WEBVTT - Ep85 "What is a Thought?" 0:00:05.240 --> 0:00:10.040 What is a thought? Is it something physical? How can 0:00:10.080 --> 0:00:13.240 you hear a voice in your head? And whose voice 0:00:13.280 --> 0:00:15.440 is it anyway? And what does this have to do 0:00:15.560 --> 0:00:19.760 with a small marine animal who eats its own brain. 0:00:23.160 --> 0:00:27.200 Welcome to Intercosmos with me, David Eagleman. I'm a neuroscientist 0:00:27.280 --> 0:00:30.200 and an author at Stanford and in these episodes we 0:00:30.280 --> 0:00:34.199 sail deeply into our three pound universe to understand some 0:00:34.240 --> 0:00:47.559 of the most surprising aspects of our lives. Today's episode 0:00:47.600 --> 0:00:52.320 is about thoughts. We have them constantly, even for the 0:00:52.360 --> 0:00:57.200 best meditators. It's difficult or impossible to stop the fire 0:00:57.240 --> 0:01:01.400 hose of words and images and ideas. We all talk 0:01:01.400 --> 0:01:04.280 about our thoughts. We sometimes act on our thoughts, we 0:01:04.400 --> 0:01:08.000 draw them with little thought bubbles and cartoons. But what 0:01:08.160 --> 0:01:12.679 in the world is a thought physically? So many years ago, 0:01:12.840 --> 0:01:16.120 a person at a party begged me to watch the 0:01:16.160 --> 0:01:20.080 movie called The Secret. So I watched it for fifteen minutes, 0:01:20.080 --> 0:01:22.760 and I regret to say that I will never get 0:01:22.800 --> 0:01:25.679 those fifteen minutes back. And I knew that this was 0:01:25.720 --> 0:01:29.760 the pinnacle of moronic when the first guy states quote, 0:01:30.600 --> 0:01:34.680 what most people don't understand is a thought has a frequency. 0:01:34.800 --> 0:01:38.399 Every thought has a frequency we can measure a thought, 0:01:38.600 --> 0:01:41.920 and so if you're thinking that thought over and over again, 0:01:42.319 --> 0:01:46.880 you're emitting that frequency on a consistent basis. And then 0:01:46.920 --> 0:01:51.560 the next Schremndrick says, thoughts are sending out that magnetic 0:01:51.760 --> 0:01:54.840 signal that is drawing the parallel back to you. That's 0:01:54.920 --> 0:01:58.840 the signal you're putting out into the universe. And then 0:01:58.880 --> 0:02:02.960 a third genius says, it has now been proven scientifically 0:02:03.600 --> 0:02:07.680 that an affirmative thought is hundreds of times more powerful 0:02:07.760 --> 0:02:10.720 than a negative thought. And every time someone thinks a 0:02:10.880 --> 0:02:14.760 thought in this movie, the graphics show the person having 0:02:14.800 --> 0:02:18.160 a thinking expression on their face, and then an energy 0:02:18.200 --> 0:02:20.560 wave bursts from their head, and then it cuts to 0:02:20.639 --> 0:02:23.120 a wide shot of the planet and you see this 0:02:23.360 --> 0:02:29.040 energy wave transmit across the universe. Now, the most striking 0:02:29.080 --> 0:02:32.840 thing about these statements in the movie is not simply 0:02:32.919 --> 0:02:35.520 that they are incorrect. To me, the shocking thing was 0:02:35.960 --> 0:02:39.000 how these guys looked right at the camera and asserted 0:02:39.040 --> 0:02:43.240 them as though these were not just completely made up, 0:02:43.280 --> 0:02:46.840 and then they used phrases like it has been scientifically proven. 0:02:47.160 --> 0:02:49.160 So in a few weeks, I'm going to do an 0:02:49.160 --> 0:02:52.960 episode about how we judge the value of any scientific 0:02:53.040 --> 0:02:55.959 idea and what it would mean to even say that 0:02:56.040 --> 0:02:58.800 something is scientifically proven. But I'm going to bite my 0:02:58.880 --> 0:03:02.320 tongue for now put that aside, because for today's episode, 0:03:02.400 --> 0:03:08.200 what I really care about is what really is a thought. 