1 00:00:05,240 --> 00:00:09,200 Speaker 1: Why do we spend one third of our lives asleep? 2 00:00:09,880 --> 00:00:12,360 Speaker 1: What does this have to do with living in an 3 00:00:12,480 --> 00:00:16,880 Speaker 1: underground cave with no light, or whether we can die 4 00:00:17,040 --> 00:00:20,400 Speaker 1: from a lack of sleep, or the length of a 5 00:00:20,600 --> 00:00:24,720 Speaker 1: day on Mars. Why are some people night owls and 6 00:00:24,880 --> 00:00:29,040 Speaker 1: some morning larks? How long is it possible to keep 7 00:00:29,080 --> 00:00:32,280 Speaker 1: yourself awake physically? And why does the Guinness Book of 8 00:00:32,280 --> 00:00:38,960 Speaker 1: World Records no longer track that record? Welcome to Inner 9 00:00:39,000 --> 00:00:42,760 Speaker 1: Cosmos with me David Eagleman. I'm a neuroscientist and author 10 00:00:42,800 --> 00:00:47,200 Speaker 1: at Stanford and in these episodes we sail deeply into 11 00:00:47,280 --> 00:00:51,680 Speaker 1: our three pound universe to understand why and how our 12 00:00:51,760 --> 00:01:04,320 Speaker 1: lives look the way they do. Today's episode is about sleep. 13 00:01:04,760 --> 00:01:07,160 Speaker 1: Why do we do it? Why do we spend so 14 00:01:07,360 --> 00:01:12,319 Speaker 1: much of our lives in this weird doppelganger state? When 15 00:01:12,360 --> 00:01:16,600 Speaker 1: you're asleep, it still looks like you, but you are 16 00:01:16,720 --> 00:01:20,560 Speaker 1: essentially shut off. And even though we're not typically aware 17 00:01:20,680 --> 00:01:23,679 Speaker 1: of being in this state, because we have no sense 18 00:01:23,720 --> 00:01:27,199 Speaker 1: of the passage of time there, we spend so much 19 00:01:27,200 --> 00:01:30,560 Speaker 1: of our lives there, more time than you spend doing 20 00:01:30,600 --> 00:01:34,400 Speaker 1: almost anything else, whether that's eating or showering or being 21 00:01:34,400 --> 00:01:39,280 Speaker 1: with friends. Or listening to podcasts. All of those presumably 22 00:01:39,360 --> 00:01:44,160 Speaker 1: take up a smaller fraction of your life. Sleeping is 23 00:01:44,200 --> 00:01:47,640 Speaker 1: at the top of your list of activities, and certainly 24 00:01:47,760 --> 00:01:50,600 Speaker 1: at the top of the list of activities that you 25 00:01:50,720 --> 00:01:57,200 Speaker 1: do consistently. Other hobbies come and go, sleep remains. So 26 00:01:57,320 --> 00:02:00,640 Speaker 1: in today's episode, we're going to talk about everything you've 27 00:02:00,680 --> 00:02:03,840 Speaker 1: ever wanted to know about sleep, and we're going to 28 00:02:03,960 --> 00:02:08,000 Speaker 1: uncover what the brain is really doing during this time. 29 00:02:08,639 --> 00:02:11,840 Speaker 1: And this is the first part of a three parter. 30 00:02:12,480 --> 00:02:15,920 Speaker 1: Next week we're going to dive into dreams. Why do 31 00:02:16,000 --> 00:02:19,399 Speaker 1: we dream? What's that about? Is it a form of consciousness? 32 00:02:19,680 --> 00:02:23,200 Speaker 1: Do all animals dream? And finally, two weeks from now, 33 00:02:23,639 --> 00:02:27,840 Speaker 1: will dive into lucid dreaming, which is where you become 34 00:02:28,360 --> 00:02:32,880 Speaker 1: consciously aware that you are in a dream state and 35 00:02:32,960 --> 00:02:36,760 Speaker 1: you are able to take control of the plot. So 36 00:02:36,919 --> 00:02:39,959 Speaker 1: join me for those episodes. They build on this one 37 00:02:40,080 --> 00:02:43,120 Speaker 1: about sleep, and I promise you there will be no 38 00:02:43,600 --> 00:02:48,760 Speaker 1: end of mind blowing surprises there. So for today's episode, 39 00:02:49,320 --> 00:02:52,320 Speaker 1: we're going to start in the early morning of May 40 00:02:52,480 --> 00:02:56,800 Speaker 1: twenty fourth, nineteen eighty seven, when a man named Kenneth 41 00:02:56,919 --> 00:03:00,880 Speaker 1: Parks is watching TV on the couch and he fall sleep, 42 00:03:01,720 --> 00:03:05,320 Speaker 1: and he gets up. He drives across the city of 43 00:03:05,360 --> 00:03:10,080 Speaker 1: Toronto where he lives, and he enters his in law's home, 44 00:03:10,760 --> 00:03:13,959 Speaker 1: and there he stabs his mother in law to death 45 00:03:14,040 --> 00:03:18,240 Speaker 1: and attempts to murder his father in law as well, 46 00:03:18,280 --> 00:03:22,280 Speaker 1: and then he drives himself to the police station and 47 00:03:22,400 --> 00:03:28,200 Speaker 1: turns himself in. Now everyone agrees that Kenneth Parks had 48 00:03:28,480 --> 00:03:31,320 Speaker 1: no motive. He loved his in laws and he had 49 00:03:31,320 --> 00:03:35,640 Speaker 1: a close relationship with them, and even more strangely, he 50 00:03:35,800 --> 00:03:40,960 Speaker 1: appears to have been asleep the whole time. Now, that 51 00:03:41,080 --> 00:03:45,760 Speaker 1: claim sounded outrageous to most people, especially as Parks had 52 00:03:45,800 --> 00:03:48,680 Speaker 1: to drive fourteen miles to get to his in law's home. 53 00:03:49,360 --> 00:03:54,000 Speaker 1: But as the case was investigated, the sleepwalking story began 54 00:03:54,120 --> 00:03:57,840 Speaker 1: to take shape. When he arrived at the police station, 55 00:03:58,040 --> 00:04:01,800 Speaker 1: he had looked down in confusion at his bloodied hands 56 00:04:01,840 --> 00:04:05,360 Speaker 1: and he said, quote, I think I may have killed 57 00:04:05,400 --> 00:04:09,200 Speaker 1: some people. He claimed to have no memory of what 58 00:04:09,240 --> 00:04:14,280 Speaker 1: had happened, and he appeared horrified when he learned the details. 59 00:04:14,760 --> 00:04:19,360 Speaker 1: He testified that he wasn't awake and he wasn't conscious 60 00:04:19,680 --> 00:04:22,800 Speaker 1: during the crime, and by the way, his testimony never 61 00:04:22,960 --> 00:04:26,880 Speaker 1: wavered throughout the whole trial. So his legal team argued 62 00:04:27,400 --> 00:04:32,520 Speaker 1: that the case represented homicidal somnambulism, which is just a 63 00:04:32,520 --> 00:04:38,080 Speaker 1: fancy way of saying killing while sleepwalking. So electrode recordings 64 00:04:38,200 --> 00:04:41,520 Speaker 1: in a sleep lab showed that the electrical activity in 65 00:04:41,520 --> 00:04:47,080 Speaker 1: his brain was highly unusual and consistent with sleepwalking. So 66 00:04:47,240 --> 00:04:51,440 Speaker 1: I'll quote the expert testimony given by a psychiatrist named 67 00:04:51,520 --> 00:04:55,960 Speaker 1: Ronald Billings. The lawyer asks, is there any evidence that 68 00:04:56,000 --> 00:04:59,719 Speaker 1: a person could formulate a plan while they were awake 69 00:04:59,800 --> 00:05:03,000 Speaker 1: and and then in some way ensure that they carry 70 00:05:03,000 --> 00:05:07,039 Speaker 1: it out in their sleep, And Billings says no, absolutely not. 71 00:05:07,640 --> 00:05:11,360 Speaker 1: Perhaps the most striking feature of what we know of 72 00:05:11,400 --> 00:05:13,760 Speaker 1: what goes on in the mind during sleep is that 73 00:05:13,839 --> 00:05:18,760 Speaker 1: it's very independent of waking mentation in terms of its 74 00:05:18,760 --> 00:05:22,960 Speaker 1: objectives and so forth. There's a lack of control of 75 00:05:23,080 --> 00:05:26,720 Speaker 1: directing our minds in sleep compared to wakefulness. In the 76 00:05:27,160 --> 00:05:31,440 Speaker 1: waking state, of course, we often voluntarily plan things, what 77 00:05:31,480 --> 00:05:34,920 Speaker 1: we call volition. We decide to do this as opposed 78 00:05:34,960 --> 00:05:38,680 Speaker 1: to that, and there is no evidence that this occurs 79 00:05:38,880 --> 00:05:43,840 Speaker 1: during the sleepwalking episode. So the lawyer asks, and assuming 80 00:05:43,880 --> 00:05:46,000 Speaker 1: he was sleepwalking at the time, would he have the 81 00:05:46,040 --> 00:05:51,440 Speaker 1: capacity to intend and Billing says no, And the lawyer says, 82 00:05:51,600 --> 00:05:55,520 Speaker 1: would he have appreciated what he was doing? And Billing 83 00:05:55,600 --> 00:05:59,640 Speaker 1: says no, he would not, And lawyer says, would he 84 00:05:59,839 --> 00:06:02,760 Speaker 1: have I've understood the consequences of what he was doing, 85 00:06:03,320 --> 00:06:06,640 Speaker 1: And Billing says no, I do not believe that he would. 86 00:06:06,720 --> 00:06:10,000 Speaker 1: I think it would all have been an unconscious activity, 87 00:06:10,440 --> 00:06:16,560 Speaker 1: uncontrolled and unmeditated. So what would your opinion be if 88 00:06:16,600 --> 00:06:21,080 Speaker 1: you were a juror on this case? Does sleepwalking sound 89 00:06:21,360 --> 00:06:25,599 Speaker 1: like an excuse? Is one either asleep or awake? Or 90 00:06:25,839 --> 00:06:29,880 Speaker 1: can a brain be caught between those two states? So 91 00:06:29,960 --> 00:06:34,360 Speaker 1: in today's podcast, we're going to explore the fundamental differences 92 00:06:34,440 --> 00:06:37,920 Speaker 1: between the states of wakefulness and sleep. We'll look at 93 00:06:37,920 --> 00:06:41,960 Speaker 1: the purpose of sleep and the way that transitions between 94 00:06:42,200 --> 00:06:46,480 Speaker 1: sleep and wakefulness can go awry, and then, armed with 95 00:06:46,520 --> 00:06:49,480 Speaker 1: our new knowledge, will return to the Parks case at 96 00:06:49,520 --> 00:06:52,800 Speaker 1: the end of this episode to see what the jury concluded. 97 00:06:53,440 --> 00:06:56,400 Speaker 1: To my mind, one of the most astonishing facts of 98 00:06:56,480 --> 00:07:00,479 Speaker 1: guroscience is that adult humans we spend a third of 99 00:07:00,520 --> 00:07:04,560 Speaker 1: our lives in the strange world of sleep, and by 100 00:07:04,600 --> 00:07:08,760 Speaker 1: the way, newborn babies spend about two thirds. So it's 101 00:07:08,800 --> 00:07:12,480 Speaker 1: insanely difficult to stay awake for more than a full 102 00:07:12,880 --> 00:07:15,520 Speaker 1: day night cycle, and if you somehow manage to stay 103 00:07:15,520 --> 00:07:19,320 Speaker 1: awake for a while, you're gonna be a bit cognitively impaired. 104 00:07:20,080 --> 00:07:24,000 Speaker 1: And in animal studies, if you deprive a rat of 105 00:07:24,080 --> 00:07:28,240 Speaker 1: sleep for weeks, the rat will die. So we can 106 00:07:28,240 --> 00:07:31,840 Speaker 1: see that sleep really matters. It's not just a choice 107 00:07:31,920 --> 00:07:35,240 Speaker 1: we make and we could do otherwise. And the massive 108 00:07:35,280 --> 00:07:38,600 Speaker 1: importance of sleep can also be gathered from the fact 109 00:07:38,640 --> 00:07:45,120 Speaker 1: that sleep is conserved through evolution. All mammals sleep, reptile sleep, 110 00:07:45,200 --> 00:07:48,360 Speaker 1: birds sleep. Even in the fruit fly, you can measure 111 00:07:48,560 --> 00:07:54,200 Speaker 1: sleep wake cycles and three days of sleep deprivation result 112 00:07:54,280 --> 00:07:58,120 Speaker 1: in the fli's death. The fact that all animals sleep 113 00:07:58,200 --> 00:08:04,480 Speaker 1: suggests that sleep is not an accident but something really fundamental. Now, 114 00:08:04,520 --> 00:08:07,240 Speaker 1: the first question we're going to ask is what is 115 00:08:07,400 --> 00:08:11,200 Speaker 1: happening under the hood, Because when you look at somebody 116 00:08:11,240 --> 00:08:15,440 Speaker 1: who's sleeping, it looks like everything is shut down. The 117 00:08:15,520 --> 00:08:20,000 Speaker 1: eyes are closed, the muscles are relaxed, breathing is regular, 118 00:08:20,120 --> 00:08:24,680 Speaker 1: there's no response to sound or light. So a century ago, 119 00:08:24,840 --> 00:08:30,000 Speaker 1: people thought that wakefulness was the natural state of the brain, 120 00:08:30,520 --> 00:08:34,440 Speaker 1: and that sleep represented a phase in which brain activity 121 00:08:34,600 --> 00:08:38,640 Speaker 1: was just decreased or shut down. But in the last century, 122 00:08:38,840 --> 00:08:42,880 Speaker 1: scientists discovered that the brain is not so much naturally 123 00:08:42,920 --> 00:08:46,680 Speaker 1: awake as it is kept awake by a whole system 124 00:08:46,720 --> 00:08:51,440 Speaker 1: of brain areas. For example, if you injure the brain stem, 125 00:08:51,640 --> 00:08:54,840 Speaker 1: that can cause you to fall into a sleep like 126 00:08:55,000 --> 00:08:58,800 Speaker 1: state that we call coma. So you need special machinery 127 00:08:58,840 --> 00:09:01,600 Speaker 1: to run in order to be awake, and as it 128 00:09:01,640 --> 00:09:06,679 Speaker 1: turns out, you also need special machinery to sleep. If 129 00:09:06,720 --> 00:09:11,679 Speaker 1: you damage part of the hypothalamus, you get long lasting 130 00:09:11,840 --> 00:09:15,959 Speaker 1: sleep difficulties. In other words, for both waking and sleeping, 131 00:09:16,480 --> 00:09:19,800 Speaker 1: you need particular networks to run. You need the activity 132 00:09:19,840 --> 00:09:24,920 Speaker 1: of certain cells. Waking is a neurally active state, and 133 00:09:25,160 --> 00:09:30,800 Speaker 1: so is sleeping. Now, people noted these things about sleep 134 00:09:30,960 --> 00:09:34,560 Speaker 1: by observing brain damage, but you can really only tell 135 00:09:34,679 --> 00:09:37,280 Speaker 1: so much from that. So how did the field make 136 00:09:37,480 --> 00:09:41,840 Speaker 1: progress from there? Mostly it was due to a technology 137 00:09:41,920 --> 00:09:45,679 Speaker 1: people had developed some time ago called electro and cephalography 138 00:09:45,880 --> 00:09:49,440 Speaker 1: or EEG, which is a technique where you stick electrodes 139 00:09:49,520 --> 00:09:53,080 Speaker 1: onto the scalp and you try to surface clues about 140 00:09:53,080 --> 00:09:56,680 Speaker 1: what's happening on the inside of the skull. But what's 141 00:09:56,760 --> 00:10:00,559 Speaker 1: fascinating is that the EEG was invented in in nineteen 142 00:10:00,640 --> 00:10:06,040 Speaker 1: twenty four, but researchers only ever measured people who were awake, 143 00:10:06,440 --> 00:10:10,560 Speaker 1: and it wasn't until almost three decades later that anyone 144 00:10:10,760 --> 00:10:15,000 Speaker 1: thought took this up to a person while they were asleep. 