1 00:00:05,040 --> 00:00:08,239 Speaker 1: What do your nightly dreams have to do with the 2 00:00:08,360 --> 00:00:12,680 Speaker 1: rotation of the planet. Why are so many musicians blind? 3 00:00:13,080 --> 00:00:16,160 Speaker 1: Can blind people learn how to echolocate like a bat? 4 00:00:16,480 --> 00:00:19,759 Speaker 1: Once we find alien life on other planets, should we 5 00:00:19,800 --> 00:00:27,040 Speaker 1: expect that aliens have dreams at night? Welcome to Inner 6 00:00:27,120 --> 00:00:32,000 Speaker 1: Cosmos with me, David Eagleman. I'm a neuroscientist and an 7 00:00:32,040 --> 00:00:36,600 Speaker 1: author at Stanford University, and I've spent my whole career 8 00:00:37,040 --> 00:00:41,880 Speaker 1: studying the intersection between how the brain works and how 9 00:00:41,960 --> 00:00:52,920 Speaker 1: we experience life. I sort of personally have a love 10 00:00:52,960 --> 00:00:58,000 Speaker 1: hate relationship with dreaming because we take it so seriously. 11 00:00:58,120 --> 00:01:01,639 Speaker 1: We find ourselves in some biziz situation that doesn't make 12 00:01:01,680 --> 00:01:06,240 Speaker 1: any sense, but while you are there, you buy it, 13 00:01:06,360 --> 00:01:11,200 Speaker 1: hook line and sinker. You are emotionally tossed around and 14 00:01:11,840 --> 00:01:16,160 Speaker 1: buffeted in the winds of situations that the moment after 15 00:01:16,200 --> 00:01:20,040 Speaker 1: you wake up you realize weren't real, and more importantly, 16 00:01:20,360 --> 00:01:23,640 Speaker 1: they typically make no sense at all. So why were 17 00:01:23,640 --> 00:01:27,520 Speaker 1: you so caught up in that situation? I've always called 18 00:01:27,640 --> 00:01:31,160 Speaker 1: dreaming sticking my head in the night blender, by which 19 00:01:31,240 --> 00:01:34,679 Speaker 1: I simply mean that I don't necessarily look forward to 20 00:01:34,720 --> 00:01:36,760 Speaker 1: it because I don't know where it's going to take me, 21 00:01:37,120 --> 00:01:40,280 Speaker 1: and I generally feel that all that emotional energy I 22 00:01:40,319 --> 00:01:44,280 Speaker 1: expend isn't that useful. But whatever your take on dreaming is, 23 00:01:44,920 --> 00:01:50,080 Speaker 1: it's one of those absolutely insanely bizarre facts about our 24 00:01:50,160 --> 00:01:55,200 Speaker 1: existence that we totally take for granted. You wake up 25 00:01:55,360 --> 00:01:58,280 Speaker 1: and you say, oh, wow, I was just having a 26 00:01:58,400 --> 00:02:01,920 Speaker 1: dance party with a pack of why monkeys. Or I 27 00:02:02,000 --> 00:02:03,960 Speaker 1: was just at work where I forgot to put on 28 00:02:04,120 --> 00:02:06,240 Speaker 1: pants and I was trying to hide behind my desk. 29 00:02:06,440 --> 00:02:09,800 Speaker 1: Or I was on a river cruise and begging a 30 00:02:09,840 --> 00:02:11,960 Speaker 1: person not to break up with me even though we're 31 00:02:11,960 --> 00:02:17,080 Speaker 1: not even dating. And I find this absolutely stunning that 32 00:02:17,160 --> 00:02:21,239 Speaker 1: it doesn't even bother us that we've just transitioned from 33 00:02:21,280 --> 00:02:25,079 Speaker 1: one reality to another, Like in one second, you went 34 00:02:25,120 --> 00:02:29,320 Speaker 1: from being in some bizarre situation to lying horizontal in 35 00:02:29,360 --> 00:02:32,400 Speaker 1: your bed, and we're so used to it that we 36 00:02:32,560 --> 00:02:36,160 Speaker 1: just say, oh, that was interesting. I just dreamed that 37 00:02:36,240 --> 00:02:38,840 Speaker 1: I was on a hang glider riding over Istanbul and 38 00:02:38,880 --> 00:02:41,080 Speaker 1: I was trying to figure out how not to crash 39 00:02:41,120 --> 00:02:43,800 Speaker 1: because there were a lot of pigeons swirling around me. 40 00:02:44,240 --> 00:02:47,200 Speaker 2: And if there's somebody there, then maybe we tell them. 41 00:02:47,080 --> 00:02:50,520 Speaker 1: Our dream and Otherwise, we just get up and we 42 00:02:50,639 --> 00:02:53,600 Speaker 1: brush our teeth and go about our day without even 43 00:02:53,680 --> 00:02:57,639 Speaker 1: giving a second thought about what just happened. We were 44 00:02:57,760 --> 00:03:01,560 Speaker 1: in one reality and totally emotional invested in it, and 45 00:03:01,600 --> 00:03:04,400 Speaker 1: then a moment later we said, hmm, I guess I'm 46 00:03:04,400 --> 00:03:07,799 Speaker 1: in this other reality now. Now this is a testament 47 00:03:08,200 --> 00:03:13,480 Speaker 1: to the human mind's ability to accept the absolutely amazing 48 00:03:13,560 --> 00:03:17,119 Speaker 1: and bizarre as something not even worth investigating. 49 00:03:17,360 --> 00:03:18,320 Speaker 2: Think about it this way. 50 00:03:18,520 --> 00:03:21,840 Speaker 1: Just imagine if dreams happened right in the middle of 51 00:03:21,880 --> 00:03:24,760 Speaker 1: your day. So you're on a walk, or you're sitting 52 00:03:24,760 --> 00:03:27,320 Speaker 1: at your desk or eating at a restaurant with friends, 53 00:03:27,760 --> 00:03:33,680 Speaker 1: and suddenly your reality morphs to a completely bizarre other reality, 54 00:03:34,200 --> 00:03:37,320 Speaker 1: and now you're on a street you've never seen before, 55 00:03:37,920 --> 00:03:41,480 Speaker 1: or you're flying, or you're falling from a building, or 56 00:03:41,520 --> 00:03:45,120 Speaker 1: you're being chased by a monster. You would be terrified 57 00:03:45,200 --> 00:03:48,560 Speaker 1: by this lack of cohesion in your reality, the fact 58 00:03:48,560 --> 00:03:51,440 Speaker 1: that you just flipped from one to another. And as 59 00:03:51,440 --> 00:03:54,480 Speaker 1: soon as you were back in this reality, you'd presumably 60 00:03:54,600 --> 00:03:57,080 Speaker 1: run to your doctor and say you just had this 61 00:03:57,160 --> 00:04:01,120 Speaker 1: bizarre hallucination and thought you were somewhere else or maybe 62 00:04:01,160 --> 00:04:04,840 Speaker 1: someone else, and you'd be terrified, But because we're so 63 00:04:05,280 --> 00:04:08,200 Speaker 1: used to dreaming, we wake up and we think, oh, 64 00:04:08,200 --> 00:04:09,400 Speaker 1: that was weird, and then we go. 65 00:04:09,400 --> 00:04:11,040 Speaker 2: About our new reality. 66 00:04:11,560 --> 00:04:15,800 Speaker 1: And in fact, one of the evergreen questions among philosophers 67 00:04:16,279 --> 00:04:19,840 Speaker 1: is whether we live in a simulation. And I'm going 68 00:04:19,920 --> 00:04:22,599 Speaker 1: to dive deep into that question in a different episode, 69 00:04:22,640 --> 00:04:25,279 Speaker 1: but for now, I'll just mention the question, which is, 70 00:04:25,320 --> 00:04:28,000 Speaker 1: how would you know if you are a brain in 71 00:04:28,080 --> 00:04:31,240 Speaker 1: a vat who is being stimulated in just the right 72 00:04:31,240 --> 00:04:34,440 Speaker 1: way to think that you're listening to a podcast and 73 00:04:34,560 --> 00:04:36,839 Speaker 1: seeing the world around you and eating. 74 00:04:36,520 --> 00:04:37,760 Speaker 2: Delicious food and so on. 75 00:04:38,200 --> 00:04:40,520 Speaker 1: Or the modern version of that is whether we are 76 00:04:40,560 --> 00:04:45,559 Speaker 1: living in a computer simulation. So I suggest the mere 77 00:04:46,160 --> 00:04:51,880 Speaker 1: existence of dreams is sufficient to prove that all this 78 00:04:52,000 --> 00:04:56,240 Speaker 1: could be a simulation, because dreams demonstrate to us so 79 00:04:56,520 --> 00:05:01,560 Speaker 1: clearly that we completely buy what ever reality we find 80 00:05:01,560 --> 00:05:04,600 Speaker 1: ourselves in, and when we find ourselves in another reality, 81 00:05:04,640 --> 00:05:07,080 Speaker 1: we say, oh, I guess that one wasn't real. 82 00:05:07,120 --> 00:05:09,159 Speaker 2: I was fooled, but this is real. 83 00:05:09,360 --> 00:05:11,279 Speaker 1: But let me leave that as a teaser for the 84 00:05:11,440 --> 00:05:13,920 Speaker 1: episode on whether we're living in a simulation and how 85 00:05:13,960 --> 00:05:18,240 Speaker 1: we'd know. For today, I want to dive into dreaming 86 00:05:18,720 --> 00:05:21,880 Speaker 1: in particular, and from the brain's point. 87 00:05:21,600 --> 00:05:23,240 Speaker 2: Of view, why do we dream? 88 00:05:23,600 --> 00:05:28,159 Speaker 1: Why does our consciousness go on these bizarre flights every 89 00:05:28,240 --> 00:05:31,360 Speaker 1: ninety minutes during the night. So as a neuroscientist, I've 90 00:05:31,440 --> 00:05:34,120 Speaker 1: always been fascinated by dreaming, by what. 91 00:05:34,080 --> 00:05:35,240 Speaker 2: The heck this is all about. 