0:03:08.840 --> 0:03:12.200 So to set the table for this, I'm going to 0:03:12.200 --> 0:03:15.520 put thoughts aside for a second and tell a story 0:03:15.800 --> 0:03:18.919 that I originally wrote in my book Incognito, And this 0:03:19.200 --> 0:03:23.480 took place in nineteen forty nine. A guy named Arthur 0:03:23.560 --> 0:03:27.519 Alberts traveled from his home in New York to villages 0:03:27.680 --> 0:03:31.200 between the Gold Coast and Timbuktoo in West Africa. And 0:03:31.240 --> 0:03:32.960 he brought his wife, and he brought a camera and 0:03:33.000 --> 0:03:36.520 a jeep, and because of his love for music, he 0:03:36.680 --> 0:03:40.560 brought a tape recorder. Now he wanted to open the 0:03:40.600 --> 0:03:43.960 ears of the Western world. So what he did was 0:03:44.040 --> 0:03:47.200 record some of the most important music to ever come 0:03:47.240 --> 0:03:52.480 out of Africa. But Alberts ran into social troubles while 0:03:52.520 --> 0:03:55.120 he was using this tape recorder because none of the 0:03:55.240 --> 0:03:59.360 natives had ever seen anything even vaguely like this before. 0:04:00.080 --> 0:04:04.040 So one native heard his voice played back to him, 0:04:04.640 --> 0:04:09.320 and he accused Alberts of quote stealing his tongue and 0:04:09.360 --> 0:04:13.880 According to the biography, Albert's only narrowly averted being pummeled 0:04:13.880 --> 0:04:17.240 by taking out a mirror and convincing the man that 0:04:17.320 --> 0:04:21.240 his tongue was still intact. So it's not difficult to 0:04:21.279 --> 0:04:25.800 see why the natives found the tape recorder so strange 0:04:25.839 --> 0:04:30.239 and counterintuitive. Just imagine that you had never ever seen 0:04:30.279 --> 0:04:34.760 this technology before. The thing is that a voice seems 0:04:35.200 --> 0:04:39.400 ephemeral and ineffable, right. A voice has no weight. You 0:04:39.440 --> 0:04:43.080 can't hold voice in your hand. A voice just exists 0:04:43.120 --> 0:04:46.320 for a moment. It's totally untouchable, and then it's gone. 0:04:46.760 --> 0:04:49.800 There doesn't seem to be any physical trace. So it 0:04:49.880 --> 0:04:54.520 comes as a surprise that a voice is physical. If 0:04:54.560 --> 0:04:57.960 you build a little machine that's sensitive enough to detect 0:04:58.200 --> 0:05:01.640 tiny compressions of the molecule in the air, you can 0:05:01.680 --> 0:05:06.240 then capture those density changes and reproduce them later. We 0:05:06.320 --> 0:05:10.440 call these little machines microphones, and we reproduce the density 0:05:10.520 --> 0:05:15.559 changes on tape or with zeros and ones, And every 0:05:15.600 --> 0:05:19.080 one of the billions of podcasts and playlists on the 0:05:19.120 --> 0:05:24.920 planet is proudly serving up bags of feathers once thought irretrievable. 0:05:25.640 --> 0:05:28.600 When Alberts played the music back from the tape recorder. 0:05:28.640 --> 0:05:35.320 One tribesman described the feat as tremendous magic. And so 0:05:35.440 --> 0:05:39.120 it goes with thoughts. What exactly is a thought? It 0:05:39.160 --> 0:05:44.159 doesn't seem to weigh anything. It feels ephemeral and ineffable. 0:05:44.640 --> 0:05:47.320 You wouldn't think that a thought has any shape or 0:05:47.360 --> 0:05:51.919 smell or any sort of physical instantiation. Thoughts seem to 0:05:51.960 --> 0:05:56.120 be a kind of tremendous magic. So it comes as 0:05:56.160 --> 0:06:00.320 a surprise that a thought is physical, just like voice is. 0:06:00.920 --> 0:06:06.599 Thoughts are underpinned by biological stuff. We know this because 0:06:06.680 --> 0:06:10.400 alterations to the brain change the kinds of thoughts we 0:06:10.440 --> 0:06:14.240 can think. In a state of deep sleep, there are 0:06:14.279 --> 0:06:19.240 no thoughts. When the brain transitions into dream sleep, there 0:06:19.279 --> 0:06:23.720 are unbidden, bizarre thoughts. During the day, we enjoy our normal, 0:06:23.839 --> 0:06:29.560 well accepted thoughts, which people enthusiastically modulate by spiking the 0:06:29.640 --> 0:06:33.760 chemical cocktails of the brain with alcohol or narcotics, or 0:06:34.160 --> 0:06:38.799 exercise or coffee. So the state of the physical material 0:06:39.279 --> 0:06:43.799 determines the state of the thoughts, and issues like obsessive 0:06:43.880 --> 0:06:48.760 compulsive disorder or schizophrenia tell us that when certain networks 0:06:48.760 --> 0:06:53.279 in the brain become overactive or miscalibrated, the character of 0:06:53.400 --> 0:06:57.400 thinking changes. It's this kind of thing that tells us 0:06:57.440 --> 0:07:01.960 that the physical stuff is irreversible, tied to the thinking. 