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Your Brain Doesn’t Work the Way You Think

Freakonomics Radio

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  • Live-Wired Brain
    • The human brain, locked in silence and darkness, constantly builds a model of the outside world.
    • This model updates continuously based on surprising and unpredictable inputs, showcasing the brain’s live-wired nature. Transcript: Steven Levitt I love podcast guests who change the way I think about some important aspect of the world. A great example is my guest today, David Eagleman. He’s a Stanford neuroscientist whose work on brain plasticity has completely transformed my understanding of the human brain and its possibilities. David Eagleman The human brain is about three pounds. It’s locked in silence and darkness. It has no idea where the information is coming from because everything is just electrical spikes and also chemical releases as a result of those spikes. And so what you have in there is this giant symphony of electrical activity going on, and its job is to create a model of the outside world. Stephen J. Dubner Welcome to People I Mostly Admire with Steve Levitt. Steven Levitt According to Eagleman, the brain is constantly trying to predict the world around it. But of course, the world is unpredictable and surprising, so the brain is constantly updating its model. The capacity of our brains to be ever-changing is usually referred to as plasticity, but Eagleman offers another term, live-wired. That’s where conversation begins. David Eagleman Plasticity is the term used in the field because the great neuroscientist or psychologist, actually, William James, coined the term because he was impressed with the way that plastic Gets manufactured, where you mold it into a shape and it holds on to that shape. And he thought that’s kind of like what the brain does. The great trick that Mother Nature figured out was to drop us into the world half-baked. If you look at the way an alligator drops into the world, it essentially is pre-programmed. It eats, mates, sleeps, does whatever it’s doing. But we spend our first several years absorbing the world around us based on our neighborhood and our moment in time and our culture and our friends and our universities. We absorb all of that such that we can then springboard off of that and create our own things. There are many things that are essentially pre-programmed in us, but we are incredibly flexible. And that is the key about live wiring. When I ask you to think of the name of your fifth grade teacher, you might be able to pull that up, even though it’s been years since you saw that fifth grade teacher, but somehow there was A change made in your brain and that stayed in place. You’ve got 86 billion neurons. Each neuron is as complicated as a city. This entire forest of neurons, every moment of your life is changing. It’s reconfiguring. It’s strengthening connections here and there. It’s actually unplugging over here and replugging over there. And so that’s why I’ve started to feel that the term plasticity is maybe underreporting what’s going on. And so that’s why I made up the term live wiring. When I went to school, I feel like they taught me the brain was organized around things like senses (Time 0:02:02)
  • Half a Brain
    • Children born without half their brain or who undergo a hemispherectomy can still develop normally.
    • This demonstrates the brain’s remarkable plasticity and adaptability. Transcript: Steven Levitt Cortex. The same neurons that are there are now doing a totally different job. So let me pose a question to listeners. Imagine you have a newborn baby and he or she looks absolutely flawless on the outside. But then upon examination, the doctors discover that half of his or her brain is just missing. A complete hemisphere of the brain, it’s never developed. It’s just empty space. I would expect that would be a fatal defect or best the child would be growing up profoundly mentally disabled. David Eagleman Turns out the kid will be just fine. You can be born without half the brain or you can do what’s called a hemispherectomy, which happens to children who have something called Rasmussen’s encephalitis, which is a form Of epilepsy that spreads from one hemisphere to the other. The surgical intervention for that is to remove half the brain. You can just imagine as a parent, the horror you would feel if your child had to go in for something like that. But you know what? Kid’s just fine. I can’t take my laptop and rip out half the motherboard and expect it to still function. But with the brain, with a live-wired system, it’ll work. So I first came to your work because (Time 0:06:00)
  • Echolocation
    • Blind people use echolocation, interpreting echoes to understand their surroundings.
    • The visual cortex gets taken over by auditory and tactile information processing in blind individuals. Transcript: Steven Levitt I was so blown away by the idea of human echolocation. Yeah. Only to discover that echolocation is only the tip of the iceberg. But could you talk just a bit about echolocation, how quickly with training it can start to substitute for sight? So it turns out that blind people can make all kinds of sounds, either with their mouth, like clicking or the tip of their cane or snapping their fingers, anything like this. David Eagleman And they can get really good at determining what is coming back as echoes and figure out, oh, okay, this is an open space in front of me here. Something in front of me. It’s probably a parked car. And, oh, there’s a little gap between two parked cars here, so I can go in here. The key is the visual part of the brain is no longer being used because for whatever reason, there’s no information coming down those pipelines anymore. So that part of the brain is taken over by audition, by hearing, and by touching other things. What happens is that the blind person becomes really good at these other things because they’ve just devoted more real estate to it. And as a result, they can pick up on all kinds of cues that would be very difficult for me and you because our hearing just isn’t that good. Steven Levitt And then in these studies, you put a blindfold on a person for two or three days and you try to teach them echolocation. If I understand correctly, even over that timescale, the echolocation starts taking over the visual part of the brain. Is that a fair assessment? That is exactly right. This was my colleagues at Harvard. David Eagleman They did this over the course of five days that demonstrated that people could get really good at, there are actually a number of studies like this. They can get really good at reading Braille. They can do things like echolocation. And the speed of it was sort of the surprise. But the real surprise for me came along when they blindfolded people tightly and put them in the brain scanner and they were making sounds or touching the hand. And they were starting to see activity in the visual cortex after 60 minutes of being blind. (Time 0:07:10)
  • REM Sleep’s Purpose
    • David Eagleman theorizes that REM sleep and dreaming protect the visual cortex from being taken over by other senses during darkness.
