Your Brain's Logic & Function | Dr. David Berson

Andrew Huberman 0:00 (Music) 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 Dr. David Berson, Professor of Medical Science, Neurobiology and Ophthalmology at Brown University. Dr. Berson's laboratory is credited with discovering the cells in the eye that set your circadian rhythms. These are the so-called intrinsically photosensitive melanopsin cells, and while that's a mouthful, all you need to know for the sake of this introduction is that those are the cells that inform your brain and body about the time of day. Dr. Berson's laboratory has also made a number of other important discoveries about how we convert our perceptions of the outside world into motor action. More personally, Dr. Berson has been my go-to resource for all things neuroscience for nearly two decades. I knew of his reputation as a spectacular researcher for a long period of time, and then many years ago, I cold-called him out of the blue. I, uh, basically corralled him into a long conversation over the phone, after which he invited me out to Brown, and we've been discussing neuroscience, and how the brain works, and the emerging new technologies, and the emerging new concepts in neuroscience for a very long time now. You're going to realize today why Dr. Berson is my go-to source. He has an exceptionally clear and organized view of how the nervous system works. You know, there are many, many parts of the nervous system, different nuclei, and connections, and circuits, and chemicals, and so forth. But it takes a special kind of person to be able to organize that information into a structured and logical framework that can allow us to make sense of how we function in terms of what we feel, what we experience, how we move through the world. Dr. Berson is truly one of a kind in his ability to synthesize and organize and communicate that information, and I give him credit as one of my mentors and one of the people that I respect most in the field of science and medical science generally. Today, Dr. Berson takes us on a journey from the periphery of the nervous system, meaning from the outside, deep into the nervous system, layer by layer, structure by structure, circuit by circuit, making clear to us how each of these individual circuits work and how they work together as a whole. It's a really magnificent description that you simply cannot get from any textbook, from any popular book, and frankly, as far as I know, from any podcast that currently exists out there. So it's a real gift to have this opportunity to learn from Dr. Berson. Again, I consider him my mentor in the field of learning and teaching neuroscience, and I'm excited for you to learn from him. One thing is for certain. By the end of this podcast, you will know far more about how your nervous system works than the vast majority of people out there, including many expert biologists and neuroscientists.

Andrew Huberman 2:55 Before we begin, I'd like to emphasize that this podcast is separate from my teaching and research roles at Stanford. It is, however, part of my desire and effort to bring zero cost to consumer information about science and science-related tools to the general public. In keeping with that theme, I'd like to thank the sponsors of today's podcast. Our first sponsor is Athletic Greens. Athletic Greens is an all-in-one vitamin mineral probiotic drink. I've been taking Athletic Greens every day since 2012, so I'm delighted that they're sponsoring the podcast. The reason I started taking Athletic Greens and the reason I still take Athletic Greens is that it covers all of my vitamin, mineral, and probiotic needs. 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Magic Spoon is a zero-sugar, grain-free, keto-friendly cereal. Now, I don't follow a ketogenic diet. The way that I eat is basically geared toward feeling alert when I want to be alert and feeling sleepy when I want to go to sleep, which for me means fasting until about 11:00 AM or noon most days. Then I eat low-carb during the day, so I'll have some meat, or fish, or chicken and some salad. That's what works for me. And in the afternoon, I remain on a more or less low-carbish diet. And then in the evening, I eat pastas and things primarily, and I throttle back on the protein, and that's what allows me to fall asleep at night. That's just what works for me. So if I want a snack in the afternoon, I want that to be a ketogenic or low-carb snack, and that snack these days is Magic Spoon. Magic Spoon is really terrific. It has zero grams of sugar, 13 to 14 grams of protein, and only four net grams of carbohydrates in each serving. It's really delicious. 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Andrew Huberman 8:02 for my discussion with Dr. David Berson. Welcome.

Dr. David Berson 8:06 Thank you.

Andrew Huberman 8:06 Yeah.

Dr. David Berson 8:07 So nice to be here.

Andrew Huberman 8:08 Great to have you. For more than 20 years, you've been my go-to source for all things nervous system, how it works, how it's structured. So today, I want to ask you some questions about that. I think people would gain a lot of insight into this machine that makes them think, and feel, and see, et cetera. If you would, could you tell us how we see? You know, a photon of light enters the eye. What happens?

Dr. David Berson 8:37 Right.

Andrew Huberman 8:38 I mean, w- how is it that I look outside, I see a truck drive by, or I look on the wall, I see a photo of my dog? How does that work?

Dr. David Berson 8:46 Right. So this is an old question obviously, and clearly in the end, the reason you have a visual experience is that your brain has got some pattern of activity that it associates with the input from the periphery. But you can have a visual experience with no input from the periphery as well. When you're dreaming-

Andrew Huberman 9:03 Mm-hmm.

Dr. David Berson 9:04 ... you're seeing things that aren't coming through your eyes.

Andrew Huberman 9:07 Are those memories?

Dr. David Berson 9:09 Uh, I would say in a sense they may reflect your visual experience. They're not necessarily specific visual memories, but of course they can be. But the point is that the experience of seeing is actually a brain phenomenon, but of course under normal circumstances we see the world because we're looking at it and we're using our eyes to look at it, and fundamentally, when we're looking at the exterior world, it's what the retina is telling the brain that matters. So there are cells called ganglion cells, these are neurons that are the key cells for communicating between eye and brain. The eye is like the camera, it's detecting the initial image, doing some initial processing, and then that signal gets sent back to the brain proper, and of course it's there at the level of the cortex that we have this conscious visual experience. There are many other places in the brain that get visual input as well doing other things with that kind of information.

Andrew Huberman 10:02 So I, I get a lot of questions about color vision. If you would, could you explain how is it that we can perceive reds and greens and blues and things of that sort?

Dr. David Berson 10:13 Right. So the first thing to understand about light is that it's just a form of electromagnetic radiation. Uh, it's vibrating. It's oscillating. But light is-

Andrew Huberman 10:24 When you say it's vibrating, it's oscillating, you mean that photons are actually moving?

Dr. David Berson 10:28 Well, in a sense, photons are, they're certainly moving through space. We think about photons as particles, and that's one way of thinking about light, but we can also think of it as a wave, like a radio wave. Either way is acceptable. And the radio waves have frequencies like the frequencies on the, your radio dial, and certain frequencies in the electromagnetic spectrum can be detected by neurons in the retina. Those are the things we see. But there's still different wavelengths within the light that can be seen by the eye, and those different wavelengths are unpacked in a sense or decoded by the nervous system to lead to our experience of color. Um, essentially different wavelengths give us the sensation of different colors through the auspices of different neurons that are tuned to different wavelengths of light.

Andrew Huberman 11:17 So when, uh, a photon... So when a little bit of light hits my eye-

Dr. David Berson 11:22 Right.

Andrew Huberman 11:22 ... goes in, the photoreceptors convert that into electrical signal.

Dr. David Berson 11:26 Right.

Andrew Huberman 11:27 How is it that a given photon of light gives me the perception, eventually leads to the perception of red versus green versus blue?