92 00:05:35,640 --> 00:05:38,479 Speaker 1: So in this episode, we're going to talk about the why, 93 00:05:39,000 --> 00:05:41,800 Speaker 1: and I'm going to tell you about some hypotheses that 94 00:05:41,839 --> 00:05:44,880 Speaker 1: people have proposed over the centuries, and then I'm going 95 00:05:44,920 --> 00:05:49,320 Speaker 1: to tell you about a new hypothesis that makes quantitative 96 00:05:49,360 --> 00:05:54,680 Speaker 1: predictions across animal species. So let's start with an interesting fact, 97 00:05:55,000 --> 00:05:59,279 Speaker 1: which is that all animals appear to have dream sleep, 98 00:05:59,520 --> 00:06:04,720 Speaker 1: also as REM sleep. REM is spelled r EM, and 99 00:06:04,760 --> 00:06:09,240 Speaker 1: it stands for rapid eye movement. So in this stage 100 00:06:09,240 --> 00:06:12,560 Speaker 1: of sleep, the eyes are darting back and forth under 101 00:06:12,600 --> 00:06:16,000 Speaker 1: the eyelids. And if you haven't really watched someone while 102 00:06:16,000 --> 00:06:20,280 Speaker 1: they're sleeping, you should in a respectful manner because you'll 103 00:06:20,279 --> 00:06:23,360 Speaker 1: see how amazing this is. Every ninety minutes or so, 104 00:06:23,440 --> 00:06:27,279 Speaker 1: their eyes start jiggling back and forth. Now here's the 105 00:06:27,320 --> 00:06:30,039 Speaker 1: cool part. If you wake them up right when this 106 00:06:30,160 --> 00:06:33,640 Speaker 1: is happening and you say, quick, what were you just 107 00:06:33,880 --> 00:06:36,599 Speaker 1: thinking about? They will tell you that they were just 108 00:06:37,200 --> 00:06:39,599 Speaker 1: riding a camel in a shopping mall, or they were 109 00:06:39,880 --> 00:06:42,640 Speaker 1: running from a pack of leprechauns, or they were flying 110 00:06:42,640 --> 00:06:45,400 Speaker 1: around their house or whatever. And this is how we know, 111 00:06:46,120 --> 00:06:49,240 Speaker 1: from years of experiments of waking people up at different 112 00:06:49,279 --> 00:06:52,359 Speaker 1: stages of sleep, this is how we know that rem 113 00:06:52,600 --> 00:06:57,400 Speaker 1: sleep is when dreams happen. Because if you wake someone 114 00:06:57,480 --> 00:07:01,120 Speaker 1: up during a deeper stage of sleep, what we call 115 00:07:01,200 --> 00:07:03,400 Speaker 1: stage one or two or three, when their eyes are 116 00:07:03,440 --> 00:07:06,599 Speaker 1: not moving, and you say, quick, what were you just 117 00:07:06,640 --> 00:07:10,640 Speaker 1: thinking about, they'll generally say nothing at all, there was 118 00:07:10,880 --> 00:07:14,640 Speaker 1: nothing going on in my consciousness. Now, for completeness, I'll 119 00:07:14,680 --> 00:07:17,280 Speaker 1: just flag that some people will point out there can 120 00:07:17,320 --> 00:07:21,200 Speaker 1: be some sort of dreaming during non rem sleep, but 121 00:07:21,320 --> 00:07:24,320 Speaker 1: this is a very different type of dreaming. When it happens, 122 00:07:24,360 --> 00:07:28,520 Speaker 1: it's just a feeling of something like a simple thought, 123 00:07:28,640 --> 00:07:32,120 Speaker 1: rather than a vivid experience like we typically think of 124 00:07:32,160 --> 00:07:36,640 Speaker 1: with dreams with its whirl of color and activity and 125 00:07:36,760 --> 00:07:41,240 Speaker 1: magnified emotions. Now, just a quick side note, some people 126 00:07:41,360 --> 00:07:45,240 Speaker 1: say I don't dream at night, but in fact you do. 127 00:07:45,520 --> 00:07:48,360 Speaker 1: Everybody does. It's just a matter of waking up at 128 00:07:48,360 --> 00:07:51,520 Speaker 1: the right time. So if I snuck into your house 129 00:07:51,760 --> 00:07:54,280 Speaker 1: and woke you up right when you were having rapid 130 00:07:54,360 --> 00:07:58,040 Speaker 1: eye movement sleep. You'd say, WHOA, I was just dreaming. 131 00:07:58,400 --> 00:08:02,360 Speaker 1: But what often happens is that we enjoy a round 132 00:08:02,400 --> 00:08:05,440 Speaker 1: of dream sleep and then we sink back into a 133 00:08:05,520 --> 00:08:07,840 Speaker 1: deeper sleep, so by the time we wake up, we 134 00:08:07,880 --> 00:08:12,080 Speaker 1: don't remember the dream. So some people get up in 135 00:08:12,120 --> 00:08:14,760 Speaker 1: the morning and they're convinced that they didn't dream at all, 136 00:08:14,840 --> 00:08:19,080 Speaker 1: while in fact they did, they simply don't remember it. Now, 137 00:08:19,080 --> 00:08:22,280 Speaker 1: the question I want to address is why we dream? 138 00:08:22,720 --> 00:08:26,600 Speaker 1: And the first clue comes from a simple observation that 139 00:08:26,640 --> 00:08:29,400 Speaker 1: this is not just a human thing, but something about 140 00:08:29,440 --> 00:08:34,240 Speaker 1: brains in general. You've seen your dog have dreams where 141 00:08:34,280 --> 00:08:37,280 Speaker 1: she kicks her legs around and barks like she's chasing 142 00:08:37,320 --> 00:08:40,559 Speaker 1: a rabbit. But it turns out that all mammals dream, 143 00:08:40,720 --> 00:08:44,800 Speaker 1: and all birds and reptiles they all exhibit rem sleep. 144 00:08:44,920 --> 00:08:47,840 Speaker 1: Even fish have a form of rem sleep. So why 145 00:08:47,960 --> 00:08:51,920 Speaker 1: is this so conserved across the whole animal kingdom. While 146 00:08:51,960 --> 00:08:55,280 Speaker 1: there are various ideas that have been proposed for why 147 00:08:55,440 --> 00:08:59,800 Speaker 1: we dream, some researchers point out that dream sleep seems 148 00:08:59,800 --> 00:09:05,520 Speaker 1: to be important for memory consolidation, which means nailing down 149 00:09:05,559 --> 00:09:08,760 Speaker 1: the memories that you take in during the day. So 150 00:09:09,080 --> 00:09:11,480 Speaker 1: you run around during the day with your eyes open 151 00:09:11,559 --> 00:09:14,320 Speaker 1: and you experience all kinds of new things. 152 00:09:14,480 --> 00:09:17,200 Speaker 2: And the idea is that when you sleep and. 153 00:09:17,240 --> 00:09:20,800 Speaker 1: Dream, you are nailing that down and taking out the 154 00:09:20,840 --> 00:09:25,520 Speaker 1: neural trash in a way that's necessary and useful for 155 00:09:25,640 --> 00:09:26,920 Speaker 1: locking down the memories. 156 00:09:27,320 --> 00:09:29,559 Speaker 2: Another popular idea has been that. 157 00:09:29,840 --> 00:09:34,160 Speaker 1: Dreams help us solve problems because the brain is able 158 00:09:34,200 --> 00:09:38,040 Speaker 1: to process information and make connections that are not possible 159 00:09:38,120 --> 00:09:41,439 Speaker 1: during waking hours. So the idea is that the brain 160 00:09:41,520 --> 00:09:44,720 Speaker 1: is in a more relaxed state during dream sleep. It's 161 00:09:44,720 --> 00:09:47,560 Speaker 1: not as focused on the external world, and this allows 162 00:09:47,600 --> 00:09:50,520 Speaker 1: it to focus on internal thoughts and ideas, which can 163 00:09:50,600 --> 00:09:54,640 Speaker 1: lead to new insights and solutions to problems. And in fact, 164 00:09:54,679 --> 00:09:57,200 Speaker 1: studies have shown that if you are trying to solve 165 00:09:57,200 --> 00:10:00,480 Speaker 1: a problem and you go to sleep, you're more likely 166 00:10:00,520 --> 00:10:03,000 Speaker 1: to solve it when you wake up than if you're 167 00:10:03,000 --> 00:10:05,600 Speaker 1: just thinking about it during the daytime. And if you're 168 00:10:05,640 --> 00:10:10,080 Speaker 1: deprived of dream sleep, you have more difficulty solving problems. 169 00:10:10,520 --> 00:10:13,640 Speaker 1: But of course this might be related to problems of 170 00:10:13,679 --> 00:10:17,840 Speaker 1: sleep in general. Others suggest that rem sleep is involved 171 00:10:17,960 --> 00:10:21,600 Speaker 1: more generally in creativity, and others talk about its role 172 00:10:21,679 --> 00:10:25,880 Speaker 1: in emotional processing. And finally, several thinkers have suggested that 173 00:10:26,040 --> 00:10:31,000 Speaker 1: dreams help us prepare for new situations like fighting or 174 00:10:31,160 --> 00:10:35,080 Speaker 1: escaping from situations, because these are things that we experience 175 00:10:35,160 --> 00:10:38,560 Speaker 1: in real life very rarely, and so the idea is 176 00:10:38,600 --> 00:10:42,400 Speaker 1: that dreams give us practice at these rare situations. 177 00:10:42,400 --> 00:10:44,040 Speaker 2: They keep the wheels greased. 178 00:10:44,559 --> 00:10:46,120 Speaker 1: And I just want to be clear that these are 179 00:10:46,160 --> 00:10:50,520 Speaker 1: all hypotheses for why we dream, and they're not exclusive. 180 00:10:50,600 --> 00:10:53,800 Speaker 1: Dreams might serve multiple roles, so it's not as though 181 00:10:53,800 --> 00:10:55,720 Speaker 1: one of these has to be right at the expense 182 00:10:55,760 --> 00:10:57,880 Speaker 1: of others. But the first thing that I hope is 183 00:10:57,920 --> 00:11:00,760 Speaker 1: clear is that there's a lot of speculation about dreams, 184 00:11:00,800 --> 00:11:03,800 Speaker 1: but we don't really have a single theory that would 185 00:11:03,880 --> 00:11:07,120 Speaker 1: qualify as the answer to why we dream. And certainly 186 00:11:07,160 --> 00:11:09,320 Speaker 1: we don't have a theory that allows us to look 187 00:11:09,400 --> 00:11:13,760 Speaker 1: across the animal kingdom to answer a different question, which 188 00:11:13,800 --> 00:11:17,400 Speaker 1: is why do different animal species, even those who are 189 00:11:17,400 --> 00:11:23,000 Speaker 1: closely related, dream different amounts. For example, if you look 190 00:11:23,040 --> 00:11:27,160 Speaker 1: at the vervet monkey and it's total sleeping time, it 191 00:11:27,200 --> 00:11:31,240 Speaker 1: only spends six percent of that sleep time in rem 192 00:11:31,440 --> 00:11:35,240 Speaker 1: In other words, having dreams, whereas another monkey, the Reesus 193 00:11:35,240 --> 00:11:39,160 Speaker 1: macaque monkey, spends eighteen percent of its time in rem sleep, 194 00:11:39,280 --> 00:11:43,280 Speaker 1: three times as much, even though they're both primate species. 