    • This theory is supported by the correlation between REM sleep duration and brain plasticity across primate species. Transcript: Steven Levitt So in your book, you talk about REM sleep. And honestly, if I had sat down and tried to come up with an explanation of REM sleep, I could elicit a thousand ideas. Your pet theory would not be one of them. So explain what REM sleep is, and then tell me why you think we do it. REM sleep is rapid eye movement sleep. David Eagleman We have this every night, about every 90 minutes, and that’s when you dream. So if you wake someone up when their eyes are moving rapidly and you say, hey, what are you thinking about? They’ll say, well, I was just riding a camel across a meadow. But if you wake them up at other parts of their sleep, they typically won’t have anything going on. So that’s how we know we dream during REM sleep. But here’s the key. My student and I realized that at nighttime, when the planet rotates, we spend half our time in darkness. And obviously, we’re very used to this electricity-blessed world. But think about this in historical time. Over the course of hundreds of millions of years, it’s really dark. I mean, half the time, you are in blackness. Now, you can still hear and touch and taste and smell the dark, but the visual system is at a disadvantage whenever the planet rotates into darkness. Can encroach on that, what we realized is it needs a way of defending itself against takeover every single night. And that’s what dreams are about. So what happens is you have these midbrain mechanisms that simply blast random activity into the visual cortex every 90 minutes during the night. And when you get activity in the visual cortex, you say, oh, I’m seeing things. And because the brain is a storyteller, you can’t activate all the stuff without feeling like there’s a whole story going on there. But the fascinating thing is when you look at the circuitry carefully, it’s super specific, much more specific than almost anything else in the brain. It’s only hitting the primary visual cortex and nothing else. And so that led us to a completely new theory about dreams. We studied 25 different species of primates, and we looked at the amount of REM sleep they have every night, and we also looked at how plastic they are as a species. It turns out that the amount of dream sleep that a creature has exactly correlates with how plastic they are, which is to say, if your visual system is in danger of getting taken over because Your brain is very flexible, then you have to have more dream sleep. And by the way, when you look at human infants, they have tons of dream sleep at the beginning when their brains are very plastic. And as they age, the amount of dream sleep goes down. Have you convinced the sleep scientists this is true, or is this just you believe in it right now? At the moment, there are 19 papers that have cited this and discussed this, and I think it’s right. I mean, look, everything can be wrong. Everything is provisional, but it’s the single theory that is quantitative. It’s the single theory about dreams that says not only here is a idea for why we dream, but we can compare across species and the predictions match exactly. No one would have suspected that you’d see a relationship between how long it takes you to walk or reach adolescence and how much dream sleep you have. But it turns out that is spawn on. (Time 0:09:10)
  • Neosensory Wristband
    • Neosensory’s wristband translates sound into vibrations, enabling deaf people to ‘hear’ through touch.