145 00:10:15,480 --> 00:10:17,760 Speaker 1: And what did they find. They found that the brain 146 00:10:17,960 --> 00:10:22,640 Speaker 1: was screaming along with activity during sleep in retrospect. By 147 00:10:22,679 --> 00:10:26,240 Speaker 1: the way, just the mere existence of dreams should have 148 00:10:26,280 --> 00:10:28,560 Speaker 1: alerted people that there must be a lot of brain 149 00:10:28,640 --> 00:10:31,480 Speaker 1: activity going on, but as I said, just no one 150 00:10:31,480 --> 00:10:35,600 Speaker 1: had thought of doing that experiment. So they found that 151 00:10:35,640 --> 00:10:38,640 Speaker 1: the brain was active during sleep, and with a little 152 00:10:38,640 --> 00:10:41,880 Speaker 1: bit of study, they soon worked out that there were patterns, 153 00:10:41,960 --> 00:10:46,200 Speaker 1: and these patterns changed, and these changes followed a regular 154 00:10:46,440 --> 00:10:50,640 Speaker 1: cycle during the night. In other words, the EEG pattern 155 00:10:50,800 --> 00:10:55,280 Speaker 1: changes in a predictable way several times during sleep. The 156 00:10:55,320 --> 00:10:59,160 Speaker 1: sleeping brain has these cycles that last about ninety minutes 157 00:10:59,720 --> 00:11:02,680 Speaker 1: and the repeat four or five times during the night. 158 00:11:03,120 --> 00:11:06,720 Speaker 1: Now what immediately became clear is that there are two 159 00:11:07,280 --> 00:11:10,800 Speaker 1: basic stages of sleep. There's this sleep that you have 160 00:11:10,920 --> 00:11:14,640 Speaker 1: where your eyes move rapidly back and forth. This is 161 00:11:14,679 --> 00:11:20,640 Speaker 1: called rem sleep for rapid eye movement. And then everything 162 00:11:20,640 --> 00:11:24,960 Speaker 1: else gets lumped into non REM sleep. So let's begin 163 00:11:25,040 --> 00:11:28,360 Speaker 1: with the non REM stage because that comprises eighty percent 164 00:11:28,440 --> 00:11:32,839 Speaker 1: of your sleep. Now, during non REM sleep, your heart 165 00:11:32,920 --> 00:11:38,000 Speaker 1: rate and breathing becomes slow and regular. The deepest stage 166 00:11:38,000 --> 00:11:41,080 Speaker 1: of this is known as slow wave sleep, and this 167 00:11:41,200 --> 00:11:45,800 Speaker 1: is named that way because the brain's electrical activity oscillates 168 00:11:46,360 --> 00:11:50,000 Speaker 1: at a low frequency and with a high amplitude. Think 169 00:11:50,040 --> 00:11:56,400 Speaker 1: of this like, wooooooo okay. Now, REM sleep is quite different. 170 00:11:56,520 --> 00:12:00,520 Speaker 1: In REM, your heart rate and your breathing beat up, 171 00:12:00,640 --> 00:12:04,760 Speaker 1: and your small muscles twitch like your facial muscles, but 172 00:12:05,559 --> 00:12:10,640 Speaker 1: your major muscle groups are paralyzed by a very elaborate 173 00:12:10,679 --> 00:12:16,920 Speaker 1: neural circuitry. So during REM, brain waves become high frequency 174 00:12:16,960 --> 00:12:23,480 Speaker 1: in low amplitude more like, which reflects more complex cognitive function. 175 00:12:24,240 --> 00:12:29,679 Speaker 1: REM sleep is sometimes called paradoxical sleep because your brain 176 00:12:29,800 --> 00:12:34,839 Speaker 1: is highly active and the EEG signature resembles that of 177 00:12:34,920 --> 00:12:38,760 Speaker 1: the waking state much more so than of deeper stages 178 00:12:38,800 --> 00:12:43,480 Speaker 1: of sleep. Now, REM sleep is the stage that usually 179 00:12:43,520 --> 00:12:49,000 Speaker 1: includes dreaming, and scientists discover this fact very simply by 180 00:12:49,120 --> 00:12:52,679 Speaker 1: waking people up during this stage and saying, Hey, what 181 00:12:52,720 --> 00:12:57,680 Speaker 1: were you just experiencing? So people generally report they had 182 00:12:58,120 --> 00:13:03,160 Speaker 1: story like dreams. During the REM stage. As a side note, 183 00:13:03,200 --> 00:13:06,600 Speaker 1: you can have dreams during non REM sleep, but this 184 00:13:06,679 --> 00:13:09,360 Speaker 1: is much less common and when it does occur, it's 185 00:13:09,480 --> 00:13:14,120 Speaker 1: generally much less visual and more like just having thoughts. Okay, 186 00:13:14,480 --> 00:13:18,280 Speaker 1: so dreaming happens during REM sleep. Now, I just want 187 00:13:18,320 --> 00:13:20,400 Speaker 1: to address the question that comes up a lot. People 188 00:13:20,400 --> 00:13:23,400 Speaker 1: sometimes say to me, I don't think I dream at night. Well, 189 00:13:23,960 --> 00:13:27,559 Speaker 1: everyone dreams. This is apart from a few rare cases 190 00:13:27,600 --> 00:13:31,640 Speaker 1: of patience with specific brain injuries. The thing that happens 191 00:13:31,760 --> 00:13:36,080 Speaker 1: is that some people have more difficulty remembering their dreams, 192 00:13:36,120 --> 00:13:38,960 Speaker 1: and therefore they think that they don't dream. But if 193 00:13:39,080 --> 00:13:43,240 Speaker 1: I awaken you during REM, you will report having just 194 00:13:43,320 --> 00:13:46,080 Speaker 1: been dreaming. Now, we're going to talk more about the 195 00:13:46,240 --> 00:13:49,439 Speaker 1: dreaming phase next week, but for now, what I want 196 00:13:49,480 --> 00:13:52,000 Speaker 1: to make clear is that your sleep cycle follows a 197 00:13:52,080 --> 00:13:57,960 Speaker 1: specific pattern. Non REM sleep proceeds into successive phases of 198 00:13:58,040 --> 00:14:01,240 Speaker 1: depth from stages one to three deeper and deeper, and 199 00:14:01,280 --> 00:14:04,320 Speaker 1: then that reverses in its shallower and shallower until you 200 00:14:04,360 --> 00:14:08,080 Speaker 1: reach REM sleep. And as this cycle continues through the night, 201 00:14:08,240 --> 00:14:13,120 Speaker 1: you tend to experience less deep sleep and more REM. Now, 202 00:14:13,240 --> 00:14:17,280 Speaker 1: although we use a single word sleep for this phenomenon. 203 00:14:17,640 --> 00:14:21,440 Speaker 1: The sleep state emerges from a collaboration of a whole 204 00:14:21,480 --> 00:14:25,400 Speaker 1: bunch of brain areas interacting in a network. These areas 205 00:14:25,520 --> 00:14:29,120 Speaker 1: all work in concert to give rise to this state 206 00:14:29,200 --> 00:14:34,000 Speaker 1: that we experience as sleep. Now, under special conditions, like 207 00:14:34,520 --> 00:14:37,200 Speaker 1: if you're deprived of rem sleep or you don't have 208 00:14:37,240 --> 00:14:41,320 Speaker 1: any light cues, the different areas can get out of 209 00:14:41,360 --> 00:14:44,160 Speaker 1: sync with each other, and that's in large part how 210 00:14:44,160 --> 00:14:48,800 Speaker 1: we can figure out the richness of the underlying mechanisms. 211 00:14:49,240 --> 00:14:52,840 Speaker 1: So let's now look at the most important parts of 212 00:14:52,920 --> 00:14:57,640 Speaker 1: the brain's sleep network. The most important player involved in 213 00:14:57,840 --> 00:15:01,520 Speaker 1: sleeping is an area of the brain called the ventrilateral 214 00:15:01,560 --> 00:15:06,080 Speaker 1: preoptic nucleus. We'll just call this the VLPO. This is 215 00:15:06,120 --> 00:15:10,760 Speaker 1: a collection of neurons in the hypothalamus, and when it 216 00:15:10,800 --> 00:15:16,280 Speaker 1: becomes active, you go to sleep. These neurons inhibit the 217 00:15:16,480 --> 00:15:20,720 Speaker 1: arousal network, which is all about wakefulness. So if there's 218 00:15:20,920 --> 00:15:27,400 Speaker 1: damage to your VLPO, you get insomnia. You can't sleep. Now, 219 00:15:27,640 --> 00:15:32,440 Speaker 1: the arousal network, which it inhibits, also inhibits it right back. 220 00:15:32,600 --> 00:15:37,720 Speaker 1: These two networks are always locked in mutual inhibition. When 221 00:15:37,840 --> 00:15:43,880 Speaker 1: either one is active, it uses inhibitory neurotransmitters to suppress 222 00:15:43,920 --> 00:15:47,680 Speaker 1: the other one. So, as a general principle of brains, 223 00:15:47,760 --> 00:15:51,880 Speaker 1: whenever you have two networks set up with mutual inhibition, 224 00:15:52,560 --> 00:15:56,600 Speaker 1: you get a system that toggles between two stable states, 225 00:15:57,080 --> 00:16:00,360 Speaker 1: in this case being asleep and being awake. You get 226 00:16:00,480 --> 00:16:02,520 Speaker 1: one state or the other, but you can't be in 227 00:16:02,600 --> 00:16:06,320 Speaker 1: both at the same time. Now, the brain doesn't just 228 00:16:06,440 --> 00:16:09,840 Speaker 1: consist of these two networks, but also other networks that 229 00:16:10,160 --> 00:16:14,440 Speaker 1: stabilize or destabilize the balance such that the brain can 230 00:16:14,480 --> 00:16:17,960 Speaker 1: hold onto one state and then make a transition into 231 00:16:18,000 --> 00:16:20,440 Speaker 1: the other state. And we'll talk about this again in 232 00:16:20,480 --> 00:16:24,440 Speaker 1: a minute when we talk about disorders like narcolepsy. So 233 00:16:25,120 --> 00:16:29,360 Speaker 1: the VLPO squelches the arousal system and you sleep. Then 234 00:16:29,440 --> 00:16:33,360 Speaker 1: the arousal system squelches the VLPO and you wake up. 235 00:16:33,920 --> 00:16:37,360 Speaker 1: But as we'll explore more next week, you've also got 236 00:16:37,720 --> 00:16:41,160 Speaker 1: dream sleep. And you get this from a principle that 237 00:16:41,520 --> 00:16:45,440 Speaker 1: puts the brain in a state that shares some qualities 238 00:16:45,520 --> 00:16:49,280 Speaker 1: of both sleeping and waking. Okay, so you have a 239 00:16:49,680 --> 00:16:54,200 Speaker 1: sleep wake cycle, and this determines two things, when you 240 00:16:54,280 --> 00:16:58,400 Speaker 1: sleep and how much you sleep. As for how much 241 00:16:58,880 --> 00:17:01,760 Speaker 1: not everyone needs to leap the same amount seven to 242 00:17:01,920 --> 00:17:04,720 Speaker 1: nine hours is recommended for adults, although a lot of 243 00:17:04,720 --> 00:17:07,800 Speaker 1: people only catch six and a half seven hours of sleep. 244 00:17:08,119 --> 00:17:10,639 Speaker 1: If you look across the whole population, you find a 245 00:17:10,680 --> 00:17:15,520 Speaker 1: really big range between four to eleven hours. Now, how 246 00:17:15,600 --> 00:17:18,080 Speaker 1: much sleep do you need? The suspicion is that that 247 00:17:18,160 --> 00:17:21,960 Speaker 1: has at least some genetic basis to it, but people 248 00:17:22,080 --> 00:17:25,720 Speaker 1: generally find out through experience about how much is required 249 00:17:25,760 --> 00:17:29,080 Speaker 1: for them to feel good. Now, how many hours you 250 00:17:29,119 --> 00:17:32,720 Speaker 1: sleep correlates with what you have done while you were awake. 251 00:17:32,760 --> 00:17:35,399 Speaker 1: If you do a bunch of activity like hiking or 252 00:17:35,440 --> 00:17:39,800 Speaker 1: weightlifting or public speaking, then you tend to sleep longer. Okay, 253 00:17:40,280 --> 00:17:42,960 Speaker 1: so that's about how much you sleep. But now let's 254 00:17:43,000 --> 00:17:45,760 Speaker 1: turn to the other aspect of the sleep wake cycle, 255 00:17:45,840 --> 00:17:50,119 Speaker 1: which is when you sleep. Why is sleep on such 256 00:17:50,240 --> 00:17:53,520 Speaker 1: a regular cycle and what is it synchronized with? The 257 00:17:53,560 --> 00:17:59,119 Speaker 1: answer involves your circadian rhythm, which is a natural internal 258 00:17:59,160 --> 00:18:03,000 Speaker 1: pattern that runs on approximately a twenty four hour cycle. 259 00:18:03,520 --> 00:18:06,800 Speaker 1: Where does the word circadian come from? Circa means about 260 00:18:06,920 --> 00:18:12,439 Speaker 1: and dion is a day. Now our circadian rhythm is 261 00:18:12,560 --> 00:18:17,119 Speaker 1: what times are sleep wake cycles? All animals appear to 262 00:18:17,160 --> 00:18:21,520 Speaker 1: have some form of a circadian cycle that influences not 263 00:18:21,600 --> 00:18:26,120 Speaker 1: just sleep in wakefulness, but also coordination, blood pressure, alertness, 264 00:18:26,240 --> 00:18:30,560 Speaker 1: body temperature, things like that. The circadian rhythm comes from 265 00:18:31,000 --> 00:18:35,840 Speaker 1: preprogrammed mechanisms in our brain, and it persists even when 266 00:18:35,840 --> 00:18:39,359 Speaker 1: there aren't any external cues like the sun going up 267 00:18:39,400 --> 00:18:44,080 Speaker 1: and down. Some animals, like the blind mole rat, maintain 268 00:18:44,160 --> 00:18:47,160 Speaker 1: their rhythms even though they live underground and don't see 269 00:18:47,200 --> 00:18:49,639 Speaker 1: the sun. I'll come back to this in humans in 270 00:18:49,720 --> 00:18:54,280 Speaker 1: just a moment. So the primary clock in mammals is 271 00:18:54,359 --> 00:18:58,639 Speaker 1: a structure called the super chiaismatic nucleus, which is in 272 00:18:58,680 --> 00:19:02,320 Speaker 1: the hypothalamus. So these cells keep a rhythm. And what's 273 00:19:02,359 --> 00:19:05,920 Speaker 1: amazing is if you culture the cells of the super 274 00:19:05,960 --> 00:19:11,359 Speaker 1: chismatic nucleus in a dish, they will maintain their own rhythm. So, 275 00:19:11,600 --> 00:19:16,760 Speaker 1: not surprisingly, when this nucleus gets damaged, that obliterates a 276 00:19:16,880 --> 00:19:22,840 Speaker 1: regular sleepwake rhythm. So the circadian rhythm is generated by 277 00:19:23,080 --> 00:19:27,679 Speaker 1: internal mechanisms and runs on its own machinery, but it 278 00:19:27,760 --> 00:19:31,919 Speaker 1: becomes entrained to cues in the environment. In other words, 279 00:19:32,000 --> 00:19:35,000 Speaker 1: it lines itself up with the environment, and the most 280 00:19:35,080 --> 00:19:39,640 Speaker 1: important cue that it uses is the light dark cycle. 