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Speaker A: Welcome to the Huberman Lab podcast, where we discuss science and science based tools for everyday life. I'm Andrew Huberman, and I'm a professor of neurobiology and ophthalmology at Stanford School of Medicine. Today, my guest is Doctor Eddie Chang. Doctor Eddie Chang is the chair of the neurosurgery depart... |
Speaker B: Hi. Hi, Andrew. |
Speaker A: Great to be here with you. This has been a long time coming just to come clean. We've known each other since we were nine years old, but then there was a long gap in which we didn't talk to one another. I heard things about you, and presumably you heard a thing or two about me, for better or for worse. And t... |
Speaker B: Oh, wow. That's fantastic. So we did bump into each other serendipitously back then. And at the time, I was a medical student at UCSF studying with Mike Merznik. In particular, I was studying how the brain organizes when you have patterns of sound. And in particular, we were studying the brain of rodents and... |
Speaker A: And what was the consequence of animals being raised in white noise environment? |
Speaker B: Well, one of the things that we didn't expect, but we found, which is quite striking, is that there's this early period in brain development where we're very susceptible to the patterns that we hear or see. In neuroscience, we call this a critical period or a sensitive period. We have this for our eyes, but ... |
Speaker A: It's fascinating, and I know it's difficult to make a direct leap from animal research to human research, but if we could speculate a little bit, I can imagine that some people grow up in homes where there's a lot of shouting and a lot of inflection. Maybe people are very verbose. Maybe others grow up in a h... |
Speaker B: Well, I think that it's, from my perspective, it's really clear that those sounds that we are exposed to from the very earliest time, even in utero, in the womb, where the sound is hearing the mother or father or friends around while in the womb, actually will influence how these things organize. And so ther... |
Speaker A: I get a lot of questions about the use of white noise during sleep. In particular, people want to know whether or not using a white noise machine or a machine or a program that makes the sound of waves, for instance, if it assists their infant in sleeping, is it going to be bad for them because it's flooding... |
Speaker B: Not yet. I think that what you're asking is a really important question, because parents are using white noise generators almost universally now, and for good reasons. It is hard to have kids up at night. I've got three kids of my own, was very tempted to think about how to use some of these tools to just so... |
Speaker A: And one probably assume that slowing the maturation of areas of the brain they're responsible for hearing, might impact one's ability to speak. Right? Because isn't it the case that if people can't hear, they actually have a harder time enunciating in a particular way? Is that right? If I were to not be able... |
Speaker B: Well, I think part of it is that over time, we develop sensitivity to the very specific speech sounds in a given language, and the sensitivity improves as we hear more and more and more of it. And then, on the other hand, we lose sensitivity to other speech sounds at the same time. But it's part of that proc... |
Speaker A: I guess the critical question that a number of people are going to be asking is, did you decide to use a white noise machine or not to help keep any of your three children asleep? |
Speaker B: Well, I think the short answer is no. I mean, I obviously did a lot of work thinking and work on this and thought about it carefully, but there are other kinds of noise, or I wouldn't even call it noise, other sounds that you can use that can be equally soothing to a baby. It's just that white noise has no s... |
Speaker A: Well, I know that after you finished your medical training, you went on to, of course, specialize in neurosurgery. And last I checked, you spend most of your days either running your laboratory or in the clinic or running the department. And your clinical work and your laboratory work involves often removing... |
Speaker B: Yeah, well, that's a fascinating question, and I'm going to just try to connect a couple of the dots here, which is that in that earlier work during medical school, I was doing a lot of what we call neurophysiology, putting electrodes into the auditory cortex and understanding how the brain responds to sound... |
Speaker A: So they're talking and listening, and you're essentially in conversation with these patients while there's a portion of their skull removed, and you are stimulating, or in some cases, removing areas of their brain. Is that right? |
Speaker B: That's exactly right. And the only thing off there is it's not essentially. It is just that the only difference between the conversation that I might have with my patient who's undergoing awake brain surgery is that I can't see their face and they can't see my face. We actually have a sterile drape that actu... |