0:07:02.000 --> 0:07:04.520 And we know this also because when people get even 0:07:04.640 --> 0:07:08.159 small bits of brain damage, let's say, because of a 0:07:08.200 --> 0:07:11.880 stroke or a tumor, that can change their capacity to 0:07:12.600 --> 0:07:16.960 understand music, or name animals or see colors, or judge risk, 0:07:17.080 --> 0:07:20.960 or make decisions, or read signals from their bodies, or 0:07:21.080 --> 0:07:24.600 understand the concept of a mirror, or hundreds of other 0:07:24.800 --> 0:07:28.400 changes in thinking that we can witness in the clinics 0:07:28.480 --> 0:07:32.360 every day, and the consequences of injury is a big 0:07:32.440 --> 0:07:36.200 part of how brain science has mapped out the general 0:07:36.320 --> 0:07:39.880 blueprints of the brain. So the bottom line lesson which 0:07:39.880 --> 0:07:45.000 has emerged over centuries is that our internal thoughts about 0:07:45.080 --> 0:07:49.000 hopes or fears or desires, they all emerge from this 0:07:49.600 --> 0:07:53.720 strange three pound organ and when the brain changes, so 0:07:53.920 --> 0:07:57.480 do our thoughts. So although it's easy to intuit that 0:07:57.680 --> 0:08:01.360 thoughts don't have a physical basis, that there are something 0:08:01.440 --> 0:08:04.800 like feathers on the wind, they in fact depend directly 0:08:04.880 --> 0:08:09.920 on what's happening in this small, enigmatic mission control center 0:08:10.400 --> 0:08:15.120 locked in the silent vault of the skull. So what 0:08:15.440 --> 0:08:19.160 is a thought. It's the result of billions of neurons 0:08:19.240 --> 0:08:23.760 firing and coordinated patterns. As we've talked about in other episodes, 0:08:23.840 --> 0:08:28.200 the neurons communicate using electrical impulses and chemical signals, and 0:08:28.280 --> 0:08:32.640 they form vast networks that operate together, such that at 0:08:32.640 --> 0:08:37.679 any moment you have some millions of neurons doing something coordinated, 0:08:37.720 --> 0:08:40.120 and in the next moment it's a different collection of 0:08:40.160 --> 0:08:43.840 neurons that are working together. Now, it may not surprise 0:08:43.880 --> 0:08:46.200 you to know that a thought is not located in 0:08:46.240 --> 0:08:49.880 one place in the brain. It's an emergent property. It's 0:08:49.880 --> 0:08:54.880 a collaboration between these millions or billions of neurons. When 0:08:54.960 --> 0:08:58.880 you have a thought, it's like a symphony playing inside 0:08:58.880 --> 0:09:02.920 your head. Every neuron involved is an instrument in the orchestra, 0:09:03.400 --> 0:09:06.840 and no single part can create the music by itself. 0:09:07.360 --> 0:09:09.319 So we're gonna come back to the brain in a moment, 0:09:09.400 --> 0:09:11.920 but before we do, I want us to really zoom 0:09:11.920 --> 0:09:16.640 in on the subjective experience. How would you describe the 0:09:16.880 --> 0:09:21.040 experience of a thought. When you try to capture what 0:09:21.160 --> 0:09:25.400 a thought is, the most commonplace to go is your 0:09:25.880 --> 0:09:29.520 inner monologue. This is the voice in your head that 0:09:29.600 --> 0:09:33.800 you use to problem solve or criticize, or plan or reflect. 0:09:34.320 --> 0:09:37.200 So take just a second to pay attention to the 0:09:37.360 --> 0:09:42.439 voice inside your head, that constant stream of chatter. Now 0:09:42.559 --> 0:09:46.840 you might think, what voice inside my head? That's the voice? Now. 0:09:47.000 --> 0:09:51.320 Your internal voice can involve deliberate problem solving, like what 0:09:51.360 --> 0:09:55.199 should I do next here? Or it can involve involuntary 0:09:55.360 --> 0:09:58.040 commentary like oh so stupid to me, why did I 0:09:58.080 --> 0:10:03.199 do that? Or it can be whole imagined conversations like Okay, 0:10:03.200 --> 0:10:04.920 I say this, and then she says that, and then 0:10:04.960 --> 0:10:07.360 I respond like this. It can be helpful for things 0:10:07.440 --> 0:10:11.440 like working memory. So for example, you're trying to log 0:10:11.480 --> 0:10:14.680 into a website and you get texted some six digit 0:10:14.800 --> 0:10:17.600 pass code, and you need to remember that code while 0:10:17.640 --> 0:10:21.720 you switch windows, So you internally say the numbers over 0:10:21.760 --> 0:10:24.920 and over. So you're using the internal voice to keep 0:10:24.960 --> 0:10:27.600 the information in mind as part of your working memory. 