281 00:19:39,800 --> 00:19:43,760 Speaker 1: In other words, the phase of the circadian rhythm is 282 00:19:43,880 --> 00:19:48,280 Speaker 1: set by the planet's rotation into and out of light 283 00:19:48,320 --> 00:19:52,880 Speaker 1: from the sun. The light information gets from the retina 284 00:19:53,320 --> 00:19:57,080 Speaker 1: to the super chismatic nucleus, which then gets to the 285 00:19:57,160 --> 00:20:01,040 Speaker 1: pineal gland and tells it to make melatonin, which you've 286 00:20:01,040 --> 00:20:05,480 Speaker 1: probably heard of. Melatonin is not directly a sleep hormone, 287 00:20:05,600 --> 00:20:10,120 Speaker 1: as people sometimes think, but instead it's a darkness hormone. 288 00:20:10,240 --> 00:20:14,879 Speaker 1: It gets its darkness information from the super chismatic nucleus, 289 00:20:15,119 --> 00:20:19,160 Speaker 1: and the cycles of melatonin just influence when you get sleepy. 290 00:20:19,840 --> 00:20:23,320 Speaker 1: So what happens if you are not seeing the sun 291 00:20:23,520 --> 00:20:26,200 Speaker 1: go up and down, Well, that's a question you can 292 00:20:26,280 --> 00:20:32,920 Speaker 1: directly explore. In nineteen seventy two, the French underground explorer 293 00:20:33,040 --> 00:20:38,080 Speaker 1: Michael Sifra descended a one hundred foot vertical shaft into 294 00:20:38,119 --> 00:20:43,159 Speaker 1: the Midnight Cave near Del Rio, Texas, and inside he 295 00:20:43,280 --> 00:20:47,120 Speaker 1: had stashed a campsite with food and water and books 296 00:20:47,240 --> 00:20:52,160 Speaker 1: enough to last him the six months of the astounding 297 00:20:52,320 --> 00:20:56,320 Speaker 1: time isolation experiment that he was about to undertake. Because 298 00:20:56,640 --> 00:21:00,199 Speaker 1: the bowels of this cave had no light clues, you 299 00:21:00,200 --> 00:21:03,280 Speaker 1: couldn't tell anything about day from night, and he had 300 00:21:03,560 --> 00:21:08,680 Speaker 1: no time pieces of any sort, he forbade any incoming 301 00:21:08,720 --> 00:21:12,800 Speaker 1: contact from the outside world. His telephone only made outgoing calls, 302 00:21:13,400 --> 00:21:18,400 Speaker 1: and in this self imposed experimental condition, he kept careful 303 00:21:18,520 --> 00:21:21,800 Speaker 1: track of his sleep and wake times by calling his 304 00:21:21,920 --> 00:21:24,960 Speaker 1: support team when he woke up, when he ate, and 305 00:21:25,000 --> 00:21:28,800 Speaker 1: when he went to sleep. He quickly lost a conscious 306 00:21:29,119 --> 00:21:32,439 Speaker 1: sense of time. Just imagine what that would be like 307 00:21:32,520 --> 00:21:35,119 Speaker 1: to have no clues to what time it is. No 308 00:21:35,359 --> 00:21:39,960 Speaker 1: cell phone, no alexa, no wristwatch, nothing, So what happened 309 00:21:40,600 --> 00:21:43,880 Speaker 1: without the ability to see the light and dark cycles 310 00:21:43,880 --> 00:21:48,080 Speaker 1: of the world. The period of his circadian rhythm drifted 311 00:21:48,119 --> 00:21:52,560 Speaker 1: to about twenty five hours, and subsequent experiments verified that 312 00:21:52,600 --> 00:21:57,320 Speaker 1: the circadian rhythm is not an exact twenty four hour clock. 313 00:21:57,400 --> 00:22:02,840 Speaker 1: It's an approximate clock. It gets nudged into rhythm with 314 00:22:03,040 --> 00:22:07,320 Speaker 1: the sun's cycle. Presumably, if we had evolved on a 315 00:22:07,480 --> 00:22:11,160 Speaker 1: different planet with a different light dark period, we would 316 00:22:11,200 --> 00:22:16,320 Speaker 1: have a different approximate period length to our internal rhythms. 317 00:22:16,920 --> 00:22:20,399 Speaker 1: What's cool is that you can use false lighting cues 318 00:22:20,840 --> 00:22:24,240 Speaker 1: to entrain a different cycle, for example, twenty three and 319 00:22:24,240 --> 00:22:27,480 Speaker 1: a half hour cycles, or scientists have done a twenty 320 00:22:27,600 --> 00:22:31,639 Speaker 1: four point sixty five hour cycle and they chose that 321 00:22:31,920 --> 00:22:35,399 Speaker 1: because that happens to be the period of day and 322 00:22:35,560 --> 00:22:40,119 Speaker 1: night on Mars, so we'll have no problem adjusting to 323 00:22:40,280 --> 00:22:44,920 Speaker 1: Martian day night cycles now. Although the period the twenty 324 00:22:44,920 --> 00:22:47,320 Speaker 1: four hours is essentially the same for all of us 325 00:22:47,359 --> 00:22:50,920 Speaker 1: Earth dwellers, the period of this rhythm, in other words, 326 00:22:50,960 --> 00:22:54,280 Speaker 1: when it hits top or bottom, that can vary across 327 00:22:54,359 --> 00:22:58,200 Speaker 1: the population. Some people are night owls, meaning that their 328 00:22:58,680 --> 00:23:02,000 Speaker 1: natural rhythm keeps them up late at night and sleeping 329 00:23:02,080 --> 00:23:05,880 Speaker 1: late into the morning, while other people are mourning larks 330 00:23:05,960 --> 00:23:09,040 Speaker 1: they are early to bed and early to rise. About 331 00:23:09,200 --> 00:23:13,119 Speaker 1: sixty percent of the population is intermediate between the two. 332 00:23:13,160 --> 00:23:17,680 Speaker 1: There's a normal amount of variation in the population between 333 00:23:17,960 --> 00:23:20,879 Speaker 1: night owls and morning larks, but some people on the 334 00:23:21,040 --> 00:23:25,400 Speaker 1: very extremes have to take really drastic measures to adapt 335 00:23:25,480 --> 00:23:29,760 Speaker 1: their lives to societal norms. So consider the case of 336 00:23:29,800 --> 00:23:33,719 Speaker 1: a woman that I'll call Melinda. Every day, Melinda and 337 00:23:33,760 --> 00:23:37,440 Speaker 1: her two children, who are aged thirteen and eleven. They 338 00:23:37,480 --> 00:23:39,760 Speaker 1: go to bed at four in the morning and they 339 00:23:39,840 --> 00:23:43,160 Speaker 1: typically wake up around noon. Now, some of her neighbors 340 00:23:43,240 --> 00:23:47,159 Speaker 1: think she's a bad mother, but Melinda and her children 341 00:23:47,280 --> 00:23:52,000 Speaker 1: suffer from something called delayed sleep phase syndrome, which is 342 00:23:52,040 --> 00:23:54,920 Speaker 1: a disorder of the circadian rhythm, in which a person 343 00:23:55,400 --> 00:23:59,440 Speaker 1: has no trouble maintaining sleep, but can't fall asleep or 344 00:23:59,480 --> 00:24:02,399 Speaker 1: wake up at the same time as the rest of society. 345 00:24:02,960 --> 00:24:07,040 Speaker 1: The family essentially lives with a constant six hours of 346 00:24:07,119 --> 00:24:12,320 Speaker 1: jet lag. Other people have what's called advanced sleep phase syndrome, 347 00:24:12,480 --> 00:24:15,400 Speaker 1: in which you fall asleep and wake up way earlier 348 00:24:15,440 --> 00:24:18,000 Speaker 1: than the rest of society. And remember what I said 349 00:24:18,000 --> 00:24:21,560 Speaker 1: about the circadian rhythm being about twenty four hours. Some 350 00:24:21,640 --> 00:24:25,640 Speaker 1: people have molecular problems which warp this, so it's much 351 00:24:25,800 --> 00:24:29,600 Speaker 1: shorter or longer than twenty four hours, and unfortunately, that 352 00:24:29,640 --> 00:24:34,199 Speaker 1: makes a person incapable of aligning their sleep patterns to 353 00:24:34,400 --> 00:24:38,840 Speaker 1: the societal norm. People with all these disorders typically work 354 00:24:39,000 --> 00:24:43,760 Speaker 1: to adapt their lives and careers around their own rhythms. 355 00:24:43,800 --> 00:24:47,760 Speaker 1: For example, Melinda has a difficult time holding on to 356 00:24:47,960 --> 00:24:51,320 Speaker 1: jobs that require her to be present early in the morning. 357 00:24:51,600 --> 00:24:54,879 Speaker 1: That's not because of a lack of dedication to her job, 358 00:24:55,040 --> 00:24:58,320 Speaker 1: but instead because of her biological clock. So, the way 359 00:24:58,359 --> 00:25:02,240 Speaker 1: she describes it, quote, instead of changing myself to keep 360 00:25:02,320 --> 00:25:05,600 Speaker 1: other people's schedule, I have changed my life so I 361 00:25:05,600 --> 00:25:09,560 Speaker 1: can function on my time. She operates a freight brokerage 362 00:25:09,640 --> 00:25:13,520 Speaker 1: business that she runs from her home. She also homeschools 363 00:25:13,520 --> 00:25:17,720 Speaker 1: her children through the afternoon and evening. Some companies have 364 00:25:17,840 --> 00:25:21,760 Speaker 1: recognized that people have different circadian rhythms and that it's 365 00:25:21,800 --> 00:25:25,840 Speaker 1: not necessary to force everyone into the same time mold. 366 00:25:26,240 --> 00:25:30,040 Speaker 1: So Netflix, for example, doesn't keep track of their employees' 367 00:25:30,119 --> 00:25:34,160 Speaker 1: work hours, just so long as their work produces results. 368 00:25:34,600 --> 00:25:39,040 Speaker 1: One Netflix executive said that rigid office hours are a 369 00:25:39,600 --> 00:25:45,040 Speaker 1: relic of the industrial age. Now, statistically, you probably have 370 00:25:45,200 --> 00:25:49,040 Speaker 1: a fairly normal circadian rhythm, but you know what it's 371 00:25:49,200 --> 00:25:52,199 Speaker 1: like when you disrupt that rhythm and how tough that 372 00:25:52,240 --> 00:25:54,840 Speaker 1: can be for your brain. When you fly to a 373 00:25:55,040 --> 00:26:00,359 Speaker 1: distant time zone, you've presumably experienced the fatigue and disorientation 374 00:26:00,680 --> 00:26:04,480 Speaker 1: of jet lag, which is just a mismatch of your 375 00:26:04,520 --> 00:26:09,880 Speaker 1: circadian time with the local day night period. You typically 376 00:26:09,920 --> 00:26:14,960 Speaker 1: get irregular sleep patterns and fatigue, maybe headaches, irritability, the 377 00:26:15,520 --> 00:26:21,240 Speaker 1: disorientation as the rhythm struggles to regain alignment. Now, from 378 00:26:21,359 --> 00:26:25,080 Speaker 1: a long term health consequence, there's no problem traveling to 379 00:26:25,119 --> 00:26:28,800 Speaker 1: different time zones once in a while, but long term, 380 00:26:29,359 --> 00:26:34,760 Speaker 1: repeated disturbances of this synchronization can have a negative impact 381 00:26:34,760 --> 00:26:40,560 Speaker 1: on health. One study compared two groups of flight attendants 382 00:26:41,000 --> 00:26:43,280 Speaker 1: who spent the same amount of time in the air, 383 00:26:43,320 --> 00:26:46,920 Speaker 1: but one group did lots of east west flights, which 384 00:26:46,960 --> 00:26:49,880 Speaker 1: means they were always changing time zones, while the other 385 00:26:49,920 --> 00:26:53,280 Speaker 1: group did north south flights, which meant they didn't have 386 00:26:53,359 --> 00:26:57,479 Speaker 1: to change their circadian rhythm. So what the study found 387 00:26:57,600 --> 00:27:02,480 Speaker 1: is that the east west flying tendance had higher stress 388 00:27:02,480 --> 00:27:05,040 Speaker 1: hormone levels and the part of their brain called the 389 00:27:05,119 --> 00:27:10,639 Speaker 1: temporal lobe was physically diminished, which led to demonstrable effects 390 00:27:10,720 --> 00:27:14,560 Speaker 1: on spatial learning and memory. And these sorts of ongoing 391 00:27:14,560 --> 00:27:18,879 Speaker 1: disturbances in the circadian rhythm are also linked to mood 392 00:27:18,920 --> 00:27:23,679 Speaker 1: disorders and obesity. So occasional travel is great, but be 393 00:27:23,720 --> 00:27:27,760 Speaker 1: careful about shifting your rhythm around too often. And since 394 00:27:27,760 --> 00:27:30,960 Speaker 1: we're talking about the rhythm, there's a question that needs 395 00:27:31,000 --> 00:27:34,760 Speaker 1: to be asked about how many times we sleep in 396 00:27:34,840 --> 00:27:38,800 Speaker 1: twenty four hours. Most of us sleep only once in 397 00:27:38,840 --> 00:27:42,919 Speaker 1: the twenty four hour cycle, but having this single long 398 00:27:43,200 --> 00:27:47,800 Speaker 1: period of daytime wakefulness is not necessarily the way our 399 00:27:47,920 --> 00:27:52,800 Speaker 1: natural rhythms evolved. You've probably noticed that you experience a 400 00:27:52,960 --> 00:27:57,199 Speaker 1: dip during the afternoon when you feel less alert. The 401 00:27:57,600 --> 00:28:01,960 Speaker 1: basic circadian rhythm that makes you sleep at nighttime contains 402 00:28:02,000 --> 00:28:05,560 Speaker 1: a bump that nudges you towards a nap in the 403 00:28:05,600 --> 00:28:10,120 Speaker 1: early afternoon. Sleeping only once at nighttime, the way most 404 00:28:10,160 --> 00:28:13,200 Speaker 1: of us do, is not the only way to achieve 405 00:28:13,359 --> 00:28:17,359 Speaker 1: good sleep. As you might guess from watching your cat 406 00:28:17,520 --> 00:28:21,679 Speaker 1: or your dog, Sleeping multiple times a day is the 407 00:28:21,880 --> 