WEBVTT - Ep 51 "Why do brains dream?" 0:00:04.760 --> 0:00:09.000 Why do brains dream? And what's going on with the 0:00:09.039 --> 0:00:13.800 bizarreness of dreams? Why doesn't your clock work in your dreams? 0:00:14.240 --> 0:00:16.080 And even though you spend a lot of your day 0:00:16.160 --> 0:00:20.120 working on cell phones and computers, why do those almost 0:00:20.320 --> 0:00:23.799 never make appearances in your dream content? There are so 0:00:23.880 --> 0:00:27.080 many cool questions that we're going to address today. Is 0:00:27.200 --> 0:00:31.320 dream content the same across cultures and across time? Are 0:00:31.440 --> 0:00:35.280 dreams experienced in black and white or in color? Why 0:00:35.280 --> 0:00:38.640 do I think about dreams as this strange love child 0:00:38.760 --> 0:00:43.280 between brain plasticity and the rotation of the planet. What 0:00:43.440 --> 0:00:47.559 is the relationship between schizophrenia and dreaming? And in the 0:00:47.600 --> 0:00:50.800 future will we be able to read out the content 0:00:51.200 --> 0:00:58.320 of somebody's dream? Welcome to Inner Cosmos with me David Eagleman. 0:00:58.600 --> 0:01:01.960 I'm a neuroscientist and author at Stanford and in these 0:01:02.000 --> 0:01:05.920 episodes we sail deeply into our three pound universe to 0:01:06.000 --> 0:01:09.640 understand why and how our lives look the way they 0:01:09.720 --> 0:01:19.320 do and how we experience our life includes our nocturnal life. 0:01:19.400 --> 0:01:23.520 We spend a third of our lives with our eyes closed, 0:01:24.000 --> 0:01:28.520 lying still and horizontal, like a meat robot that's been 0:01:28.640 --> 0:01:33.080 switched off. But why in the last episode, we talked 0:01:33.120 --> 0:01:36.960 all about sleep, why brains do that, and why all 0:01:37.000 --> 0:01:40.080 animals do that, and what is happening in the brain 0:01:40.240 --> 0:01:44.280 during sleep. Today we're going to zoom in on one 0:01:44.319 --> 0:01:48.360 of my favorite subjects, a very strange thing the brain does, 0:01:48.440 --> 0:01:52.560 which we call dreaming. We spend a fraction of our 0:01:52.600 --> 0:01:57.320 sleep time locked in a different reality, swimming around in 0:01:57.480 --> 0:02:01.400 plots which aren't real, and they're often not even realistic, 0:02:02.000 --> 0:02:07.680 but which nonetheless convince us entirely. And today we're going 0:02:07.760 --> 0:02:11.400 to see what that's all about. Humans have been writing 0:02:11.440 --> 0:02:14.919 about dreams and pondering about them for a long time, 0:02:15.080 --> 0:02:17.680 and essentially we have evidence of this from the beginning 0:02:17.720 --> 0:02:23.160 of writing. We see detailed dream reports from ancient Egyptians 0:02:23.240 --> 0:02:27.280 and Romans and Chinese. The Bible is full of dreams. 0:02:27.360 --> 0:02:31.040 Every culture in the world has been fascinated by these 0:02:31.080 --> 0:02:34.320 strange nocturnal journeys that we go on. And as we'll 0:02:34.360 --> 0:02:38.960 see shortly, there's an interesting surprise, which is that dream content, 0:02:39.120 --> 0:02:42.120 in other words, the kind of things that people dream about, 0:02:42.560 --> 0:02:47.600 is essentially the same across cultures and across time, and 0:02:47.639 --> 0:02:50.480 that serves as a clue that will allow us to 0:02:50.680 --> 0:02:54.560 unlock some mysteries about what otherwise feels like a deeply 0:02:54.720 --> 0:02:59.560 mysterious experience that we enjoy or suffer every night of 0:02:59.600 --> 0:03:03.320 our life lives. So strap in for an episode full 0:03:03.320 --> 0:03:06.760 of surprises. So let's start with a poem that Lord 0:03:06.760 --> 0:03:11.120 Byron wrote in eighteen sixteen called The Dream. He wrote, 0:03:11.520 --> 0:03:15.840 sleep hath its own world and a wide realm of 0:03:16.040 --> 0:03:22.240 wild reality. And dreams, in their development have breath and tears, 0:03:22.320 --> 0:03:26.000 and tortures and the touch of joy. They leave a 0:03:26.080 --> 0:03:31.640 weight upon our waking thoughts. So dreams are indeed a 0:03:32.200 --> 0:03:35.800 wild reality. The thing we all find so amazing about 0:03:35.880 --> 0:03:40.720 dreaming is its bizarreness. You're seeing new things, you hold 0:03:41.080 --> 0:03:45.080 strange beliefs, and you fall for it all hook line 0:03:45.120 --> 0:03:48.680 and sinker. Whatever your brain serves up to you, you 0:03:48.720 --> 0:03:52.040 believe it entirely. So we'll talk about all this, But 0:03:52.120 --> 0:03:56.240 let's first zoom in on what's happening inside the brain. 