195 00:11:43,600 --> 00:11:45,520 Speaker 1: So it's never been clear to me how any of 196 00:11:45,559 --> 00:11:48,920 Speaker 1: the hypotheses previously proposed would account for any of this. 197 00:11:49,360 --> 00:11:52,800 Speaker 1: But recently, my colleague and I proposed a very new 198 00:11:53,000 --> 00:11:56,079 Speaker 1: kind of theory about dreaming, and it's one that I'm 199 00:11:56,160 --> 00:12:00,959 Speaker 1: very excited about because it gives accurate quantity tative predictions 200 00:12:01,040 --> 00:12:06,000 Speaker 1: across species, something that no other hypothesis even strives to do. 201 00:12:06,320 --> 00:12:08,400 Speaker 1: But before I tell you about that, I need to 202 00:12:08,480 --> 00:12:11,640 Speaker 1: lay some foundation. So let's start with the story of 203 00:12:11,679 --> 00:12:15,760 Speaker 1: a young boy named Ronnie who was born blind. He 204 00:12:15,880 --> 00:12:18,400 Speaker 1: was born in North Carolina, and when he was just 205 00:12:18,520 --> 00:12:22,800 Speaker 1: past year old, his mother abandoned him. She said that 206 00:12:22,920 --> 00:12:27,439 Speaker 1: his blindness was her punishment from God. So he ended 207 00:12:27,520 --> 00:12:30,840 Speaker 1: up being raised in poverty by his grandparents until he 208 00:12:30,920 --> 00:12:33,080 Speaker 1: was five, and then he was sent off to a 209 00:12:33,160 --> 00:12:36,960 Speaker 1: school for the sightless. When he was six years old, 210 00:12:37,000 --> 00:12:40,320 Speaker 1: his mother came by just once and she had another child, 211 00:12:40,400 --> 00:12:44,040 Speaker 1: now a little girl, and his mother said, ron I 212 00:12:44,080 --> 00:12:46,920 Speaker 1: want you to feel her eyes. You know, her eyes 213 00:12:46,920 --> 00:12:50,520 Speaker 1: are so pretty she didn't shame me the way that 214 00:12:50,559 --> 00:12:53,520 Speaker 1: you did. She can see, and that was the last 215 00:12:53,520 --> 00:12:56,680 Speaker 1: time he ever had contact with his mother. So most 216 00:12:56,720 --> 00:13:00,360 Speaker 1: of us can't even imagine a childhood this hard. But 217 00:13:00,480 --> 00:13:04,000 Speaker 1: the silver lining became the fact that Ronnie had a 218 00:13:04,040 --> 00:13:08,080 Speaker 1: gift for music. His instructors spotted this talent and he 219 00:13:08,160 --> 00:13:12,920 Speaker 1: started to formally study classical music with the violin, and 220 00:13:13,080 --> 00:13:15,520 Speaker 1: in no time, this kid was a virtuoso. 221 00:13:15,640 --> 00:13:16,680 Speaker 2: And from there he went. 222 00:13:16,559 --> 00:13:21,600 Speaker 1: On to master guitar and piano and several other string 223 00:13:21,679 --> 00:13:24,800 Speaker 1: and woodwind instruments, and by the time he grew into 224 00:13:24,880 --> 00:13:28,920 Speaker 1: young adulthood, he became one of the most popular performers 225 00:13:29,080 --> 00:13:31,920 Speaker 1: of his day. His name was Ronnie Millsap, and you 226 00:13:31,960 --> 00:13:33,320 Speaker 1: may or may not have heard of him, but in 227 00:13:33,360 --> 00:13:38,360 Speaker 1: the seventies and eighties he dominated pop music and country 228 00:13:38,400 --> 00:13:43,520 Speaker 1: western markets. He released thirty five country music hits at 229 00:13:43,559 --> 00:13:45,559 Speaker 1: the number one slot, and he. 230 00:13:45,600 --> 00:13:47,439 Speaker 2: Earned six Grammy Awards. 231 00:13:48,240 --> 00:13:51,680 Speaker 1: Now you might think it's amazing that Ronnie Millsap could 232 00:13:51,720 --> 00:13:55,720 Speaker 1: be blind and have such an amazing musical career, but 233 00:13:55,920 --> 00:13:59,240 Speaker 1: this is actually not such an uncommon story. Think of 234 00:13:59,280 --> 00:14:05,440 Speaker 1: Andrea about or Ray, Charles Stevie Wonder, or Diane Shore 235 00:14:05,800 --> 00:14:10,680 Speaker 1: or Jose Feliciano or Jeff Healy. All of them are blind. 236 00:14:11,320 --> 00:14:14,640 Speaker 1: For all of them, their brains learned to rely on 237 00:14:14,679 --> 00:14:18,360 Speaker 1: the signals of sound and touch in their environment, and 238 00:14:18,400 --> 00:14:23,400 Speaker 1: they became better at processing those signals then cited people. 239 00:14:23,680 --> 00:14:27,440 Speaker 1: As I write about my book Live Wired, Musical stardom 240 00:14:27,560 --> 00:14:30,400 Speaker 1: is not guaranteed for people who are blind, but brain 241 00:14:30,520 --> 00:14:36,240 Speaker 1: reorganization is guaranteed because if a sense is not getting used, 242 00:14:36,480 --> 00:14:41,640 Speaker 1: like vision, it gets taken over by neighboring senses. There's 243 00:14:41,680 --> 00:14:46,280 Speaker 1: nothing special about the cells, the neurons in the visual 244 00:14:46,400 --> 00:14:49,080 Speaker 1: cortex at the back of your brain. They are simply 245 00:14:49,600 --> 00:14:54,560 Speaker 1: neurons that happened to be involved in processing edges or 246 00:14:54,600 --> 00:14:57,560 Speaker 1: colors for people who have functioning eyes. But if you 247 00:14:57,600 --> 00:15:01,840 Speaker 1: go blind, these exact same neurons can process other types 248 00:15:01,880 --> 00:15:06,640 Speaker 1: of information, So the territory gets redeployed. It gets taken 249 00:15:06,720 --> 00:15:10,880 Speaker 1: over by hearing and by touch, and you get better 250 00:15:10,960 --> 00:15:15,480 Speaker 1: at those other senses. For Ronnie Millsap, his visual cortex 251 00:15:15,560 --> 00:15:18,479 Speaker 1: was not getting used because his eyes were not functioning, 252 00:15:19,000 --> 00:15:22,240 Speaker 1: so these other brain areas took over and he got 253 00:15:22,280 --> 00:15:27,720 Speaker 1: better at those as a result. Perfect musical pitch, for example, 254 00:15:27,880 --> 00:15:31,880 Speaker 1: is much more common in the blind population, and blind 255 00:15:31,960 --> 00:15:35,920 Speaker 1: people are up to ten times better at determining whether 256 00:15:36,000 --> 00:15:39,520 Speaker 1: a musical pitch is subtly wobbling up and down. 257 00:15:40,000 --> 00:15:42,119 Speaker 2: Why, it's just because. 258 00:15:41,880 --> 00:15:47,040 Speaker 1: They have more brain territory devoted to the task of listening. 259 00:15:47,480 --> 00:15:50,320 Speaker 1: There was a recent experiment in which people who were 260 00:15:50,560 --> 00:15:54,520 Speaker 1: sighted or blind had one ear plugged up, and then 261 00:15:54,560 --> 00:15:57,520 Speaker 1: they were asked to point to the locations of sounds 262 00:15:57,560 --> 00:16:01,280 Speaker 1: in the room and pinpointing where a sound is coming 263 00:16:01,320 --> 00:16:04,960 Speaker 1: from normally requires a comparison of the signals at both years, 264 00:16:05,320 --> 00:16:08,600 Speaker 1: So it was expected that everyone would fail miserably at 265 00:16:08,600 --> 00:16:11,480 Speaker 1: this task, and that's what happened with the people who 266 00:16:11,480 --> 00:16:15,600 Speaker 1: could see. But for the blind participants, they were able 267 00:16:15,640 --> 00:16:20,000 Speaker 1: to generally tell where the sounds were positioned. How it's 268 00:16:20,040 --> 00:16:24,440 Speaker 1: because the exact shape of the cartilage of the outer ear, 269 00:16:24,880 --> 00:16:29,000 Speaker 1: even just one ear, it bounces sound around in subtle 270 00:16:29,000 --> 00:16:33,360 Speaker 1: ways that gives clues to location, but only if one 271 00:16:33,400 --> 00:16:37,640 Speaker 1: is highly attuned to pick up on those very subtle signals. 272 00:16:38,080 --> 00:16:42,920 Speaker 1: So people with sight, they have less cortex devoted to sound, 273 00:16:42,960 --> 00:16:48,200 Speaker 1: and so their ability to extract subtle sound information it's underdeveloped, 274 00:16:48,880 --> 00:16:53,400 Speaker 1: But with blind people that skill gets developed. And this 275 00:16:53,560 --> 00:16:57,640 Speaker 1: sort of extreme talent with sound, this is common among 276 00:16:57,680 --> 00:17:01,480 Speaker 1: the blind. Take a young man named Ben Underwood. When 277 00:17:01,520 --> 00:17:04,800 Speaker 1: he was two years old, Ben stopped seeing out of 278 00:17:04,840 --> 00:17:07,159 Speaker 1: his left eye and his mother took him to the 279 00:17:07,200 --> 00:17:10,480 Speaker 1: doctor and they soon discovered that he had retinal cancer 280 00:17:10,720 --> 00:17:14,080 Speaker 1: that was in both eyes. So they tried chemotherapy, they 281 00:17:14,119 --> 00:17:19,080 Speaker 1: tried radiation, but that didn't work, and finally the surgeons 282 00:17:19,200 --> 00:17:22,200 Speaker 1: had to remove both of his eyes. And you can 283 00:17:22,280 --> 00:17:25,359 Speaker 1: imagine the pain that the family went through here. But 284 00:17:25,440 --> 00:17:28,879 Speaker 1: by the time Ben was seven years old, he devised 285 00:17:28,920 --> 00:17:33,920 Speaker 1: a technique that was totally unexpected and unbelievably useful, which 286 00:17:33,960 --> 00:17:37,639 Speaker 1: is that he would click with his mouth and he 287 00:17:37,680 --> 00:17:41,560 Speaker 1: would listen for the returning echoes. And in this way 288 00:17:41,800 --> 00:17:46,560 Speaker 1: he could hear the locations of an open doorway, or 289 00:17:46,640 --> 00:17:49,959 Speaker 1: of a person, or of a parked car, or a 290 00:17:50,040 --> 00:17:53,960 Speaker 1: garbage can and so on. He was echo locating. He 291 00:17:54,080 --> 00:17:57,600 Speaker 1: was bouncing his sound waves off objects in the environment, 292 00:17:57,840 --> 00:18:17,080 Speaker 1: and he was listening to what returned. Now, I saw 293 00:18:17,119 --> 00:18:20,080 Speaker 1: a documentary about Ben a little while ago, and it 294 00:18:20,240 --> 00:18:23,760 Speaker 1: kicked off with the statement that Ben was quote the 295 00:18:23,840 --> 00:18:27,400 Speaker 1: only person in the world who can see with echolocation. Now, 296 00:18:27,480 --> 00:18:30,160 Speaker 1: first of all, we don't really know if he's seeing 297 00:18:30,240 --> 00:18:32,080 Speaker 1: in the same way that you and I might. 