0:10:27.920 --> 0:10:30.480 There's so many places where the internal voice comes in. 0:10:30.559 --> 0:10:34.199 We tend to talk to ourselves when we're planning something, 0:10:34.240 --> 0:10:38.400 when we're weighing options. The internal dialogue seems to be 0:10:38.679 --> 0:10:43.240 really helpful in simulating different scenarios. So you're running your 0:10:43.280 --> 0:10:47.000 internal voice all the time and subjectively, it seems to 0:10:47.040 --> 0:10:51.360 be a mental space that can seem almost as vivid 0:10:51.440 --> 0:10:55.200 as external speech. It follows all the rules of grammar 0:10:55.240 --> 0:10:59.520 and syntax, and it can be emotionally laiden with encouragement 0:10:59.640 --> 0:11:05.080 or criticism or anywhere in between. Now, how does this happen? 0:11:05.160 --> 0:11:09.240 How can you generate a voice internally and hear it well? 0:11:09.320 --> 0:11:12.680 When we eavesdrop on the brain, let's say, using brain 0:11:12.760 --> 0:11:16.360 imaging like fMRI, what we find is a network of 0:11:16.520 --> 0:11:22.040 areas involved in speech production, like Broca's area, which is 0:11:22.080 --> 0:11:25.200 a key region involved in talking out loud. And we 0:11:25.280 --> 0:11:30.560 find areas involved in language comprehension like Wernicke's area and 0:11:30.600 --> 0:11:34.040 the auditory cortex more generally, as though you're listening to 0:11:34.160 --> 0:11:38.080 spoken language from somebody else talking. And also what we 0:11:38.200 --> 0:11:42.439 see is a network that we summarize as the default 0:11:42.559 --> 0:11:45.880 mode network. And this is a network that becomes active 0:11:45.960 --> 0:11:49.600 when you're not focused on monitoring the outside world, but 0:11:49.720 --> 0:11:53.000 instead when you think about yourself, where you daydream or 0:11:53.080 --> 0:11:55.800 you reflect on your past, or you imagine your future. 0:11:56.520 --> 0:11:59.360 So all these networks are cranked up when you're talking 0:11:59.360 --> 0:12:02.440 to yourself. And one really important point, when you're generating 0:12:02.480 --> 0:12:06.800 your own speech is that you have something called corollary discharge, 0:12:06.920 --> 0:12:10.080 which just means that when your brain generates internal speech, 0:12:10.160 --> 0:12:13.000 it sends a copy of what it's doing to other 0:12:13.080 --> 0:12:16.000 parts of the brain to let them know this is coming. 0:12:16.080 --> 0:12:18.320 I'm the one who did this. That's how the rest 0:12:18.360 --> 0:12:21.360 of the brain knows that the inner voice is self 0:12:21.480 --> 0:12:26.520 generated instead of confusing it with external speech. As a 0:12:26.559 --> 0:12:29.559 side note, if you're a regular listener to this podcast, 0:12:29.640 --> 0:12:31.840 you know that I've been publishing on the topic of 0:12:31.880 --> 0:12:36.760 schizophrenia for many years, and my hypothesis is that auditory 0:12:36.800 --> 0:12:41.880 hallucinations in schizophrenia might have to do with a miscalibration 0:12:42.080 --> 0:12:46.040 of the timing of signals such that the internal voice 0:12:46.559 --> 0:12:51.160 gets misinterpreted as someone else's voice. In other words, when 0:12:51.160 --> 0:12:54.880 you're talking to yourself under normal conditions, you generate the voice, 0:12:55.080 --> 0:12:58.280 then you hear the voice, and the corollary discharge tells 0:12:58.320 --> 0:13:00.880 you that it was your own. But there's something wrong 0:13:00.920 --> 0:13:04.199 with the timing of the corollary discharge. Then it doesn't 0:13:04.200 --> 0:13:06.480 seem like you're the one who generated the voice, and 0:13:06.559 --> 0:13:09.719 you have to attribute the voice to someone else. The 0:13:09.760 --> 0:13:13.920 internal voice feels like it must be external. If you're 0:13:13.960 --> 0:13:17.960 interested in more on this hypothesis about schizophrenia, check out 0:13:18.000 --> 0:13:21.880 episodes thirty three and forty four. Okay, so back to 0:13:21.920 --> 0:13:25.680 the internal voice, which in normal circumstances we understand as 0:13:25.880 --> 0:13:29.520 our voice in our heads. Here's my question, is this 0:13:29.679 --> 0:13:33.880 inner monologue really the main way that we think? What 0:13:34.000 --> 0:13:38.160 if some of our thoughts don't come with words at all? 0:13:38.240 --> 0:13:41.520 So that's the question that psychologist Russell Hurlbert set out 0:13:41.559 --> 0:13:44.640 to answer with a set of experiments in the nineteen nineties. 