0:03:56.960 --> 0:04:02.360 Dreaming occurs during rapid eye moos movement or rem sleep, 0:04:03.120 --> 0:04:05.720 where your eyes are darting back and forth. There's nothing 0:04:05.800 --> 0:04:08.200 coming in the eyes, of course, they're shut, so all 0:04:08.240 --> 0:04:13.160 the activity is internally generated. For good housekeeping, all just 0:04:13.240 --> 0:04:17.680 note that rem sleep isn't necessarily equivalent to dream sleep, 0:04:17.880 --> 0:04:21.040 but that's when most dreaming occurs. Now, how do we 0:04:21.120 --> 0:04:24.480 know that, Well, it's because if you wait until someone 0:04:24.720 --> 0:04:27.480 enters rems sleep, their eyes are going back and forth, 0:04:27.680 --> 0:04:29.920 and then you shake them awake and you say, hey, 0:04:30.400 --> 0:04:34.880 what were you just experiencing? They'll tell you WHOA, I 0:04:35.040 --> 0:04:38.440 was just panicking because I was at work but realized 0:04:38.480 --> 0:04:40.520 I had forgotten to put on pants, and I was 0:04:40.600 --> 0:04:43.800 hiding behind the plant pots and figuring out how to 0:04:44.000 --> 0:04:47.280 escape before the meeting started. But if you wake them 0:04:47.360 --> 0:04:50.479 up during the rest of the ninety minute sleep cycle, 0:04:50.920 --> 0:04:53.640 during the stages that we call slow wave sleep, and 0:04:53.680 --> 0:04:57.240 you say, hey, what were you just experiencing, they'll generally 0:04:57.279 --> 0:05:02.120 say nothing, I wasn't there. Now, for completeness, I'll mention 0:05:02.279 --> 0:05:07.400 that sometimes people report some form of mental activity during 0:05:07.560 --> 0:05:10.880 slow wave sleep, but when they do, this is usually 0:05:10.920 --> 0:05:15.400 just a thought or making a plan. But it lacks 0:05:15.440 --> 0:05:21.520 the visual vividness and the hallucinatory components of typical dreams. 0:05:21.760 --> 0:05:25.440 So dreaming of the sort we're interested in today happens 0:05:25.520 --> 0:05:32.280 during rem sleep. Now, although dreams seem so untethered and ethereal, 0:05:32.760 --> 0:05:36.520 there are specific things happening under the hood. Dreaming depends 0:05:36.560 --> 0:05:40.920 on the normal functioning of a particular network of brain areas. 0:05:41.320 --> 0:05:45.200 This is primarily in the limbic and paralymbic and association areas. 0:05:45.560 --> 0:05:48.200 Now we know that from brain imaging, but also because 0:05:48.320 --> 0:05:53.200 damage in this network can produce temporary or permanent dream 0:05:53.560 --> 0:05:59.440 loss or impairment like loss of visual dream imagery. Now, 0:05:59.480 --> 0:06:01.880 not all of those areas might sound familiar to you, 0:06:01.920 --> 0:06:04.960 but you've probably heard of the limbic system, which sits 0:06:04.960 --> 0:06:08.880 at the heart of your emotions. So presumably this is 0:06:08.920 --> 0:06:13.880 why dreams are so overloaded with high emotion. And I 0:06:13.920 --> 0:06:16.960 also want to mention a brain era that is suppressed 0:06:17.120 --> 0:06:20.560 during rem sleep, and that is the hippocampus. This is 0:06:20.560 --> 0:06:24.440 an area that's required to convert short term memory into 0:06:24.480 --> 0:06:27.080 long term memory. And this is why when you wake 0:06:27.160 --> 0:06:31.200 up from a dream, you can remember it so clearly, 0:06:31.279 --> 0:06:35.279 but after about fifteen minutes it just slips away from you. 0:06:35.279 --> 0:06:38.560 You just can't hold on to what happened. This is 0:06:38.560 --> 0:06:42.440 because you have the short term memory just fine, but 0:06:42.560 --> 0:06:45.880 you're not converting it into long term memory, and so 0:06:46.000 --> 0:06:50.000 it simply fades before your eyes. And by the way, 0:06:50.040 --> 0:06:53.000 I think this experience that we have every morning can 0:06:53.440 --> 0:06:56.520 enhance our empathy about what it would be like to 0:06:56.560 --> 0:07:00.480 have something like Alzheimer's disease, because a person with Allsheimers 