298 00:18:32,040 --> 00:18:32,720 Speaker 2: Think of site. 299 00:18:33,040 --> 00:18:36,320 Speaker 1: But much more importantly, Ben was not the only one 300 00:18:36,400 --> 00:18:41,520 Speaker 1: using echolocation. Thousands of blind people do this. In fact, 301 00:18:41,920 --> 00:18:45,680 Speaker 1: the phenomenon has been discussed since at least the nineteen forties, 302 00:18:45,720 --> 00:18:50,160 Speaker 1: when the word echolocation was first coined in an article 303 00:18:50,240 --> 00:18:54,600 Speaker 1: in the journal Science, and this was titled Echolocation by 304 00:18:54,800 --> 00:19:00,680 Speaker 1: Blind Men, bat and Radar. The author wrote, quote, many 305 00:19:00,720 --> 00:19:04,480 Speaker 1: blind persons develop, in the course of time a considerable 306 00:19:04,560 --> 00:19:10,160 Speaker 1: ability to avoid obstacle by means of auditory cues received 307 00:19:10,520 --> 00:19:14,960 Speaker 1: from sounds of their own making. And this included clicking 308 00:19:15,160 --> 00:19:19,320 Speaker 1: or their own footsteps, or cane tapping or finger snapping. 309 00:19:20,040 --> 00:19:23,520 Speaker 1: So the author demonstrated that their ability to echo locate 310 00:19:23,840 --> 00:19:27,679 Speaker 1: was drastically reduced if you put in distracting noises or 311 00:19:27,720 --> 00:19:32,760 Speaker 1: put ear plugs in them. Anyway, the general story is straightforward. 312 00:19:32,800 --> 00:19:36,399 Speaker 1: If a sense is not getting used, it gets taken 313 00:19:36,440 --> 00:19:40,640 Speaker 1: over by neighboring senses. So, for example, if you're blind, 314 00:19:40,800 --> 00:19:45,120 Speaker 1: the territory gets redeployed to hearing and to touch. There's 315 00:19:45,160 --> 00:19:48,639 Speaker 1: nothing special about the neurons and the visual cortex. They 316 00:19:48,720 --> 00:19:52,240 Speaker 1: just happen to be involved in processing vision if you 317 00:19:52,320 --> 00:19:56,080 Speaker 1: have functioning eyes, but if you go blind, these exact 318 00:19:56,160 --> 00:20:00,199 Speaker 1: same neurons can process other types of information. Now, in 319 00:20:00,280 --> 00:20:05,280 Speaker 1: recent decades, there have been thousands of papers demonstrating brain plasticity, 320 00:20:05,359 --> 00:20:08,600 Speaker 1: that is, the brain's ability to reconfigure and adjust its 321 00:20:08,600 --> 00:20:11,439 Speaker 1: own circuitry, And in my book Livewireed, I attempt to 322 00:20:11,520 --> 00:20:15,880 Speaker 1: build up frameworks to surface the big lessons from these papers. 323 00:20:16,040 --> 00:20:19,840 Speaker 1: But to my mind, the biggest surprise about brain plasticity 324 00:20:20,320 --> 00:20:25,200 Speaker 1: is its speed. So some years ago, researchers at McGill 325 00:20:25,320 --> 00:20:29,200 Speaker 1: University took several adults who had recently lost their site, 326 00:20:29,200 --> 00:20:31,320 Speaker 1: and they put them into a brain scanner and the 327 00:20:31,400 --> 00:20:36,040 Speaker 1: participants were asked to listen to sounds. Now, not surprisingly, 328 00:20:36,160 --> 00:20:40,520 Speaker 1: the sounds caused activity in their auditory cortex, but the 329 00:20:40,600 --> 00:20:44,360 Speaker 1: sounds also caused activity in their occipital core. 330 00:20:44,480 --> 00:20:46,159 Speaker 2: Text that's at the back of the brain. 331 00:20:46,560 --> 00:20:49,040 Speaker 1: It's normally what we would think of as visual cortex, 332 00:20:49,520 --> 00:20:52,600 Speaker 1: and that activity would not have been seen there even 333 00:20:52,640 --> 00:20:55,960 Speaker 1: a few weeks earlier when the participants had sight. Now, 334 00:20:55,960 --> 00:20:59,240 Speaker 1: the activity wasn't as strong as that scene in people 335 00:20:59,280 --> 00:21:02,040 Speaker 1: who have been blowing for a long time. But it 336 00:21:02,080 --> 00:21:06,960 Speaker 1: was detectable in the occipital cortex nonetheless, and this demonstrated 337 00:21:07,000 --> 00:21:11,919 Speaker 1: that the brain can implement changes rapidly when vision disappears, 338 00:21:12,119 --> 00:21:16,000 Speaker 1: but how rapidly so. Next, my colleagues at Harvard, led 339 00:21:16,040 --> 00:21:20,320 Speaker 1: by Alvaro pascal Leone, began to wonder about the speed 340 00:21:20,359 --> 00:21:24,080 Speaker 1: at which these major takeovers can happen, and they noted 341 00:21:24,119 --> 00:21:28,840 Speaker 1: that instructors at a school for the blind were required 342 00:21:28,880 --> 00:21:32,160 Speaker 1: to blindfold themselves for seven full days so that they 343 00:21:32,160 --> 00:21:36,360 Speaker 1: could gain a first hand understanding of their students' living experiences. 344 00:21:36,880 --> 00:21:41,600 Speaker 1: So when these cited instructors blindfolded themselves, they became aware 345 00:21:41,680 --> 00:21:46,639 Speaker 1: of enhanced skills with sounds. They could orient to things better, 346 00:21:46,680 --> 00:21:49,959 Speaker 1: and they could judge their distance, and they could identify things. 347 00:21:50,240 --> 00:21:55,479 Speaker 1: Several described identifying people more rapidly and accurately just as 348 00:21:55,520 --> 00:21:58,199 Speaker 1: they started talking, or even just given the cadence of 349 00:21:58,240 --> 00:22:01,760 Speaker 1: their footsteps, And the instructions learned new things like how 350 00:22:01,800 --> 00:22:05,840 Speaker 1: to differentiate cars just by the sounds of their motors. 351 00:22:06,320 --> 00:22:10,919 Speaker 1: So this god pascal Leone and his colleagues, considering what 352 00:22:11,000 --> 00:22:14,400 Speaker 1: would happen if a sighted person were blindfolded in. 353 00:22:14,400 --> 00:22:16,960 Speaker 2: The laboratory for several days. 354 00:22:17,000 --> 00:22:20,679 Speaker 1: So they launched this experiment and what they found was 355 00:22:20,720 --> 00:22:23,760 Speaker 1: nothing short of remarkable. They discovered that when you were 356 00:22:24,040 --> 00:22:29,439 Speaker 1: temporarily blinded, there was neural reorganization, just like we see 357 00:22:29,720 --> 00:22:32,919 Speaker 1: in blind subjects, and it was rapid. In one of 358 00:22:32,920 --> 00:22:36,679 Speaker 1: their studies, people who could see normally were blindfolded for 359 00:22:36,760 --> 00:22:40,720 Speaker 1: five days and they were put through intensive braille training, 360 00:22:40,920 --> 00:22:43,120 Speaker 1: and at the end of the five days, the subjects 361 00:22:43,160 --> 00:22:47,120 Speaker 1: had become quite good at detecting the subtle differences between 362 00:22:47,200 --> 00:22:51,080 Speaker 1: braille characters, much better than a control group of cited 363 00:22:51,080 --> 00:22:54,240 Speaker 1: participants who had the same training without the blindfold. But 364 00:22:54,320 --> 00:22:57,359 Speaker 1: what was especially striking was what happened to their brains 365 00:22:57,480 --> 00:23:00,719 Speaker 1: when you measured them in the scanner. Within fire five days, 366 00:23:01,040 --> 00:23:06,199 Speaker 1: the blindfolded participants had recruited their occipital cortex when they 367 00:23:06,200 --> 00:23:11,119 Speaker 1: were touching objects. So control subjects, not surprisingly used only 368 00:23:11,480 --> 00:23:14,679 Speaker 1: a different part of their brain called the somatisensory cortex, 369 00:23:15,040 --> 00:23:18,640 Speaker 1: and the blindfolded subjects they were also showing these occipital 370 00:23:18,680 --> 00:23:22,159 Speaker 1: responses to sounds and words. 371 00:23:22,400 --> 00:23:23,240 Speaker 2: And by the way, you. 372 00:23:23,200 --> 00:23:29,320 Speaker 1: Could disrupt this new occipital lobe activity by magnetic pulses, 373 00:23:29,680 --> 00:23:33,200 Speaker 1: and then the braille reading advantage of the blindfolded subjects 374 00:23:33,240 --> 00:23:36,560 Speaker 1: went away, so that indicates the recruitment of the brain 375 00:23:36,640 --> 00:23:39,840 Speaker 1: area was not an accidental side effect, but this was 376 00:23:39,880 --> 00:23:44,639 Speaker 1: a critical piece of the improved behavioral performance. And importantly, 377 00:23:44,720 --> 00:23:48,240 Speaker 1: because of the plasticity of the brain, when the blindfold 378 00:23:48,280 --> 00:23:51,719 Speaker 1: got removed, the response of the occipital. 