygdala, which probably helps explain why many dreams contain various degrees of emotions. So we are emotionally engaged in them. And we know that parts of the prefrontal cortex, the part of your brain that sits about an inch or so above your eyes, is deactivated. And so this also explains why

these areas of the brain are important for what we call executive functions, judgment, critical thinking, planning, things that are general features of our dreams. What is more of a mystery is how the brain goes about selecting specific images and how it weaves them together and why. What about the aspect of dreams and memory that has to do with memory of events during waking life? It's been proposed that dreams do something to help us remember. But what? I mean, what's the right statement? What do we think today? Maybe to take a step back, we know that sleep plays a very important role in different forms of memory. So we know, for instance, that different stages of non-REM sleep help consolidate our memories. So this is more similar to if you're learning facts and you want to remember facts. In REM sleep, we know that

our memories are more associated to our knowledge of the world, our semantic understanding of the world. So it's not so much about facts, but when and how do you use these facts. So non-REM sleep is sort of more important to make you smart if you want, and REM sleep is what allows you to be a little bit wiser. Now we think that dreams may play a role in some of these processes. We know that unlike some of the conceptualizations of dreams from the 70s and 80s from neurophysiologists, dreams are far from random. Our brain clearly shows a preference for incorporating emotionally salient experiences from our waking life, but then it does things that it cannot do in wakefulness. Namely, it takes that experience and searches through

all of its memory banks for weakly associated experiences that tie into it. And why would it do that? Well, that's how the brain goes about understanding the world around it. For every two hours we spend awake, it appears that the brain needs to shut off all external input for an hour to make sense of what we've experienced. And that is what sleep is, in part. One idea is that dreams play a role in this by going, well, we've experienced this today. What usefulness might this have in the future? Well, there's this famous saying that memory is not about the past, memory is about the future. And what is meant by that is that the reason you can remember things is not so that when you're retired and having a drink with an old friend on your porch. You can go, oh, remember when we were kids and we

took that ride out to the lake. That's not why we've evolved to have capacities for memory. Memory is what allows you to, when you're driving down the road and you look in your rear view mirror and you see these flashing blue and red lights to go, oh yes, that's an emergency vehicle or a police car. I need to move to the right and let it pass. It's what allows you to predict and understand what unfolds before you and to make the correct reactions and interpretations of the world around you. And so dreams take in what we've experienced, and this is probably due to the particular neurochemistry of the brain when it is asleep, specifically in REM sleep, it seeks out weak associations of this. So your brain

is sort of opening drawers and goes, does it fit with this? Does it fit with this? And depending on how you react in your dreams, your cognitive reactions, your emotional reactions. Your dreaming brain uses information to say, yes, this is a useful connection. Yes, this is a plausible link. And this is what helps us build our understanding of the world. So when we wake up, we literally wake up with a somewhat clearer day-by-day understanding of ourselves and the world around us. The other thing that I think people often take for granted or don't give enough weight to is that when we dream, the brain does two amazing things. It does lots of amazing things, but two in particular. A, it creates you. You have a body, you see things, your dreams are

often from a first-person perspective, but it also creates your dream environment, including everyone you meet. I mean, you got to keep in mind that you are in your bed asleep. You're not hearing things from the outside world, you're not seeing things, yet you're immersed in this environment where you are talking to people, where you are hearing them speak back. And even in phenomena such as lucid dreams, dreams in which you know that you are dreaming, you have little idea of what happens next in your dream. Your brain is keeping this information from you. So in a lucid dream, you might make a dream character appear, for instance. But then if you ask them a question, who are you? What are you doing in my dream? What is the most important thing I should remember out of this? You have no idea what the character

is going to say. But your brain does. Your brain is what is creating this character. And so when people say, oh, you can do anything in your dream, or you are the producer and main actor of your dreams, I don't think that's correct. You're not at the wheel of the dream construction process. Your brain is, and your brain intentionally keeps much of the information of what's going to be happening next and how things unfold away from you. Why? Because it needs to know how you're going to react to this ever-evolving narrative, which dreams also have all kinds of shifts in their structures, you know, in times of place and locations and transformations. That's part of their inherent bizarreness. But this is a reflection of all