0:07:00.880 --> 0:07:03.320 says on the phone, Okay, I'll be right down there 0:07:03.360 --> 0:07:05.800 in a moment, and they hang up, and then the 0:07:05.880 --> 0:07:09.600 memory of that just slips away. So even though you 0:07:09.680 --> 0:07:13.000 might tell a relative with Alzheimer's, come on, just try 0:07:13.080 --> 0:07:16.840 harder to remember. Just think about somebody telling that to 0:07:16.880 --> 0:07:20.760 you about your dreams in the morning. So back to 0:07:20.800 --> 0:07:23.560 the Byron poem, the line that I thought was interesting 0:07:23.760 --> 0:07:28.600 was they leave a weight upon our waking thoughts because 0:07:28.840 --> 0:07:32.040 they don't directly interact with our waking thoughts, but instead 0:07:32.080 --> 0:07:36.040 they can just put a spin on our mood, even 0:07:36.080 --> 0:07:39.840 if we don't remember why. Okay, so what do we 0:07:39.960 --> 0:07:44.160 see in the brain when dreaming begins, Well, just before 0:07:44.240 --> 0:07:48.000 the onset of your eyes darting back and forth, you 0:07:48.080 --> 0:07:51.440 have a group of neurons in the brain stem, specifically 0:07:51.480 --> 0:07:54.600 in an area called the ponds, and these crank up, 0:07:54.920 --> 0:07:58.920 and these trigger several consequences. The first is that your 0:07:59.160 --> 0:08:04.320 major muscle groups get paralyzed. This is called atonia. So 0:08:04.560 --> 0:08:08.520 you've got this elaborate neural circuitry that keeps the body 0:08:08.640 --> 0:08:13.040 paralyzed during dreaming. And by the way, the very elaborateness 0:08:13.080 --> 0:08:18.720 of this circuitry emphasizes the biological importance of dream sleep. 0:08:19.040 --> 0:08:22.600 You don't get this kind of complexity by accident. Presumably, 0:08:23.040 --> 0:08:27.280 dreaming would be unlikely to evolve and remain without an 0:08:27.320 --> 0:08:30.600 important function behind it. So why do we get this 0:08:30.680 --> 0:08:34.640 paralysis of the muscles. It allows the possibility for the 0:08:34.640 --> 0:08:40.080 brain to experience things and simulate reality without actually moving 0:08:40.120 --> 0:08:43.560 the body. The second consequence of these neurons in the 0:08:43.600 --> 0:08:47.040 ponds is that they trigger these waves of activity known 0:08:47.040 --> 0:08:51.360 as PGO waves, and these are key to the experience 0:08:51.600 --> 0:08:56.360 of dreaming. These PGO waves travel to a tiny area 0:08:56.480 --> 0:08:59.760 called the geniculate nucleus and from there these waves of 0:08:59.760 --> 0:09:03.440 activity slam into the occipital cortex at the back of 0:09:03.480 --> 0:09:07.640 your head. In other words, they drive activity into the 0:09:07.840 --> 0:09:11.280 visual system. So that's why these are called PGO waves. 0:09:11.320 --> 0:09:14.520 Because they start in the ponds, p move to the 0:09:14.600 --> 0:09:18.679 geniculate g and go to the occipital cortex. Oh pgoh 0:09:18.960 --> 0:09:22.280 I mention all this detail. Because PGO waves are the 0:09:22.440 --> 0:09:28.200 neural correlate of dreaming, the visual areas become alive with 0:09:28.280 --> 0:09:33.280 activity allowing us to see our dreams. You blast activity 0:09:33.280 --> 0:09:37.800 into the visual cortex and you enjoy visual experience even 0:09:37.840 --> 0:09:42.560 though your eyes are closed. Now, interestingly, when you measure 0:09:42.640 --> 0:09:47.040 electrical activity across the brain with EEG, when you do 0:09:47.080 --> 0:09:50.040 this during rem sleep, it looks really similar to that 0:09:50.160 --> 0:09:54.960 during the waking state. You see similar patterns in both states, 0:09:55.240 --> 0:09:58.679 for example, lots of gamma wave frequency, which is generally 0:09:58.720 --> 0:10:03.280 thought to reflect something about cognitive processing, with the exception 0:10:03.640 --> 0:10:08.160 of the paralyzed muscles and the lack of external visual 0:10:08.200 --> 0:10:11.520 input because your eyes are closed, the states of rem 0:10:11.559 --> 0:10:15.120 sleep and of wakefulness they kind of resemble one another. 0:10:15.400 --> 0:10:17.600 And this is what we might expect from a state 0:10:17.679 --> 0:10:23.960 of consciousness that's altered. But it's some sort of consciousness nonetheless. Okay, 0:10:24.080 --> 0:10:27.160 so that's what's happening in the brain when we dream. 