Speaker A: And is that because occasionally you'll encounter a brain area, maybe you're stimulating, you're considering removing that brain area, and suddenly the patient will start stuttering or will have a hard time formulating a sentence. Is that essentially what you're looking for? You're looking for regions in whi... |
Speaker B: Exactly. So the first thing that we do is that we use a small electrical stimulator to probe different parts of the areas that we think might be related and important for language or talking or even movements of your arm and leg. That's what we call brain mapping. And we use a small electrical current that's... |
Speaker A: What are some of the more surprising, or maybe even if you want to offer one of the more outrageous examples of things that people have suddenly done or failed to be able to do as a consequence of this brain mapping? |
Speaker B: Well, I think the thing to me that has been the most striking is that some of these areas you stimulate and altogether you can shut down. Someone's talking person says, I wanted to say it, but I couldn't get the words out. And even though I've seen this thousands of times now, it's still exciting every time ... |
Speaker A: Do you ever see emotional responses from stimulation in particular areas? And do you ever hear or see emotional responses that are associated with particular types of speech? Because, for instance, curse words are known to people with Tourette's, often will curse. Not always, but sometimes they'll have tics ... |
Speaker B: Oh, well, definitely. I've seen cases where you can invoke anxiety, stress, and I think that there are also areas that you can stimulate. You can also evoke the opposite of that, sort of like a calm state. |
Speaker A: I think that brain areas is slightly hyperactive in you, or at least more than me. And all the years I've known you, you've always been, at least externally, a very calm person. I mean, I always find it amusing that you work on speech and language and you have a very calming voice. Right. And I'm being reall... |
Speaker B: Absolutely, yeah. So there are areas, for example, the orbitofrontal cortex, that we showed that if you stimulate there, the orbital frontal cortex is a part of the brain that's above the eyes. That's why they call it orbital frontal, meaning it's above the eye or the orbit and in the frontal lobe. And it's ... |
Speaker A: How was that discovered? Because I know a lot of people out there have anxiety in the absence of a brain scan, or why would one suspect that maybe they have a tumor or some other condition that was causing those neurons to become hyperactive? |
Speaker B: Yeah, that's really important, because so many people have anxiety, and the vast, vast majority are not having that because they're having seizures in the brain. I think one of the ways that this was diagnosed was that the nature of when she was having these panic attacks was not triggered by anything. They ... |
Speaker A: Speaking of epilepsy, a number of people out there have epilepsy or know people who do. Are the drugs for epilepsy satisfactory? You know, I think about things like Depakote and adjusting the excitation and inhibition of the brain. Are there good drugs for epilepsy? We know there are not great drugs for a lo... |
Speaker B: Yeah, great question. Well, a lot of people have seizures that can be completely controlled by their medications. A lot. But there's about a one third of people who have epilepsy, which we define as anyone who's had three or more seizures, that about a third of them actually don't have control with all of th... |
Speaker A: And you said a third of people with epilepsy might need neurosurgery. |
Speaker B: Well, what I mean by that is they continue to have seizures that are not controlled by all medications, and there's going to be another subset of those that may benefit from a surgery. It's probably not that whole third. It's a subset of that. It's just to say that epilepsy can be really hard to get fixed. A... |
Speaker A: I've heard before that the ketogenic diet was originally formulated in order to treat epilepsy, in particular in kids. Is that true? And why would being in a ketogenic state with low blood glucose reduce seizures? |
Speaker B: That's a great question, and to be honest, I don't know actually if it was originally designed to treat seizures. But I can tell you for sure that for some people, just like with some medications, it can be a life changing thing. It can completely change the way that the brain works. And it's not something t... |
Speaker A: I've heard similar things about the ketogenic diet for people with Alzheimer's dementia, that there's nothing particularly relevant about ketosis to Alzheimer's per se. But because Alzheimer's changes the way that neurons metabolize energy, that shifting to an alternate fuel source can sometimes make people ... |