00:28:26,800 Speaker 1: norm throughout the animal kingdom. This is known as polyphasic sleep, 408 00:28:26,880 --> 00:28:30,639 Speaker 1: referring to multiple phases, and there are lots of ways 409 00:28:30,720 --> 00:28:34,960 Speaker 1: to do polyphasic sleep. For example, one technique is to 410 00:28:35,560 --> 00:28:39,800 Speaker 1: sleep twice, one for six hours during the night and 411 00:28:39,880 --> 00:28:44,240 Speaker 1: again in the afternoon for ninety minutes. There's another commonly 412 00:28:44,360 --> 00:28:47,280 Speaker 1: used pattern, which is to sleep for half an hour 413 00:28:47,760 --> 00:28:51,920 Speaker 1: every six hours. This was the sleep pattern of Buckminster 414 00:28:52,000 --> 00:28:57,680 Speaker 1: Fuller or other people nap fifteen to thirty minutes every 415 00:28:57,800 --> 00:29:01,720 Speaker 1: four hours, which was allegedly the sleep pattern of Leonardo 416 00:29:01,800 --> 00:29:05,959 Speaker 1: da Vinci. One advantage of polyphasic sleep is that the 417 00:29:06,000 --> 00:29:09,280 Speaker 1: total number of hours can be greatly reduced from the 418 00:29:09,400 --> 00:29:12,800 Speaker 1: usual eight in some cases down to just a few hours, 419 00:29:12,840 --> 00:29:18,840 Speaker 1: apparently without ill effects. Polyphasic sleep is common in historically 420 00:29:18,920 --> 00:29:24,080 Speaker 1: older cultures and in current non industrialized societies, especially during 421 00:29:24,080 --> 00:29:29,360 Speaker 1: the winter months. Even in industrialized countries, many cultures engage 422 00:29:29,400 --> 00:29:33,080 Speaker 1: in a daily post lunch nap. This is known as 423 00:29:33,080 --> 00:29:38,080 Speaker 1: a siesta in Spanish speaking countries, a riposo in Italy, 424 00:29:38,440 --> 00:29:42,440 Speaker 1: and in Japan it's known as an in emuri. And 425 00:29:42,480 --> 00:29:46,280 Speaker 1: you know who naturally goes in for polyphasic sleep. Infants, 426 00:29:46,640 --> 00:29:49,400 Speaker 1: they're up and down all day, and you know who else, 427 00:29:49,680 --> 00:29:53,720 Speaker 1: the elderly. Polyphasic sleep, also, by the way, is often 428 00:29:53,880 --> 00:29:58,080 Speaker 1: adopted in the military, especially when you have a situation 429 00:29:58,240 --> 00:30:02,280 Speaker 1: that doesn't allow for long periods of being down and 430 00:30:02,480 --> 00:30:06,360 Speaker 1: un alert. But as I said, many adults have a 431 00:30:06,560 --> 00:30:10,400 Speaker 1: monophasic sleep schedule. And so one question that's been asked 432 00:30:10,480 --> 00:30:14,120 Speaker 1: is does that indicate that humans have evolved to be 433 00:30:14,280 --> 00:30:18,000 Speaker 1: different than most of our animal cousins. And the answer 434 00:30:18,120 --> 00:30:21,720 Speaker 1: is probably not. It probably just shows that we are 435 00:30:21,800 --> 00:30:25,920 Speaker 1: merely capable of fighting off sleep when we don't want it, 436 00:30:25,960 --> 00:30:30,120 Speaker 1: for example with the help of caffeine, or forcing ourselves 437 00:30:30,120 --> 00:30:32,080 Speaker 1: to sleep when we feel we should be getting it, 438 00:30:32,120 --> 00:30:52,760 Speaker 1: for example with the help of sleeping pills. Okay, so 439 00:30:52,840 --> 00:30:56,000 Speaker 1: we talked about the patterns of sleep, like when you 440 00:30:56,080 --> 00:30:59,840 Speaker 1: sleep and how often in a cycle. Now let's zoom 441 00:30:59,840 --> 00:31:03,959 Speaker 1: out the camera to the really foundational question of why 442 00:31:04,480 --> 00:31:07,680 Speaker 1: brains sleep at all, because the thing to note is 443 00:31:07,720 --> 00:31:13,680 Speaker 1: that sleep entails lost time and reduced defenses. So it's 444 00:31:13,720 --> 00:31:18,360 Speaker 1: striking that across all species in the animal kingdom, everyone's 445 00:31:18,400 --> 00:31:22,600 Speaker 1: doing it. In fact, animals in situations that don't easily 446 00:31:22,640 --> 00:31:27,600 Speaker 1: allow for sleep, they have evolved elaborate mechanisms to get 447 00:31:27,680 --> 00:31:32,120 Speaker 1: that sleep. For example, the bottle nosed dolphin can't just 448 00:31:32,160 --> 00:31:35,280 Speaker 1: go to sleep because it has to periodically come to 449 00:31:35,360 --> 00:31:38,239 Speaker 1: the surface to breathe. So what does it do. It 450 00:31:38,280 --> 00:31:41,880 Speaker 1: has one side of its brain sleep at a time. 451 00:31:42,600 --> 00:31:46,080 Speaker 1: This mechanism has been found in other dolphin and whale species, 452 00:31:46,400 --> 00:31:49,560 Speaker 1: and what it does is allow them to come up 453 00:31:49,600 --> 00:31:52,520 Speaker 1: to the surface to breathe, and it also allows them 454 00:31:52,600 --> 00:31:56,520 Speaker 1: to swim around and avoid predators and even have social 455 00:31:56,520 --> 00:32:00,440 Speaker 1: interaction during sleep when the mammalian brain would other wise 456 00:32:00,520 --> 00:32:04,320 Speaker 1: be in its own world. So all this underscores an 457 00:32:04,360 --> 00:32:09,040 Speaker 1: important clue for us, given the missed opportunities while asleep 458 00:32:09,080 --> 00:32:13,040 Speaker 1: and the dangers of sleeping, as well as the convoluted 459 00:32:13,440 --> 00:32:18,440 Speaker 1: evolutionary adaptations that come about to allow it. Sleep, clearly 460 00:32:18,480 --> 00:32:22,280 Speaker 1: seems to perform some function for the nervous system. But 461 00:32:22,320 --> 00:32:25,160 Speaker 1: what is it. There are lots of theories for why 462 00:32:25,200 --> 00:32:30,719 Speaker 1: we sleep, and these fall essentially into four categories. The 463 00:32:30,800 --> 00:32:37,320 Speaker 1: first is that sleep is restorative. It replenishes our energy stores. 464 00:32:37,640 --> 00:32:42,080 Speaker 1: In other words, sleep may be a metabolic necessity, helping 465 00:32:42,160 --> 00:32:45,760 Speaker 1: the body recover from the work it did while awake. 466 00:32:46,120 --> 00:32:49,280 Speaker 1: And in fact, researchers have long known that the amount 467 00:32:49,400 --> 00:32:53,440 Speaker 1: of slow wave sleep correlates with the amount of exercise 468 00:32:53,520 --> 00:32:55,840 Speaker 1: that you do when you're awake, and if you're deprived 469 00:32:55,920 --> 00:32:58,560 Speaker 1: of slow wave sleep by being woken up every time 470 00:32:58,600 --> 00:33:01,760 Speaker 1: you enter that stage, you're going to be physically pooped out. 471 00:33:02,160 --> 00:33:05,640 Speaker 1: A related idea is that REM sleep allows you to 472 00:33:05,920 --> 00:33:10,640 Speaker 1: replenish the stalks of certain neurotransmitters that you used when 473 00:33:10,680 --> 00:33:15,400 Speaker 1: you were awake. But this sleep as restoration hypothesis is 474 00:33:15,440 --> 00:33:18,240 Speaker 1: not totally clear because you have a lot of activity 475 00:33:18,400 --> 00:33:21,640 Speaker 1: during REM sleep and even during non REM sleep, And 476 00:33:21,720 --> 00:33:25,360 Speaker 1: there's a bigger reason why this hypothesis doesn't seem perfect. 477 00:33:25,920 --> 00:33:30,240 Speaker 1: Although sleep is necessary to all species, there doesn't appear 478 00:33:30,320 --> 00:33:32,640 Speaker 1: to be a fixed amount required, and when you look 479 00:33:32,640 --> 00:33:36,640 Speaker 1: at something like horses, they sleep only about three hours 480 00:33:36,680 --> 00:33:42,280 Speaker 1: per night, whereas koala bears sleep nineteen hours. Now the 481 00:33:42,480 --> 00:33:47,400 Speaker 1: high activity of horses and the low activity of koalas 482 00:33:47,800 --> 00:33:53,520 Speaker 1: doesn't seem to accord with this sleep as restoration hypothesis. 483 00:33:53,880 --> 00:33:56,280 Speaker 1: So it might have something to do with why we sleep, 484 00:33:56,520 --> 00:33:59,800 Speaker 1: but it's certainly not the full answer. Okay, So this 485 00:34:00,040 --> 00:34:02,640 Speaker 1: second theory about why we sleep is that we do 486 00:34:02,720 --> 00:34:06,720 Speaker 1: it because it's a survival advantage. So here's the idea. 487 00:34:07,280 --> 00:34:10,799 Speaker 1: Most animals find the search for food and water to 488 00:34:10,920 --> 00:34:16,040 Speaker 1: be easier during the sunlight hours. At night, it's best 489 00:34:16,120 --> 00:34:20,560 Speaker 1: for these animals to save energy and avoid getting eaten 490 00:34:21,040 --> 00:34:25,120 Speaker 1: and evade dangers such as falling off a cliff. So 491 00:34:25,680 --> 00:34:30,680 Speaker 1: this framework proposes that sleep protects organisms that can't see 492 00:34:30,719 --> 00:34:34,239 Speaker 1: well in the dark and would face greater risks if 493 00:34:34,239 --> 00:34:36,839 Speaker 1: they were active at night. So the idea is, if 494 00:34:36,840 --> 00:34:39,160 Speaker 1: you just curl up in the corner of the cave, 495 00:34:39,640 --> 00:34:43,320 Speaker 1: you stay out of trouble. Now, this framework of sleeping 496 00:34:43,360 --> 00:34:46,960 Speaker 1: to stay out of trouble. This is also imperfect because 497 00:34:47,560 --> 00:34:51,160 Speaker 1: darkness as a survival threat can be addressed by the 498 00:34:51,239 --> 00:34:55,640 Speaker 1: evolution of night vision, and it doesn't apply to nocturnal 499 00:34:55,680 --> 00:34:59,120 Speaker 1: animals which sleep during the day. And also the theory 500 00:34:59,160 --> 00:35:03,239 Speaker 1: doesn't shed any light on the unusual sleep habits of 501 00:35:03,719 --> 00:35:07,760 Speaker 1: for example, the bottle nose dolphin. So onto the third 502 00:35:07,920 --> 00:35:11,360 Speaker 1: theory about why we sleep, which is that sleep allows 503 00:35:11,440 --> 00:35:16,480 Speaker 1: us to simulate rare situations. So let's start with the 504 00:35:16,480 --> 00:35:21,600 Speaker 1: observation that young animals like babies, spend a much larger 505 00:35:21,640 --> 00:35:26,200 Speaker 1: percentage of their sleep time in dream sleep. Now that 506 00:35:26,320 --> 00:35:33,640 Speaker 1: observation has invited these speculations that the nocturnal neural simulations 507 00:35:34,320 --> 00:35:38,520 Speaker 1: may be a really useful or necessary exercise for animals 508 00:35:38,560 --> 00:35:43,399 Speaker 1: to test out activities in the real world. Presumably one 509 00:35:43,440 --> 00:35:47,239 Speaker 1: wants to practice all these programs while your muscles are 510 00:35:47,280 --> 00:35:50,640 Speaker 1: shut down, and according to some versions of this theory, 511 00:35:51,200 --> 00:35:55,200 Speaker 1: the periodic stimulation of the cortex in this sort of 512 00:35:55,320 --> 00:35:59,960 Speaker 1: semi random manner can maintain circuits that you need for survival, 513 00:36:00,080 --> 00:36:05,680 Speaker 1: but they rarely get activated like emergency defense procedures. So 514 00:36:05,880 --> 00:36:10,320 Speaker 1: a specific version of this framework called threat simulation theory, 515 00:36:10,840 --> 00:36:16,719 Speaker 1: suggests that sleep exists to simulate threatening events and rehearse 516 00:36:17,280 --> 00:36:22,520 Speaker 1: threat perception and threat avoidance. The theory suggests that people 517 00:36:22,920 --> 00:36:27,200 Speaker 1: exposed to more survival threats in waking life should more 518 00:36:27,360 --> 00:36:33,520 Speaker 1: commonly experience threat dreams at night. So interestingly, researchers tested 519 00:36:33,520 --> 00:36:38,360 Speaker 1: that idea by comparing participants in a high crime area 520 00:36:38,400 --> 00:36:41,680 Speaker 1: in South Africa to those living in a low crime 521 00:36:41,719 --> 00:36:46,719 Speaker 1: area in Wales, and they obtained detailed dream reports over 522 00:36:46,760 --> 00:36:50,719 Speaker 1: a really long period of time. Now, contrary to the 523 00:36:50,760 --> 00:36:54,600 Speaker 1: predictions of the threat simulation theory, people in the high 524 00:36:54,640 --> 00:36:58,920 Speaker 1: crime area actually reported a lower number of threat dreams 525 00:36:59,200 --> 00:37:02,760 Speaker 1: than those in the low crime area. And in South Africa, 526 00:37:02,800 --> 00:37:07,759 Speaker 1: the percentage of realistic threats and dreams was lower than expected. 527 00:37:07,920 --> 00:37:11,160 Speaker 1: It was only about twenty percent and escape from these 528 00:37:11,200 --> 00:37:16,239 Speaker 1: threats occurred in less than two percent, suggesting that it's 529 00:37:16,280 --> 00:37:20,400 Speaker 1: not really much of a simulation. So tests have so 530 00:37:20,560 --> 00:37:25,360 Speaker 1: far failed to give much support to the threat simulation theory, 531 00:37:26,320 --> 00:37:29,359 Speaker 1: and that leads us to theory number four about why 532 00:37:29,400 --> 00:37:33,400 Speaker 1: we sleep, And this one has the strongest legs, and 533 00:37:33,480 --> 00:37:39,279 Speaker 1: the idea is that sleep plays a role in information processing. Specifically, 534 00:37:39,560 --> 00:37:44,160 Speaker 1: the idea is that sleep allows the brain to cement 535 00:37:44,440 --> 00:37:49,880 Speaker 1: in important memories and to deprogram the miscellaneous events that 536 00:37:49,920 --> 00:37:53,240 Speaker 1: shouldn't get stored. Of all the different theories, the data 537 00:37:53,280 --> 00:37:57,399 Speaker 1: seemed to strongly support this idea that sleep plays an 538 00:37:57,520 --> 00:38:00,279 Speaker 1: informational role. So I'm going to zoom in on this 539 00:38:00,360 --> 00:38:02,799 Speaker 1: for the next few minutes. The first part of the 540 00:38:02,840 --> 00:38:07,840 Speaker 1: idea here is that we sleep to lock in information. So, 541 00:38:08,000 --> 00:38:10,760 Speaker 1: for example, let's say I teach you some new task 542 00:38:10,880 --> 00:38:14,000 Speaker 1: on the computer and you're getting better and better at it. 543 00:38:14,440 --> 00:38:16,440 Speaker 1: If I look at how much better you got, I'll 544 00:38:16,440 --> 00:38:20,040 Speaker 1: see you got a lot better if you slept between 545 00:38:20,360 --> 00:38:22,920 Speaker 1: session one and session two. But if you spent the 546 00:38:22,920 --> 00:38:26,640 Speaker 1: same number of hours awake in between those sessions, you 547 00:38:26,680 --> 00:38:30,720 Speaker 1: didn't get much better. So this started suggesting to neuroscientists 548 00:38:30,840 --> 00:38:35,160 Speaker 1: that sleep had something to do with getting better at 549 00:38:35,200 --> 00:38:39,240 Speaker 1: the task. And in part this is because a nap 550 00:38:39,440 --> 00:38:41,920 Speaker 1: turns out to be as good as getting a night 551 00:38:42,000 --> 00:38:44,759 Speaker 1: of sleep. So if you get even a sixty to 552 00:38:44,840 --> 00:38:48,319 Speaker 1: ninety minute daytime nap, you do just as well as 553 00:38:48,360 --> 00:38:52,800 Speaker 1: someone who slept the whole night. But why does learning improve? 