0:13:44.640 --> 0:13:48.440 And here's how it works. Imagine that you are given 0:13:48.480 --> 0:13:54.559 a beeper that beeps off at random times during your day, 0:13:54.600 --> 0:13:57.280 and the instant a beeps, your job is to write 0:13:57.360 --> 0:14:01.240 down whatever was just in your mind. Beep, what are 0:14:01.240 --> 0:14:05.960 you thinking about right now? So when Hurlbert analyzed the data, 0:14:06.000 --> 0:14:09.360 he found that only about twenty six percent of people's 0:14:09.400 --> 0:14:13.199 thoughts were verbal, meaning that they involved actual words or 0:14:13.240 --> 0:14:19.360 inner speech. The other seventy four percent completely nonverbal. So 0:14:19.440 --> 0:14:23.840 what does nonverbal thought mean? Well, when your thoughts are 0:14:24.040 --> 0:14:27.120 suddenly probe, lots of people find that they were just 0:14:27.200 --> 0:14:32.000 thinking about, for example, vivid mental images like picturing a 0:14:32.040 --> 0:14:36.680 beach or remembering somebody's face, or thinking about some moment 0:14:36.760 --> 0:14:38.920 they just saw at the restaurant, and that's all their 0:14:38.960 --> 0:14:41.320 thought was at that moment. It was visual. There were 0:14:41.360 --> 0:15:00.600 no words involved, just pictures. So what's going on in 0:15:00.640 --> 0:15:05.000 the brain when you have these kind of vivid mental images. Well, 0:15:05.200 --> 0:15:07.560 if I were to ask you to think about a 0:15:07.840 --> 0:15:12.760 Siberian tiger, your prefrontal cortex right behind the forehead takes 0:15:12.800 --> 0:15:16.280 on the task and starts broadcasting to see who can 0:15:16.560 --> 0:15:20.600 fulfill the request. So your memory systems chug into place 0:15:20.680 --> 0:15:24.600 to determine what a Siberian tiger is, combining all the 0:15:24.720 --> 0:15:29.040 different examples of Siberian tigers that you've seen before, and 0:15:29.080 --> 0:15:34.480 your visual cortex is recruited to generate a picture. Your 0:15:34.480 --> 0:15:38.880 emotion centers might even contribute, shading this thought with feelings 0:15:38.880 --> 0:15:42.560 of alertness or awe or fear. So when you think 0:15:42.600 --> 0:15:47.560 about that Siberian tiger, hundreds of millions of neurons across 0:15:47.720 --> 0:15:51.440 different areas of your brain are lighting up, working together 0:15:51.560 --> 0:15:56.560 to create something that feels whole and immediate. And of course, 0:15:56.600 --> 0:16:00.000 if you're a musician and the pager beeps, you might 0:16:00.080 --> 0:16:03.400 find that you're thinking about something auditory. You're thinking about 0:16:03.840 --> 0:16:07.000 which notes would sound great. Right after this transition from 0:16:07.000 --> 0:16:10.000 this chord to this court. But there's no words involved 0:16:10.040 --> 0:16:13.000 in that, and in the brain we can measure activity 0:16:13.040 --> 0:16:16.480 in your auditory cortex while you're doing that, And if 0:16:16.520 --> 0:16:21.080 you're a perfumer, you might be doing smell imagery. You're 0:16:21.120 --> 0:16:24.440 thinking about the way that this other perfume smell than 0:16:24.480 --> 0:16:26.280 how you're trying to get a little closer to that. 0:16:26.880 --> 0:16:31.360 But as you are internally smelling, there are no words 0:16:31.400 --> 0:16:36.040 associated with that. It's just olfactory imagery. And this sort 0:16:36.080 --> 0:16:39.800 of sensory thinking can come in all kinds of flavors, 0:16:39.880 --> 0:16:43.360 like feeling the warmth from the sun on your face 0:16:43.920 --> 0:16:47.800 or the tightness of your chest during stress. So that's 0:16:47.800 --> 0:16:51.840 what Hurlbert found people were thinking about quite often when 0:16:51.880 --> 0:16:56.960 you probe them at random, sensory imagery without language. But 0:16:57.040 --> 0:16:58.880 that was just the beginning. The kind of thoughts that 0:16:59.000 --> 0:17:03.840 people were went beyond just sensory imagery. Lots of other 0:17:03.880 --> 0:17:07.840 times people described they were thinking about how