the weak associations that your brain is exploring, but it's also trying to see how do you react to that. And so we think that, again, dreams play a role in our understanding of the world, and our understanding of the world is largely based on what do we remember of it and what sense do we make of these events. And much of this is semantically based. You know, if I say I had an accident, the word accident has all kinds of associations and meanings for us. Same things for objects, forests and a glass and wine. All of these things have different meanings to us. And so when you dream of a glass, there is no physical glass in front of you. Your brain is creating that, and you have all kinds of metaphors and associations to that simple object. Now, if we think about interpersonal relations

and things infinitely more complex, all these associations get even greater and more complex as dreams unfold. You've gone in so many interesting directions there. I mean, the one that's really hitting me is this philosophical one that is so profoundly mysterious where you use phrases like, your brain is keeping certain things from you. And it makes me wonder wonder who's the you in that sentence. Because most people think of their brain as themselves, but clearly, there's something more subtle going on. Absolutely. And some people argue that the same can be argued for waking

consciousness, and that's debatable. But I think that when it comes to dreams, this unique form of altered consciousness, that's a lot less debatable. A very concrete example of how also your brain uses your reactions, your thoughts, to then how they feed back into how the dream evolves. I can give you two examples. Sometimes people have these delightful flying dreams. and so they're soaring through the air and looking down at the landscape and go, this is absolutely marvelous. And then the thought occurs to them, how is it that I am flying? And as soon as that doubt appears, that question appears, what almost invariably happens is that they start falling to the ground. And so dreams are this continual interplay between what the brain is, the environment it's putting you in, and your reactions to it. And that, I think,

is one of the key aspects of the functions of dreams. I mean, there are many things sleep does that we don't have to experience for it to do. So it can consolidate information, it secretes hormones, it regulates many things, and all of that is done without a conscious experience. So one question is, why do we have to experience dreams for the brain to sort of do this memory processing work? Well, I think that we need to experience it because the brain needs to dream to make sense of the world. It needs to understand how you react to the dream it's constructing and how the dream environment, which again, because it's created from your brain, is your conception of the world, your conception of your parents, of your siblings, of your work,

of your self-worth, of your doubts, how does this react to what you think and do in your dreams? And this constant ever-evolving interplay between you and the dream world, which is kept hidden from you, is all useful for your brain to make sense of your waking experiences. And so, yeah, so the you in there is really just a small part of what your brain is doing in the dreams. And again, I really think there's compelling evidence that your dreaming brain keeps much information hidden from you, if you want, and that we even see this in, as I mentioned, in lucid dreams. Good. Let's go to lucid dreams, because I mentioned there were several directions that come

very naturally from what you spoke of a few minutes ago. So lucid dreams would be one. The other is you mentioned very briefly something about neurochemical aspects of dreaming and how that's tied into the strange associations and stuff like that. So I'd like to get to that too, but why don't we start with lucid dreaming and the related theme of dream engineering. For people who haven't heard of lucid dreaming, tell us again, what is that? Lucid dreams are essentially dreams in which the person becomes aware that he or she is dreaming while still in the dream. Then once people have this awareness, they can use this knowledge that they are dreaming

to try to manipulate or if you want, influence how the dream unfolds. So that in essence is what lucid dreaming is. And lucid dreaming has many interesting features, but one of them is that it opens up a whole new window into the study of dreams in the sleep laboratory. Is it something that people do sort of naturally and automatically, or do you have to be taught how to do it? Some people report having had lucid dreams all their lives, so as far back as they remember. These are a minority, a small percentage of the general population, and some of them are

actually surprised when they learn that not everyone has this ability. Most people, about half of the population, will report having had at least one lucid dream in their lives, often when they were young children or adolescents, and maybe about 20% of people will say that they have about one lucid dream or more per month. Now there are these people who have lucid dreams almost nightly on a weekly basis, and you can study them in the laboratory. And when I say it opens up a whole new window, and this has now been done in over a dozen labs across the world, is that believe it or not, lucid dreamers can, while asleep and dreaming, communicate to you, the experimenter in the lab, that they are in fact dreaming. And they can communicate by means of volitional eye movements.