Dr. David Berson 11:35 Right. So, uh, if you imagine that in the first layer of the retina where this transformation occurs from electromagnetic radiation into neural signals, that you have different kinds of sensitive cells that are expressing, they're making different molecules within themselves for this expressed purpose of absorbing photons, which is the first step in the process of seeing. Now, it turns out that altogether there are about five proteins like this that we need to think about in the typical retina, but for seeing color really it's three of them. So there are three different proteins, each absorbs light with a different, you know, preferred frequency, and then the nervous system keeps track of those signals, uh, uh, co- compares and contrasts them to extract some understanding of the wavelength composition of light. So you can see just by looking at a landscape, oh, it must be late in the day because things are looking golden. That's all, you know, a function of our absorbing...... the light that's coming from the, the world and interpreting that with our brain because of the different composition of the, the, the light that's reaching our eyes.

Andrew Huberman 12:46 Is it fair to assume that my perception of red is the same as your perception of red-

Dr. David Berson 12:50 Well, that's a great question.

Andrew Huberman 12:51 ... and that mine is better?

Dr. David Berson 12:52 (laughs)

Andrew Huberman 12:52 No, I'm just kid- I'm just kidding. (laughs)

Dr. David Berson 12:55 It's a great question, it's a deep philosophical question, it's a question that really s- probably can't even ultimately be answered, uh, by the usual empirical scientific processes 'cause it's really about a, you know, a- an individual's experience. Um, what we can say is that the biological mechanisms that we think are important for seeing color, for example, seem to be very highly similar from one individual to the next, whether it be human beings or other animals. Um, and so we think that the physiological process looks very similar on the front end. But, you know, once you're at the level of perception, or understanding, or experience, that's something that's a little bit tougher to nail down with the, the sorts of, you know, uh, scientific approaches that we ap- approach biological vision with, let's say.

Andrew Huberman 13:46 You mentioned that there are five

Andrew Huberman 13:47 different cone types essentially, eh cones being the cells that absorb light of different wavelengths. Um, I often wondered, eh, when I had my dog, uh, what h- he saw and how his vision differs from our vision, and certainly there are animals that can see things that we can't see.

Dr. David Berson 14:05 Right.

Andrew Huberman 14:05 What are some of the more outrageous examples of that?

Dr. David Berson 14:09 Of seeing things that we can't?

Andrew Huberman 14:10 Seeing things in, in, in the extreme.

Dr. David Berson 14:12 Right.

Andrew Huberman 14:12 Uh, you know, uh, dogs, I'm, I'm guessing see reds more as oranges, is that right? 'Cause they, they don't have these, the same array of, of neurons that we have for, for seeing color.

Dr. David Berson 14:22 Right. So the first thing is, it's not really five types of cones, there are really three types of cones. And if you look at the way that color vision is thought to work, you can sort of see that it has to be three different signals. There are a couple of other types of pigments, one is really mostly for dim light vision. When you're walking around in a moonless night and you're seeing things, uh, with very low light, that's the rod cell and that uses its own pigment. Um, and then there's another class of pigments we'll probably talk about a little bit later, this melanopsin pigment.

Andrew Huberman 14:54 I thought you were referring to, like, ultraviolet, and infrared, and, and things of that sort.

Dr. David Berson 14:58 Right, right.

Andrew Huberman 14:59 Okay.

Dr. David Berson 14:59 So in the case of a typical, um, well, let's put it this way, in, in human beings, most of us have three cone types and we can see colors that re- that, that stem from that. In most mammals, including your dog, um, or your cat, there really are only two cone types, and that limits the kind of vision that they can have in the domain of wavelength or color as we'd say. So really a, a dog sees the world kind of like a particular kind of color-blind human might see the world, because instead of having three channels to compare and contrast, they only have two channels, and that makes it much more difficult to figure out exactly which wavelength you're, you're looking at.

Andrew Huberman 15:40 Do, uh, colorblind people suffer much as a consequence of being colorblind?

Dr. David Berson 15:44 Well, you know, we're, it's, it's like so many other disabilities, we are, um, you know, the, the r- the world is built for people of th- the most common type, so i- in some cases, the expectation can be there that somebody can see something that they won't be able to if they're missing one of their cone types, let's say. So in those moments, that can be a real problem. Um, you know, if there's a lack of contrast to their visual system, they will be blind to that. In general, it's a fairly modest, uh, visual, um, uh, limitation as things go, you know, for example, if not being able to see acutely can be much more damaging, not being able to read, you know, fine print, for example.

Andrew Huberman 16:26 Yeah, I suppose if I had to give up, um, uh, the ability to see certain colors or give up the ability to see clearly-

Dr. David Berson 16:33 Right.

Andrew Huberman 16:33 ... I'd certainly trade out color for clarity.

Dr. David Berson 16:37 Right. Of course, color's very meaningful to us as human beings, you know, um, so we would hate to give it up, but obviously dogs and cats and all kinds of other mammals do perfectly well in the world without the-

Andrew Huberman 16:48 Yeah, because we take care of them. I spend most of my time-

Dr. David Berson 16:50 (laughs)

Andrew Huberman 16:50 ... taking care of that dog. Uh, he took care of me too. Uh, let's talk about

Andrew Huberman 16:56 the, that odd photo pigment, um, photo pigment of course being the thing that absorbs light of a particular wavelength, and let's talk about these specialized ganglion cells that communicate certain types of information from eye to the brain that are so important for so many things. What I'm referring to here, of course, is your co-discovery of the so-called intrinsically photosensitive cells, the neurons in the eye that do so many of the things that don't actually have to do with perception, but have to do with important biological functions. What I would love for you to do is, um, explain to me why once I heard you say, "We have a bit of fly eye-"

Dr. David Berson 17:37 (laughs)

Andrew Huberman 17:37 "... in our eye."

Dr. David Berson 17:38 Yeah.

Andrew Huberman 17:38 And you showed this slide of, like, a giant fly from a horror movie-

Dr. David Berson 17:43 Yeah.

Andrew Huberman 17:44 ... uh, trying to attack this woman-

Dr. David Berson 17:45 Yeah.

Andrew Huberman 17:46 ... and maybe it was an eye also. So what does it mean that we have a bit of a fly eye in our eye?

Dr. David Berson 17:54 Yeah, so th- this is, th- this last pigment is a really peculiar one. Um, it, one can think about it as really the initial sensitive element in a system that's designed to tell your brain about how bright things are in your world. Uh, and the thing that's really peculiar about this pigment is that it's in the wrong place in a sense. When you think about the structure of the retina, you think about a layer cake essentially, you've got s- this thin membrane at the back of your eye, but it's actually a stack of thin layers, and the outermost of those layers is where these photoreceptors you were talking about earlier are sitting. That's where the film of your camera is essentially, that's where the photons do their magic with the photo pigments and turn it into a neural signal.

Andrew Huberman 18:39 I like that. Never really thought of the photoreceptors as the film of the camera, but that makes sense.