to do 0:17:07.920 --> 0:17:11.480 something physical, like how to position their hands for reaching 0:17:11.520 --> 0:17:14.520 into the oven, or how to remove the cover off 0:17:14.560 --> 0:17:17.240 the printer, or how far to turn the steering wheel 0:17:17.240 --> 0:17:20.040 to get their car into the parking spot. But they 0:17:20.080 --> 0:17:23.399 were thinking about how to do these moves, and there 0:17:23.440 --> 0:17:27.080 were no words involved. It was a physical activity they 0:17:27.080 --> 0:17:31.640 were simulating. This is called motoric imagery. Their brains were 0:17:32.040 --> 0:17:35.680 thinking their way through something. And other thoughts are even 0:17:35.720 --> 0:17:39.879 more difficult to pin down than imagining senses or imagining 0:17:39.960 --> 0:17:45.040 movement because they're more abstract, like a vague sense of 0:17:45.280 --> 0:17:50.719 unease with no clear words or pictures attached. So thoughts 0:17:50.800 --> 0:17:53.520 come in many flavors, and I'll just make a thirty 0:17:53.560 --> 0:17:56.439 second side note here about whether it makes sense to 0:17:56.600 --> 0:18:01.120 call the activity in the unconscious brain think. For example, 0:18:01.400 --> 0:18:04.040 you're trying to remember the name of that song and 0:18:04.080 --> 0:18:05.919 it's on the tip of your tongue, but you just 0:18:06.000 --> 0:18:09.639 can't remember it. And then hours later, when you're not 0:18:09.680 --> 0:18:13.800 even thinking about it, the answer suddenly pops into your mind. 0:18:14.240 --> 0:18:17.800 Your unconscious mind has been working on it in the background, 0:18:17.880 --> 0:18:20.600 even though you had no awareness of it. So should 0:18:20.600 --> 0:18:25.320 we call that thinking even when it happens unconsciously. Just 0:18:25.359 --> 0:18:28.320 for the purposes of having a clear definition, it's probably 0:18:28.359 --> 0:18:30.320 going to make the most sense to call that something 0:18:30.440 --> 0:18:34.760 like processing, and will reserve the word thought for the 0:18:35.040 --> 0:18:38.919 conscious conclusion of that behind the scenes activity, So at 0:18:39.000 --> 0:18:41.159 least for the moment, I'm not going to call the 0:18:41.320 --> 0:18:47.760 unconscious activity thought. So this simple experiment of pinging people 0:18:47.760 --> 0:18:50.439 at random to ask them what they're thinking, what's in 0:18:50.480 --> 0:18:54.119 their minds at this exact moment, This experiment tells us 0:18:54.160 --> 0:18:58.359 something important, which is that thinking is not just talking 0:18:58.359 --> 0:19:01.679 to ourselves. It's broader than that. We have different kinds 0:19:01.680 --> 0:19:04.679 of thoughts in different formats. We have inner speech, but 0:19:04.720 --> 0:19:08.919 we also have mental imagery, like when you're visualizing what 0:19:09.000 --> 0:19:11.439 your kitchen red design could look like, and you have 0:19:11.840 --> 0:19:17.879 abstract thinking like when you're contemplating infinity or justice or love. 0:19:18.240 --> 0:19:20.840 And possibly there are still other things which could fall 0:19:20.920 --> 0:19:24.560 under the umbrella of thought. So thinking is a rich, 0:19:25.040 --> 0:19:28.600 multi dimensional experience. Okay, so here's where we are so far. 0:19:28.680 --> 0:19:32.440 We talked about the internal voice and visualization and imagining 0:19:32.480 --> 0:19:35.879 sound or smell or bodily feelings, and imagining motor movement, 0:19:36.200 --> 0:19:39.040 and even abstract sorts of thoughts. But if you've been 0:19:39.040 --> 0:19:41.040 listening to these episodes for a while, you know that 0:19:41.119 --> 0:19:47.320 I'm obsessed with the difference between people's internal experiences and 0:19:47.440 --> 0:19:50.800 thinking is no exception. When we look at the diversity 0:19:50.880 --> 0:19:55.800 of thought, some people seem to lean more towards verbal thinking. 0:19:55.840 --> 0:20:00.439 They talk things out in their heads. Others are visual things, 0:20:00.480 --> 0:20:05.120 seeing vivid mental images as their primary mode of thinking. 