Speaker B: Yeah, that's right. So a lot of its focus has really been on kids with epilepsy, but certainly it's a safe thing to try, so a lot of adults will try it as well. |
Speaker A: Interesting. I'd like to take a quick break and acknowledge one of our sponsors, athletic greens. Athletic greens, now called ag one, is a vitamin mineral probiotic drink that covers all of your foundational nutritional needs. I've been taking athletic greens since 2012, so I'm delighted that they're sponsor... |
Speaker B: Sure. Well, like I mentioned before, depending on how the seizure activity spreads in the brain or how it actually propagates, if it stays in one particular spot and doesn't spread to the entire brain, it can have really different manifestation. It can represent really differently. So absalom seizures, just ... |
Speaker A: What are some other types of seizures? |
Speaker B: Well, you know, I think some of the other kinds are, the classic ones are temporal lobe seizures. So these are ones that come from the medial structures, like the amygdala and hippocampus. Oftentimes, people, when they have seizures coming from that, they may taste something very unusual, like a metallic tas... |
Speaker A: I'm told that I've had nocturnal seizures, and I've woken up sometimes from sleep having felt as if I was having a convulsion, a sort of sense of buzzing in the back of the head. It's happened to me two or three times in college. My girlfriend. Well, I woke up and my girlfriend was very distraught, like, you... |
Speaker B: Oh, well. |
Speaker A: And do I need brain surgery? |
Speaker B: Nocturnal seizures are just another form. Like, again, epilepsy. And seizures can have so many different forms of not just, like, where in the brain, but also when they happen. And there are some people who, for whatever reason, it's very timed to the circadian rhythm. There's actually not just happening at ... |
Speaker A: Interesting. Well, it eventually stopped happening, so I stopped worrying about it. But I haven't had seizures since returning to speech and language. When I was getting weaned in neuroscience, I learned that we have an area of the brain for producing speech, and we have an area of the brain for comprehendin... |
Speaker B: Well, I love that question, because for me, it's very central to the research we do, and it's where the intersection between what we do in the laboratory and our research interfaces with what I see in patients. And one of the things that fascinated me early on in my medical training was in doing some of thes... |
Speaker A: Certainly what I was taught. |
Speaker B: Is that right? |
Speaker A: Oh, every. Yeah. And certainly what we still. We still teach undergraduates, graduate students and medical students, that. |
Speaker B: Well, that's what I learned, too, in medical school. And what I saw in reality when I started taking care of patients was that it's not so simple. In fact, part of it is fundamentally wrong. So, just in a nutshell, nowadays, after looking at this very carefully over hundreds of patients, we've shown that sur... |
Speaker A: Not long ago, you and me and my good friend Rick Rubin were having a conversation about medicine and science, and Rick asked the question, what percentage of what you learned in graduate and or medical school do you think is correct? And you had a very interesting answer. Would you share it with us? |
Speaker B: I don't know. I don't remember the exact, but I would say that with regard to the brain in particular, I would say about 50% gets it right and accurate and is helpful. But another 50% is just the approximation and oversimplification of what's going on. The example that we talked about, language, just an exam... |
Speaker A: It's early days, and we'll get into some of the technical advances that are allowing some correction of the errors that the field has made. And look, no disrespect to the brain explorers that came before us and the ones that come after us will correct us. Right? That's the way the game is played. But what I'... |
Speaker B: Well, that's one of those things that is, again, like, mostly true, not 100%. And what I mean by that is that it's complicated. So for people who are right handed, 99% of the time, the language part of the brain is on the left side. |
Speaker A: And what is the equivalent brain area on the right side doing if it's not doing language? |
Speaker B: Well, you know, the thing that's incredible is if you look at the right side and you look at it very carefully, either under an MRI or you actually look at the brain under slides at a microscope, it looks very, very similar. It's not identical, but it looks very, very similar. All the gyri, which are the bum... |
Speaker A: Is handedness genetic in any way? I mean, when I grew up, a pen or pencil or crayon was placed into my hand, presumably, or I started using. My father was left handed. And then where he grew up in South America, they forced him to. To force himself to become right handed. Actually, he used to restrict the mo... |