    • This sensory substitution demonstrates the brain’s ability to interpret data regardless of its input channel. Transcript: Steven Levitt So we talked about echolocation, which uses sound to accomplish tests that are usually done by vision. And you’ve started a company called Neosensory, which uses touch to accomplish tasks that are usually done with hearing. David Eagleman Can you explain the science behind that? Given that all the data running around in the brain is just data and the brain doesn’t know where it came from, all it knows is, oh, here are electrical spikes, it tries to figure out what To do with it. I got really interested in this idea of sensory substitution, which is, can you push information into the brain via an unusual channel? Originally, we built a vest that was covered with vibratory motors, and we captured sound for people who are deaf. So the vest captures sound, breaks it up from high to low frequency, and you’re feeling the sound on your torso. By the way, this is exactly what the inner ear does. It breaks up sound from high to low frequency and ships that off to the brain. So we’re just transferring the inner ear to the skin of the torso. And it worked. People who are deaf could come to hear the world that way. So I spun this out of my lab as a company, Neosensory, and we shrunk the vest down to a wristband and we’re on wrists of deaf people all over the world. The other alternative for somebody who’s deaf is a cochlear implant, an invasive surgery. This is much cheaper and does as good a job. Just make sure I understand it. Steven Levitt Sounds happen and this wristband hears the sounds and then shoots electrical impulses into your wrist that correspond to the high and low frequency. David Eagleman It’s actually just vibratory motors. So it’s just like the buzzer in your cell phone, but we have a string of these buzzers all along your wrist. And we’re actually taking advantage of an illusion, which is if I have two motors next to each other and I stimulate them both, you will feel one virtual point right in between. And as I change the strength of those two motors relative to each other, I can move that point around. So we’re actually stimulating 128 virtual points along the wrist. Do people train, you give them very direct feedback? Or is it more organic? Great question. It started off where we were doing a lot of training on people. And what we realized is it’s all the same if we just let it be organic. The key is we just encourage people, be in the world. And that’s it. You see the dog’s mouth moving and you feel the barking on your wrist. Or you close the door and you feel that on your wrist, or you say something, you know, most deaf people can speak and they know what their motor output is and they’re feeling the input. Okay, so hearing (Time 0:12:25)
  • Neuralink and Nanorobotics
    • Neuralink’s innovation lies in its robotic electrode implantation, not the concept of brain-computer interfaces.
    • Eagleman suggests that nanorobotics, offering non-invasive access to individual neurons, holds greater promise for future brain research. Transcript: Steven Levitt Elon Musk’s company Neuralink has gotten a ton of attention lately. Could you explain what they’re trying to do and whether you think that’s a promising avenue to explore? David Eagleman What they’re doing is they’re putting electrodes into the brain to read from and talk to the neurons there. Steven Levitt So what we’ve been talking about so far has been sending signals to the brain. But what Neuralink is trying to do is take signals out of the brain. Is that right? That is correct. Everything we’ve been talking about so far with sensory substitution, that’s a way of pushing information in and non-invasive. David Eagleman And what Neuralink is, you have to drill a hole in the head to get to the brain itself. But then you can do reading and writing invasively. That actually has been going on for 60 years. The language of the brain is electrical stimulation. And so with a little tiny wire, essentially, you can zap a neuron and make it pop off, or you can listen to when it’s chattering along going pop, pop, pop, pop, pop, pop, pop, pop. There’s nothing actually new about what Neuralink is doing, except that they’re making a one-ton robot that sews the electrodes into the brain so it can do it smaller and tighter and Faster than a neurosurgeon can. And by the way, there are a lot of great companies doing this sort of thing with electrodes. As people get access to the brain, we’re finally getting to a point. We’re not there yet, but we’re getting to a point where we’ll finally be able to push theory forward. There’s really no shortage of theoretical ideas in neuroscience. But fundamentally, we don’t have enough data because, as I mentioned, you’ve got these 86 billion neurons all doing their thing, and we have never measured what all these things are Doing at the same time. So we have technologies like functional magnetic resonance imaging, fMRI, which measures big blobby volumes of, oh, there was some activity there and some activity there. But that doesn’t tell us what’s happening at the level of individual neurons. We can currently measure some individual neurons, but not many of them. Be like if an alien asked one person in New York City, hey, what’s going on here? And then tried to extrapolate to understand the entire economy of New York City and how that’s all working. So I think we’re finally getting closer to the point where we’ll have real data about, wow, this is what thousands or eventually hundreds of thousands or millions of neurons are actually Doing in real time at the same moment. And then we’ll be able to really get progress. I actually think the future is not in things like Neuralink, but the next level past that, which is nanorobotics. This is all theoretical right now, but I don’t think this is more than 20, 30 years off, where you do three-dimensional printing, atomically precise. You make molecular robots, hundreds of millions of these, and then you put them in a capsule and you swallow the capsule and these little robots swim around and they go into your neurons, These cells in your brain. And from there, they can send out little signals saying, hey, this neuron just fired. And once we have that sort of thing, then we can say non-invasively, here’s what all these neurons are doing at the same time. And then we’ll really understand the brain. I’ve (Time 0:22:24)
  • Active Learning
    • Traditional passive learning is less effective than interactive projects.