379 00:23:51,200 --> 00:23:52,720 Speaker 2: Cortext to touch or sound. 380 00:23:53,040 --> 00:23:56,680 Speaker 1: That disappeared within a day, and at that point the participants' 381 00:23:56,720 --> 00:24:01,879 Speaker 1: brains returned to looking indistinguishable from every other sighted person 382 00:24:01,920 --> 00:24:06,159 Speaker 1: out there. Now here's the key study that really influenced me. 383 00:24:06,560 --> 00:24:11,040 Speaker 1: These same investigators very carefully mapped out the brain using 384 00:24:11,160 --> 00:24:16,440 Speaker 1: more powerful neuroimaging techniques. So volunteers were blindfolded really tightly, 385 00:24:16,560 --> 00:24:19,000 Speaker 1: and they were put in the scanner and they were 386 00:24:19,119 --> 00:24:22,680 Speaker 1: asked to perform a touching task that required really fine 387 00:24:22,720 --> 00:24:27,080 Speaker 1: discrimination with their fingers. And what these investigators saw was 388 00:24:27,160 --> 00:24:32,440 Speaker 1: activity emerging in the primary visual cortex the occipital lobe 389 00:24:32,480 --> 00:24:36,359 Speaker 1: after an hour. And the shock of these findings was 390 00:24:36,359 --> 00:24:41,600 Speaker 1: their sheer speed. So the reorganization of territory that brains do, 391 00:24:41,760 --> 00:24:45,679 Speaker 1: it's not like the glacial drifting of continental plates, but 392 00:24:45,840 --> 00:24:50,920 Speaker 1: it can be remarkably fast. The brain is always sprung 393 00:24:51,080 --> 00:24:54,840 Speaker 1: tight like a mouse trap to implement rapid change. 394 00:24:55,280 --> 00:24:58,719 Speaker 2: So the key is that the brain's changes. 395 00:24:58,640 --> 00:25:02,760 Speaker 1: Are even fast sure than even the most optimistic neuroscientist 396 00:25:02,880 --> 00:25:06,160 Speaker 1: would have dared to guess at the beginning of this century. 397 00:25:06,640 --> 00:25:09,840 Speaker 1: So let's zoom back out to the bigger picture. So 398 00:25:10,640 --> 00:25:14,400 Speaker 1: for survival you need things like sharp teeth and fast legs. 399 00:25:14,760 --> 00:25:19,680 Speaker 1: You also need neural flexibility. This is what allows brains 400 00:25:19,720 --> 00:25:24,320 Speaker 1: to optimize their performance in a variety of environments. But 401 00:25:24,400 --> 00:25:29,159 Speaker 1: the competition in the brain has a potential downside as well, 402 00:25:29,359 --> 00:25:32,879 Speaker 1: which is this, whenever there's an imbalance of activity in 403 00:25:32,920 --> 00:25:36,800 Speaker 1: the senses, a potential takeover can happen, and that can 404 00:25:36,880 --> 00:25:41,880 Speaker 1: happen really rapidly, So a redistribution of the resources that 405 00:25:41,920 --> 00:25:45,320 Speaker 1: can be really useful when a limb has been lost 406 00:25:45,560 --> 00:25:49,920 Speaker 1: or a sense has been lost. But the rapid conquest 407 00:25:49,960 --> 00:25:55,119 Speaker 1: of territory, you might have to actively counterbalance this in 408 00:25:55,200 --> 00:25:59,399 Speaker 1: other scenarios. And this consideration led me and my former 409 00:25:59,480 --> 00:26:04,560 Speaker 1: student Dawn Vaughan to propose a new theory for what 410 00:26:04,680 --> 00:26:08,399 Speaker 1: happens to brains in the dark of the night. So 411 00:26:08,480 --> 00:26:10,600 Speaker 1: now we're back to the main question of this episode. 412 00:26:10,720 --> 00:26:14,359 Speaker 1: What does dreaming have to do with the rotation of 413 00:26:14,440 --> 00:26:18,120 Speaker 1: the planet. And this is one of the unsolved mysteries 414 00:26:18,160 --> 00:26:19,119 Speaker 1: in neurosciences. 415 00:26:19,200 --> 00:26:21,199 Speaker 2: Why brains dream? 416 00:26:21,320 --> 00:26:25,480 Speaker 1: What these bizarre nighttime hallucinations are about. 417 00:26:25,920 --> 00:26:26,919 Speaker 2: Do they have meaning? 418 00:26:26,960 --> 00:26:30,280 Speaker 1: Are they simply random neural activity in search of a 419 00:26:30,320 --> 00:26:36,080 Speaker 1: coherent narrative? And why are dreams so richly visual igniting 420 00:26:36,119 --> 00:26:40,439 Speaker 1: the occipital cortex every night in this conflagration of activity. 421 00:26:40,840 --> 00:26:42,120 Speaker 2: So here's our idea. 422 00:26:42,800 --> 00:26:48,119 Speaker 1: In the chronic and unforgiving competition for brain real estate, 423 00:26:48,240 --> 00:26:51,760 Speaker 1: the visual system has a unique problem to deal with. 424 00:26:52,160 --> 00:26:56,040 Speaker 1: Because of the rotation of the planet, we are cast 425 00:26:56,119 --> 00:26:59,920 Speaker 1: into darkness for an average of twelve hours every cycle. 426 00:27:00,200 --> 00:27:03,520 Speaker 1: And obviously, I'm referring to ninety nine point nine nine 427 00:27:03,680 --> 00:27:07,280 Speaker 1: nine percent of our species evolutionary history. I'm not talking 428 00:27:07,320 --> 00:27:11,040 Speaker 1: about the current electricity blessed times. So it used to 429 00:27:11,119 --> 00:27:13,480 Speaker 1: be really, really dark at night. And I just told 430 00:27:13,560 --> 00:27:19,000 Speaker 1: you about how sensory deprivation triggers neighboring territories in the 431 00:27:19,040 --> 00:27:23,280 Speaker 1: brain to take over. So how does the visual system 432 00:27:23,720 --> 00:27:28,479 Speaker 1: deal with this unfair disadvantage? And we suggest that it 433 00:27:28,520 --> 00:27:34,760 Speaker 1: does so by keeping the occipital cortex active during the night. 434 00:27:35,280 --> 00:27:39,600 Speaker 1: We suggest that dreaming exists to keep the visual cortex 435 00:27:40,000 --> 00:27:44,479 Speaker 1: from being taken over by neighboring areas. Because the rotation 436 00:27:44,560 --> 00:27:47,879 Speaker 1: of the planet doesn't affect your ability to touch and 437 00:27:47,920 --> 00:27:51,879 Speaker 1: hear and taste and smell, only vision suffers in the dark, 438 00:27:52,359 --> 00:27:57,080 Speaker 1: and as a result, the visual cortex finds itself in danger. 439 00:27:57,160 --> 00:28:00,359 Speaker 1: Every night of takeover by the other sense is just 440 00:28:00,400 --> 00:28:04,480 Speaker 1: like with the blindfolded subjects, and given the amazing speed 441 00:28:04,560 --> 00:28:09,199 Speaker 1: with which these changes in territory can happen, this is 442 00:28:09,200 --> 00:28:13,920 Speaker 1: a real threat. So dreams are the means by which 443 00:28:14,400 --> 00:28:19,000 Speaker 1: the visual cortex prevents takeover. So to dig into this 444 00:28:19,119 --> 00:28:24,879 Speaker 1: idea a little more, let's zoom out. Although a sleeper 445 00:28:25,480 --> 00:28:30,560 Speaker 1: looks relaxed and shut down, the brain is fully electrically active, 446 00:28:31,119 --> 00:28:33,879 Speaker 1: so during most of the night there's no dreaming. But 447 00:28:34,000 --> 00:28:37,240 Speaker 1: during rem sleep there's a lot of things that happen. 448 00:28:37,440 --> 00:28:41,200 Speaker 1: So the heart rate and the breathing speed up, your 449 00:28:41,280 --> 00:28:45,880 Speaker 1: small muscles twitch, and your brain waves become smaller and faster, 450 00:28:46,440 --> 00:28:48,040 Speaker 1: and dreaming happens. 451 00:28:48,640 --> 00:28:48,880 Speaker 2: Now. 452 00:28:49,000 --> 00:28:52,240 Speaker 1: REM sleep is triggered by a particular set of neurons 453 00:28:52,240 --> 00:28:54,960 Speaker 1: in the brain stem in a structure called the ponds, 454 00:28:55,200 --> 00:28:58,320 Speaker 1: and that travels to a small nucleus in the thalamus, 455 00:28:58,400 --> 00:29:02,200 Speaker 1: and from there, these waves of electrical activity come banging 456 00:29:02,200 --> 00:29:04,800 Speaker 1: into the occipital cortex at the back of your head. 457 00:29:05,040 --> 00:29:08,280 Speaker 1: Now that's the area of your brain where your visual 458 00:29:08,320 --> 00:29:11,920 Speaker 1: system is. So when these visual areas become alive with 459 00:29:12,080 --> 00:29:17,800 Speaker 1: activity in their cells, that is experienced as visual we see. 460 00:29:18,400 --> 00:29:22,240 Speaker 1: And that's why dreams are pictorial like a film. If 461 00:29:22,280 --> 00:29:25,280 Speaker 1: the activity we're banging into a part of the cortex 462 00:29:25,320 --> 00:29:29,040 Speaker 1: involved in smell, then dreams would just be a smell story, 463 00:29:29,320 --> 00:29:32,040 Speaker 1: but it hits the visual area, and so we find 464 00:29:32,080 --> 00:29:36,440 Speaker 1: ourselves thrown into a movie. Now, if you're seeing all 465 00:29:36,520 --> 00:29:38,920 Speaker 1: kinds of stuff, you might wonder why you're not reacting 466 00:29:38,960 --> 00:29:41,920 Speaker 1: to that with your body, And that's because the circuitry 467 00:29:41,920 --> 00:29:46,840 Speaker 1: involved in dreaming also paralyzes your major muscle groups so 468 00:29:46,840 --> 00:29:49,560 Speaker 1: that you don't act out your dream. You shut down 469 00:29:49,600 --> 00:29:53,480 Speaker 1: your muscles so that you can simulate world experience without 470 00:29:53,560 --> 00:29:58,360 Speaker 1: actually moving your body around, and that combination crafts the 471 00:29:58,480 --> 00:30:03,160 Speaker 1: experience of dreaming. The electrical waves slamming into the occipital 472 00:30:03,160 --> 00:30:07,160 Speaker 1: cortex make your visual system alive with activity, and the 473 00:30:07,280 --> 00:30:12,080 Speaker 1: muscular paralysis keeps you from acting out the dreams. Now, 474 00:30:12,280 --> 00:30:19,680 Speaker 1: we theorize that the circuitry behind visual dreams is not accidental. Instead, 475 00:30:19,760 --> 00:30:23,440 Speaker 1: to prevent takeover, the visual system is forced to fight 476 00:30:23,520 --> 00:30:27,840 Speaker 1: for its territory by generating these short bursts of activity 477 00:30:27,880 --> 00:30:32,320 Speaker 1: every ninety minutes or so when the planet rotates into darkness. 