Dr. David Berson 18:42 Yeah, or, like, the sensitive chip on, you know, CCD chip in your, in your cellphone. It's the surface on which the light pattern is imaged by the optics of the eye...... and now you've got an array of sensors that's capturing that information and creating a bitmap essentially, uh, but now it's in neural signals distributed across the surface of the, the retina. So all of that was known to be going on 150 years ago. A couple of types of photoreceptors, cones and rods. If you look a little bit more closely, three types of cones. That's where the transformation from electromagnetic radiation to, um, to neural signals was thought to take place. But it turns out that this last photopigment is in the other end of the retina, the innermost part of the retina, and that's where the so-called ganglion cells are. Those are the cells that talk to the brain, the ones that actually can communicate directly what information comes to them from the photoreceptors. And here, you've got a case where actually some of the output neurons that we didn't think had any business being directly sensitive to light were actually making this photopigment, absorbing light, and converting that to neural signals and sending it to the brain. So that made it pretty su- surprising and unexpected, but there are many other surprising things about these cells.

Andrew Huberman 20:01 So, and wh- what is the relationship to the fly eye?

Dr. David Berson 20:05 Right. So the, the link there is that if you ask how the photopigment now communicates downstream from the initial absorption event to get to the electrical signal, that's a complex cellular process. It involves many chemical steps. And if you look at how photoreceptors in our eyes work, you can see what that cascade is, how that chain works. If you look in the eyes of flies, or other insects, or other invertebrates, there's a very similar kind of chain the, but the specifics of how the signals get from the absorption event by the pigment to the electrical response that the nervous system can understand are characteristically different between fuzzy, furry creatures like us and insects, for example, like the fly.

Andrew Huberman 20:56 I see.

Dr. David Berson 20:56 So, these funny, extra photoreceptors that are in the wrong layer doing something completely different are actually using a chemical cascade that looks much more like what you would see in a fly photoreceptor than what you would see in a human photoreceptor, a rod or a cone, for example.

Andrew Huberman 21:14 So, it sounds like it's a very primitive part of, uh, primitive aspect of biology that we maintain.

Dr. David Berson 21:20 Exactly right. Exactly right.

Andrew Huberman 21:22 You know, and, and despite the fact that dogs can't see as many colors as we can and cats can't see as many colors as we can, we have all this extravagant stuff for seeing color, and then you got this other pigment sitting in the wrong, not wrong, but in a different, uh, part of the eye sending, uh, processing light very differently-

Dr. David Berson 21:39 Right.

Andrew Huberman 21:40 ... and sending that information into the brain. So, what do these cells do? I mean, th- presumably they're there for a reason.

Dr. David Berson 21:47 They are, and the i- the interesting thing is that one cell type, like this, carrying one kind of signal, which I would call a brightness signal essentially, can do many things in the brain.

Andrew Huberman 22:02 When you say brightness signal, you mean that it... Like right now, I have these cells. Do I have these cells?

Dr. David Berson 22:06 You do.

Andrew Huberman 22:06 Of course not. I'm, I'm joking. I hope I have these cells in my eye. Um, and they're paying attention to how bright it is overall, but they're not paying attention, for instance, to the edge of your ear or what else is going on in the room.

Dr. David Berson 22:16 Right. So, so it's the difference between knowing what the objects are on the table and knowing whether it's bright enough to be daylight right now. So what, why does your nervous system de need, need to know whether it's daylight right now? Well, one thing it needs to know, that is your circadian clock. You know, if you travel across time zones to Europe, now your internal clock thinks it's California time, but the rotation of the earth is, you know, for, you know, a different part of the planet. You're, the rising and setting of the sun is not at all what your body is anticipating. So you've got an internal representation of the rotation of the earth in your own brain. That's your circadian system, is keeping time, but now you've played a trick on your nervous system. You put yourself in a different place where the sun is rising at the, quote, "wrong" time. Well, that's not good for you, right? So you got to get back on track. One of the things this system does is sends a, "Oh, it's daylight now," signal to the brain, which compares with its internal clock, and if that's not right, it tweaks the clock gradually until you get over your jet lag and you feel back on track again.

Andrew Huberman 23:24 So, the jet lag case makes a lot of sense to me, but presumably these, uh, elements didn't evolve for jet lag.

Dr. David Berson 23:31 Right.

Andrew Huberman 23:32 So what, wh- wh- what are they doing on a day-to-day basis?

Dr. David Berson 23:35 Right. Well, one way to think about this is that the clock that you have in, not just your brain, in all the cells of y- or almost all of the cells of your body, they're all oscillating. They're all, you know-

Andrew Huberman 23:49 They got little clocks in them.

Dr. David Berson 23:49 ... little clocks within themselves.

Andrew Huberman 23:51 Yeah.

Dr. David Berson 23:51 They're all, they're all clocks. Um, you know, they need to be synchronized appropriately, uh, and the whole thing has to be built in biological machinery. This is actually a beautiful story about how gene expression can control gene expression, and if you set it up right, you can set up a little thing that just sort of hums along at a particular frequency. In our case, it's humming along at 24 hours 'cause that's how our earth rotates, and it's all built into our biology, so this is great, but the reality is that the clock can only be so good. I mean, we're talking about biology here. It's not precision engineering, and so it can be a little bit off.

Andrew Huberman 24:34 Well, also it doesn't... It's in our brain, so it doesn't have access to any regular unerring signal.

Dr. David Berson 24:39 Well, if in the absence of the rising and setting of the sun it doesn't, if you put someone in a cave, their biological clock will keep time to within a handful of minutes of 24 hours. That's no problem for one day.... but if this went on without any correction, eventually you'd be out of phase, and this is actually one of the things that blind patients often complain about if they've got retinal blindness, is insomnia, and, uh-

Andrew Huberman 25:08 'Cause their brain's awake in the middle of the night.

Dr. David Berson 25:10 ... or sleepiness during the day. Exactly. They're not synchronized. Their clock is there, but they're drifting out of phase because their clock's only good to, you know, 24.2 hours or 23.8 hours. Little by little, they're drifting, so you need a synchronization signal. So even if you never cross time zones, and, of course, we didn't back on the savanna, we stayed within walking distance of where we were, uh, you still need a synchronizer 'cause otherwise you have nothing to actually confirm when the rising and the setting of the sun is. That's what you're trying to synchronize yourself to.

Andrew Huberman 25:44 I'm fascinated

Andrew Huberman 25:45 by the circadian clock and the fact that all the cells of our body have essentially a 24-hour-ish clock in them.

Dr. David Berson 25:53 Right.

Andrew Huberman 25:54 We hear a lot about these circadian rhythms and circadian clocks, the fact that we need light input from these special neurons in order to set the clock, but I've never really heard it described how the clock itself works and how the clock signals to all the rest of the body when, you know, the liver should be doing one thing-

Dr. David Berson 26:12 Right.

Andrew Huberman 26:12 ... and when the stomach should be doing another. I know you've done some work on the clock, so if you would just maybe briefly describe where the clock is, what it does, and some of the, you know, top contour of how it tells the cells of the body what to do.

Dr. David Berson 26:29 Right. So the first thing to say is that, as you said, the clock is all over the place. Most of the tissues in your body have clocks. Uh-

Andrew Huberman 26:37 Yeah. We probably have, what, millions of clocks in our body.

Dr. David Berson 26:40 Yeah, I would say that's-

Andrew Huberman 26:40 Yeah.