554 00:38:52,960 --> 00:38:58,760 Speaker 1: The evidence generally suggests that you reactivate memories during sleep 555 00:38:58,840 --> 00:39:02,920 Speaker 1: and that on lies locking them in. And this is 556 00:39:02,960 --> 00:39:08,840 Speaker 1: because memories require a consolidation period in which the experience 557 00:39:08,880 --> 00:39:12,800 Speaker 1: becomes part of long term memory, and the consolidation stage 558 00:39:13,160 --> 00:39:16,759 Speaker 1: requires sleep. So let me give you an example. Let's 559 00:39:16,800 --> 00:39:20,480 Speaker 1: imagine that you train a rat to run around a 560 00:39:20,600 --> 00:39:24,200 Speaker 1: track for a food reward. Now there are neurons that 561 00:39:24,239 --> 00:39:28,000 Speaker 1: we call place cells in the hippocampus, and if you 562 00:39:28,120 --> 00:39:32,000 Speaker 1: record their electrical activity, you'll find that this network of 563 00:39:32,040 --> 00:39:36,279 Speaker 1: cells has a distinct pattern, a distinct signature of activity, 564 00:39:36,600 --> 00:39:41,880 Speaker 1: depending on precisely where the rat is in the maze. 565 00:39:42,360 --> 00:39:46,479 Speaker 1: So the rat occupies all these different locations, and each 566 00:39:46,480 --> 00:39:50,600 Speaker 1: of those is represented by a different pattern among the 567 00:39:50,719 --> 00:39:55,120 Speaker 1: place cells. Okay, so now the rat goes to sleep, 568 00:39:55,239 --> 00:39:59,279 Speaker 1: and if you continue recording from these neurons, you'll find 569 00:39:59,600 --> 00:40:04,120 Speaker 1: this same sequence representing this position, then this next position, 570 00:40:04,160 --> 00:40:08,240 Speaker 1: then this next position. You find the same sequence playing 571 00:40:08,280 --> 00:40:11,360 Speaker 1: out while the rat is in rem sleep, the same 572 00:40:11,400 --> 00:40:14,560 Speaker 1: sequence that he ran while he was awake. It's like 573 00:40:14,680 --> 00:40:20,200 Speaker 1: he's rehearsing the trajectory that he learned. It's so closely 574 00:40:20,200 --> 00:40:23,040 Speaker 1: correlated with what he did when he was awake that 575 00:40:23,200 --> 00:40:27,040 Speaker 1: researchers who study this claim that the animal is dreaming 576 00:40:27,400 --> 00:40:32,000 Speaker 1: about running the maze. They can take that activity and 577 00:40:32,160 --> 00:40:36,120 Speaker 1: reconstruct where the rat would be in the maze if 578 00:40:36,160 --> 00:40:38,920 Speaker 1: it were awake, and they can further guess whether the 579 00:40:38,960 --> 00:40:43,040 Speaker 1: animal is dreaming about running from position to position or 580 00:40:43,120 --> 00:40:46,399 Speaker 1: standing still in one spot. Now, this sort of thing 581 00:40:46,480 --> 00:40:49,719 Speaker 1: doesn't just happen in rats. This same kind of rehearsal 582 00:40:49,840 --> 00:40:55,560 Speaker 1: happens in songbirds, whose neural activity during sleep resembles their 583 00:40:56,000 --> 00:41:00,160 Speaker 1: song production activity. So the idea is that this replay 584 00:41:00,320 --> 00:41:04,520 Speaker 1: is part of consolidating events into long term memory. In 585 00:41:04,560 --> 00:41:08,920 Speaker 1: other words, the hypothesis is that the information replayed during 586 00:41:09,040 --> 00:41:14,640 Speaker 1: sleep determines what we later remember. And this idea is 587 00:41:14,680 --> 00:41:18,440 Speaker 1: consistent with human studies in which we see that the 588 00:41:18,640 --> 00:41:24,400 Speaker 1: learning of repetitive tasks relies on REM's sleep to improve 589 00:41:24,520 --> 00:41:29,360 Speaker 1: your performance. In some cases, this offline practice session seems 590 00:41:29,400 --> 00:41:32,840 Speaker 1: to be just as useful as practicing the new task 591 00:41:32,960 --> 00:41:37,920 Speaker 1: when awake, So both rats and humans perform recently learned 592 00:41:38,040 --> 00:41:43,480 Speaker 1: tasks better after a period of sleep. And these dreaming 593 00:41:43,760 --> 00:41:48,320 Speaker 1: rat studies are consistent with a human study in which 594 00:41:48,360 --> 00:41:53,080 Speaker 1: participants learned to play the video game Tetris. That night, 595 00:41:53,440 --> 00:41:58,239 Speaker 1: they dreamt of falling Tetris blocks. Now here's the really 596 00:41:58,280 --> 00:42:03,040 Speaker 1: wacky thing. When subjects with amnesia were trained on the game, 597 00:42:03,760 --> 00:42:08,320 Speaker 1: they reported these same dreams of these colorful falling blocks, 598 00:42:08,520 --> 00:42:11,520 Speaker 1: but they had no idea why they were dreaming about 599 00:42:11,560 --> 00:42:16,480 Speaker 1: such things. So, just as rats dream about repetitive tasks 600 00:42:16,560 --> 00:42:21,239 Speaker 1: performed during the day, the Tetris players dreamed about their 601 00:42:21,480 --> 00:42:25,240 Speaker 1: new video game experience. Now, although a lot of research 602 00:42:25,280 --> 00:42:28,520 Speaker 1: has study the effects of rem sleep on learning, I 603 00:42:28,560 --> 00:42:31,000 Speaker 1: just want to be clear that slow wave sleep is 604 00:42:31,040 --> 00:42:35,560 Speaker 1: also important, and you find the slow wave activity most 605 00:42:35,680 --> 00:42:40,000 Speaker 1: strongly in the brain areas involved in some new task. 606 00:42:40,200 --> 00:42:44,000 Speaker 1: So if I have you do some complex I hand 607 00:42:44,040 --> 00:42:49,040 Speaker 1: coordination task, we'll see enhanced slow wave sleep activity in 608 00:42:49,160 --> 00:42:52,520 Speaker 1: those areas that were involved. That's where we find the 609 00:42:52,520 --> 00:42:55,920 Speaker 1: most action. And what we find is that the more 610 00:42:55,960 --> 00:42:59,320 Speaker 1: slow wave sleep you see in a region, the better 611 00:42:59,400 --> 00:43:04,960 Speaker 1: you get at the task. Okay, Now, if sleep consolidates memories, 612 00:43:05,480 --> 00:43:10,279 Speaker 1: that raises an important question, which experienced events are the 613 00:43:10,360 --> 00:43:14,480 Speaker 1: important ones to cement in and which events should be 614 00:43:14,520 --> 00:43:17,839 Speaker 1: taken out with the neural trash. In other words, if 615 00:43:17,880 --> 00:43:21,319 Speaker 1: your brain is taking in information all the time, are 616 00:43:21,360 --> 00:43:26,960 Speaker 1: you ever at risk of cementing in associations that are accidental? 617 00:43:27,160 --> 00:43:30,680 Speaker 1: Like you shut the refrigerator door and just at that 618 00:43:30,800 --> 00:43:34,520 Speaker 1: moment a dog barks outside, and your brain might say, oh, 619 00:43:34,560 --> 00:43:37,879 Speaker 1: there must be a relationship between those two events. Even 620 00:43:37,880 --> 00:43:41,400 Speaker 1: though it was totally spurious, it was accidental. As it 621 00:43:41,480 --> 00:43:44,360 Speaker 1: turns out, people have been thinking about this question for 622 00:43:44,360 --> 00:43:48,080 Speaker 1: a long time. I found a quotation from seventeen forty 623 00:43:48,160 --> 00:43:53,320 Speaker 1: nine where the English philosopher David Hartley suggested that quote 624 00:43:54,040 --> 00:43:57,840 Speaker 1: the wilderness of our dreams seems to be of singular 625 00:43:58,080 --> 00:44:01,920 Speaker 1: use to us by interrupting and breaking the course of 626 00:44:02,040 --> 00:44:07,960 Speaker 1: our associations. For if we were always awake, some accidental 627 00:44:08,000 --> 00:44:13,680 Speaker 1: associations would be so much cemented by continuance as that 628 00:44:14,160 --> 00:44:21,200 Speaker 1: nothing could afterward disjoin them, which would be madness. End quote. 629 00:44:21,320 --> 00:44:24,200 Speaker 1: Now this idea was taken up by Francis Crick and 630 00:44:24,320 --> 00:44:28,680 Speaker 1: Graham Mitchison, who in nineteen eighty three hypothesized that we 631 00:44:29,000 --> 00:44:34,080 Speaker 1: dream to forget. That is, they suggested that rem sleep 632 00:44:34,400 --> 00:44:41,520 Speaker 1: erases these spurious associations between neurons before they inappropriately lock 633 00:44:41,640 --> 00:44:47,840 Speaker 1: into place. So this theory posits forgetting as an active 634 00:44:47,960 --> 00:44:51,920 Speaker 1: nightly practice, which is quite different from the traditional view 635 00:44:52,040 --> 00:44:57,399 Speaker 1: of forgetting as a slow global degradation of information. Now, 636 00:44:57,440 --> 00:45:01,200 Speaker 1: there are various reasons to take this hypothesis seriously. So 637 00:45:01,640 --> 00:45:05,759 Speaker 1: look at artificial neural networks. They have this tendency to 638 00:45:05,840 --> 00:45:09,920 Speaker 1: turn into memory mud when you expose them to too 639 00:45:10,000 --> 00:45:15,120 Speaker 1: many associations, and Krick and Mitchison were inspired to make 640 00:45:15,160 --> 00:45:18,600 Speaker 1: their proposal not only by the fact that such networks fail, 641 00:45:18,680 --> 00:45:21,759 Speaker 1: but the way in which they fail, because when these 642 00:45:21,840 --> 00:45:29,440 Speaker 1: artificial networks become overloaded, their output can mistakenly associate incorrect inputs, 643 00:45:29,680 --> 00:45:33,919 Speaker 1: or give the same output irrespective of the input, or 644 00:45:34,360 --> 00:45:38,719 Speaker 1: respond to stimuli that wouldn't normally evoke a response. And 645 00:45:38,800 --> 00:45:45,359 Speaker 1: these types of pathological output loosely seem to parallel fantasy 646 00:45:45,520 --> 00:45:50,280 Speaker 1: and obsession and hallucinations, all of which occur in humans 647 00:45:50,640 --> 00:45:55,279 Speaker 1: if they don't get REM sleep. So the idea is 648 00:45:55,320 --> 00:45:59,160 Speaker 1: that daily experience with the world leads to these rich 649 00:45:59,360 --> 00:46:04,160 Speaker 1: changes in your synapses, and sleep goes through and erases 650 00:46:04,400 --> 00:46:10,080 Speaker 1: the spurious associations that could otherwise become fantasies or obsessions 651 00:46:10,200 --> 00:46:14,239 Speaker 1: or hallucinations. In fact, I'll just note that some mammals, 652 00:46:14,320 --> 00:46:18,080 Speaker 1: like the spiny ant eater, don't have REM sleep, and 653 00:46:18,120 --> 00:46:22,600 Speaker 1: they also have larger than normal brains, and that suggests 654 00:46:22,680 --> 00:46:28,120 Speaker 1: the possibility that animals without remsleep require a larger brain 655 00:46:28,560 --> 00:46:34,200 Speaker 1: to prevent overloading. Now, we talked about rehearsal and forgetting, 656 00:46:34,520 --> 00:46:38,120 Speaker 1: and those ideas operate hand in hand, but there's something 657 00:46:38,120 --> 00:46:42,080 Speaker 1: else too, which is that intelligent brains like we find 658 00:46:42,080 --> 00:46:46,919 Speaker 1: in humans also require something else, not just writing down 659 00:46:46,960 --> 00:46:53,440 Speaker 1: precisely what happened, but restructuring memories, thinking through things, and 660 00:46:53,480 --> 00:46:56,400 Speaker 1: that lies at the heart of what we call understanding 661 00:46:56,440 --> 00:47:01,920 Speaker 1: and insight, and sleep appears to be involved in that process, 662 00:47:02,719 --> 00:47:06,799 Speaker 1: so people often claim to have gained insight into a 663 00:47:06,880 --> 00:47:11,440 Speaker 1: problem through sleep. Otto Levy won the Nobel Prize for 664 00:47:11,560 --> 00:47:15,840 Speaker 1: discovering neurotransmission with an experiment he did on the frog's heart. 665 00:47:16,080 --> 00:47:19,399 Speaker 1: Now here's the key thing. He had long believed that 666 00:47:19,680 --> 00:47:23,080 Speaker 1: chemical transmission occurred in the nervous system, but he had 667 00:47:23,120 --> 00:47:26,279 Speaker 1: no idea how to prove that until the night when 668 00:47:26,280 --> 00:47:30,320 Speaker 1: he woke up having dreamt the outline of the experiment. 669 00:47:30,680 --> 00:47:34,040 Speaker 1: He got up and jotted the experiment down, But the 670 00:47:34,080 --> 00:47:36,960 Speaker 1: next morning he discovered that he couldn't read his own handwriting. 