478 00:30:32,920 --> 00:30:37,480 Speaker 1: It's a self defense system that evolved in the face 479 00:30:37,520 --> 00:30:43,120 Speaker 1: of constant competition for sensory real estate. Dreams are a 480 00:30:43,280 --> 00:30:48,520 Speaker 1: screen saver. So the idea is that vision carries mission 481 00:30:48,560 --> 00:30:52,640 Speaker 1: critical information for the brain, but vision is stolen away 482 00:30:52,800 --> 00:30:56,400 Speaker 1: for half of our hours. It's like we're blindfolded for 483 00:30:56,440 --> 00:31:00,520 Speaker 1: half our time here on Earth. So dreams, we say, suggest, 484 00:31:01,040 --> 00:31:06,240 Speaker 1: are the strange love child of neural plasticity and the 485 00:31:06,360 --> 00:31:10,040 Speaker 1: rotation of the planet. Now, one key point to appreciate 486 00:31:10,200 --> 00:31:16,000 Speaker 1: is that these nighttime volleys of activity are very anatomically precise. 487 00:31:16,360 --> 00:31:18,560 Speaker 1: They start in the brain stem and they end up 488 00:31:18,560 --> 00:31:22,560 Speaker 1: in only one place, the occipital cortex. If the circuitry 489 00:31:22,960 --> 00:31:26,520 Speaker 1: sort of randomly grew its branches, we'd expect it to 490 00:31:26,560 --> 00:31:28,600 Speaker 1: connect with all kinds of areas in the brain, but 491 00:31:28,680 --> 00:31:34,640 Speaker 1: it doesn't. It aims with anatomical precision at one area alone, 492 00:31:34,800 --> 00:31:39,560 Speaker 1: a tiny structure called the lateral geniculate nucleus which broadcasts 493 00:31:39,800 --> 00:31:44,680 Speaker 1: specifically to the occipital cortex and through a neuroanatomous lens. 494 00:31:44,760 --> 00:31:50,240 Speaker 1: This is really specific circuitry and that suggests an important role, 495 00:31:50,680 --> 00:31:54,840 Speaker 1: and we suggest that role is defense of the visual system. 496 00:31:54,920 --> 00:31:59,680 Speaker 1: So we call this the defensive activation theory. Now, I 497 00:31:59,760 --> 00:32:01,840 Speaker 1: want to address a question that might be coming up 498 00:32:01,840 --> 00:32:05,360 Speaker 1: for you, which is what about dream content? Why did 499 00:32:05,440 --> 00:32:09,840 Speaker 1: dreams seem to be about something rather than just random 500 00:32:10,000 --> 00:32:12,800 Speaker 1: dots of light? Well, the important thing to understand is 501 00:32:12,840 --> 00:32:17,120 Speaker 1: that the brain is a natural storyteller. When there's activity 502 00:32:17,160 --> 00:32:20,400 Speaker 1: in there, it shapes that into a story of what 503 00:32:20,440 --> 00:32:23,680 Speaker 1: it's seeing. For those of you who know about latent 504 00:32:23,880 --> 00:32:27,720 Speaker 1: diffusion models in AI, that's exactly the same thing. So 505 00:32:28,040 --> 00:32:32,840 Speaker 1: Dolly two and stable diffusion. These are image generators, and 506 00:32:32,880 --> 00:32:36,880 Speaker 1: they work by starting with random activity and that coheres 507 00:32:37,120 --> 00:32:40,640 Speaker 1: into a picture of something in exactly the same way. 508 00:32:40,840 --> 00:32:44,880 Speaker 1: The brain can't see random activity. It has to wrap 509 00:32:44,920 --> 00:32:49,680 Speaker 1: that into something particular that it is seeing. Now, why 510 00:32:49,720 --> 00:32:53,880 Speaker 1: are dreams a story instead of just a picture? The 511 00:32:54,040 --> 00:32:58,000 Speaker 1: key is that everything in the brain is linked by association. 512 00:32:58,440 --> 00:33:01,440 Speaker 1: So when you think of a rabbit, that's linked with 513 00:33:01,520 --> 00:33:05,920 Speaker 1: everything you've ever associated with. Rabbits carrots and shadow puppets 514 00:33:05,920 --> 00:33:09,440 Speaker 1: and the velveteen rabbit and Easter and Alice in Wonderland, 515 00:33:09,480 --> 00:33:14,400 Speaker 1: and maybe a French restaurant that serves rabbit and Roger Rabbit. 516 00:33:14,120 --> 00:33:14,600 Speaker 2: And so on. 517 00:33:15,040 --> 00:33:18,600 Speaker 1: This is how an associative neural network is structured. Everything 518 00:33:18,720 --> 00:33:24,080 Speaker 1: is linked by association. So what happens during dreams is 519 00:33:24,080 --> 00:33:27,560 Speaker 1: that this random activity gets shot into the visual system 520 00:33:27,800 --> 00:33:30,800 Speaker 1: and synapses that are hot from the day will tend 521 00:33:30,800 --> 00:33:33,960 Speaker 1: to get activated again. But from there the activity will 522 00:33:34,000 --> 00:33:39,040 Speaker 1: tend to drift along these associative pathways, and that's why 523 00:33:39,120 --> 00:33:43,640 Speaker 1: dreams seem to have a unifying thread, but they're also 524 00:33:43,920 --> 00:33:49,160 Speaker 1: characterized by bizarreness. The storyline drifts from thing to thing 525 00:33:49,240 --> 00:33:51,400 Speaker 1: in a way that's not quite like the real world 526 00:33:51,880 --> 00:33:56,280 Speaker 1: because it's activity that's moving through this associative neural network, 527 00:33:56,680 --> 00:33:59,960 Speaker 1: and we experience whatever is getting triggered in whatever world, 528 00:34:00,720 --> 00:34:03,719 Speaker 1: So it's tied to our experience from the day and 529 00:34:03,760 --> 00:34:05,760 Speaker 1: of the world we know. But it's a very loose 530 00:34:06,160 --> 00:34:10,040 Speaker 1: sort of story, and the brain is a natural storyteller, 531 00:34:10,120 --> 00:34:13,799 Speaker 1: so things get tied together as best they can, and 532 00:34:13,840 --> 00:34:17,720 Speaker 1: we shouldn't overlook the fact that we are storytellers. 533 00:34:17,760 --> 00:34:18,960 Speaker 2: Even after we wake up. 534 00:34:19,040 --> 00:34:22,960 Speaker 1: So when you tell your spouse or your friend, wow, 535 00:34:23,000 --> 00:34:26,200 Speaker 1: this happened, and then this happened, we can't help but 536 00:34:26,800 --> 00:34:30,640 Speaker 1: impose a narrative over the images we saw. And so 537 00:34:30,760 --> 00:34:35,440 Speaker 1: sometimes the series of images we experienced gets even a 538 00:34:35,600 --> 00:34:39,480 Speaker 1: stronger storyline put on top of it. And by the way, 539 00:34:39,520 --> 00:34:41,279 Speaker 1: I just want to mention one other thing. You might 540 00:34:41,360 --> 00:34:46,040 Speaker 1: wonder how it makes sense that sometimes you hear sounds 541 00:34:46,120 --> 00:34:48,480 Speaker 1: or feel touch or have a smell in a dream 542 00:34:48,719 --> 00:34:51,840 Speaker 1: if the activity is only going into the visual cortex, well, 543 00:34:51,920 --> 00:34:55,080 Speaker 1: that seems to happen sometimes. And that's because although the 544 00:34:55,120 --> 00:34:57,759 Speaker 1: activity is only going in the visual system, it can 545 00:34:57,880 --> 00:35:01,320 Speaker 1: cascade out and keep going to other parts of the brain. 546 00:35:01,480 --> 00:35:05,120 Speaker 1: Everything is connected to everything else with pretty short pathways. 547 00:35:05,440 --> 00:35:08,560 Speaker 1: But it's important to note that dreams are almost entirely 548 00:35:09,080 --> 00:35:12,640 Speaker 1: visual because that's the only place where the activity is 549 00:35:12,680 --> 00:35:35,120 Speaker 1: getting injected. Now, something you might wonder, given this defensive 550 00:35:35,160 --> 00:35:36,320 Speaker 1: activation theory. 551 00:35:36,040 --> 00:35:39,600 Speaker 2: That I've described so far, what about blind people? 552 00:35:39,680 --> 00:35:42,480 Speaker 1: Do they have dreams or do you think they have 553 00:35:42,560 --> 00:35:45,240 Speaker 1: no dreaming at all because their brains don't care about 554 00:35:45,239 --> 00:35:48,440 Speaker 1: the light in the dark. The answer is that people 555 00:35:48,520 --> 00:35:52,040 Speaker 1: who are blind, of course, they have dreams. But if 556 00:35:52,040 --> 00:35:54,920 Speaker 1: they've been blind from birth or from a very young age, 557 00:35:54,960 --> 00:36:00,440 Speaker 1: they have no visual experience in their dreams because their 558 00:36:00,560 --> 00:36:03,560 Speaker 1: visual system was taken over by other senses like hearing 559 00:36:03,640 --> 00:36:07,920 Speaker 1: in touch, and so they have those sensory experiences in 560 00:36:08,000 --> 00:36:10,680 Speaker 1: their dreams because the activity is still going into the 561 00:36:10,680 --> 00:36:13,640 Speaker 1: occipital lobe. It's just that that's no longer visual. So 562 00:36:13,760 --> 00:36:16,399 Speaker 1: their dream is something like, I was feeling my way 563 00:36:16,400 --> 00:36:19,840 Speaker 1: around my living room, but it was weird because someone 564 00:36:19,840 --> 00:36:21,240 Speaker 1: had rearranged all the furniture. 