Speaker B: Absolutely no question about it. Handedness is not entirely, but strongly genetic. So there is something about the ties all of this. And what does handedness, for example, have to do with where the part of your brain that controls language? Well, it turns out that the parts that control the hand are very clo... |
Speaker A: You're bilingual, correct? |
Speaker B: Yeah. |
Speaker A: You speak English and Chinese? |
Speaker B: Yeah. |
Speaker A: For people that are bilingual and that learn two or more bilinguals, too, obviously, but learn both languages, or let's say more languages from an early time in life, do they use the same brain area to generate that language? Or perhaps they use the left side to speak English and the right side to speak Chin... |
Speaker B: I think we know a lot about bilingualism in the brain. The answers are still out there, the final answers on it. And part of the answer is, yes, absolutely. We use some parts of the brain very similarly. We actually have a study in the lab right now where we're looking at this, wherever people who speak one ... |
Speaker A: Fascinating. Okay, so we've talked about brain areas and a little bit about lateralization. I want to get back to the hands and some things related to emotion in a little bit. But maybe now we could go into those brain areas and start to ask the question what exactly is represented or mapped there? And for p... |
Speaker B: Sure. Let's get into this, Andrew, because this is one of the most exciting stuff that's happening right now, is understanding how the brain processes these exact questions. And you asked me earlier, what is difference between speech and language? Speech corresponds to the communication signal. It correspond... |
Speaker A: And for those of you out there that aren't familiar with thinking about things in the so called frequency space, bass tones would be lower frequencies and high pitched tones would be higher frequencies, just to make sure everyone's on the same page. So the sound of my voice, the sound of your voice, or any s... |
Speaker B: Oh, extraordinarily precise. I mean, we take these millisecond cues, the millisecond differences between the sound coming to one ear, let's say, your right ear versus your left, to understand what direction that sound came from. Those are only millisecond differences, and that's how precise this works. But o... |
Speaker A: And what are those sites doing? Or could you give us some examples of what those sites are doing? So, for instance, are they sites that are specific for. Or we could say, even listening for consonants or for vowels or for inflection or for emotionality? What's in there? Okay, well, what makes these cells fir... |
Speaker B: Yeah. What gets them excited, what gets them going is hearing speech in particular. There are some of these really focal sites, again, just on the order of millimeter or at some level, single neurons that are tuned to consonants. Some are tuned to vowels, some are tuned to particular features of consonants. ... |
Speaker A: Now, I'm going to be thinking about this. So, plosive, like plosives, like saying the word plosive does. Requires that. |
Speaker B: Exactly. So what's cool about that is that we actually have no idea what's going on in our mouth when we speak. We really have no idea. |
Speaker A: Some people definitely have no idea. |
Speaker B: Well, not just, like, in terms of what you're saying sometimes, but actually like, how you're actually moving. |
Speaker A: Right? |
Speaker B: You know, the different parts of vocal tract. And I have a feeling if we actually required understanding, we would never be able to speak because it's so complex. It's such a complex feat. Some people would say it's the most complex motor thing that we do as a species is speaking. Not the extreme feats of ac... |
Speaker A: Athleticism, but speaking, especially when one observes opera or people who freestyle rappers. And, of course, it's not just the lips, it's the tongue. And you've mentioned two other structures. Pharynx and larynx are the main ones. Can you tell us just educate us at a superficial level, what the pharynx and... |
Speaker B: Okay, sure. So I'll talk primarily about the larynx here for a second, which is that if you think about when we're speaking, really what we're doing is we're shaping the breath. So even before you get to the larynx, you got to start with the expiration. So we fill up our lungs and then we push the air out. T... |
Speaker A: Yours is 200. |
Speaker B: No, ours is most male voices are around 100, and then the average female. |
Speaker A: Voice is around 200. As you know, I've always had the same voice. This was a point of shame when I was a kid. But, folks, my voice never changed. I always had the same voice. This is a discussion for another time. |
Speaker B: Yeah, well, it's a great voice, a great baritone voice, but I know in your voice it's a low frequency voice. And the reason why men and women generally have different voice qualities is it has to do with the size of the larynx and the shape of it. In general, men have a larger voice box, or larynx, and the v... |