671 00:47:37,239 --> 00:47:40,640 Speaker 1: So the next night he had the same dream, and 672 00:47:40,680 --> 00:47:43,760 Speaker 1: in his biography he relates of that second night quote, 673 00:47:44,040 --> 00:47:47,960 Speaker 1: I awoke again at three o'clock and I remembered what 674 00:47:48,040 --> 00:47:51,920 Speaker 1: the experiment was. I got up, immediately, went to the laboratory, 675 00:47:52,040 --> 00:47:56,640 Speaker 1: made the experiment, and at five o'clock the chemical transmission 676 00:47:56,680 --> 00:48:01,240 Speaker 1: of the nervous system was conclusively proved. So he seems 677 00:48:01,320 --> 00:48:04,560 Speaker 1: to have gotten insight from his dream. And in fact, 678 00:48:04,600 --> 00:48:09,040 Speaker 1: this connection between sleeping and insight has been supported by 679 00:48:09,080 --> 00:48:13,800 Speaker 1: the results of careful experiments. So, in one report, people 680 00:48:14,000 --> 00:48:18,080 Speaker 1: practiced some cognitive task in which they learned to respond 681 00:48:18,239 --> 00:48:22,839 Speaker 1: to particular cues with particular responses. Now, practice made them 682 00:48:22,880 --> 00:48:25,759 Speaker 1: better at the task, but although they didn't know it, 683 00:48:25,800 --> 00:48:30,960 Speaker 1: there was a hidden rule underlying the order of the sequences. 684 00:48:31,280 --> 00:48:33,880 Speaker 1: So if you could figure out that hidden rule, that 685 00:48:34,080 --> 00:48:37,680 Speaker 1: improved your performance. After the initial training on the task, 686 00:48:37,760 --> 00:48:41,680 Speaker 1: one group got eight hours of sleep, another group stayed 687 00:48:41,680 --> 00:48:44,239 Speaker 1: awake during the same hours of the night, and a 688 00:48:44,280 --> 00:48:47,280 Speaker 1: third group was awake for the same number of hours 689 00:48:47,360 --> 00:48:50,319 Speaker 1: during the day. So one group slept and the other 690 00:48:50,440 --> 00:48:54,160 Speaker 1: two did not. Then they were retested and it turns 691 00:48:54,200 --> 00:48:57,359 Speaker 1: out those who had slept for the eight hours were 692 00:48:57,440 --> 00:49:01,120 Speaker 1: twice as likely to gain insight into the hidden rule, 693 00:49:01,480 --> 00:49:05,799 Speaker 1: irrespective of the time of day. So that result suggests 694 00:49:05,920 --> 00:49:10,960 Speaker 1: that sleep facilitated the discovery of the hidden rule, perhaps 695 00:49:11,000 --> 00:49:17,560 Speaker 1: by restructuring memory. So all these are possible reasons why 696 00:49:17,640 --> 00:49:24,600 Speaker 1: we sleep, to rehearse, to forget, and to restructure memory. Now, 697 00:49:24,880 --> 00:49:27,160 Speaker 1: one more thing I want to cover in this episode 698 00:49:27,320 --> 00:49:32,160 Speaker 1: is the issue of sleep deprivation. So while economists worry 699 00:49:32,160 --> 00:49:36,279 Speaker 1: about the national debt, sleep scientists have become concerned about 700 00:49:36,360 --> 00:49:40,560 Speaker 1: the national sleep debt because with the demands of modern life, 701 00:49:40,840 --> 00:49:44,520 Speaker 1: lots of us get less sleep than the demands of 702 00:49:44,520 --> 00:49:47,880 Speaker 1: our brains and bodies would call for. And the effects 703 00:49:47,920 --> 00:49:52,080 Speaker 1: of mild sleep deprivation, for example, losing a few hours 704 00:49:52,160 --> 00:49:55,120 Speaker 1: of sleep for one night, this is surely familiar to you. 705 00:49:55,400 --> 00:49:59,120 Speaker 1: You get irritable, you get muscle aches, you yawn, you 706 00:49:59,160 --> 00:50:04,799 Speaker 1: have trouble maintains attention. With more severe sleep deprivation, say 707 00:50:04,920 --> 00:50:08,000 Speaker 1: lasting two or three days or longer, you can also 708 00:50:08,000 --> 00:50:11,880 Speaker 1: get micro sleeps, which are brief sleep periods in the 709 00:50:12,000 --> 00:50:14,600 Speaker 1: range of seconds or even a fraction of a second, 710 00:50:15,160 --> 00:50:20,120 Speaker 1: and these show up as a short moment of cognitive absence. 711 00:50:20,480 --> 00:50:23,880 Speaker 1: So for drivers on the road this is not uncommon 712 00:50:23,960 --> 00:50:29,920 Speaker 1: and it's very dangerous. Unfortunately, people who experience micro sleeps 713 00:50:30,000 --> 00:50:33,560 Speaker 1: will often be unaware that they were just sleeping. They 714 00:50:33,600 --> 00:50:37,080 Speaker 1: will believe themselves to have been awake, or maybe they 715 00:50:37,080 --> 00:50:41,320 Speaker 1: think they've temporarily spaced out. Many people who operate heavy 716 00:50:41,360 --> 00:50:46,279 Speaker 1: machinery or vehicles will experience these brief moments, and this 717 00:50:46,360 --> 00:50:51,080 Speaker 1: often leads to dire consequences and long term sleep deprivation 718 00:50:51,760 --> 00:50:55,120 Speaker 1: often caused by disorders of sleep and wakefulness. This can 719 00:50:55,160 --> 00:50:59,360 Speaker 1: result in really detrimental health like hypertension or diabetes, or 720 00:50:59,400 --> 00:51:03,120 Speaker 1: heart disease or stroke. The studies performed over the decades 721 00:51:03,239 --> 00:51:06,120 Speaker 1: generally converge on a common theme, which is that the 722 00:51:06,160 --> 00:51:10,360 Speaker 1: effects of sleep deprivation are often more detrimental to the 723 00:51:10,520 --> 00:51:14,160 Speaker 1: mind than to the body. So subjects with sleep deprivation 724 00:51:14,440 --> 00:51:19,160 Speaker 1: often perform fine on physical tasks the next day, although 725 00:51:19,160 --> 00:51:22,480 Speaker 1: their stamina tends to diminish a bit faster, But the 726 00:51:22,520 --> 00:51:27,640 Speaker 1: most striking effects are on cognition and mood. Sleep deprivation 727 00:51:28,160 --> 00:51:31,800 Speaker 1: is a real world problem because you've got medical residents 728 00:51:31,800 --> 00:51:35,080 Speaker 1: and pilots and soldiers and truck drivers and lots of 729 00:51:35,080 --> 00:51:39,200 Speaker 1: others who work long shifts that lead to sleep deprivation, 730 00:51:39,640 --> 00:51:43,839 Speaker 1: and that can lead to poor decision making, which in 731 00:51:43,920 --> 00:51:47,719 Speaker 1: turn leads to avoidable accidents. For example, there have been 732 00:51:47,840 --> 00:51:51,399 Speaker 1: years of research on doctors which make it clear that 733 00:51:51,520 --> 00:51:55,680 Speaker 1: sleep deprivation causes them to make more errors when they 734 00:51:55,680 --> 00:51:59,520 Speaker 1: read charts, and they have lower performance because of a 735 00:51:59,600 --> 00:52:03,360 Speaker 1: distant inclination to apply effort, and they have decreased mood 736 00:52:03,480 --> 00:52:08,000 Speaker 1: and poor attitudes. A review of sleep deprivation studies on 737 00:52:08,120 --> 00:52:12,360 Speaker 1: physicians showed that doctors could still respond without trouble to 738 00:52:12,880 --> 00:52:15,760 Speaker 1: novel situations if they have to learn a new routine, 739 00:52:16,480 --> 00:52:22,279 Speaker 1: but their decreased vigilance led to more mistakes in the 740 00:52:22,560 --> 00:52:45,640 Speaker 1: routine and repetitive tasks that characterize a night in the hospital. Now, 741 00:52:45,640 --> 00:52:47,319 Speaker 1: I just want to say that we always need to 742 00:52:47,360 --> 00:52:51,800 Speaker 1: interpret sleep deprivation studies with an eye towards what else 743 00:52:51,800 --> 00:52:54,399 Speaker 1: could be going on, because often there's lots of other 744 00:52:54,440 --> 00:52:59,240 Speaker 1: stuff too, like stress. So you will feel unwell after 745 00:52:59,280 --> 00:53:01,920 Speaker 1: a night of red used to sleep, but interpret that 746 00:53:02,000 --> 00:53:05,000 Speaker 1: with a little bit of caution, because often the poor 747 00:53:05,080 --> 00:53:08,799 Speaker 1: night of sleep comes from a stress inducer like an 748 00:53:08,840 --> 00:53:12,000 Speaker 1: important exam or a deadline or whatever, and the poor 749 00:53:12,000 --> 00:53:15,040 Speaker 1: physical feelings that you have the next day might be 750 00:53:15,080 --> 00:53:18,799 Speaker 1: caused in part by the effects of distress rather than 751 00:53:18,800 --> 00:53:22,520 Speaker 1: the sleep deprivation itself. Okay, Now, before moving on from 752 00:53:22,520 --> 00:53:26,080 Speaker 1: sleep deprivation, I just want to mention that sometimes people 753 00:53:26,120 --> 00:53:31,160 Speaker 1: can stay awake for remarkably long periods. In nineteen sixty four, 754 00:53:31,239 --> 00:53:34,600 Speaker 1: there was a seventeen year old named Brandy Gardner who 755 00:53:34,640 --> 00:53:37,520 Speaker 1: decided he was going to shoot for the world record 756 00:53:37,920 --> 00:53:42,920 Speaker 1: for sleep deprivation. So, in collaboration with Stanford sleep researcher 757 00:53:43,000 --> 00:53:48,080 Speaker 1: William Dement and physician John Ross, he was continuously monitored 758 00:53:48,400 --> 00:53:53,560 Speaker 1: and he kept himself awake for a record breaking eleven days. 759 00:53:54,280 --> 00:53:56,440 Speaker 1: He then went to sleep, and he woke up feeling 760 00:53:56,480 --> 00:53:59,760 Speaker 1: fine fourteen hours and forty minutes later, and on subsequent 761 00:53:59,880 --> 00:54:02,760 Speaker 1: night he slept a normal eight hours. In other words, 762 00:54:02,920 --> 00:54:06,319 Speaker 1: he didn't require catching up on a sleep debt. He 763 00:54:06,400 --> 00:54:11,439 Speaker 1: merely fell back into his normal rhythm. Now. Dement reported 764 00:54:11,480 --> 00:54:15,160 Speaker 1: that the sleep deprivation's main effect was on Randy's mood, 765 00:54:15,480 --> 00:54:18,920 Speaker 1: involving all the changes that are typical of fatigue, and 766 00:54:18,960 --> 00:54:23,040 Speaker 1: Dement wrote that the deprivation had little effect on Randy's 767 00:54:23,080 --> 00:54:27,800 Speaker 1: cognitive abilities, pointing out that on the tenth day, Randy 768 00:54:27,840 --> 00:54:30,279 Speaker 1: won a game of pinball, and on day eleven he 769 00:54:30,320 --> 00:54:33,520 Speaker 1: gave a press conference in which he appeared healthy and 770 00:54:33,600 --> 00:54:37,960 Speaker 1: his speech was unslurred. But it should be noted that Ross, 771 00:54:38,000 --> 00:54:42,600 Speaker 1: the physician, presented a somewhat different story. Beyond the mood swings, 772 00:54:43,040 --> 00:54:48,920 Speaker 1: He reported extreme problems with Randy's ability to concentrate. For example, 773 00:54:48,960 --> 00:54:52,120 Speaker 1: when Randy was asked to start at one hundred and 774 00:54:52,239 --> 00:54:56,600 Speaker 1: continuously subtract seven. Randy stopped about a third of the 775 00:54:56,600 --> 00:54:59,759 Speaker 1: way through. He stated that he had forgotten what he 776 00:54:59,840 --> 00:55:05,040 Speaker 1: was doing. He also appeared to have paranoia and hallucinations, 777 00:55:05,440 --> 00:55:07,560 Speaker 1: as well as a delusion by the fourth day that 778 00:55:07,600 --> 00:55:10,520 Speaker 1: he was a famous football player. At one point, he 779 00:55:11,120 --> 00:55:14,640 Speaker 1: mistook a street sign for a person, So the effects 780 00:55:14,640 --> 00:55:17,799 Speaker 1: of staying awake that long may not have been as 781 00:55:17,880 --> 00:55:22,439 Speaker 1: harmless as Dement portrayed. In any case, the fact that 782 00:55:22,480 --> 00:55:27,560 Speaker 1: such an extraordinary stretch without sleep is even possible serves 783 00:55:27,640 --> 00:55:30,960 Speaker 1: as an important data point for any theory of sleep. 784 00:55:31,480 --> 00:55:35,640 Speaker 1: Other sleep deprivation records have been set, apparently extending to 785 00:55:35,840 --> 00:55:39,560 Speaker 1: eighteen days and seventeen hours, but these are less documented 786 00:55:39,920 --> 00:55:43,400 Speaker 1: and didn't monitor for micro sleeps. What's interesting is that 787 00:55:43,440 --> 00:55:47,440 Speaker 1: the Guinness Book of World Records no longer maintains a 788 00:55:47,600 --> 00:55:52,160 Speaker 1: sleep deprivation record because they have decided smartly that they 789 00:55:52,160 --> 00:55:56,319 Speaker 1: don't want to encourage people to risk health consequences. By 790 00:55:56,360 --> 00:55:59,680 Speaker 1: the way, I'll just note that many people report sleeping 791 00:55:59,719 --> 00:56:04,160 Speaker 1: poor in being sleep deprived, but measurements taken at home 792 00:56:04,280 --> 00:56:07,880 Speaker 1: or in a sleep lab sometimes reveal that the person 793 00:56:07,960 --> 00:56:11,080 Speaker 1: slept better than they believed they did. Sometimes a period 794 00:56:11,120 --> 00:56:14,160 Speaker 1: of wakefulness in the middle of the night gives the 795 00:56:14,520 --> 00:56:18,200 Speaker 1: lasting impression of a poor night's sleep, when in fact 796 00:56:18,320 --> 00:56:21,560 Speaker 1: it wasn't that long. But in general, there are fewer 797 00:56:21,600 --> 00:56:24,759 Speaker 1: things important than making sure that you are getting a 798 00:56:24,760 --> 00:56:28,480 Speaker 1: good night's sleep. Finally, an episode about sleep wouldn't be 799 00:56:28,520 --> 00:56:32,840 Speaker 1: complete if I didn't talk about sleep disorders. Although lots 800 00:56:32,840 --> 00:56:36,239 Speaker 1: of people get sleep deprivation because of their circumstances and 801 00:56:36,280 --> 00:56:41,520 Speaker 1: stressful work, some people suffer chronic sleep disorders, and this, 802 00:56:41,680 --> 00:56:45,000 Speaker 1: by the way, is the most common medical complaints, second 803 00:56:45,040 --> 00:56:48,880 Speaker 1: only to pain. There are currently about one hundred different 804 00:56:48,920 --> 00:56:52,640 Speaker 1: types of sleep wake disorders. Almost all of these can 805 00:56:52,680 --> 00:56:57,400 Speaker 1: be grouped into four categories. There's