0:20:05.600 --> 0:20:09.919 And some people experience thoughts more like abstract concepts without 0:20:09.960 --> 0:20:12.399 the voice or the images. And this goes hand in 0:20:12.480 --> 0:20:15.440 hand with something I've talked about in many episodes, which 0:20:15.480 --> 0:20:19.280 is that, as far as we can tell, subjective experiences 0:20:19.440 --> 0:20:23.080 exist on a spectrum. So let's zoom in on the 0:20:23.160 --> 0:20:27.000 inner voice. Some people report having constant chatter in their heads, 0:20:27.280 --> 0:20:32.680 while other people have little or no inner verbalization. That's 0:20:32.680 --> 0:20:37.280 called an endophasia no internal voice. As an example, when 0:20:37.280 --> 0:20:41.200 it comes to the inner monologue, my wife's internal radio 0:20:41.359 --> 0:20:43.879 is very loud, she says, she's always hearing it at 0:20:43.920 --> 0:20:47.360 full volume. For me, it happens to be pretty quiet 0:20:47.400 --> 0:20:49.880 most of the time. I'm going to link some papers 0:20:49.920 --> 0:20:53.720 in the show notes about studies on the variation of 0:20:53.800 --> 0:20:58.080 the internal voice. And when it comes to visualization, I've 0:20:58.119 --> 0:21:03.720 talked in other episodes about this from a fantasia to hyperfantasia. 0:21:03.760 --> 0:21:06.960 In other words, the spread from not really picturing anything 0:21:07.040 --> 0:21:12.119 visually in your mind to having very rich, colorful, movie 0:21:12.359 --> 0:21:17.320 like visualizations. And everyone is somewhere along that spectrum. Now, 0:21:17.320 --> 0:21:19.720 we haven't really measured this yet, but when it comes 0:21:19.720 --> 0:21:24.880 to more subtle issues of abstract thinking, like contemplating infinity 0:21:24.960 --> 0:21:27.760 or justice or love, it may be that people are 0:21:27.800 --> 0:21:33.080 having very different experiences of how strongly or intensely they're 0:21:33.200 --> 0:21:36.680 feeling that. Now, it's a little difficult to design an 0:21:36.720 --> 0:21:39.960 experiment to probe this, because it's purely an issue of 0:21:40.000 --> 0:21:43.879 somebody's subjective report, and it's not always easy to know 0:21:43.920 --> 0:21:49.560 if people are reporting accurately. But if this subjective experience 0:21:49.560 --> 0:21:52.800 of abstract thought is like everything else we've measured so far, 0:21:53.200 --> 0:21:57.119 it is surely going to differ from person to person. 0:21:57.640 --> 0:22:01.159 So it seems to me there's probably massive of divergence 0:22:01.280 --> 0:22:04.240 in what we mean from person to person when we 0:22:04.320 --> 0:22:09.280 talk about the experience of thought. If we can only 0:22:09.400 --> 0:22:13.520 know what the experience is inside another head, we might 0:22:13.760 --> 0:22:18.040 suddenly understand why Susan immediately sees the solution to the 0:22:18.080 --> 0:22:22.159 math problem, and why Amy keeps in mind so well 0:22:22.400 --> 0:22:25.520 what everyone else's emotion is, and why Steve is so 0:22:25.680 --> 0:22:29.800 interested in fixing broken radios, and why Tim spends all 0:22:29.840 --> 0:22:32.840 his intellectual efforts figuring out how to get other people 0:22:32.880 --> 0:22:35.000 to do work for him. And so on with the 0:22:35.080 --> 0:22:38.400 differences between every person you know. And by the way, 0:22:38.440 --> 0:22:42.280 this diversity in the inner experience this has real world implications. 0:22:42.640 --> 0:22:46.439 So just think about how people learn or solve problems. 0:22:47.000 --> 0:22:52.280 Schools and workplaces often prioritize verbal reasoning. But what if 0:22:52.280 --> 0:22:57.119 somebody's thoughts arrive more like pictures or more like physical sensations. 0:22:57.200 --> 0:23:01.080 What if their best ideas can't be put in words immediately? 0:23:01.640 --> 0:23:04.880 I think as we bring the individual differences in thinking 0:23:05.320 --> 0:23:09.879 into focus, we'll be able to increasingly build education to 0:23:10.000 --> 0:23:14.800 take advantage of the full spectrum of human cognition and 0:23:14.960 --> 0:23:18.439 understanding this diversity of thought. This also has implications for 0:23:18.640 --> 0:23:24.240 mental health. Verbal thoughts, for example, are strongly linked to rumination, 0:23:24.440 --> 0:23:27.959 which is the endless loops of self talk that fuel 0:23:28.080 --> 0:23:33.200 anxiety or depression. And meanwhile, nonverbal sensations like a tight 0:23:33.320 --> 0:23:36.359 