0:10:27.320 --> 0:10:31.199 But why do we dream? Well, there are various hypotheses 0:10:31.240 --> 0:10:33.800 about this, and I mentioned one last week, which is 0:10:33.800 --> 0:10:38.480 that maybe dreams allow us to simulate rare situations. In 0:10:38.520 --> 0:10:44.760 other words, these nocturnal neural simulations might allow us and 0:10:44.800 --> 0:10:49.240 all animals to test out activities without the danger and 0:10:49.400 --> 0:10:51.440 risk of doing so in the real world. So you 0:10:51.520 --> 0:10:56.240 can practice through different scenarios with your muscles all shut down. 0:10:56.800 --> 0:11:00.920 So people who advocate this theory suggest that the periodic 0:11:01.120 --> 0:11:05.080 stimulation of the cortex in this semi random and non 0:11:05.120 --> 0:11:09.520 specific manner this can maintain circuits that are really important 0:11:09.559 --> 0:11:13.480 for survival, but they rarely get activated because you don't 0:11:13.520 --> 0:11:16.920 run into emergencies that often. So the idea is that 0:11:16.960 --> 0:11:20.480 you're just sending in random activity, keeping the engine oiled 0:11:20.880 --> 0:11:24.640 in case you need one of these programs sometime, and 0:11:24.760 --> 0:11:27.800 some researchers suggest that it's even more specific than that. 0:11:27.920 --> 0:11:32.679 A version of this framework called threat simulation theory, suggests 0:11:32.720 --> 0:11:36.840 that dreams exist to simulate threatening events and to rehearse 0:11:36.960 --> 0:11:39.720 what to do in the face of threat, and that 0:11:39.800 --> 0:11:42.880 seems on its surface at least consistent with the high 0:11:42.920 --> 0:11:47.800 prevalence of violence and aggression in dreams. But I want 0:11:47.800 --> 0:11:51.080 to note that there's no data that directly supports this idea, 0:11:51.160 --> 0:11:55.480 and I mentioned last week that this theory suggests that 0:11:55.520 --> 0:11:59.200 people exposed to more survival threats in waking life might 0:11:59.280 --> 0:12:02.800 have a more common experience of threat dreams at night, 0:12:03.160 --> 0:12:06.600 but the data do not support that. Also, the threat 0:12:06.640 --> 0:12:10.240 perception theory doesn't explain the fact that most dreams are 0:12:10.280 --> 0:12:14.960 totally meaningless and bizarre instead of involving any meaningful threat 0:12:15.000 --> 0:12:18.160 perception or threat avoidance. So back to the question of 0:12:18.280 --> 0:12:21.640 why we dream. A few years ago, my colleague Don 0:12:21.720 --> 0:12:25.200 Vaughan and I proposed a new theory which is the 0:12:25.240 --> 0:12:30.200 only one that makes quantitative predictions across species. And if 0:12:30.240 --> 0:12:33.440 you heard episode eleven you may remember about this. That 0:12:33.480 --> 0:12:36.920 theory has to do with brain plasticity. And here's the idea. 0:12:37.160 --> 0:12:40.320 In a nutshell, we know that if a person goes blind, 0:12:40.960 --> 0:12:44.959 other senses start to take over what was the visual cortex. 0:12:45.000 --> 0:12:47.840 In other words, the territory of the visual system is 0:12:47.840 --> 0:12:51.760 not fixed permanently, but instead the wiring of the brain 0:12:51.840 --> 0:12:55.600 is quite fluid, and there's a takeover that happens. Okay, now, 0:12:55.640 --> 0:12:58.160 it turns out that if you take a normally cited 0:12:58.200 --> 0:13:03.120 person and you blindfold, you can start seeing the beginnings 0:13:03.240 --> 0:13:07.880 of this takeover in neuroimaging starting in about one hour. 0:13:08.400 --> 0:13:12.120 And that really surprised us because of how fast the 0:13:12.160 --> 0:13:16.240 takeover starts to happen. So what does this rapidity of 0:13:16.360 --> 0:13:19.480 the takeover of the cortex have to do with dreaming? 