Dr. David Berson 26:40 ... that's probably fair. You have millions of cell types, you probably have millions of clocks. Um, the, the role of the central pacemaker for the circadian system is to coordinate all of these, and this is, uh, there's a little nucleus, a little, uh, collection of nerve cells in your brain that's called the suprachiasmatic nucleus, the SCN, uh, and it is sitting in a funny place for the rest of the structures in the nervous system that get direct retinal input. It's sitting in the hypothalamus, which you can think about as sort of the great coordinator of drives and-

Andrew Huberman 27:18 The source of all our pleasures and all our problems.

Dr. David Berson 27:20 Right.

Andrew Huberman 27:21 Or most our problems. (laughs)

Dr. David Berson 27:22 Yes, it really is. But it's sort of, you know, deep in your brain, things that drive you to do things. If you're freezing cold, you put on a coat, you, you, you ch- you shiver, all these things are coordinated by the hypothalamus. So this pathway that we're talking about from the retina and from these peculiar cells that are encoding light intensity are sending signals directly into a center that's surrounded by all of these centers that control autonomic nervous system and, uh, your hormonal systems. Um, so this is, uh, a part of the, your, your visual system that doesn't really reach the level of consciousness. It's not something you, you think about. It's happening under the radar kind of all the time, uh, and the signal is working its way into the- this central clock coordinating center. Now, what happens then is not that well understood, but it's clear that this is a neural center that has the same ability to communicate with other parts of your brain as any other neural center, and clearly there are circuits that involve connections between neurons that, uh, you know, are, are conventional, but in addition it's quite clear that there are also sort of humoral effects, that things are being- are oozing out of the cells, uh, in the center and maybe into the circulation or, or just, uh, diffusing through the brain to some extent that can also affect, uh, neurons elsewhere. But the hypothalamus uses everything to control the rest of the bodies, and that's true of the suprachiasmatic nucleus, this, this circadian center as well. Um, e- it can get its fingers into the autonomic nervous system, the, the humoral system, and, of course, up to the centers of the brain that organize coordinated rational behavior.

Andrew Huberman 29:12 So if I understand correctly, we have this group of cells, the suprachiasmatic nucleus. It's got a 24-hour rhythm. It- that rhythm is more or less matched to what's going on in our external world by the specialized set of neurons in our eye, but then the e- the master clock itself, the SCN, releases things in the blood, humoral signals, um, that go out various places in the body, and then you said to the autonomic system, which is regulating more or less how alert or calm we are, as well as our thinking and our cognition. Uh, um, so the... I'd love to talk to you about the autonomic part. Uh, presumably that's through melatonin, it's through, um, uh, adrenaline. Wh- how, how is it that, that, uh, this clock is impacting how, uh, the autonomic system, how alert or calm we, we feel?

Dr. David Berson 30:02 Right. So there, there are pathways by which the suprachiasmatic nucleus can access both the parasympathetic and sympathetic nervous system.

Andrew Huberman 30:12 Just so people know, the sympathetic nervous system is the one that tends to make us more alert and the parasympathetic nervous system is the portion of the autonomic nervous system makes us feel more calm.

Dr. David Berson 30:22 Right.

Andrew Huberman 30:22 In, in broad context.

Dr. David Berson 30:23 To first, yeah, to first approximation, right. So this is... Both of these systems are within the grasp of the circadian system through hypothalamic circuits. One of the circuits that will be, I think, of particular interest to some of your listeners is a pathway that involves this sympathetic branch of the autonomic nervous system, the fight or flight system, that is actually through a very circuitous route enervating the pineal gland, which is sitting in the middle of your brain.

Andrew Huberman 30:55 The so-called third eye.

Dr. David Berson 30:57 Right.So this is the-

Andrew Huberman 30:58 We'll have to get back to why it's called the third eye, because, yeah.

Dr. David Berson 31:01 That's an interesting history.

Andrew Huberman 31:02 You can't call something the third eye and not, and just, you know.

Dr. David Berson 31:05 Just leave it there.

Andrew Huberman 31:05 Just leave it there.

Dr. David Berson 31:06 Right.

Andrew Huberman 31:07 Right.

Dr. David Berson 31:08 Anyway, this is the major source of melatonin in your body.

Andrew Huberman 31:11 So light comes into my eye.

Dr. David Berson 31:14 Yes.

Andrew Huberman 31:15 Passed off to the suprachiasmatic nucleus-

Dr. David Berson 31:17 Yep.

Andrew Huberman 31:17 ... essentially, not the light itself, but the, the-

Dr. David Berson 31:19 Signal.

Andrew Huberman 31:20 ... signal representing the light.

Dr. David Berson 31:21 Sure.

Andrew Huberman 31:21 Then the SCN, the suprachiasmatic nucleus, can impact the melatonin system-

Dr. David Berson 31:27 Right.

Andrew Huberman 31:27 ... vi- via the pineal.

Dr. David Berson 31:28 Right. The way this is seen is that if you were to measure your melatonin level over the course of the day, if you could do this, you know, hour by hour, you'd see that it's really low during the day, very high at night. But if you get up in the middle of the night and go to the bathroom and turn on the bright full ru- fluorescent light, your melatonin level is slammed to the floor. Light is directly impacting your hormonal levels, um, through this mechanism that we des- described. So this is one of the routes by which light can act on your hormonal status through pathways that are completely beyond what you normally would think about, right? You're thinking about the s- the things in the bathroom, "Oh, there's the toothbrush."

Andrew Huberman 32:11 Mm-hmm.

Dr. David Berson 32:12 You know, there's the tube of toothpaste. But meanwhile, this other system is just counting photons and saying, "Oh, wow, there's a lot of photons right now. Let's shut down the melatonin release."

Andrew Huberman 32:22 Uh, this is one of the main reasons why I've encouraged people to avoid bright light exposure in the middle of the night, not just blue light, but bright light of any wavelength. Because there's this myth out there that blue light, because it's the optimal signal for activating this pathway and shutting down melatonin, is the only wavelength of light that can shut it down. But am I correct in thinking that if a light is bright enough-

Dr. David Berson 32:46 Right.

Andrew Huberman 32:47 ... it doesn't matter if it's blue light, green light, purple light, even red light-

Dr. David Berson 32:51 Right.

Andrew Huberman 32:51 ... you're going to slam melatonin down to the ground? Which is not a good thing to happen in the middle of the night, correct?

Dr. David Berson 32:58 Right, right. Yeah, I mean, a- any, any light will affect the system to some extent. The blue light is somewhat more effective, but don't fool yourself to, in- into thinking that if you use red light that means you're, you know, you're avoiding the effect. You s- it's certainly still there, and certainly if it's very bright, it'll be more effective in driving the system than dim blue light would be.

Andrew Huberman 33:20 Interesting. A lot of people wear blue blockers.

Dr. David Berson 33:22 Right.

Andrew Huberman 33:22 Um, and in a kind of odd twist of misinformation out there, um, a lot of people wear blue blockers during the middle of the day.

Dr. David Berson 33:31 Right.

Andrew Huberman 33:31 Which basically makes no sense, because during the middle of the day is when you want to get a lot of bright light and including blue light into your eyes, correct?