insomnia, which is difficulty 806 00:56:57,520 --> 00:57:03,120 Speaker 1: falling asleep or maintaining sleep. There's hypersomnia, which is extreme 807 00:57:03,320 --> 00:57:09,960 Speaker 1: daytime sleepiness, and there's parasomnia's which is complex behaviors performed 808 00:57:10,040 --> 00:57:14,080 Speaker 1: during sleep. And then there's the circadian rhythm disorders, which 809 00:57:14,080 --> 00:57:16,440 Speaker 1: I already discussed before. So I'm going to turn to 810 00:57:16,480 --> 00:57:21,040 Speaker 1: these other three. So let's talk insomnia first. So this 811 00:57:21,160 --> 00:57:24,800 Speaker 1: is the most common sleep problem, and it involves not 812 00:57:24,960 --> 00:57:28,120 Speaker 1: getting enough sleep to feel rested from the brain's point 813 00:57:28,160 --> 00:57:32,520 Speaker 1: of view, insomnia happens when both your sleep and arousal 814 00:57:32,600 --> 00:57:36,400 Speaker 1: systems are simultaneously active. By the way, it's an interesting 815 00:57:36,440 --> 00:57:41,240 Speaker 1: side note, there's often a link between insomnia and psychiatric disorders, 816 00:57:41,360 --> 00:57:44,520 Speaker 1: and the link is bidirectional, meaning either can lead to 817 00:57:44,560 --> 00:57:49,960 Speaker 1: the other. Now, to deal with insomnia, some people take hypnotics, 818 00:57:50,040 --> 00:57:53,200 Speaker 1: which are sleep aids, and although people have used lots 819 00:57:53,200 --> 00:57:58,040 Speaker 1: of compounds as hypnotics over the millennia, such as opium 820 00:57:58,040 --> 00:58:02,160 Speaker 1: and barbituates, these often lead to addiction and sometimes to 821 00:58:02,280 --> 00:58:06,760 Speaker 1: breathing problems. Over the counter hypnotics that are approved by 822 00:58:06,760 --> 00:58:10,680 Speaker 1: the Food and Drug Administration, they're all antihistamines, and these 823 00:58:10,720 --> 00:58:14,760 Speaker 1: can produce next morning sleepiness or several other side effects 824 00:58:14,800 --> 00:58:20,439 Speaker 1: and eventually tolerance to the sedating effects. Now unregulated, over 825 00:58:20,480 --> 00:58:24,280 Speaker 1: the counter sleep aids like valerian or hops or lavender 826 00:58:24,360 --> 00:58:28,440 Speaker 1: or melatonin generally appear to be of no benefit for insomnia. 827 00:58:28,840 --> 00:58:32,480 Speaker 1: There are only a few pharmaceutical treatments for insomnia, and 828 00:58:32,600 --> 00:58:36,360 Speaker 1: most commonly these include drugs that modulate the effect of 829 00:58:36,400 --> 00:58:42,280 Speaker 1: the neurotransmitter called GABA. Now, insomnia can take a heavy 830 00:58:42,480 --> 00:58:46,520 Speaker 1: toll on mood and productivity, and in the most extreme 831 00:58:46,680 --> 00:58:50,440 Speaker 1: and rare cases, it can actually be fatal. I'll tell 832 00:58:50,440 --> 00:58:53,760 Speaker 1: you a case that's really terrifying. Think about what it 833 00:58:53,800 --> 00:58:58,360 Speaker 1: would be like to never sleep again. In nineteen seventy eight, 834 00:58:58,400 --> 00:59:01,560 Speaker 1: there was an Italian woman in her forties who went 835 00:59:01,600 --> 00:59:07,000 Speaker 1: to the doctor with terrible insomnia. Sleeping aids were totally useless. 836 00:59:07,080 --> 00:59:11,440 Speaker 1: She simply couldn't fall asleep anymore, and as the toll 837 00:59:11,520 --> 00:59:14,640 Speaker 1: of the disorder grew over the course of a few months, 838 00:59:15,120 --> 00:59:18,360 Speaker 1: she could no longer walk and could barely speak, and 839 00:59:18,400 --> 00:59:22,400 Speaker 1: within one year of the onset of this insomnia, she 840 00:59:22,720 --> 00:59:27,520 Speaker 1: died with her body exhausted. A year later, the woman's 841 00:59:27,560 --> 00:59:31,680 Speaker 1: sister presented with exactly the same symptoms, and she soon 842 00:59:31,840 --> 00:59:36,160 Speaker 1: died the same death. For both women, their minds remained 843 00:59:36,240 --> 00:59:40,320 Speaker 1: fine as their bodies disintegrated. So there was a physician 844 00:59:40,360 --> 00:59:43,840 Speaker 1: named Ignotio Reuter who was a nephew by marriage to 845 00:59:43,880 --> 00:59:46,960 Speaker 1: these two sisters. He was drawn to this mystery and 846 00:59:47,040 --> 00:59:51,160 Speaker 1: began to plumb his wife's family tree for clues, and 847 00:59:51,280 --> 00:59:56,360 Speaker 1: he discovered that this fatal insomnia had struck down other 848 00:59:56,520 --> 00:59:59,600 Speaker 1: ancestors of theirs, and he suspected he was on the 849 00:59:59,640 --> 01:00:04,600 Speaker 1: trail A rare genetic disorder. So when his wife's uncle, Silvano, 850 01:00:04,840 --> 01:00:09,920 Speaker 1: came to visit, Reuter spotted the early onset of the symptoms, 851 01:00:10,000 --> 01:00:14,280 Speaker 1: and he convinced Silvano to go to an Italian sleep clinic, 852 01:00:14,720 --> 01:00:20,560 Speaker 1: where his worsening insomnia and progressive decline were documented on video, 853 01:00:21,200 --> 01:00:23,520 Speaker 1: and then Silvano died at the age of fifty two. 854 01:00:24,080 --> 01:00:28,440 Speaker 1: Now Silvano's brain was quickly removed and flown to a 855 01:00:28,600 --> 01:00:33,120 Speaker 1: lab at Case Western Reserve University in Cleveland, and there 856 01:00:33,440 --> 01:00:38,840 Speaker 1: a neuropithologist named pure Luigi Gambetti examined the brain and 857 01:00:38,960 --> 01:00:42,640 Speaker 1: noticed that it was shot through with tiny holes, like 858 01:00:42,720 --> 01:00:46,840 Speaker 1: a sponge. This reminded him of something that he'd seen before, 859 01:00:47,320 --> 01:00:50,920 Speaker 1: a brain disease known as kraitzfeld yakub, which is the 860 01:00:51,360 --> 01:00:57,160 Speaker 1: human form of mad cow disease. So Gambetti called Stanley Prusner, 861 01:00:57,600 --> 01:01:01,800 Speaker 1: a scientist who had recently suggested that these brain diseases 862 01:01:01,840 --> 01:01:07,160 Speaker 1: were caused by abnormal proteins called prions. So Prusner performed 863 01:01:07,200 --> 01:01:13,440 Speaker 1: studies and confirmed that this insomniac family had a prion disorder, 864 01:01:13,760 --> 01:01:16,880 Speaker 1: and he won the nineteen ninety seven Nobel Prize for 865 01:01:17,000 --> 01:01:20,160 Speaker 1: his investigation of prions in part for the work on 866 01:01:20,240 --> 01:01:24,360 Speaker 1: this family. Now, in the intervening years, more than thirty 867 01:01:24,440 --> 01:01:27,960 Speaker 1: other families who are carriers of this genetic disorder have 868 01:01:28,080 --> 01:01:34,560 Speaker 1: been discovered, and this is now known as fatal familial insomnia. Thankfully, 869 01:01:34,800 --> 01:01:38,960 Speaker 1: most types of insomnia are typically much milder and more treatable. 870 01:01:39,320 --> 01:01:42,560 Speaker 1: For example, one of the most common forms is restless 871 01:01:42,680 --> 01:01:47,840 Speaker 1: leg syndrome, where upon falling asleep, a person feels unbearable 872 01:01:47,880 --> 01:01:51,840 Speaker 1: discomfort in the legs that calls for relief by stomping 873 01:01:51,920 --> 01:01:55,400 Speaker 1: or rubbing or twitching the legs. And this restless leg 874 01:01:55,560 --> 01:01:58,920 Speaker 1: syndrome is experienced by about five to fifteen percent of 875 01:01:58,920 --> 01:02:03,200 Speaker 1: the population and appears to have a genetic component. But fortunately, 876 01:02:03,600 --> 01:02:10,160 Speaker 1: medications can successfully address restless leg syndrome in most cases. Okay, 877 01:02:10,200 --> 01:02:14,000 Speaker 1: so that's a quick overview of insomnia. But there's also 878 01:02:14,040 --> 01:02:19,560 Speaker 1: the opposite of insomnia, known as hypersomnia. People with hypersomnia 879 01:02:19,920 --> 01:02:24,960 Speaker 1: have excessive sleepiness. Now this is different from being tired 880 01:02:25,040 --> 01:02:27,640 Speaker 1: because of a late night. This exists at such a 881 01:02:27,760 --> 01:02:30,960 Speaker 1: high level that one has no choice but to nap 882 01:02:31,080 --> 01:02:35,320 Speaker 1: frequently during the day, including inappropriate times such as in 883 01:02:35,360 --> 01:02:37,920 Speaker 1: the middle of a conversation or a meeting. Or lunch. 884 01:02:38,640 --> 01:02:43,320 Speaker 1: The naps typically provide little relief from the excessive sleepiness, 885 01:02:43,880 --> 01:02:49,120 Speaker 1: so hypersomnia often comes with anxiety and disorientation upon waking 886 01:02:49,200 --> 01:02:54,320 Speaker 1: and diminished energy and memory problems. As you can imagine, 887 01:02:54,440 --> 01:03:00,320 Speaker 1: hypersomniacs often can't participate in the normal settings of fail family, 888 01:03:00,360 --> 01:03:03,920 Speaker 1: in work life. Sometimes this disorder occurs as a result 889 01:03:04,000 --> 01:03:08,400 Speaker 1: of taking medications for depression or having excess body weight 890 01:03:08,520 --> 01:03:12,640 Speaker 1: or suffering brain damage, and treatment options typically target the 891 01:03:13,040 --> 01:03:17,360 Speaker 1: symptoms because often the cause is unknown. This hypersomnia this 892 01:03:17,480 --> 01:03:21,400 Speaker 1: is the main symptom of narcilepsy, which is something you've 893 01:03:21,440 --> 01:03:25,640 Speaker 1: surely heard of, where people have sudden attacks of sleepiness 894 01:03:25,680 --> 01:03:30,240 Speaker 1: and will fall asleep. Aside from having extreme fatigue and 895 01:03:30,320 --> 01:03:35,360 Speaker 1: frequent naps, narcalptics ironically can also have pretty poor nighttime sleep. 896 01:03:35,600 --> 01:03:39,479 Speaker 1: They have other issues too, like sometimes right when they're 897 01:03:39,880 --> 01:03:43,200 Speaker 1: in between wake and sleep, they'll have hallucinations or they'll 898 01:03:43,200 --> 01:03:49,160 Speaker 1: do automatic behaviors in which they spontaneously produce purposeless sounds 899 01:03:49,240 --> 01:03:54,040 Speaker 1: or acts with no conscious intervention or censorships where sometimes 900 01:03:54,040 --> 01:03:57,760 Speaker 1: in a person with narcilepsy, there muscles will suddenly weaken 901 01:03:58,320 --> 01:04:01,520 Speaker 1: and this can manifest as a slight sagging all the 902 01:04:01,560 --> 01:04:05,920 Speaker 1: way to a complete shutdown of the muscles leading to collapse. No, 903 01:04:05,920 --> 01:04:11,120 Speaker 1: how do we understand this? Note that narcoleptics fall abruptly 904 01:04:11,200 --> 01:04:14,960 Speaker 1: into REM sleep directly from the waking state, whereas normally 905 01:04:15,000 --> 01:04:17,600 Speaker 1: you pass through the stages of non rem sleep first. 906 01:04:17,880 --> 01:04:22,080 Speaker 1: In REM sleep, the major skeletal muscles are shut down, 907 01:04:22,520 --> 01:04:25,520 Speaker 1: and in narcilepsy, this is what happens. The body drops 908 01:04:25,840 --> 01:04:29,880 Speaker 1: straight into REM sleep and causes the major muscle groups 909 01:04:30,080 --> 01:04:34,240 Speaker 1: to just stop functioning. So this mistimed activity to the 910 01:04:34,320 --> 01:04:39,280 Speaker 1: muscles also plays a role in another common symptom of narclepsy, 911 01:04:39,320 --> 01:04:43,240 Speaker 1: which is sleep paralysis, and here the shutdown of the 912 01:04:43,320 --> 01:04:46,640 Speaker 1: muscles lasts longer than it's supposed to, such as the 913 01:04:46,720 --> 01:04:49,800 Speaker 1: brain wakes up but the body is unable to move 914 01:04:49,880 --> 01:04:53,920 Speaker 1: for a short period. Narclepsi appears to be a genetic condition, 915 01:04:54,440 --> 01:04:57,440 Speaker 1: and it results from a lower level of a hormone 916 01:04:57,480 --> 01:05:03,680 Speaker 1: called ourexin, also known as hypocretan. This hormone promotes wakefulness, 917 01:05:04,160 --> 01:05:08,200 Speaker 1: so in the late nineteen nineties, researchers discovered that people 918 01:05:08,200 --> 01:05:14,080 Speaker 1: with narcolepsy have fewer neurons producing this orexin or hypocretin, 919 01:05:14,440 --> 01:05:18,120 Speaker 1: and they realized that narcilepsy can be an autoimmune disorder 920 01:05:18,480 --> 01:05:23,640 Speaker 1: in which the immune system attacks these neurons. Now, remember 921 01:05:23,680 --> 01:05:27,840 Speaker 1: earlier I talked about these two mutually inhibitory networks that 922 01:05:27,880 --> 01:05:31,080 Speaker 1: take care of wake and sleep. The current view is 923 01:05:31,120 --> 01:05:36,440 Speaker 1: that the orexin hypocreting system stabilizes this system in the 924 01:05:36,480 --> 01:05:39,560 Speaker 1: waking state, and if you don't have the proper level 925 01:05:39,600 --> 01:05:43,680 Speaker 1: of these molecules, the flip flop of these networks is 926 01:05:43,840 --> 01:05:50,280 Speaker 1: unstable and can switch states at inappropriate times. Okay, so 927 01:05:50,320 --> 01:05:53,040 Speaker 1: that's what I want to tell you about hypersomnia, where 928 01:05:53,040 --> 01:05:55,840 Speaker 1: the balance is disrupted in the direction of too much 929 01:05:55,880 --> 01:05:59,480 Speaker 1: sleep instead of too little. And there's one more category 930 01:05:59,520 --> 01:06:03,360 Speaker 1: of sleep to that's important. We've been talking about the 931 01:06:03,400 --> 01:06:07,040 Speaker 1: states of sleep and waking as a flip flop system. 