0:13:20.080 --> 0:13:23.439 While in the incessant competition for territory in the brain, 0:13:23.960 --> 0:13:27.720 the visual system has a special challenge because of the 0:13:27.760 --> 0:13:32.800 planet's rotation, we experience darkness for about twelve out of 0:13:32.840 --> 0:13:36.040 every twenty four hours. And obviously I'm talking about our 0:13:36.120 --> 0:13:42.280 evolutionary history, not the recently electrically blessed times. In other words, 0:13:42.360 --> 0:13:47.200 our ancestors all spent their lives as inadvertent participants in 0:13:47.240 --> 0:13:51.040 a blindfold experiment every single night. So how did their 0:13:51.160 --> 0:13:55.679 visual cortex defend its territory when you've got no data 0:13:55.720 --> 0:13:59.080 coming in through the eyes. So our proposal is that 0:13:59.160 --> 0:14:03.160 the visual corret tex preserves its territory by finding a 0:14:03.160 --> 0:14:05.640 way to remain active at night. And we call this 0:14:05.720 --> 0:14:11.240 the defensive activation theory. And the purpose of dreaming here 0:14:11.960 --> 0:14:15.560 is to keep cells in the visual cortex active, and 0:14:15.600 --> 0:14:19.120 that's how it resists conquest by the territories of the 0:14:19.480 --> 0:14:22.960 other senses. Vision is the only one of the senses 0:14:23.040 --> 0:14:27.000 that's disadvantaged by darkness. You can still touch and smell, 0:14:27.040 --> 0:14:29.200 and taste and hear in the dark, and so it's 0:14:29.240 --> 0:14:33.960 the only sense that needs internally generated activity to maintain 0:14:34.160 --> 0:14:37.960 its borders during the long night. So, as a result, 0:14:38.000 --> 0:14:42.280 about every ninety minutes you get this internally generated activity 0:14:42.280 --> 0:14:47.320 that blasts exclusively into the visual cortex, and so dreams 0:14:47.360 --> 0:14:52.720 are experienced as primarily visual. So several predictions immediately fall 0:14:52.760 --> 0:14:58.240 out of the defensive activation theory. First, because brain plasticity 0:14:58.280 --> 0:15:01.440 diminishes with age, this would suggest that the amount of 0:15:01.480 --> 0:15:05.200 time spent in REM sleep should also decrease as one 0:15:05.320 --> 0:15:08.080 moves through the lifespan, and that turns out to be 0:15:08.120 --> 0:15:12.840 exactly what happens. REM sleep in humans accounts for half 0:15:13.000 --> 0:15:16.480 of an infant's sleep time, but as a person grows older, 0:15:16.880 --> 0:15:21.800 the percentage of remsleep decreases steadily. In other words, diminishing 0:15:21.880 --> 0:15:26.360 plasticity of the brain correlates with less REM sleep. But 0:15:26.400 --> 0:15:30.360 more importantly, we made a more quantified prediction. We said, hey, 0:15:30.760 --> 0:15:34.960 maybe the more flexible and animal's brain is the more 0:15:35.160 --> 0:15:38.920 REM sleep it requires to defend its visual cortex. So 0:15:39.040 --> 0:15:43.040 Don and I studied the plasticity in twenty five species 0:15:43.080 --> 0:15:46.440 of primates and we found that the species with more 0:15:46.480 --> 0:15:50.720 plastic brains spend more time in REMS sleep every night. 0:15:51.000 --> 0:15:54.560 So you'd think that these two measures REM sleep and 0:15:54.680 --> 0:15:58.200 brain plasticity they would be totally unconnected, So it was 0:15:58.320 --> 0:16:02.080 very surprising to find that they are tightly linked. So 0:16:02.280 --> 0:16:08.080 dreaming defends the visual cortex. Now, the circuitry that underpins dreaming. 0:16:08.240 --> 0:16:12.240 This is so ancient and deeply wired that even people 0:16:12.280 --> 0:16:15.240 who are blind have it. But note that blind people 0:16:15.280 --> 0:16:20.480 don't have visual dreams. Instead, their nighttime hallucinations involve the 0:16:20.600 --> 0:16:24.960 other senses, like feeling their way around an oddly arranged 0:16:25.040 --> 0:16:30.440 kitchen or hearing strangers speaking. Why because other sensory errors 0:16:30.520 --> 0:16:35.080 have annexed the underused visual cortex. So think about it 0:16:35.120 --> 0:16:38.360 this way. People who can see and those with visual impairments, 0:16:38.560 --> 0:16:42.600 they both have activity shooting into their occipital lobe during dreaming, 0:16:42.960 --> 0:16:47.880 but the senses processed by that territory are different. The 0:16:47.960 --> 0:16:52.720 defensive activation theory also makes more general predictions. If dream 0:16:52.800 --> 0:16:56.000 sleep is triggered by the absence of visual input during 0:16:56.000 --> 0:16:59.720 the night, we might presume that a person deprived of 0:16:59.840 --> 0:17:05.359 vision while awake could similarly experience dreamlike visual hallucinations. And 0:17:05.359 --> 0:17:09.560 that is exactly what happens when people have degenerating vision, 0:17:09.840 --> 0:17:12.919 or they end up in solitary confinement or even just 0:17:12.960 --> 0:17:16.480 in a dark float tank. Any situation in which vision 0:17:16.520 --> 0:17:22.000 gets deprived, the brain starts fighting back and having hallucinations. 