Dr. David Berson 33:39 Absolutely. And not just for the reasons we've been talking about in terms of circadian effects. There are major effects of light on mood, um, and seasonal affective disorder apparently is essentially a reflection of this same system in reverse. If you're living in the northern climes and y- you know, you're not getting that much light during the middle of the, the winter in Stockholm, um, you might be prone to depression and phototherapy might be just the ticket for you. And that's because there's a direct effect of light on mood. There's, there's an example where if you don't have enough light, it's a problem. So I think you're exactly right. It's not about, is light good or bad for you? It's about w- what kind of light and when, uh, that, that makes the difference.

Andrew Huberman 34:25 Yeah, the general rule of thumb that I've been living by is to get as much bright light in my eyes, ideally from sunlight, anytime I want to be alert.

Dr. David Berson 34:32 Right.

Andrew Huberman 34:32 And doing exactly the opposite when I want to be asleep-

Dr. David Berson 34:36 Yeah.

Andrew Huberman 34:36 ... or getting drowsy.

Dr. David Berson 34:37 And, and there are, there are aspects of this that, that spin out way beyond the conversation we're having now to things like this. It turns out that

Dr. David Berson 34:45 the incidence of myopia-

Andrew Huberman 34:47 Near-sightedness.

Dr. David Berson 34:48 Near-sightedness, right, is strongly related to the amount of time that kids spend outdoors.

Andrew Huberman 34:55 H- in, in what direction of effect?

Dr. David Berson 34:57 The more they spend time outdoors, the less sh- near-sightedness they have. So this is all about-

Andrew Huberman 35:02 And, and is that because they're viewing things at a distance or because they're getting a lot of blue light?

Dr. David Berson 35:06 This-

Andrew Huberman 35:06 Uh, sunlight.

Dr. David Berson 35:07 ... it's a great question. It is not fully resolved what the epidemiological, what the basis of that epidemiological finding is. One possibility is the amount of light, which would make me think about this melanopsin system again, but it might very well be a question of accommodation. That is the process by which you focus on near or far things. If you're never outdoors, everything is nearby. If you're outdoors, you're focusing far. So this is-

Andrew Huberman 35:30 Unless you're on your phone.

Dr. David Berson 35:31 Right, exactly.

Andrew Huberman 35:32 Which there's a, a tremendous amount of interest these days in, you know, watches and things that count steps. I'm beginning to realize that we should probably have a device that can count photons during the day.

Dr. David Berson 35:45 Right.

Andrew Huberman 35:45 And can also count photons at night. And tell us, "Hey, you're getting too many photons. You're going to shut down your melatonin at night." Or, "You're not getting enough photons today. You didn't get enough bright light," whether or not it's from artificial light or from sunlight. The, I guess the... Where would you put it? I guess you'd put on top of your head or s- you'd probably want it someplace outward facing.

Dr. David Berson 36:02 Right. It, probably what you need is as many photons over as much of the retina as possible to recruit as much of this system, you know, as possible.

Andrew Huberman 36:11 In thinking about other effects of this non-image forming pathway, uh, that involves these special cells in the eye and the SCN, you

Andrew Huberman 36:20 had a paper a few years ago looking at retinal input to an area of the brain, uh, which has a fancy name, the perihabenula, but names don't necessarily matter, that had some important effects on mood and other aspects of, of light. What, maybe you could tell us a little bit about what is the perihabenula?

Dr. David Berson 36:42 Oh, wow. So, I mean, that's a fancy term, but I think the way to think about this is there's a chunk of the brain that is sitting as part of a bigger chunk that's really the linker between peripheral sensory input of all kinds, virtually all kinds-... uh, whether it's auditory input or tactile input, um, or visual input to the region of your brain, the cortex, that allows you to think about these things and make plans around them and to integrate them and that, that kind of thing. Uh, so, um, you know, we've known about a pathway that gets from the retina through this sort of linker center, it's called the thalamus, and then on up to the cortex.

Andrew Huberman 37:30 It's like a train station.

Dr. David Berson 37:31 Exactly. But you want to arrive at the destination, right? Now you're at Grand Central and now you can do your, your thing 'cause you're up at the cortex. So this is th- the standard pattern. You have sensory input coming from the periphery, you've got these peripheral elements that are, are doing the initial stages of-

Andrew Huberman 37:45 The, the eye, the ear, the nose...

Dr. David Berson 37:47 ... the eye, the, your skin of your fingertips, right? You know, the, the taste buds on your tongue. They're taking this raw information in and they're doing some pre-processing maybe or, you know, the early circuits are. But eventually most of these signals have to pass through the gateway to the cortex which is the thalamus. And we've known for years, for, for decades, many decades, what the major throughput pathway from the retina to the cortex is and where it ends up. It ends up in the visual cortex. You know, you pat the back of your head, that's where the, where the receiving center is for the main pathway from retina to cortex. But wait a minute, there's more. There's this little side pathway that goes through a different part of that linking thalamus center, the gateway to the cortex.

Andrew Huberman 38:32 It's like a local, it's like a local train...

Dr. David Berson 38:33 Yeah.

Andrew Huberman 38:34 ... from Grand Central to...

Dr. David Berson 38:35 But it's, it's, it's, it's in a weird part of the neighborhood, right? It's a, it's a completely different, it's, it's like a little trunk line that branches off and goes out into the hinterlands and it's going to the part of this linker center that's talking to a completely different part of cortex way up front, frontal lobe, which is much more involved in things like planning or, uh, self-image or...

Andrew Huberman 38:57 Self-image, literally how one thinks about themselves?

Dr. David Berson 38:59 Use oneself and do you feel good about yourself or, uh, you know, what's your plan for next Thursday? Um, you know, it's, it's a, it's a very high level center in the highest level of your nervous system and this is the region that is getting input from this pathway, which is mostly worked out in its function by Samer Hattar's lab. I know you had him on the podcast.

Andrew Huberman 39:23 Mm-hmm. We didn't talk about this pathway though.

Dr. David Berson 39:24 This pathway at all, right. So, uh, uh, Diego, uh, uh, Fernandez and, and Samer and the folks that work with them were able to show that this pathway doesn't just exist and get you to a weird place, but if you activate it at kind of the wrong time of day, animals can become depressed. And if you silence it under the right circumstances, then weird lighting cycles that would normally make them act sort of depressed no longer have that effect.

Andrew Huberman 39:57 Hmm. So it sounds to me like there's this pathway from eye to this unusual train route through the structure we call the thalamus, then up to the front of the brain that relates to things of self-perception, kind of higher level functions. I, I find that really interesting because most of what I think about when I think about these fancy, well, or these primitive rather, uh, neurons that don't pay attention to the shapes of things, but instead to brightness, I think of, well, it regulates melatonin-

Dr. David Berson 40:26 Right.

Andrew Huberman 40:26 ... circadian clock, mood, hunger, the really kind of, um, vegetative stuff, if you will.

Dr. David Berson 40:32 Right. Right.

Andrew Huberman 40:32 And this is interesting because I think a lot of people experience depression, not just people that live at th- you know, in Scandinavia in the middle of winter.

Dr. David Berson 40:42 Right.

Andrew Huberman 40:42 And we are very much divorced from our normal interactions with light. It also makes me realize that these intrinsically photosensitive cells that set the clock, et cetera, are involved in a lot of things. I mean, they seem to regulate a dozen or more different basic functions.

Dr. David Berson 41:01 Right.