565 00:36:21,280 --> 00:36:24,040 Speaker 2: And then I felt something strange in the corner. 566 00:36:23,840 --> 00:36:26,520 Speaker 1: And I realized it was a bear, and I ran 567 00:36:26,600 --> 00:36:28,719 Speaker 1: and I could hear it behind me, and so on 568 00:36:28,800 --> 00:36:31,439 Speaker 1: this sort of thing. All their experiences in the dream 569 00:36:31,600 --> 00:36:36,520 Speaker 1: involved sound and touch, but not sight. In those born blind, 570 00:36:36,600 --> 00:36:39,520 Speaker 1: you still have these volleys of spikes blasting into the 571 00:36:39,560 --> 00:36:42,240 Speaker 1: back of the brain because that's where the circuitry is going, 572 00:36:42,680 --> 00:36:45,000 Speaker 1: but that part of the brain is no longer visual, 573 00:36:45,040 --> 00:36:48,879 Speaker 1: and their experiences are not visual. And this tells us 574 00:36:49,000 --> 00:36:54,480 Speaker 1: that the circuitry underlying dreaming it's very basic, low level circuitry. 575 00:36:54,560 --> 00:36:58,719 Speaker 1: It's not dependent on the experiences you have during your lifetime, 576 00:36:59,080 --> 00:37:02,560 Speaker 1: and the fundamental nature of this circuitry is also consistent 577 00:37:02,600 --> 00:37:06,000 Speaker 1: with the fact that we find it conserved across the 578 00:37:06,080 --> 00:37:10,480 Speaker 1: animal kingdom. Now, like any scientific idea, the defensive activation 579 00:37:10,640 --> 00:37:13,239 Speaker 1: theory could be correct or could not be. 580 00:37:13,520 --> 00:37:14,840 Speaker 2: So how would we know. 581 00:37:15,320 --> 00:37:17,759 Speaker 1: Well, we can start looking at the predictions that come 582 00:37:17,880 --> 00:37:21,839 Speaker 1: out of this hypothesis. First is just a general observation, 583 00:37:22,360 --> 00:37:24,960 Speaker 1: which is that you can look at the fall off 584 00:37:25,120 --> 00:37:28,960 Speaker 1: in REM's sleep with age. So the fraction of our 585 00:37:29,120 --> 00:37:34,279 Speaker 1: sleeping time that we spend in REM steadily decreases as 586 00:37:34,320 --> 00:37:37,640 Speaker 1: we get older. So as an infant you spend half 587 00:37:37,719 --> 00:37:40,440 Speaker 1: your sleeping time in REM, and as an adult you 588 00:37:40,480 --> 00:37:43,360 Speaker 1: spend only ten to twenty percent of sleep time in REM, 589 00:37:43,400 --> 00:37:46,279 Speaker 1: and when you're elderly you spend even less. And this 590 00:37:46,400 --> 00:37:50,160 Speaker 1: is consistent with the fact that infant's brains are much 591 00:37:50,200 --> 00:37:53,920 Speaker 1: more plastic, and so the competition for territory is really intense, 592 00:37:54,320 --> 00:37:58,399 Speaker 1: and as you get older, things settle into place and 593 00:37:58,520 --> 00:38:02,680 Speaker 1: cortical takeovers are harder to do. So the fall off 594 00:38:02,719 --> 00:38:06,759 Speaker 1: in plasticity parallels the fall off of time that you 595 00:38:06,800 --> 00:38:09,880 Speaker 1: spend in REM sleep. And by the way, this fall 596 00:38:09,960 --> 00:38:14,040 Speaker 1: off in REM is seen across species, so puppies and 597 00:38:14,160 --> 00:38:18,879 Speaker 1: kittens and every kind of baby has more rem sleep. Now, 598 00:38:18,960 --> 00:38:22,120 Speaker 1: this observation by itself isn't proof of anything, but it's 599 00:38:22,160 --> 00:38:23,239 Speaker 1: an interesting correlation. 600 00:38:23,560 --> 00:38:24,719 Speaker 2: But could we look. 601 00:38:24,680 --> 00:38:28,799 Speaker 1: Across species to see if we can make meaningful predictions 602 00:38:29,160 --> 00:38:32,280 Speaker 1: about which species dreams a lot and which a little. 603 00:38:32,600 --> 00:38:37,560 Speaker 1: In other words, how much time each species spends in 604 00:38:37,680 --> 00:38:40,960 Speaker 1: dream time. So the idea is that for a brain 605 00:38:41,000 --> 00:38:43,520 Speaker 1: that is born with a lot of plasticity, a lot 606 00:38:43,520 --> 00:38:46,640 Speaker 1: of flexibility, you need to keep the visual system well 607 00:38:46,719 --> 00:38:49,920 Speaker 1: protected at night. But some animals are born with a 608 00:38:49,960 --> 00:38:54,200 Speaker 1: lot less plasticity, Their brains are more ready to go, 609 00:38:54,640 --> 00:38:57,680 Speaker 1: and so the need to have this defensive activation at 610 00:38:57,760 --> 00:39:02,560 Speaker 1: night would be less. Take primate like the vervet monkey. 611 00:39:02,920 --> 00:39:05,719 Speaker 1: Within three weeks, it learns how to walk, and it 612 00:39:05,840 --> 00:39:10,480 Speaker 1: stops weaning within four months, and it reaches adolescens in 613 00:39:10,640 --> 00:39:13,400 Speaker 1: four years and it can reproduce. Now, look at a 614 00:39:13,440 --> 00:39:17,920 Speaker 1: baby human. We're primates also, But in contrast to the 615 00:39:18,000 --> 00:39:22,280 Speaker 1: vervet monkey, the human primate doesn't walk for a year, 616 00:39:22,640 --> 00:39:25,440 Speaker 1: and it doesn't wean until three years, and it doesn't 617 00:39:25,520 --> 00:39:31,160 Speaker 1: reach adolescens for thirteen years. Why it's because human brains 618 00:39:31,440 --> 00:39:36,160 Speaker 1: drop into the world half baked, and we're incredibly flexible. 619 00:39:36,320 --> 00:39:39,680 Speaker 1: That's how we absorb the language and culture and the 620 00:39:39,719 --> 00:39:45,000 Speaker 1: knowledge around us. We're super flexible, and the consequence is 621 00:39:45,000 --> 00:39:49,960 Speaker 1: that we have an unusually long childhood. But other animals 622 00:39:50,080 --> 00:39:53,759 Speaker 1: arrive more let's call it pre programmed, and they're just 623 00:39:53,840 --> 00:39:58,239 Speaker 1: following more basic instructions of eat, mate, run, approach and 624 00:39:58,280 --> 00:40:02,160 Speaker 1: so on. There's no vervet monkey culture to absorb. They 625 00:40:02,160 --> 00:40:04,520 Speaker 1: don't go to vervet monkey schools so that they can 626 00:40:04,600 --> 00:40:07,759 Speaker 1: learn about the discoveries of other monkeys before them so 627 00:40:07,800 --> 00:40:11,879 Speaker 1: they can springboard to the next steps. Instead, they live 628 00:40:11,960 --> 00:40:15,399 Speaker 1: essentially the same life as all the generations before them. 629 00:40:15,880 --> 00:40:20,279 Speaker 1: So different species, even closely related primate species, can have 630 00:40:20,480 --> 00:40:25,120 Speaker 1: very different levels of plasticity. And the question is how 631 00:40:25,160 --> 00:40:27,840 Speaker 1: does this translate to the amount of dreaming they do 632 00:40:28,080 --> 00:40:32,480 Speaker 1: each night. And our hypothesis is that the more plastic 633 00:40:32,520 --> 00:40:36,040 Speaker 1: species need more dreaming at night to make sure that 634 00:40:36,080 --> 00:40:39,040 Speaker 1: big changes don't happen and the visual system doesn't get 635 00:40:39,080 --> 00:40:39,680 Speaker 1: taken over. 636 00:40:40,160 --> 00:40:42,320 Speaker 2: If you are a less plastic. 637 00:40:41,880 --> 00:40:45,400 Speaker 1: Species, the brain is essentially more fixed into place and 638 00:40:45,400 --> 00:40:49,560 Speaker 1: there's less risk of takeover of the visual system in 639 00:40:49,600 --> 00:40:54,960 Speaker 1: the darkness. So we studied twenty five primate species and 640 00:40:55,000 --> 00:40:58,399 Speaker 1: we research the plasticity of their brain, or at least 641 00:40:58,440 --> 00:41:01,120 Speaker 1: correlates of plasticity, like how long it takes for them 642 00:41:01,120 --> 00:41:04,640 Speaker 1: to walk or to wean from their mothers, or how 643 00:41:04,719 --> 00:41:08,480 Speaker 1: long until they reach adolescence. And we also research the 644 00:41:08,560 --> 00:41:12,880 Speaker 1: percentage of their sleep time that each species spends in 645 00:41:13,080 --> 00:41:16,640 Speaker 1: REM sleep. Typically, this is measured by setting up infrared 646 00:41:16,760 --> 00:41:19,560 Speaker 1: cameras and watching the animals sleep through the night and 647 00:41:19,600 --> 00:41:22,799 Speaker 1: figuring out what percentage of their sleep time they have 648 00:41:22,920 --> 00:41:26,600 Speaker 1: this rapid eye movement going on underneath their eyelids. And 649 00:41:26,640 --> 00:41:30,319 Speaker 1: what's striking is that this varies pretty widely. So the 650 00:41:30,480 --> 00:41:34,480 Speaker 1: vervet monkey spends six percent of its sleep time in 651 00:41:34,680 --> 00:41:38,240 Speaker 1: REM and then you have a spider monkey spending seven percent, 652 00:41:38,320 --> 00:41:41,560 Speaker 1: and a yellow babboon spending eight percent, and a barbary 653 00:41:41,640 --> 00:41:45,000 Speaker 1: macaque monkey spending nine percent, all the way to a 654 00:41:45,000 --> 00:41:50,240 Speaker 1: bornean orangutan spending twelve percent, to a chimpanzee spending sixteen percent, 655 00:41:50,560 --> 00:41:55,400 Speaker 1: to a reeseus macaque monkey spending eighteen percent, to humans 656 00:41:55,640 --> 00:42:00,840 Speaker 1: spending twenty one percent of their sleeping time in REM. Now, 657 00:42:01,200 --> 00:42:05,719 Speaker 1: we compiled all this data and we found statistically significant 658 00:42:05,760 --> 00:42:11,440 Speaker 1: correlations between plasticity and the amount of remsleep In other words, 659 00:42:11,800 --> 00:42:15,759 Speaker 1: the less plastic an animal is, the less remsleep it 660 00:42:15,800 --> 00:42:18,600 Speaker 1: has during the night, and animals with brains that are 661 00:42:18,680 --> 00:42:23,640 Speaker 1: more plastic, whose brains have more territory shifting around, they 662 00:42:23,640 --> 00:42:26,960 Speaker 1: have more rem sleep. And by the way, as a control, 663 00:42:27,040 --> 00:42:31,000 Speaker 1: we gathered four other variables across these species, like weight 664 00:42:31,080 --> 00:42:34,040 Speaker 1: and length and how many offspring they have and average lifespan. 