0:17:22.480 --> 0:17:26.920 So that's the idea. Dreams are a screensaver. The brain 0:17:26.960 --> 0:17:30.800 puts activity into the visual cortex to prevent it from 0:17:30.800 --> 0:17:34.720 getting ruined during the night. Okay, so you might say, fine, 0:17:34.800 --> 0:17:39.399 your hypothesis seems plausible, But why do dreams seem to 0:17:39.440 --> 0:17:43.560 be stories? After all, we don't just see random snow 0:17:43.760 --> 0:17:47.600 like on an old television. We experience stories, and in fact, 0:17:47.960 --> 0:17:52.240 there are various stories of someone discovering something in dreams, 0:17:52.359 --> 0:17:55.960 like Kurkule thinking of the structure of the Benzene ring 0:17:56.080 --> 0:17:59.000 based on a dream he had of two snakes biting 0:17:59.000 --> 0:18:02.679 each other's tails, or Paul McCartney dreaming the melody for 0:18:02.720 --> 0:18:07.240 the song Yesterday. So what's up with dream content? The 0:18:07.359 --> 0:18:12.200 key is that the brain is a storytelling machine. Your 0:18:12.240 --> 0:18:17.840 brain is deeply carved with roadways that represent your experience 0:18:17.880 --> 0:18:20.120 in the world, and these are stored in what are 0:18:20.119 --> 0:18:24.520 called associative neural networks, which means that everything connects to 0:18:24.560 --> 0:18:28.159 other things based on how they relate. So if I 0:18:28.200 --> 0:18:31.560 ask you to think of a mouse that's physically connected 0:18:31.600 --> 0:18:34.919 in your brain's networks to your concept of cheese or 0:18:34.960 --> 0:18:38.919 exterminators or mickey mouse or mazes, or running wheels, or 0:18:38.960 --> 0:18:43.240 mouse traps or pet stores everything else you've ever associated 0:18:43.560 --> 0:18:48.360 with a mouse. So all concepts are related and linked 0:18:48.400 --> 0:18:53.280 physically to what happens during sleep and dreaming. Well, the 0:18:53.400 --> 0:18:57.199 synapses that are used during the day tend to be 0:18:57.480 --> 0:19:01.560 slightly more chemically active, say, they're more hot from the 0:19:01.600 --> 0:19:05.440 activity of the day, and so your dreams usually involve 0:19:05.880 --> 0:19:08.200 something from the day or something that's on your mind. 0:19:08.600 --> 0:19:13.000 They often involve the memories and desires and fears and 0:19:13.119 --> 0:19:17.159 hopes that are brewing in your inner life. But the 0:19:17.280 --> 0:19:21.359 associations are much looser. So maybe you have something about 0:19:21.359 --> 0:19:23.840 your boss or something that happened in a class or whatever, 0:19:24.160 --> 0:19:28.000 but the dream quickly goes off in some weird direction. 0:19:28.240 --> 0:19:32.800 The associations are looser, and so we end up dreaming 0:19:32.920 --> 0:19:37.840 stories with looser associations, following paths along the associative neural 0:19:37.880 --> 0:19:41.960 network that we might not otherwise take. But things make sense, 0:19:42.200 --> 0:19:46.359 at least in the light of dream logic. So even 0:19:46.359 --> 0:19:50.520 if the visual cortex is just getting volleys of random activity, 0:19:51.040 --> 0:19:53.920 you get meaning out of it. You get some sort 0:19:53.960 --> 0:19:58.200 of story. Now people often wake up and say, no, way, 0:19:58.240 --> 0:20:01.480 that wasn't random, That was a metaphor. I'm trying to 0:20:01.520 --> 0:20:04.400 decide if I should quit this job, and I had 0:20:04.440 --> 0:20:07.200 a dream that I went into the office and the 0:20:07.240 --> 0:20:09.960 floor was tilted at forty five degrees and no matter 0:20:10.000 --> 0:20:12.480 what I did, I kept slipping back down. And that 0:20:12.640 --> 0:20:16.440 was a metaphor about the impossibility of my advancement. There, 0:20:16.600 --> 0:20:20.960 that was a sign from my unconscious. Okay, so maybe 0:20:21.359 --> 0:20:25.560 the interesting thing about interpreting the content of dreams is 0:20:25.600 --> 0:20:28.840 that they might be one