Andrew Huberman 41:03 I want to ask you about a different aspect of the visual system now which is the one that relates to our sense of balance. So I, I love boats, but I hate being on them. I love the ocean from shore because I get incredibly seasick of just... It's awful. I think I'm going to get seasick if I think about it too much.

Dr. David Berson 41:21 (laughs)

Andrew Huberman 41:22 And once I went on a boat trip, I came back and I actually got s- I got m- motion sick or wasn't seasick 'cause I was up rafting. So there's a system that somehow gets messed up. They always tell us if you're feeling sick to look at the horizon, et cetera, et cetera.

Dr. David Berson 41:37 Right.

Andrew Huberman 41:37 So what is the link between our visual system and our balance system and why does it make us nauseous sometimes when the world is moving in a way that we're not accustomed to?

Dr. David Berson 41:47 Right.

Andrew Huberman 41:47 I realize this is a big question-

Dr. David Berson 41:48 It is.

Andrew Huberman 41:48 ... because it involves eye movement, et cetera.

Dr. David Berson 41:51 Right.

Andrew Huberman 41:51 But let's maybe just walk in at the simplest layers of vision, vestibular, so-called balance system, and then maybe we can piece the system together for people so that they can understand it. And then also we should give them some tools for adjusting their, uh, nausea when their, uh, when their vestibular system is out of whack.

Dr. David Berson 42:12 (laughs) Cool. So yeah, I mean, the thi- the first thing to think about is that the vestibular system is, uh, designed to allow you to see how you're, or detect, sense how you're moving in the world, through the world. Um, it's a funny one because it's about your movement in relationship to the world in a sense and yet it's sort of interoceptive in the sense that it is really in the end sensing the movement of your own body. So-

Andrew Huberman 42:46 Okay. So interoception we should probably delineate for people is when you're focusing on your internal state-

Dr. David Berson 42:50 Exactly.

Andrew Huberman 42:50 ... as opposed to something outside you.

Dr. David Berson 42:52 Right. So vision-

Andrew Huberman 42:52 But is it, is it a, it's a gravity sensing system?

Dr. David Berson 42:55 It's, well, it's partly a gravity sensing system in the, in the sense that gravity is a force that's acting on you as if you were m- moving through the world in the opposite direction.

Andrew Huberman 43:06 All right, now you got to explain that.

Dr. David Berson 43:08 (laughs)

Andrew Huberman 43:08 You got to explain that one to me.

Dr. David Berson 43:10 Okay, so basically the idea is that, um, if we leave gravity aside, we're just sitting in- in a- in a car, in the passenger seat and the driver hits the accelerator and you start moving forward, you sense that. If your eyes were closed, you'd sense it. If your ears were plugged and your eyes were closed, you'd still know it.

Andrew Huberman 43:31 Yeah, many people take off on the plane like this, they're dreading the flight, and they know when it's- the plane is taking off.

Dr. David Berson 43:36 Sure. That's your vestibular system talking, because anything that jostles you out of the current position you're in right now will be detected by the vestibular system, pretty much. Uh, so this is a complicated system, but it's basically in your inner, you know, ear, very close to where you're hearing.

Andrew Huberman 43:54 Why'd they put it there?

Dr. David Berson 43:56 Uh, there's-

Andrew Huberman 43:57 And I don't know who they is. (laughs)

Dr. David Berson 43:58 I don't really know. They're sort of derived. Derived from-

Andrew Huberman 44:00 I'm just kidding. There's a, to steal our friend Russ VanGelder's explanation, "We weren't consulted at the design phase," and no one-

Dr. David Berson 44:06 That's- that's a great line.

Andrew Huberman 44:07 Yeah.

Dr. David Berson 44:07 That's a great line.

Andrew Huberman 44:08 Yeah, um, but it's interesting it's in the ear, right?

Dr. David Berson 44:12 Yeah, it's, uh, yeah, it's deep in there and it's served by the same nerve actually that serves the hearing system. One way to think about it is both the hearing system and this vestibular self-motion sensing system are really detecting the signal in the same way. They're hairy cells and they're excited-

Andrew Huberman 44:32 Literally hairy cells?

Dr. David Berson 44:32 Yeah, sort of. They got little cilia sticking up off the surfaces, and depending on which way you bend those, the cells will either be inhibited or excited. They're not even neurons, but then they talk to neurons with a neuron-like process and off you go. Now you've got an auditory signal if you're sensing things bouncing around in your cochlea, which is-

Andrew Huberman 44:52 Sound waves.

Dr. David Berson 44:53 ... sympathetically the bouncing of your eardrum, which is unsympathetically the sound waves in the world, but in the case of the vestibular apparatus, evolution has built a system that detects the motion of, say, fluid going by those hairs, and if you put a- a sensor like that in a tube that's fluid filled, now you've got a sensor that will be activated when you rotate that tube around the axis that passes through the middle of it. Those who are just listening won't- won't be able to sort of visualize that.

Andrew Huberman 45:22 No, I think that makes sense. I- I always think of it as three hula hoops.

Dr. David Berson 45:25 Right, three hula hoops.

Andrew Huberman 45:26 One standing up, one lying down on the ground.

Dr. David Berson 45:28 Right, one the other direction.

Andrew Huberman 45:29 You know, and one the other way. Yeah.

Dr. David Berson 45:30 Three directions. Uh, you know, the people who fly will talk about roll, pitch, and yaw, that kind of thing. So three axes f- of encoding, just like in the cones of the retina-

Andrew Huberman 45:41 So it's the yes, the no-

Dr. David Berson 45:42 No.

Andrew Huberman 45:42 ... and then I always say it's, and then the puppy head tilt.

Dr. David Berson 45:44 Yeah, the puppy head tilt.

Andrew Huberman 45:45 Yeah.

Dr. David Berson 45:45 That's the- the other one. So the- the point is that your- your brain is eventually going to be able to unpack what these sensors are telling you about how you just rotated your head in very much the way that the three types of cones we were talking about before are reading the incoming photons in the wavelength domain differently, and if you compare and-

Andrew Huberman 46:07 Red, green, blue.

Dr. David Berson 46:07 Yeah, you can compare and contrast, you get red, green, blue. So it's same basic idea. If you have three sensors and you array them properly, now you can tell if you're rotating your head left or right, up or down. That's the sensory signal coming back into your brain confirming that you've just made a movement that you willed.

Andrew Huberman 46:26 But what about on the plane? Because when I'm on the plane, I'm completely stationary. The plane's moving-

Dr. David Berson 46:30 Right.

Andrew Huberman 46:31 ... but my head hasn't moved-

Dr. David Berson 46:32 Right.

Andrew Huberman 46:32 ... so I'm just moving forward. Gravity is constant.

Dr. David Berson 46:35 Exactly. So-

Andrew Huberman 46:36 How does- how do I know I'm accelerating?

Dr. David Berson 46:37 So- so what's happening now is your brain is sensing the motion and the- the brain is smart enough also to- to ask itself, "Did I will that movement or did that come from the outside?" So now in terms of sort of understanding what the- the vestibular signal means, it's got to be embedded in the context of what you tried to do or what el- your other sensory s- uh, systems are telling you about what's happening right now.