chest or a racing heart, these are the things that 0:23:36.440 --> 0:23:40.679 dominate panic attacks. So really, understanding how differently people think 0:23:40.960 --> 0:23:43.879 and how to measure that could help us to manage 0:23:43.920 --> 0:23:48.320 these mental states more effectively. Okay, so we've been talking 0:23:48.359 --> 0:23:52.160 about our private internal experience of thoughts, but we still 0:23:52.200 --> 0:23:55.399 haven't nailed down with a thought is exactly and what 0:23:55.560 --> 0:23:59.080 could this possibly have to do with a c squirt 0:23:59.520 --> 0:24:03.520 finding its home? So let's start there. The sea squirt 0:24:04.200 --> 0:24:07.679 is a small marine creature that begins life as a 0:24:08.200 --> 0:24:11.639 free swimming larva. It has a little brain and a 0:24:11.680 --> 0:24:15.240 nervous system that helps it navigate and search for a 0:24:15.320 --> 0:24:20.600 suitable place to settle. Now, once it finds its permanent spot, 0:24:20.800 --> 0:24:24.399 it attaches itself to a surface like a barnacle, and 0:24:24.480 --> 0:24:29.800 then it undergoes a dramatic transformation because in this phase, 0:24:29.920 --> 0:24:34.119 once it's docked, it no longer needs its brain for 0:24:34.400 --> 0:24:39.040 movement or navigation, so it eats its brain for nutrition. 0:24:39.200 --> 0:24:42.959 It digests its own brain, and it uses that as 0:24:43.080 --> 0:24:47.720 nutrients for other bodily functions. So this illustrates two things. First, 0:24:48.040 --> 0:24:52.600 how incredible it is that some organisms can radically adapt 0:24:52.720 --> 0:24:55.960 their anatomy to fit their new role. But more importantly, 0:24:55.960 --> 0:24:59.000 for today's purpose, the main lesson from the sea squirt 0:24:59.080 --> 0:25:02.560 is that you only we need a brain for one purpose, 0:25:02.920 --> 0:25:07.919 and that is to move. If you've stopped moving, a 0:25:08.000 --> 0:25:12.520 brain serves only as a little snack for nutrition. And 0:25:12.560 --> 0:25:15.320 that's an idea that's been floating around in neuroscience for 0:25:15.400 --> 0:25:19.000 well over a century. The reason for the brain's evolution 0:25:19.720 --> 0:25:22.720 is movement control. The need to move and interact with 0:25:22.760 --> 0:25:27.399 the environment is the driving force behind the development of 0:25:27.560 --> 0:25:30.879 the nervous system. In other words, brains exist for one purpose, 0:25:30.920 --> 0:25:34.280 and that is to get around. So now let's return 0:25:34.320 --> 0:25:38.920 to thinking. The big idea for today is that thinking 0:25:39.600 --> 0:25:44.720 is like a physical movement. You're moving stuff around on 0:25:44.760 --> 0:25:48.560 the inside, but nothing on the outside. You are moving 0:25:49.040 --> 0:25:53.280 concepts instead of limbs. In other words, thinking is simply 0:25:53.320 --> 0:25:58.520 an outgrowth of the same brain mechanisms that govern moving. 0:26:00.000 --> 0:26:02.879 This idea reached way back into the scientific literature, but 0:26:02.920 --> 0:26:05.119 the most complete version of the argument that I know 0:26:05.240 --> 0:26:08.920 comes from the neuroscientist Rudolfo Ginas in his book called 0:26:09.280 --> 0:26:12.000 Eye of the Vortex. The key is that to get 0:26:12.119 --> 0:26:16.600 good at movements, your brain works to predict the outcome 0:26:16.680 --> 0:26:20.760 of possible actions. So as brains grew more sophisticated, they 0:26:20.760 --> 0:26:25.879 could run simulations that didn't necessarily result in overt behavior. 0:26:26.160 --> 0:26:29.920 So the brain generates predictions about the environment, and then 0:26:30.000 --> 0:26:32.679 it tries things out and it adjusts things based on 0:26:32.760 --> 0:26:36.879 the feedback, and that's how it refines future predictions. The 0:26:37.000 --> 0:26:40.560 key idea is that this predictive function of the brain 0:26:41.080 --> 0:26:45.480 eventually extended into the realm of cognition. So a thought 0:26:45.560 --> 0:26:51.119 is like an internalized movement simulations of possible actions or 0:26:51.119 --> 0:27:12.960 scenarios that don't necessarily result in overt behavior. When we think, 0:27:13.080 --> 0:27:16.760 the brain is doing a kind of mental rehearsal, like 0:27:17.040 --> 0:27:23.280