    • Encourage students to run experiments and actively engage with information, mirroring real-world data analysis. Transcript: Steven Levitt Now, I have to imagine that the way we teach in traditional classrooms with a teacher or professor at a blackboard lecturing to a huge group of passive students, as a neuroscientist, That must make you cringe, right? It does increasingly, yes. How should we teach? David Eagleman I think the next generation is going to be smarter than we are simply because of the broadness of the diet that they can consume. Whenever they’re curious about something, they jump on the internet, they get the answer straight away or from Alexa or from ChatGPT, they just get the answers. And that is massively useful for a few reasons. One is that when you are curious about something, you have the right cocktail of neurotransmitters present to make that information stick. So if you get the answer to something in the context of your curiosity, then it’s going to stay with you. Whereas you and I grew up in an era where we had lots of just-in information. What do you mean by that? Oh, you know, like just in case you ever need to know that the Battle of Hastings happened in 1066, here you go. Steven Levitt And you want to contrast that with just-in information. Exactly. I need to know how to fix my car. And so the internet tells me, and then I can really remember it because I need it. David Eagleman That’s exactly it. And so, look, you know, for all of us with kids, I know you’ve got kids, I’ve got kids, and we feel like, oh, my kid’s on YouTube and wasting time. There’s a lot of amazing resources and things that they learn on YouTube or even on TikTok, anywhere. There’s lots of garbage, of course, but it’s better than what we grew up with. When you and I wanted to know something, we would ask our mothers to drive us down to the library and we would thumb through the card catalog and hope there was something on it there that Steven Levitt Wasn’t too outdated. You were more ambitious than me. I would just ask my mother. And I have since learned that every single thing my mother taught me was completely wrong. But I still believe them because of this part of the brain that locks in things that you learn long ago. I still have to fight every day against the falsehoods my mother taught me. I wish I had told her to take me to the library. David Eagleman My mother was a biology teacher and my father was a psychiatrist. And so they had all kinds of good information. I’m just super optimistic about the next generation of kids. Now, as far as how we teach, things got complicated with the advent of Google. And now it’s twice as complicated with ChatGPT. Happily, we already learned these lessons 20 years ago. What we need to do is just change the way that we ask questions of students. We can no longer just assume that fill in the blank or even just writing a paper on something is the optimal way to have them learn something. But instead, they need to do interactive projects like run little experiments with each other. And, you know, the kind of thing that you and I both love to do in our careers, which is, OK, go out and find this data and run this experiment and see what happens here. That’s the kind of opportunities that kids will have now. (Time 0:37:41)
  • Possibilianism
    • Possibilianism advocates for actively exploring possibilities, rather than adhering to strict atheism or religious dogma.
    • It embraces scientific inquiry to understand our existence in a vast, mysterious cosmos. Transcript: Steven Levitt David Eagleman is a professor, a CEO, leader of a nonprofit called the Center for Science and Law, host of TV shows on PBS and Netflix, and the founder of Possibilianism. David Eagleman Like every curious person trying to figure out what we’re doing here, what’s going on. It just feels like there are two stories. Either there’s some religion story, or there’s the story of strict atheism, which I tend to agree with. But it tends to come with this thing of, look, we’ve got it all figured out. There’s nothing more to ask here. There is a middle position, which people call agnosticism. But usually that means, I don’t know, I’m not committing to one thing or the other. I got interested in defining this new thing that I call possibilianism, which is to try to go out there and do what a scientist does, which is an active exploration of the possibility Space. What the heck is going on here? We live in such a big and mysterious cosmos. Everything about our existence is sort of weird. Obviously, the whole Judeo-Christian tradition, that’s one little point in that possibility space, or the possibility that there’s absolutely nothing and we’re just atoms and We die. But there’s lots of other possibilities. And so I’m not willing to commit to one team or the other without having sufficient evidence. (Time 0:43:43)
  • LLMs as Parrots
    • Large language models (LLMs) excel at statistically predicting words but lack an internal world model.
    • Unlike humans, they cannot answer simple questions requiring real-world understanding, acting as sophisticated parrots. Transcript: Steven Levitt People are super excited right now about these generative AI models, the large language models. What’s your take on it? David Eagleman Essentially, these artificial neural networks took off from a very simplified version of the brain, which is, hey, look, you’ve got units and they’re connected. And what if we can change the strength between these connections? And in a very short time, that has now become this thing that has read everything ever written on the planet and can give extraordinary answers. But it’s not yet the brain or anything like it. It’s just taking the very first idea about the brain and running with it. What a large language model does not have is an internal model of the world. It’s just acting as a statistical parrot. It’s saying, okay, given these words, what is the next word most likely to be given everything that I’ve ever read on the planet? And so it’s really good at that, but it has no model of the world, no physical model. And so things that a six-year can answer, it is stuck on. Now, this is not a criticism of it in the sense that it can do all kinds of amazing stuff and it’s going to change the world, but it’s not the brain yet, and there’s still plenty of work to Be done to get something that actually acts like the brain. Steven Levitt Do you think that it is a solvable problem to give these models a theory of mind, a model of the world? David Eagleman I suspect so, because there are 8.2 billion of us who have this functioning in our brains. And as far as we can tell, we’re just made of physical stuff. We’re just very sophisticated algorithms. Steven Levitt And it’s just a matter of cracking what that algorithm is. If we were to come back in 100 years, what do you think would be most different? I know that’s a hard prediction to make, but what do you see is transforming (Time 0:47:13)