665 00:42:34,280 --> 00:42:38,160 Speaker 1: And as expected, all of those measures show no significant 666 00:42:38,239 --> 00:42:41,520 Speaker 1: correlations with the amount of remsleep, but the measures of 667 00:42:41,560 --> 00:42:45,480 Speaker 1: how plastic an animal was did correlate, And if you're 668 00:42:45,480 --> 00:42:48,040 Speaker 1: interested in the details, you can read our scientific publication 669 00:42:48,239 --> 00:42:51,400 Speaker 1: linked to the podcast website. Now, there are several ways 670 00:42:51,440 --> 00:42:54,839 Speaker 1: to test this framework further. For example, what happens if 671 00:42:54,840 --> 00:42:58,440 Speaker 1: somebody doesn't get the normal amount of dream sleep. Well, 672 00:42:58,440 --> 00:43:03,680 Speaker 1: as it turns out, sleep can be suppressed by certain antidepressants. 673 00:43:04,040 --> 00:43:09,800 Speaker 1: For the cognianty these are monoamine oxidase inhibitors and tricyclic antidepressants. Anyway, 674 00:43:10,040 --> 00:43:13,160 Speaker 1: the defensive activation theory would predict that if you're not 675 00:43:13,360 --> 00:43:16,879 Speaker 1: getting adequate rem sleep, you're going to have some sort 676 00:43:16,880 --> 00:43:21,080 Speaker 1: of visual consequences, and so it's interesting that patients on 677 00:43:21,160 --> 00:43:26,760 Speaker 1: these medications characteristically get blurry vision. Now this is typically 678 00:43:26,800 --> 00:43:29,160 Speaker 1: marked up to dry eyes, but I want to note 679 00:43:29,200 --> 00:43:32,440 Speaker 1: our alternative hypothesis here, which is that it might be 680 00:43:32,480 --> 00:43:36,120 Speaker 1: related to more takeover of the visual cortex. I don't 681 00:43:36,160 --> 00:43:38,200 Speaker 1: know for sure that this is true yet, but this 682 00:43:38,239 --> 00:43:40,600 Speaker 1: is a direction the research is going to go. And 683 00:43:40,800 --> 00:43:44,440 Speaker 1: also we can test across a huge variety of animal species, 684 00:43:44,520 --> 00:43:48,719 Speaker 1: not just primates. For example, some mammals are born immature, 685 00:43:48,880 --> 00:43:51,440 Speaker 1: meaning that they're unable to walk, or get food, or 686 00:43:51,480 --> 00:43:54,680 Speaker 1: regulate their own temperature, or defend themselves. These are animals 687 00:43:54,680 --> 00:43:59,680 Speaker 1: like humans and ferrets and platypuses. Other mammals are born mature, 688 00:44:00,239 --> 00:44:03,200 Speaker 1: such as guinea pig or sheep or giraffe. They come 689 00:44:03,239 --> 00:44:06,040 Speaker 1: out of the womb with teeth and fur and open 690 00:44:06,080 --> 00:44:09,480 Speaker 1: eyes and ability to regulate their own temperature, and they 691 00:44:09,560 --> 00:44:11,959 Speaker 1: walk within an hour of being born, and they eat 692 00:44:12,000 --> 00:44:15,960 Speaker 1: solid food. So here's the important clue. As a general rule, 693 00:44:16,480 --> 00:44:20,440 Speaker 1: the animals born immature have much more rem sleep, up 694 00:44:20,440 --> 00:44:23,640 Speaker 1: to eight times as much, and this difference is especially 695 00:44:23,719 --> 00:44:27,279 Speaker 1: clear in the first months of life. In our interpretation, 696 00:44:27,400 --> 00:44:30,560 Speaker 1: when a highly plastic brain drops into the world, it 697 00:44:30,680 --> 00:44:34,279 Speaker 1: needs to constantly fight to keep things balanced. But when 698 00:44:34,320 --> 00:44:37,680 Speaker 1: a brain arrives mostly solidify, there's less need for it 699 00:44:37,719 --> 00:44:41,080 Speaker 1: to engage in this nighttime fighting. I just want to 700 00:44:41,080 --> 00:44:43,279 Speaker 1: mention as a caveat that there's likely to be many 701 00:44:43,400 --> 00:44:48,120 Speaker 1: surprises here because an animal's sleeping and dreaming can be 702 00:44:48,239 --> 00:44:51,160 Speaker 1: very different depending on lots of other things. For example, 703 00:44:51,480 --> 00:44:56,760 Speaker 1: take the elephant. They have a really surprisingly small amount 704 00:44:56,800 --> 00:44:59,840 Speaker 1: of rem sleep a few minutes at most, and it 705 00:45:00,000 --> 00:45:03,600 Speaker 1: first blush, I thought this weighed against our hypothesis, But 706 00:45:03,680 --> 00:45:07,560 Speaker 1: it turns out that elephants sleep very little, around two 707 00:45:07,600 --> 00:45:10,720 Speaker 1: hours a night, and they have excellent night vision because 708 00:45:10,760 --> 00:45:14,239 Speaker 1: of specializations in their retinas, and as a result, their 709 00:45:14,320 --> 00:45:17,800 Speaker 1: visual corettix is active during almost all hours of the 710 00:45:17,880 --> 00:45:20,640 Speaker 1: day and the night, and so that doesn't face the 711 00:45:20,680 --> 00:45:25,000 Speaker 1: same threat of encroachment from the other senses. So the 712 00:45:25,080 --> 00:45:28,760 Speaker 1: hypothesis predicts that elephants should have very little rems sleep. 713 00:45:29,000 --> 00:45:31,600 Speaker 1: So stay tuned on the future of this hypothesis. But 714 00:45:31,640 --> 00:45:34,080 Speaker 1: I wanted to take the chance to walk you through 715 00:45:34,080 --> 00:45:36,480 Speaker 1: a few of the details about how you might think 716 00:45:36,480 --> 00:45:39,160 Speaker 1: about a question like dreaming and come up with new 717 00:45:39,200 --> 00:45:43,560 Speaker 1: frameworks and then test those. Now, one last idea to 718 00:45:43,600 --> 00:45:47,560 Speaker 1: close this out, what does our defensive activation theory mean 719 00:45:48,160 --> 00:45:52,240 Speaker 1: for aliens on other planets. In Live, wied I proposed 720 00:45:52,280 --> 00:45:54,799 Speaker 1: a hypothesis that we won't actually be able to test 721 00:45:54,920 --> 00:45:58,160 Speaker 1: until the very distant future when we discover life on 722 00:45:58,239 --> 00:46:02,319 Speaker 1: other planets. Some planet, especially those that are orbiting red 723 00:46:02,400 --> 00:46:06,000 Speaker 1: dwarf stars, become locked into place such that they always 724 00:46:06,040 --> 00:46:10,040 Speaker 1: have the same surface facing their star. They have permanent 725 00:46:10,120 --> 00:46:12,919 Speaker 1: day on one side and permanent night on the other. 726 00:46:13,360 --> 00:46:17,560 Speaker 1: If life forms on that planet were to have plastic 727 00:46:17,680 --> 00:46:21,160 Speaker 1: brains that are even vaguely similar to ours, the prediction 728 00:46:21,280 --> 00:46:23,880 Speaker 1: would be that those on the daylight side of the 729 00:46:23,880 --> 00:46:27,080 Speaker 1: planet might have vision like us, but they would not 730 00:46:27,239 --> 00:46:30,959 Speaker 1: have dreams. They wouldn't need them because they never get 731 00:46:31,040 --> 00:46:34,759 Speaker 1: plunged into darkness, and the same prediction would apply for 732 00:46:34,960 --> 00:46:39,640 Speaker 1: very fast spinning planets. If their nighttime is shorter than 733 00:46:39,680 --> 00:46:42,480 Speaker 1: the time of a sensory takeover in the brain, then 734 00:46:42,480 --> 00:46:46,279 Speaker 1: they also wouldn't need dreams. So thousands of years from 735 00:46:46,360 --> 00:46:51,200 Speaker 1: now we might finally know whether we dreamers are in 736 00:46:51,239 --> 00:46:53,239 Speaker 1: the universal minority. 737 00:46:57,840 --> 00:46:59,000 Speaker 2: That's all for this week. 738 00:46:59,280 --> 00:47:01,759 Speaker 1: To find out more and to share your thoughts, head 739 00:47:01,760 --> 00:47:05,600 Speaker 1: over to Eagleman dot com, Slash Podcasts, and you can 740 00:47:05,640 --> 00:47:10,080 Speaker 1: also watch full episodes of Inner Cosmos on YouTube. Subscribe 741 00:47:10,080 --> 00:47:12,399 Speaker 1: to my channel so you can follow along each week 742 00:47:12,440 --> 00:47:16,400 Speaker 1: for new updates. I'd love to hear your questions, so 743 00:47:16,520 --> 00:47:20,600 Speaker 1: please send those to podcasts at eagleman dot com and 744 00:47:20,640 --> 00:47:23,400 Speaker 1: I will do a special episode where I answer questions. 745 00:47:23,880 --> 00:47:27,319 Speaker 1: Until next time, I'm David Eagleman, signing off to you 746 00:47:27,840 --> 00:47:29,200 Speaker 1: from the Inner Cosmos.