hundred percent random, but they 0:20:28.880 --> 0:20:32.399 act like a Rorshack blot, which is to say, you 0:20:32.440 --> 0:20:35.840 can assign any sort of meaning to them. You remember 0:20:35.840 --> 0:20:38.440 a Rorshack blot, which is where you squish some ink 0:20:38.520 --> 0:20:41.320 between two pages, and then you pull the pages apart 0:20:41.520 --> 0:20:43.879 and you get some random shape, and you ask people 0:20:43.920 --> 0:20:48.640 to interpret what they're seeing to assign meaning to it. 0:20:48.760 --> 0:20:51.040 And it's easy enough to say, yeah, that looks like 0:20:51.119 --> 0:20:53.520 this thing in my life, maybe this issue that's been 0:20:53.600 --> 0:20:56.560 chewing at me. And that's how doctor Rhorshak used this 0:20:56.760 --> 0:21:01.240 to determine what had meaning in a person's mind. But 0:21:01.280 --> 0:21:04.639 you would never say the blob of ink carried meaning. 0:21:04.760 --> 0:21:08.640 It's all about the imposition of meaning by the viewer. 0:21:09.280 --> 0:21:12.720 And this, I suggest could be what happens with dreams 0:21:12.840 --> 0:21:17.080 as well. You interpret the ink blob, and that interpretation 0:21:17.680 --> 0:21:20.800 might have significance to your life, but you imposed that 0:21:20.920 --> 0:21:24.960 meaning instead of it being inherent in the dream. Here's 0:21:25.000 --> 0:21:29.560 an interesting parallel. Pablo Picasso once said, we all know 0:21:29.920 --> 0:21:33.879 that art is not truth. Art is a lie that 0:21:34.000 --> 0:21:36.840 makes us realize the truth, and that could be the 0:21:36.840 --> 0:21:40.160 same thing with dreams. They are a lie that makes 0:21:40.240 --> 0:21:43.240 us realize the truth. So in this sense, it's the 0:21:43.240 --> 0:21:46.199 same thing. If you're thinking about some problem and you 0:21:46.280 --> 0:21:48.920 go to the bookshelf and you pull off any random 0:21:48.920 --> 0:21:51.080 book and turn to a random page and you read 0:21:51.119 --> 0:21:55.560 the sentence. Often it will very tangentially give you some 0:21:56.200 --> 0:21:58.800 push to the thing that you're trying to solve. But 0:21:58.840 --> 0:22:01.920 that doesn't mean the awe of the book cared about 0:22:01.960 --> 0:22:05.680 you and wrote that sentence with that future moment in mind. 0:22:05.720 --> 0:22:07.879 It simply tells us that lots of things in the 0:22:07.920 --> 0:22:11.440 world are like lots of other things and can therefore 0:22:11.520 --> 0:22:14.680 be interpreted. And I do just want to add one 0:22:14.720 --> 0:22:17.840 more word of caution to the game of dream interpretation. 0:22:18.400 --> 0:22:20.840 By the time you turn to the person next to 0:22:20.840 --> 0:22:22.679 you and say, oh my gosh, I just had the 0:22:22.760 --> 0:22:26.840 strangest dream and you tell them, you are forced to 0:22:26.880 --> 0:22:30.800 add another layer of narrative scaffolding so that it makes 0:22:30.840 --> 0:22:34.640 sense as a story that you're telling. So a narrative 0:22:34.680 --> 0:22:38.240 that's very thin can seem to have more flesh after 0:22:38.320 --> 0:22:41.800 you've pushed it through your storytelling machinery. In other words, 0:22:41.840 --> 0:22:45.399 we layer on narrative structure to give our dreams a 0:22:45.520 --> 0:22:48.520 shape that they didn't actually have. And so especially if 0:22:48.520 --> 0:22:51.320 you've had a dream that you've told over and over, 0:22:51.720 --> 0:22:54.320 it usually has more of a scaffolding than it actually 0:22:54.560 --> 0:22:59.679 started with. Nonetheless, the content of dreams has always fascinated humans, 0:23:00.080 --> 0:23:05.080 spurring societies to invent cultural uses for dreams in religious 0:23:05.080 --> 0:23:11.000 ceremonies and medicinal practices, or doomed attempts to predict the future. 