There's the sleep paralysis when we are in REM sleep, but there are many parts of our bodies which are not paralyzed. You know, your respiratory system, your tongue, and your eyes. And again, because even if you move your eyes, you're not going to injure yourself. You get up and jump out of bed while you might crash headfirst into a wall. So the paralysis is just sufficient to keep us relatively immobile. Same thing when you see, you know, your cat or dog twitching about, the keys that they don't move. But if you watch even your dog in REM sleep, you will see their eyes darting back and forth or a young child under their closed eyelids. Now lucid dreamers can use this feature by doing these predetermined extreme left right left right left right eye movements in their

dreams and they can get picked up by these electrodes that monitor the actual eye movements of the person sleeping in the lab under their closed eyelids. So when you're looking at polysomnographic recordings of a lucid dreamer, you can see these sort of random eye movements from REM sleep. And all of a sudden, you'll see these extreme left, right, left, right eye signals. And that is the lucid dreamer telling you, hey, I know I'm in a lab. I now know I'm dreaming. And here's signal one. Not only that, now I'm going to carry out the task that you asked me to carry out in my dream.

And these tasks can be singing, counting to 10, clenching your fist, even having sex. And when you are done, you send a second signal. sex and when you are done you send a second signal. And so now researchers know that between signal one and two the person was doing singing or they were running or doing squats and then you can look at well what's going on in the brain when a person sings or counts or has an orgasm. And so you sort of start getting around the problem of having to wait till the person wakes up to ask them their dream because these people are sort of time stamping when they begin and end specific activities in their

dreams. That's really quite to me even to this day mind-boggling to have a participant sleeping in a sleep lab, fast asleep in REM sleep, dreaming, communicating with you. This has allowed researchers to learn more about how the body and the brain responds to different forms of dream content. And by and large, what these studies tell us is that certainly your brain, and to a lesser extent your body, respond to dreamt activities as you would expect them to respond if you were doing them while awake. Now last year, this kind of research got taken a step further, and this gets even more science fiction-like. Two-way communication with lucid dreamers was demonstrated in multiple labs across

the world, some of them based in Europe, in the States. And so here they not only had lucid dreamers do these eye signals to communicate they were lucid, but then the experimenters could use external stimuli, a bit like what some of the researchers like Alfred Murray back in the 1860s tried to do to influence dreams. So they could present for instance this repeated question at a low intensity. You've got to find a sweet spot where it might get incorporated into the person dreams and not wake them up. So they might ask eight minus six, eight minus six, or they may flash some lights over their closed eyelids in the hope that these visual stimuli get incorporated. In the example of the eight minus six, what the people do to answer is two

series of eye movements to say the answer is two. And so these studies you could do with eye movements, but also you could ask them yes, no questions. And so you might ask them, do you like chocolate? And if the answer is yes, the person can try smiling, like a huge smile in their dream. And if you're monitoring muscles, facial muscles, you can actually see slight contractions around the lips. So you know the person is smiling, which is an answer yes. If you say, you know, do you like crochet? And the answer is no. The person can really frown like with their eyebrows in their dream. And again, if you have electrodes monitoring these facial muscles, so muscles around the eyebrows of the person, you will see a discharge and that is an answer no. So these

are rudimentary steps, but that allow not only dreamers to communicate with external experimenters in the lab, but you can also have experimenters ask questions to the dreamer and then have this two-way communication going on. So this is proof of concept that two-way communication with lucid dreamers is possible, and it opens up a whole new window to being able to actually tell people to do specific things in their dreams and look at how the brain and body respond. So if you stare at an object, if you yell, if you're listening to, you know, glorious music, if you're at a concert, if you try to read. So it opens up a window to a whole new dynamic of studying how dreams unfold and how our brains and bodies are involved in this process.