Andrew Huberman 47:02 I see. So, oh, that's very interesting. I, but it's not conscious, or at least if it's conscious, it's very, it, not conscious, it's- it's definitely very fast, right? The moment that plane starts moving, I know that I didn't get up out of-

Dr. David Berson 47:13 Right.

Andrew Huberman 47:14 ... my chair and run forward.

Dr. David Berson 47:15 Right.

Andrew Huberman 47:16 But I'm not really thinking about getting up out of my chair.

Dr. David Berson 47:18 I guess-

Andrew Huberman 47:18 I just know.

Dr. David Berson 47:19 ... I guess the way I think about it is that the nervous system is, quote, aware at many levels. When it gets all the way up to the cortex and we're thinking about it, you're talking about it, you know, that's cortical, but the- the lower levels of the brain that don't require you to actually actively think about it, they're just doing their thing, are also made aware, right? A lot of this is happening under the surface of what you're thinking. These are reflexes.

Andrew Huberman 47:48 Okay. So we've got this gravity sensing system-

Dr. David Berson 47:52 Right.

Andrew Huberman 47:53 ... um, for, I'm nodding for those that are listening, for a yes mo- movement of the head, a no movement of the head, or the tilting of the head from side to side.

Dr. David Berson 48:02 Right.

Andrew Huberman 48:03 And then you said that knowledge about whether or not activation of that system comes from my own movements or something acting upon me, like the plane moving-

Dr. David Berson 48:12 Right.

Andrew Huberman 48:12 ... has to be combined with other signals.

Dr. David Berson 48:15 Right.

Andrew Huberman 48:15 And so how is the visual information or information about the visual world combined with balance information?

Dr. David Berson 48:22 Right. So, yeah, I mean, I guess maybe the best way to think about how these two systems work together is to think about what happens when you suddenly rotate your head to the left. When you suddenly rotate your head to the left, your eyes are actually rotating to the right automatically. You- you do this in complete darkness. If you had an eye, in- infrared camera and watched yourself in complete darkness, you can't see anything, you're rotating your head to the left, your eyes would rotate to the right. That's your vestibular system saying, "It's, I'm going to try to compensate for the head rotation so my eyes are still looking in the same place." Why is that useful? Well, if it's always doing that, then the image of the world on your retina will be pretty stable most of the time and that actually helps vision-

Andrew Huberman 49:14 Have they built this into cameras for, uh, image stabilization? 'Cause when I move when I take a picture with my phone, it's blurry. It's not s- it's not clear.

Dr. David Berson 49:22 Well, actually, you know, you might want to get a better phone, because now what they have is software in the better apps that will do a kind of image stabilization post hoc, by doing a registration of the images that are bouncing around.

Andrew Huberman 49:35 I see.

Dr. David Berson 49:35 They say this, the edge of the house was here.

Andrew Huberman 49:37 Mm-hmm.

Dr. David Berson 49:38 So let's get that aligned in each of your images. So you may not be aware, if you're using a good new phone, that if you walk around a, a landscape and hold your phone, that, you know, there's all this image stabilization going on. But it's built into standard cinematic, you know, technology now, because if you tried to do a handheld camera, things would be b- bouncing around, things would be unwatchable. You wouldn't be able to really understand what's going on in the scene. So the, the brain works really hard to mostly stabilize the image of the world on your retina. Now, of course, you're moving through the world, so you can't stabilize everything, but the more you can stabilize most of the time, the better you can see, and that's why, when we're scanning a scene, looking around at things, we're making very rapid eye movements for very short periods of time, and then we just rest. But we're not the only ones that do that. If you ever watch a hummingbird, it does exactly the same thing at a feeder, right?

Andrew Huberman 50:35 Jolting.

Dr. David Berson 50:35 But it's with its body.

Andrew Huberman 50:36 Jolting around.

Dr. David Berson 50:37 It's going to make a quick movement, and then it's going to be stable. And when you watch a pigeon walking on

Dr. David Berson 50:43 the sidewalk, it does this funny head bobbing thing, but what it's really doing is racking its head back on its neck while its body goes forward so that the image of the visual world stays static.

Andrew Huberman 50:54 Is that why they're doing that? Really?

Dr. David Berson 50:56 Yes. And you- you've seen the funny chicken videos on YouTube, right?

Andrew Huberman 50:59 Right.

Dr. David Berson 50:59 You take a chicken, move it up and down-

Andrew Huberman 51:01 Yeah, the head stays.

Dr. David Berson 51:01 ... and the head stays in one place. It's all the same thing. All of these animals are trying hard to keep the image of the world stable on their retina as much of the time as they possibly can, and then when they've got to move, make it fast, make it quick, and then s- stabilize again.

Andrew Huberman 51:15 That's why the pigeons have their head back?

Dr. David Berson 51:16 It is, yeah.

Andrew Huberman 51:18 Wow.

Dr. David Berson 51:19 Yeah. I mean, if you-

Andrew Huberman 51:20 I think I just need to pause there for a second-

Dr. David Berson 51:22 (laughs)

Andrew Huberman 51:22 ... and digest that. Amazing. Um, in case people aren't, um ... Well, there's no reason why people would know what we're doing here, but essentially what we're doing is we're building up from sensory, you know, light onto the eye, m- color, to what the brain does with that, the, the integration of that, you know, circadian clock, melatonin, et cetera. And now what we're doing is we're talking about multi-sensory or multimodal, combining one sense, vision, with another sense, balance.

Dr. David Berson 51:50 Right.

Andrew Huberman 51:50 And it turns out that pigeons know more about this than I do, because pigeons know to keep their head back as they walk forward.

Dr. David Berson 51:57 Right.

Andrew Huberman 51:58 All right, so that gets us to this issue of motion sickness.

Dr. David Berson 52:02 Right.

Andrew Huberman 52:02 And if it ... You don't have to go out on a boat. Anytime I go to New York, I sit in an Uber or in a cab in the back, and if I'm looking at my phone while the car is driving, I feel nauseous by the time I arrive at my destination.

Dr. David Berson 52:16 Right.

Andrew Huberman 52:17 I always try and look out the front of the windshield, because I'm told that helps, but it's a little tiny window.

Dr. David Berson 52:22 Right.

Andrew Huberman 52:22 And I end up feeling slightly less sick if I do that. So what's going on with the vision and the balance system that causes a kind of a nausea? And actually, if I keep talking about this-

Dr. David Berson 52:36 (laughs) Yeah.

Andrew Huberman 52:36 ... I'll probably will get sick. I don't throw up easily, but, um, but for some reason, motion sickness is a, is a real thing for me.

Dr. David Berson 52:42 It's a problem for a lot of people. I, I mean, I think the, the fundamental problem typically when you get motion sick is what they call visual vestibular conflict. That is, you have two sensory systems that are talking to your brain about how you're moving through the world, and as long as they agree, you're fine. So if you're driving, you know, your body senses that you're moving forward, your vestibular systems, you know, is, is picking up this acceleration of the car, and your visual system is seeing the consequences of forward motion in the sweeping of the scene past you. Everything is hunky-dory, right? No problem. But when you are headed forward, but you're looking at your cellphone, what is your retina seeing? Your retina is seeing the stable image of the screen. There's absolutely no motion in that screen.