932 01:06:07,360 --> 01:06:10,400 Speaker 1: But keep in mind that the arousal network or the 933 01:06:10,400 --> 01:06:14,200 Speaker 1: sleep network consists of lots and lots of sub areas, 934 01:06:14,240 --> 01:06:18,160 Speaker 1: and these areas typically work together in a smooth manner 935 01:06:18,720 --> 01:06:22,120 Speaker 1: so that when the networks switch, all the appropriate systems 936 01:06:22,160 --> 01:06:25,520 Speaker 1: come online when the others go offline. But given the 937 01:06:25,600 --> 01:06:29,800 Speaker 1: complexity and size of these networks, the brain sometimes gets 938 01:06:29,880 --> 01:06:34,480 Speaker 1: caught between stages. In other words, some neural areas have 939 01:06:34,640 --> 01:06:38,680 Speaker 1: completed the switchover and others have not, and in these 940 01:06:38,760 --> 01:06:45,080 Speaker 1: cases we find Parasomnia's where you get actions performed during 941 01:06:45,200 --> 01:06:50,040 Speaker 1: sleep that are not under voluntary control, for example, sleep 942 01:06:50,120 --> 01:06:54,840 Speaker 1: walking also known as somnambulism, like we saw in Kenneth 943 01:06:54,920 --> 01:06:59,080 Speaker 1: Parks at the beginning of this episode. Parasomnias used to 944 01:06:59,080 --> 01:07:01,920 Speaker 1: be thought of as a disorder, but they're now understood 945 01:07:02,000 --> 01:07:05,840 Speaker 1: to represent a mixture of the waking state and some 946 01:07:06,120 --> 01:07:10,360 Speaker 1: stage of sleep, either rem or non rem. These parasomnias 947 01:07:10,440 --> 01:07:14,160 Speaker 1: come into being as the brain transitions from one state 948 01:07:14,240 --> 01:07:20,200 Speaker 1: to the next. Now, non rem parasomnias are these disorders 949 01:07:20,200 --> 01:07:23,760 Speaker 1: that happen when a sleeper's brain tries to jump directly 950 01:07:23,800 --> 01:07:26,600 Speaker 1: from a deep sleep into the waking state and it 951 01:07:26,680 --> 01:07:30,120 Speaker 1: becomes caught in between. So you get things like sleepwalking, 952 01:07:30,160 --> 01:07:33,360 Speaker 1: but you also get things like talking in one sleep 953 01:07:33,480 --> 01:07:38,040 Speaker 1: called some niloquy, or sleep eating or teeth grinding, or 954 01:07:38,600 --> 01:07:42,600 Speaker 1: night terrors in which a sleeper will bolt upright in fear, 955 01:07:43,160 --> 01:07:46,040 Speaker 1: often with a scream or a gasp, and have a 956 01:07:46,120 --> 01:07:50,840 Speaker 1: temporary inability to regain consciousness. Now, most of these non 957 01:07:50,920 --> 01:07:55,800 Speaker 1: rem parasomnias exist more commonly in childhood, and they tend 958 01:07:55,920 --> 01:07:59,360 Speaker 1: to diminish in frequency with age. Now you also have 959 01:08:00,040 --> 01:08:04,200 Speaker 1: REM parisomnia's, and the most common of these is REM 960 01:08:04,400 --> 01:08:08,280 Speaker 1: sleep behavior disorder, in which the paralysis of the muscles 961 01:08:08,320 --> 01:08:12,040 Speaker 1: that normally happens during REM is not there, so sleepers 962 01:08:12,120 --> 01:08:16,680 Speaker 1: will act out their dreams, which usually results in injury 963 01:08:16,800 --> 01:08:20,120 Speaker 1: to themselves or others. Ninety percent of patients with this 964 01:08:20,240 --> 01:08:23,439 Speaker 1: disorder are male, and they'll sometimes try to deal with 965 01:08:23,479 --> 01:08:27,200 Speaker 1: this problem by tying themselves directly to the bed or 966 01:08:27,520 --> 01:08:32,559 Speaker 1: constructing fortresses of pillows. Happily, this can typically be dealt 967 01:08:32,600 --> 01:08:38,080 Speaker 1: with with gabba enhancing pharmaceuticals. Now, as the neuroscience of 968 01:08:38,280 --> 01:08:43,360 Speaker 1: sleep progresses, new parasomnias are being identified. For example, there's 969 01:08:43,400 --> 01:08:50,960 Speaker 1: a fairly newly described parisomnia, which is sleep sex or sexomnia, 970 01:08:51,160 --> 01:08:55,560 Speaker 1: in which a person engages in sexual acts while asleep. 971 01:08:56,040 --> 01:08:59,840 Speaker 1: Several defendants in sexual assault trials have been found not 972 01:09:00,320 --> 01:09:04,559 Speaker 1: guilty because of their sex omnia. Now, many people decry 973 01:09:04,600 --> 01:09:07,840 Speaker 1: this plea as an excuse, and possibly sometimes it is, 974 01:09:08,280 --> 01:09:11,320 Speaker 1: but sex omnia is a real thing, and people can 975 01:09:11,360 --> 01:09:15,920 Speaker 1: have full experiences with no conscious awareness or memory of them. 976 01:09:16,360 --> 01:09:18,639 Speaker 1: And when people do become aware. There's typically a lot 977 01:09:18,680 --> 01:09:22,400 Speaker 1: of distress and shame, so people often don't even go 978 01:09:22,520 --> 01:09:25,880 Speaker 1: to the doctor for help, but they should because this 979 01:09:25,920 --> 01:09:30,240 Speaker 1: can often be dealt with with antidepressant and anti anxiety medications. 980 01:09:30,960 --> 01:09:34,080 Speaker 1: So now that you have listened to this episode, you 981 01:09:34,360 --> 01:09:38,599 Speaker 1: understand that there are detectable differences in the activity of 982 01:09:38,720 --> 01:09:43,080 Speaker 1: the sleeping brain in people with parasomnias. Although we tend 983 01:09:43,520 --> 01:09:47,800 Speaker 1: to assume that the brain must be either awake or asleep, 984 01:09:48,200 --> 01:09:52,840 Speaker 1: many well studied phenomenon like the parasomnia's result from the 985 01:09:52,880 --> 01:09:57,639 Speaker 1: brain truly caught in an intermediate state between the two. 986 01:09:58,320 --> 01:10:01,800 Speaker 1: In a network of on hundred billion neurons, there's room 987 01:10:01,880 --> 01:10:06,639 Speaker 1: for a tremendous diversity of different modes of activity, many 988 01:10:06,680 --> 01:10:10,880 Speaker 1: of which were only just beginning to understand. So let's 989 01:10:10,920 --> 01:10:14,280 Speaker 1: wrap up today's episode. It's not clear why we spend 990 01:10:14,400 --> 01:10:18,480 Speaker 1: so much of our live sleeping. Arguments from different angles 991 01:10:18,880 --> 01:10:23,240 Speaker 1: suggest that sleep promotes restoration of the energy you burned 992 01:10:23,280 --> 01:10:25,680 Speaker 1: during the day, or keeps us out of trouble in 993 01:10:25,720 --> 01:10:29,600 Speaker 1: the dark, or allows us to practice neural programs that 994 01:10:29,640 --> 01:10:32,920 Speaker 1: we don't otherwise get the chance to do, and or 995 01:10:33,439 --> 01:10:39,160 Speaker 1: it helps us consolidate memories. These suggestions are not exclusive, 996 01:10:39,800 --> 01:10:42,720 Speaker 1: nor perhaps are they complete, and it remains to be 997 01:10:42,800 --> 01:10:48,960 Speaker 1: understood how sleep restructures memory and inspires insight. Now, at 998 01:10:49,000 --> 01:10:52,160 Speaker 1: the beginning of this episode, I introduced Kenneth Parks, the 999 01:10:52,200 --> 01:10:55,240 Speaker 1: man who killed his mother in law and assaulted his 1000 01:10:55,280 --> 01:10:59,599 Speaker 1: father in law during an apparent sleep walking episode. The 1001 01:10:59,680 --> 01:11:04,760 Speaker 1: idea of murdering in one sleep tends to challenge the 1002 01:11:04,800 --> 01:11:08,160 Speaker 1: belief of the public, and people will typically dig into 1003 01:11:08,240 --> 01:11:12,920 Speaker 1: the position that the plea is a fraudulent excuse. But 1004 01:11:13,000 --> 01:11:16,680 Speaker 1: whatever the merits of any individual case, we know that 1005 01:11:16,800 --> 01:11:22,040 Speaker 1: sleepwalking is a real phenomenon. We saw that transitions between 1006 01:11:22,400 --> 01:11:27,200 Speaker 1: waking and sleeping result from these opposing networks, and that 1007 01:11:27,640 --> 01:11:34,000 Speaker 1: parasomnia's can result when these networks don't hand off power smoothly. Now, 1008 01:11:34,080 --> 01:11:37,519 Speaker 1: a normal sleep cycle moves from very deep sleep into 1009 01:11:37,640 --> 01:11:42,120 Speaker 1: more and more shallow sleep and eventually into wakefulness. But 1010 01:11:42,320 --> 01:11:48,920 Speaker 1: Kenneth Parks's EEG revealed that he had a parasomnia about 1011 01:11:49,040 --> 01:11:52,960 Speaker 1: ten to twenty times each night. His brain networks attempted 1012 01:11:53,000 --> 01:11:59,800 Speaker 1: to transition directly from deep slow wave sleep directly into wakefulness. 1013 01:12:00,200 --> 01:12:02,479 Speaker 1: The jury came to understand that there was no way 1014 01:12:02,640 --> 01:12:07,200 Speaker 1: for him to fake EEG results intentionally, and so those 1015 01:12:07,320 --> 01:12:12,800 Speaker 1: measurements proved critical to his defense, and after hours of deliberation, 1016 01:12:13,320 --> 01:12:17,680 Speaker 1: the jury found Kenneth Parks not guilty. Now, there are 1017 01:12:17,720 --> 01:12:21,479 Speaker 1: other cases that have fared differently. In nineteen ninety seven, 1018 01:12:21,600 --> 01:12:25,960 Speaker 1: Scott Fallader was accused of stabbing his wife forty four 1019 01:12:26,000 --> 01:12:31,480 Speaker 1: times and holding her head underwater. He pled homicidal somnambulism, 1020 01:12:31,920 --> 01:12:34,879 Speaker 1: but he was convicted and sentenced to life in prison. 1021 01:12:35,479 --> 01:12:39,679 Speaker 1: In total, there have been dozens of homicidal somnambulism cases 1022 01:12:40,200 --> 01:12:44,440 Speaker 1: tried in North America going back to the sixteen hundreds, 1023 01:12:45,000 --> 01:12:48,920 Speaker 1: and more recently, parasomnia defenses have been offered in cases 1024 01:12:48,920 --> 01:12:52,559 Speaker 1: of sleep sex. Can the legal system assume that some 1025 01:12:52,640 --> 01:12:56,880 Speaker 1: of these defenses are fake? Perhaps, but presumably not all 1026 01:12:57,000 --> 01:13:00,240 Speaker 1: of them. In many cases, defendants have been a quit 1027 01:13:00,479 --> 01:13:04,680 Speaker 1: after careful measurements of their brain activity. So back to 1028 01:13:04,760 --> 01:13:10,719 Speaker 1: Kenneth Parks. Most somnambulists are nonviolent. But note that Parks 1029 01:13:10,760 --> 01:13:13,599 Speaker 1: had insomnia, and he was depressed, and he was trying 1030 01:13:13,640 --> 01:13:17,800 Speaker 1: to overcome a gambling problem, and he had financial and 1031 01:13:17,880 --> 01:13:21,920 Speaker 1: marital problems, and he had also been massively sleep deprived 1032 01:13:21,920 --> 01:13:25,360 Speaker 1: from not having slept the night before that event. So, 1033 01:13:25,479 --> 01:13:28,639 Speaker 1: although it's difficult to know exactly how these factors played 1034 01:13:28,640 --> 01:13:32,800 Speaker 1: a role the physiology of his brain as measured in 1035 01:13:32,840 --> 01:13:36,920 Speaker 1: an EEG laboratory, this was the clinching piece of evidence 1036 01:13:37,400 --> 01:13:41,599 Speaker 1: in convincing the jury that he did, in fact suffer 1037 01:13:41,640 --> 01:13:45,639 Speaker 1: from abnormal transitions from slow wave sleep to the waking state, 1038 01:13:45,920 --> 01:13:51,479 Speaker 1: transitions that made his actions involuntary. So cases like this 1039 01:13:51,520 --> 01:13:57,320 Speaker 1: one highlight the mysterious and poorly understood border lands between 1040 01:13:58,040 --> 01:14:01,880 Speaker 1: wakefulness and sleep. So the amazing thing to me is 1041 01:14:01,920 --> 01:14:06,160 Speaker 1: that your brain can operate in three very different states. 1042 01:14:06,240 --> 01:14:10,439 Speaker 1: There's the waking state, there's rem sleep, and there's non 1043 01:14:10,520 --> 01:14:14,960 Speaker 1: rem sleep. And these three states differ fundamentally. They represent 1044 01:14:15,080 --> 01:14:19,360 Speaker 1: the same machinery running very different tasks. One of the 1045 01:14:19,400 --> 01:14:23,920 Speaker 1: amazing features of the brain is its ability to transition 1046 01:14:24,240 --> 01:14:28,519 Speaker 1: between these states, usually without a problem. And although the 1047 01:14:28,560 --> 01:14:33,599 Speaker 1: parasomnias represent cases in which the brain has trouble getting 1048 01:14:33,680 --> 01:14:38,040 Speaker 1: a state fully locked into place, it's amazing that these 1049 01:14:38,120 --> 01:14:42,559 Speaker 1: don't happen more often. So this episode has been an 1050 01:14:42,600 --> 01:14:47,559 Speaker 1: introduction to the main landscape about the sleeping brain. Join 1051 01:14:47,640 --> 01:14:50,120 Speaker 1: me next week as we zoom in the camera to 1052 01:14:50,200 --> 01:14:54,080 Speaker 1: the topic of dreams and the whole wild world of 1053 01:14:54,120 --> 01:14:56,880 Speaker 1: what we know and don't know about them. And then 1054 01:14:56,880 --> 01:15:00,559 Speaker 1: two weeks from now will come to lucid dream, where 1055 01:15:00,560 --> 01:15:03,280 Speaker 1: you become aware that you're in a dream and you 1056 01:15:03,320 --> 01:15:06,960 Speaker 1: get to grab a hold of the script. Until then, 1057 01:15:07,360 --> 01:15:10,080 Speaker 1: make sure that you're getting sufficient sleep, although you are 1058 01:15:10,160 --> 01:15:13,160 Speaker 1: not consciously there for most of it. It is one 1059 01:15:13,200 --> 01:15:20,320 Speaker 1: of the most important things that your brain does. Go 1060 01:15:20,360 --> 01:15:23,880 Speaker 1: to eagleman dot com slash podcast for more information and 1061 01:15:23,960 --> 01:15:28,120 Speaker 1: to find further reading. Send me an email at podcasts 1062 01:15:28,160 --> 01:15:32,040 Speaker 1: at eagleman dot com with questions or discussions, and check 1063 01:15:32,080 --> 01:15:35,360 Speaker 1: out and subscribe to Inner Cosmos on YouTube for videos 1064 01:15:35,400 --> 01:15:39,000 Speaker 1: of each episode and to leave comments. Until next time. 1065 01:15:39,360 --> 01:15:42,560 Speaker 1: I'm David Eagleman and this is Inner Cosmos.