So all of this sounds like maybe science fiction, but it's actually science. It's, well, it's an amazing thing that you're telling us. Let me ask the sort of due diligence question that I'm sure some of our listeners have, which is, could it be a sham? Could people be faking it? Now, I'm sure, you know, scientists doing this are responsible and know what they're doing. But just tell us some of the evidence that makes it clear that these people truly are in REM sleep. They're not sort of playing games with us, being awake, but pretending to be asleep. How do we know they're really asleep? One of the key features of REM sleep is this motor paralysis. And you can monitor the motor paralysis, and this has been done ever since sleep physiology has been studied in the labs, with a few electrodes, including some

that are put under your chin. And you have a muscle under your chin that usually shows some baseline level of motor activity, even though you're not moving your chin. But this goes down to zero in REM sleep. This is not something you can do volitionally. It's something that you only observe in REM sleep. And in these studies, these indices of muscle paralysis are intact. There's also different kinds of reflexes that are only inhibited in REM sleep. One of them is called this H-reflex, and if you test for those, you also see their inhibition. So by all criteria, which is either by the kinds of eye movements that they are making, by their EEG signatures, and by this muscle atonia that is only seen REM sleep, all of these studies show

that these participants are in unequivocal REM sleep. So they are not faking that. Now, other people could certainly fake that at home and say, oh, I'm doing XYZ. And not only is that possible, I think it's actively being done when I examine some YouTube videos and so on, but for these studies that I was mentioning right now, there was really great care in showing that the examples that were kept for the data are the ones really where there was no doubt on any of these parameters, as assessed by outside dream specialists looking at these electrophysiological signals that this really corresponds to unequivocal REM sleep. Are you in your lab studying lucid dreaming? We have and we've also studied outside of the lab clinical applications of lucid dreaming

including for the treatment of nightmares. But I'm particularly interested in how lucid dreaming can be used to better understand how the brain goes about creating dream characters. So for me personally, dream characters is one aspect of dreams that fascinates me the most. Again, because dream characters not only say and do things that are unexpected to us. So again, when we ask a dream character something and they answer in a way that's surprising us, because our brain creates them, I really think we are surprising ourself in a very real sense. Dream characters also act and behave and respond in ways as if they had their own consciousness. Now we know they don't, probably, because they're just a creation of your figment of imagination.

But when you meet your ex and he or she is really mad at you, they look really mad. They have facial expressions about how angry they are at what you have done, or if you fall madly in love, or if you're being pursued by an aggressor. These people's expressions of emotions, how they speak, their intonations, all are consistent with what we experience during wakefulness with people who are conscious entities. And so some of them are two-dimensional like extras in a play, but other characters really give us this feeling that they are sentient beings. If just by the way they look at you, you have a feeling of being looked at by someone who really has their own perceptions of the world. And so you can use lucid dreaming to explore this. So for instance, I've been collaborating with an artist in England, Dave Green, who uses lucid dreams to

create artworks. And I've had him ask dream characters to create artworks for him. Now, when he asked characters, you know, in his lucid dreams, could you do a drawing for me, please? The responses he gets are really quite intriguing. So he had one gentleman tell him, well, I can't draw. And when Dave asked him, well, why is that? He goes, well, because I'm from Czechoslovakia. He had another woman who said, you know, could you draw? And then she goes, oh, of course.

And she goes, I'm excellent at drawing. I took lessons when I was a child. So she's elaborating this whole story about, you know, that's surprising Dave about how she has all these skills. He gives her a sheet of paper, pencil. She does this drawing. When he looks at it, it's just a series of alphanumeric codes. And he goes, this isn't a drawing. And she goes, yes, it is. Now your job is to figure out the key to what it all means. Right? So there's all of these intriguing examples. And already back in the 80s, there's a German researcher, Paul Tholle, who also explored some of these questions in lucid dreams about asking dream characters various things. You know,

can you sing? Can you come up with words that I don't know? But one interesting thing is that dream characters are really poor at math, even basic math. So if you ask a dream character, you know, what is four plus three, some of them will say six. Now that's intriguing because you, the dreamer knows the answer, but the dream character seems to get it wrong. And so again, why is that? And you have other reactions in the studies by Paul Tholai, this German researcher. You had people being asked these math problems, and some would run away. Some of these dream characters would just run away.