0:23:12.000 --> 0:23:15.359 Sigmund Freud, who lived decades before modern brain science, he 0:23:15.400 --> 0:23:19.680 thought that dreams provided an inroad into the underlying functions 0:23:19.720 --> 0:23:23.840 of the brain and especially the subconscious. He suggested, as 0:23:23.920 --> 0:23:28.720 had many before him, that dreams concealed hidden meanings that 0:23:28.840 --> 0:23:32.680 were just at the threshold of breaking through the barrier 0:23:32.800 --> 0:23:37.520 to consciousness. More specifically, he proposed that dreams constitute a 0:23:37.640 --> 0:23:43.040 disguised attempt at wish fulfillment. Similarly, Carl Jung positive that 0:23:43.160 --> 0:23:48.760 dreams may offset features of a character personality that you 0:23:48.880 --> 0:23:52.520 might ignore while you're awake. In general, both those theories 0:23:52.560 --> 0:23:56.360 have been criticized because they can't be proven wrong, and 0:23:56.520 --> 0:24:00.960 critics have pointed out that the wish fulfillment interpretation seems 0:24:01.080 --> 0:24:06.320 improbable in view of the recurring nightmares that attend post 0:24:06.359 --> 0:24:09.320 traumatic stress disorder. So I am, of course not the 0:24:09.359 --> 0:24:13.080 first to propose that dreams might have no inherent meaning. 0:24:13.359 --> 0:24:17.080 The psychiatrists j al And Hobson and Robert McCarley suggest 0:24:17.160 --> 0:24:20.040 that dreams may have no meaning at all, and they 0:24:20.080 --> 0:24:23.560 have a model they call the activation synthesis model, which 0:24:23.560 --> 0:24:26.840 proposes that random activity from the brain stem goes to 0:24:26.880 --> 0:24:30.120 the cortex, which tries to turn it into motor output. 0:24:30.680 --> 0:24:34.040 But given the paralysis of the major muscle groups, the 0:24:34.119 --> 0:24:39.560 brain has to explain the paradox between outgoing motor signals 0:24:39.920 --> 0:24:44.879 and a lack of expected sensory feedback. So in this situation, 0:24:45.280 --> 0:24:51.600 the cortex synthesizes an explanation, essentially weaving a story from 0:24:51.600 --> 0:24:56.280 the random inputs. Now Hobson and McCary faced criticism for 0:24:56.359 --> 0:24:59.600 this aspect of their theory because dreams often do have 0:24:59.640 --> 0:25:02.920 a relation relationship to life experience. So in that light, 0:25:02.960 --> 0:25:07.320 they made modifications to allow that dream content relates to 0:25:07.440 --> 0:25:09.760 memories and fears and desires and hopes and so on, 0:25:10.320 --> 0:25:13.879 but that these provide the background context and not the 0:25:13.920 --> 0:25:19.120 exact content of the cortexas interpretation of the random activity. 0:25:19.520 --> 0:25:22.359 So which is it, Does dream content tell us anything 0:25:22.400 --> 0:25:25.440 at all? Or nothing? Well, here's how we can approach 0:25:25.520 --> 0:25:29.199 the problem. When you look at one person's dreams like 0:25:29.240 --> 0:25:31.359 you think about your own dreams, you may not be 0:25:31.440 --> 0:25:34.560 able to use the content as a key to unlock 0:25:34.720 --> 0:25:37.840 much about the brain. But as you move from considering 0:25:38.000 --> 0:25:42.280 one dreamer to doing the science and looking at thousands 0:25:42.280 --> 0:25:45.120 of dream reports and hundreds of thousands from all over 0:25:45.160 --> 0:25:48.520 the world, you can start to see the fence lines. 0:25:48.880 --> 0:25:53.119 You see that dreams aren't a wild unleashing where anything 0:25:53.160 --> 0:25:58.000 can happen. Instead, dreams have particular rules to the stories, 0:25:58.359 --> 0:26:01.680 and that gives us hints. So what are those rules? Well, 0:26:01.720 --> 0:26:03.639 I recently read a very cool new book by my 0:26:03.680 --> 0:26:07.240 colleague Rahul John day Al called This Is Why You Dream, 0:26:07.359 --> 0:26:10.639 and he outlines a series of studies that demonstrate a 0:26:10.760 --> 0:26:16.720 remarkable consistency of themes. Across cultures and across decades, the 0:26:16.880 --> 0:26:21.920 same kinds of dreams are reported, for example, being unable 0:26:22.000 --> 0:26:25.240 to find one's way or being late for an important event. 0:26:25.600 --> 0:26:29.760 In dreams, both men and women usually experience more aggression 0:26:29.840 --> 0:26:33.439 than friendliness, although men in almost all societies have greater 0:26:33.520 --> 0:26:37.000 physical aggression in their dreams than women do. Everyone experiences 0:26:37.040 --> 0:26:41.400 more misfortune than good fortune. People experience more negative emotions 0:26:41.440 --> 0:26:45.520 than positive emotions. So the cross cultural research suggests that 0:26:45.720 --> 0:26:49.159 dreams are similar across a wide range of cultures in 0:26:49.200 --> 0:26:52.720