Speaker A: Fascinating, and immediately makes me wonder about more primitive or non learned vocalizations, like crying or laughter. Babies will cry. Babies will show laughter. Are those sorts of vocalizations produced by the language areas like Wernicke's, or do they have their own unique neural structures? |
Speaker B: Yeah, interesting question. So we call those vocalizations. A vocalization is basically where someone can create a sound, like a cry or a moan, that kind of sounds. And it also involves the exhalation of air. It also involves some phonation at the level of larynx, where the vocal folds come together to creat... |
Speaker A: For example, the intricacy of these circuits in the brain and their connections to the pharynx and larynx is just. It's almost overwhelming in terms of thinking about just how complicated it must be. And yet some general features and principles are starting to emerge from your work and from the work of other... |
Speaker B: That's been one of the most important questions we've been trying to answer for the past decade. So, there is a part of the brain that we call the primary auditory cortex, and the primary auditory cortex is deep in the temporal lobe. And if you looked at that part of the brain, there is a map of different so... |
Speaker A: So if I say that exactly, as opposed to a plosive, where I'd say explosive, now, of course, I'm emphasizing here. Well, this explains something and solves a mystery, which is recently I've been fascinated by the work of a physician, scientist back east, Doctor Shana Swan, who's done a lot of work on things t... |
Speaker B: That's exactly right. In fact, we have a term for that that's called a consonant cluster. So sometimes syllables will just have one consonant. But when we start stacking certain syllables in a sequence, and there's rules that actually govern which consonants can be in a particular sequence for a given langua... |
Speaker A: Can we say that there is a most complicated language out there? Or among the most complicated? Would it be Russian? |
Speaker B: It's definitely high up there. English is up there too, actually. Yeah, German as well. |
Speaker A: And in terms of learning multiple languages during development, my understanding is that if one wants to become bilingual or trilingual, best to learn those languages simultaneously during development, ideally before age twelve, if one hopes to note, have an accent in speaking them later. Is that correct, or... |
Speaker B: Well, basically, the earlier and the earlier is better. The more intense it is, and the more immersive it is, the longer that you can be exposed to that is really important. A lot of people can get exposed to early and basically lose it, even though it's, quote unquote during that sensitive period. Unless it... |
Speaker A: So returning to what's mapped, what the representations are in the brain, I'm starting to get a picture now based on these plosives and these sounds. And what I find so interesting and logical about that is it maps to the motor structures and the actual pronunciation of the sounds, not necessarily to the mea... |
Speaker B: Yeah. So to address the first part is that we've got this map of these different parts of consonants and vowels. When we look at how they lay out in this part of the brain that we call Wernicke's area, we've spent a lot of time really just dissecting this millimeter by millimeter. The term that you use is ve... |
Speaker A: What is the current treatment for dyslexia? I've heard that it's a deficit in some of the motion processing systems of the visual system. Their eyes are jumping as opposed to more linear reading across. Or I suppose if it were Chinese, who'd be. I want to presume people are always reading English. Or I suppo... |
Speaker B: Yeah, absolutely. So, again, I think in the beginning, people might have thought this was purely a visual abstraction or something really just about the visual system. But there's been more recognition that it could be both, or it could be either, depending on the particular instance. It's very clear that th... |
Speaker A: Yeah, I'm a big fan of listening to audiobooks, and of course, I also listen to podcasts quite a lot. But I also am a strong believer, based on the research that I've seen, that reading books, physical books, could be on kindle, I suppose. But reading a physical book is useful for being able to articulate we... |
Speaker B: Yeah, that's a really fascinating point. There's this idea that there's, like, this proper way to speak. Like that. There's the right way. For example, what are the appropriate, you know, like, for example, in school, you're oftentimes told, like, you should say it like this, not say it like that, you know, ... |
Speaker A: Speaking of learning new languages, I'm assuming it's possible to learn new languages throughout the lifespan, correct? |
Speaker B: Yeah. |
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