In two cases, the person broke down crying, and they were like, oh no, not math. Hey, we're used to that that I'm a math professor that happens in real life too absolutely but again it's this unpredictable nature in these characters and why do they act and behave in these ways why does your your brain decide to have them react in this way? And how does this impact how dreams are formed and evolved? So lucid dreaming allows us to learn more about the basic neurobiology of dreams, but also is a window into these more subjective, perplexing questions that relate to issues of consciousness and how dreams and particular dream characters are created. So I want to make sure I'm understanding these amazing stories that

you've just told us. So Dave Green, if I understood the story right, is himself a lucid dreamer? Correct. And he's then telling you these stories of what happened in his lucid dream when he encountered dream characters and challenged them with questions of, say, to draw something or do math problems or whatever. That's how we know the things that you're telling us. Yes, absolutely. Now, some of these things have been studied in laboratory context, but with Dave, he's someone who just would draw in his dreams at first, and then when he would wake up would try to remember what he had drew and sort of reproduce them so sort of using his lucid dreams as a form of creativity and so when we started discussing some of his work that's where I asked him well

instead of you yourself doing the drawings why don't you try to seek out dream characters in your dream and ask them to do the drawings for you and see what happens next. So that's what led to sort of these stories and ongoing collaborations. It's really interesting research. Well, we mentioned the phrase dream engineering before. Does this qualify as dream engineering? Dream engineering is something tangentially related. So it's this emerging scientific field where people are trying to use different technologies and methods to try to influence people's dream content. And so it can go from sleep wearables to the use of smells, sounds, again, these external stimuli, environments that appear to have an impact on how and what people dream about. So it's a way of trying to influence dreams. So this can go from immersive virtual reality training, for instance,

this can go from immersive virtual reality training, for instance, to have flying dreams that has been shown to work, to being exposed in your sleep to different smells. So we know that positive smells, such like those of a rose or a meal that you like, don't get directly incorporated into your dreams, but they foster positive emotions in dreams. Just like negative smells don't get necessarily directly incorporated in dreams, but might change the valence of the emotional content in your dreams more negatively. So there's all these different techniques to try to influence how and why people dream about, and this is broadly known as dream engineering, a very quickly moving, evolving field within dream research. I've heard that there was a letter that you signed with a group of other dream scientists and sleep scientists about concerns about dream engineering.

Could you tell us about that letter and what you're concerned about? So dream engineering is really a very, very early field. So some of the first papers on this just came out a few years ago. And it has a lot of tremendous potential to be used for therapeutic uses, for learning about the brain, for consciousness, for treating post-traumatic stress disorder, since we know that sleep and dreams are involved in processing emotional memories. But like in many new technologies, it also has potential downsides. And to some of us in the field, really scary potential applications. And I'll give you some examples of this.

And by the way, yes, the letter that we signed, there's over 40 sleep and dream researchers from across the world that signed this. Our concern isn't so much that things are dangerous now, but it has the potential to be, and we'd rather be proactive about making politicians, decision makers, and the general public aware of these issues before it's too late. Our concern is that more and more people are sleeping with sleep-related tech, with iPhones or cell phones that can record, for example, any vocalizations during their sleep. This can be really useful, for instance, if you want to know whether you're snoring, whether you have sleep apnea. But information is being collected on what stages

of sleep you may be in. People who have sleep wearables and keep them on at night, we know what your heart rate, respiration rate is. From this, you can sort of infer, are you in REM sleep, non-REM sleep? And we know that the brain, while it is asleep, processes information in ways that it doesn't while we are awake, and that even if you have no recollection, no memories for events that took place during the night while you were asleep, they can still impact your behavior. Let me give you a very clear example of this. In one study, smokers who were interested in quitting smoking were brought into a lab, and they were simply told, well, look, we may present smells to you, and we're interested in knowing how these

smells might impact your sleep, but you might be in a control group and have no smells presented to you. And that was that. And they had to keep track of how many cigarettes they were smoking and other things before coming to the lab and after the lab. Unbeknownst to them, they were presented for a very short period of time. Cigarette smell paired with, for instance, rotten eggs or rotten fish smell, and that was it. They were woken up

in the morning and they were asked, do you have any recollection of, you know, any stimuli? They would say no. Do you remember your dreams? No. And so they have no memory of being exposed to these smells. But what happens a week later? On average, they diminish their consumption of cigarettes by 30%. To me, the fascinating thing is if you do this pairing while these people are awake, it has zero impact on their cigarette consumption. So you can see that you can do things in people's sleep that are much more effective unbeknownst to them than if you were to do them while you were awake because your brain is processing information in very different ways than during wakefulness. You can also change people's preference for

candies. So you can ask people before they come to sleep at the lab, oh, by the way, do you prefer M&Ms or Skittles? And people will say, oh, you know, I prefer Skittles. And during the night, you can present them with auditory stimuli saying M&Ms, M&Ms. Again, briefly in selected periods of their sleep, they have no recollection of this. It does not wake them up. But when they are done their sleep in the morning and you ask them, oh, by the way, do you still prefer Skittles or M&Ms? And some of them will go over 70%. You know what? It's strange. But you know, if I had a choice, I'd take M&Ms now. And if you ask them why, they don't know. They can't tell you. Again, these are just very simple examples,

but this technology is quickly evolving. Now, if you think of the amount of money advertisers are willing to spend to get 30 seconds of your attention, imagine what they are willing to spend to get several hours of your attention on a nightly basis for which you have no memory, but for which the effects might be even stronger than anything you could do during wakefulness. Now, we're not saying this exists now, but we think it's coming down the pipeline. We're bombarded with advertisement on social media, on highways, on television, before films, after films. We also believe that sleep should probably remain one area that is free of these kinds of influences. And I wouldn't want my great grandchildren to have to pay $10 a month to opt out of advertisement in their dreams.

Oh, God. I see. Talk about a nightmare. What a suggestion. Let's talk, as we're winding down here, about the future of dream research. How about we talk a little about a model that you and your colleague Bob Stickhold have proposed called NextUp? these core features of dreams. And many theories of dreams have been fairly unidimensional, trying to explain why they are bizarre, or why they are emotional, or only as they tie to REM sleep. And so we've come up with a model that tries to explain the experience of dreams, why they are forgotten, while taking also into account what we know. And we know a lot about the general content of dreams, of lucid dreams, of nightmares, of everyday dreams, of recurrent dreams, and also of the neurobiological processes that take place in the brain while we are dreaming and the different kinds of dream-related experiences we have across sleep stages. So next up basically proposes that dreaming is a unique form

of sleep dependent memory evolution and that what it tries to do is that it tries to extract new knowledge from existing information through the discovery and strengthening of these loosely associated, unexpected, and often previously unexplored associations to our waking concerns. So we think that like as you are falling asleep, you often have these thoughts or images that may go through your mind and that they are often related to your ongoing concerns. And this is probably part of your brain trying to tag what is the most important thing for me to try to process later on in sleep. We also know, for instance, that in REM sleep, you have reduced or absent levels of a neuromodulator called serotonin. And this probably creates a state in which the brain is biased towards accepting dream associations as

meaningful. Reduced serotonin is what you see in the brain, for instance, if you take psilocybin, magic mushrooms, or LSD. And one thing that characterizes these experiences is that they are often imbued with a sense of importance and meaning. And the same thing seems to occur in REM sleep. Another neuromodulator, norepinephrine, is greatly reduced in REM sleep, and this is what allows us to usually keep a focus, to plan ahead, and so this is probably also one reason why dreams are hyper-associative, why there are these bizarre elements and scene shifts. They, again, reveal how the brain is trying to explore possibilities, trying to make sense of the main events we've

experienced during the day and see where they fit in with our conception of the world. So we think that the brain needs to dream, we need to have these experiences for the sleeping brain to actually make sense to predict possible future scenarios and how to best react and perceive them in the future. Oh, thank you so much, Tony. This has been a really enlightening conversation about dreaming, about sleep. It's really been a pleasure having you today. Thank you very much for having me, and I thoroughly enjoyed our exchange on sleep and dreams. We'll be back with more episodes of The Joy of Why in 2023. Is there a burning science question or a math question that you'd like to have us answer? Send us an email at joy at quantummagazine.org to let us know. In the meantime, check out the Quanta Science podcast on all the platforms where you listen to podcasts or at the Quanta Magazine website.

Thanks for listening, and we hope you'll join us next time for more of The Joy of Why. The Joy of Why is a podcast from Quanta Magazine, an editorially independent publication supported by the Simons Foundation. independent publication supported by the Simons Foundation. Funding decisions by the Simons Foundation have no influence on the selection of topics, guests, or other editorial decisions in this podcast or in Quantum Magazine. The Joy of Why is produced by Susan Vallett and Polly Stryker. Our editors are John Rennie and Thomas Lin. Our theme music was composed by Richie Johnson, and I'm your host, Steve Strogatz.

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