Andrew Huberman 53:33 Or the motion is dis- or some other motion-

Dr. David Berson 53:35 Or some oth-

Andrew Huberman 53:35 ... like a movie or, yeah.

Dr. David Berson 53:36 You're watching, if you're playing a game or you're watching a video, a football game, you know, the motion is uncoupled with what's actually happening to your body. Your brain doesn't like that. Your brain likes everything to be, you know, aligned, and if it's not, it's going to complain to you. So-

Andrew Huberman 53:50 By making me feel nauseous?

Dr. David Berson 53:51 ... by making you feel nauseous, and maybe you'll change your behavior, so you're getting-

Andrew Huberman 53:54 I'm getting punished.

Dr. David Berson 53:55 Yeah, for, for, for, for setting it up so your-

Andrew Huberman 53:58 For looking at my phone.

Dr. David Berson 53:58 ... signals are in conflict. Right.

Andrew Huberman 53:59 By the vestibular-

Dr. David Berson 54:01 You'll learn.

Andrew Huberman 54:01 ... visuals. (laughs)

Dr. David Berson 54:02 (laughs)

Andrew Huberman 54:04 In time. I love it. Um, I love the idea of, of reward signals, and we've done a lot of, uh, discussion about this on this podcast of things like dopamine reward and things, but also punishment signals, and, um, I, I love this example. Uh, well, maybe marching a little bit further along this pathway, um, visual input is combined with balance input. Where does that occur? And maybe, 'cause I have some hint of where it occurs-

Dr. David Berson 54:32 Right.

Andrew Huberman 54:32 ... uh, you could tell us a little bit about this, uh, kind of mysterious little mini brain, um, that they call the cerebellum.

Dr. David Berson 54:39 Cerebellum. Yeah. So, you know, the way I try to describe the cerebellum to my students is that it serves sort of like the air traffic control system functions in air travel, so that it's a system that's very complicated, and it's really dependent on great information. So it's taking in information about everything that's happening everywhere, not only through your sensory systems, but it's listening in to all the little centers elsewhere in your brain that are computing what you're going to be doing next and so forth. So it's just ravenous for that kind of information.

Andrew Huberman 55:15 So it really is like a little mini brain.

Dr. David Berson 55:17 It is.

Andrew Huberman 55:18 Okay.

Dr. David Berson 55:18 It's, it's, it's got access to all those signals.... um, and it really has an important role in con- in, in coordinating and shaping movements. But, y- you know, if you suddenly eliminated the air traffic control system, planes could still take off and land but you might have some unhappy accidents in the, in the process. So, the cerebellum is kind of like that. It's not that you would be paralyzed if your ce- cerebellum was gone because you'd still have motor neurons, you'd still have ways to talk to your muscles, um, you'd still have reflex centers. And it's not like you would have any sensory loss because you'd still have your cortex getting all of those beautiful signals that you can think about, but you wouldn't be coordinating things so well anymore. The timing between input and output might be off. Or if you were trying to practice a new athletic move like an overhead serve in tennis, you'd be just terrible at learning the- the, all of the sequences of muscle movements and the feedback from your sensory a- apparatus that would let you really hit that ball exactly where you wanted to after the nth rep, right? You know, the thousandth rep or something, you get much better at it. So, the cerebellum's all involved in things like motor learning and refining the precisions of, of movements so that they get you where you want to go. If you reach for a glass of champagne, that you don't knock it over or stop short. Um, you know, that's what it's good at.

Andrew Huberman 56:54 Are there people who have selective damage to the cerebellum?

Dr. David Berson 56:57 Absolutely.

Andrew Huberman 56:58 And, and what, uh, I, I'm familiar with, um ... Well, Korsakoff's is, is different, right? Isn't that a B vitamin deficiency from, in chronic alcoholics?

Dr. David Berson 57:07 Right.

Andrew Huberman 57:07 And they have a, they tend to walk kind of bow-legged and they can't coordinate their movements. Is that ... Uh, that has some ... That mem- memory bodies but also cerebellum?

Dr. David Berson 57:16 I'm not sure about the cerebellar involvement there, but, you know, the, the typical thing would be, um, a patient who has a cerebellar stroke or a tumor, for example, um, might be, um, not that steady on their feet. You know, if, if the, uh, you know, dynamics of the situation, you're standing on a s- on a street car with your, with no h- no pole to hold onto, they might not be as good at adjusting all of the little movements of the car. Um, you know, there's a kind of tremor that can occur as they're reaching for things, um, because th- they reach a little too far and then they cr- over-correct and come back, uh, things like that. So, it's, it's, um, very common neurological, uh, phenomenon actually. Uh, cerebellar ataxia is what the neurologists call it, and it can happen not just with cerebellar damage but damage to the tracts that feed the information into the cerebellum or-

Andrew Huberman 58:12 Right, they just deprive the structure.

Dr. David Berson 58:13 Exactly. Or output from the cerebellum.

Andrew Huberman 58:15 And so the cerebellum is where a lot of visual and, and balance information is combined?

Dr. David Berson 58:19 And a very key place in the cerebellum, which is, uh, it's really one of the oldest parts in terms of evolution.

Andrew Huberman 58:27 Talking about the flocculus?

Dr. David Berson 58:28 The flocculus, right. This is a, it's a critical place in the cerebellum where visual and vestibular information comes together for recording just the kinds of movements we were talking about, this image stabilizing network. It's all happening there, and there's learning happening there as well, so that if your vestibular apparatus is a little bit damaged somehow, your visual system is actually talking to your cerebellum saying, "There's a problem here. There's an error," and your cerebellum is learning to do better by increasing the output of the vestibular system to compensate for whatever that loss was. So, it's a little error correction system that's sort of typical of cerebellar function and it can happen in many, many different domains. This is just one of the domains of sensory motor integration that, uh, takes place there.

Andrew Huberman 59:16 So, I should stay off my phone in the Ubers. If I'm on a boat, I should essentially look and, as much as possible, act as if I'm driving the, the machine.

Dr. David Berson 59:25 Right.

Andrew Huberman 59:26 Um, that'd be weird if I was in the passenger seat pretending I was driving the machine, but I do always feel better if I'm sitting in the front seat passenger side.

Dr. David Berson 59:32 Right, right. The more of the vi- of the visual world that you can see as if you were actually the one doing the mo- motion, I would think.

Andrew Huberman 59:39 Let's stay in the inner ear for a minute as we continue to march around the nervous system. When you take off in the plane or when you land or sometimes in the middle of air, your ears get clogged, or at least my ears get clogged. That's because of pressure build up in the various tubes of the inner ear, et cetera. We'll get into this. But years ago, our good,

Andrew Huberman 1:00:03 our good friend Harvey Karten, who's a, another world-class neuroanatomist, gave a lecture and, uh, talked about how plugging your nose and blowing out versus plugging your nose and sucking in can, should be done at different times depending on whether or not you're taking off or landing, and I always see people trying to un-pop their ears.

Dr. David Berson 1:00:26 Right.

Andrew Huberman 1:00:27 And when you do scuba diving, you learn how to do this without necessarily, I can do it, uh, by just kind of moving my jaw now 'cause I've done a, a little bit of diving, but what's the story there? Um, we don't have to get into all the differences in atmospheric pressure, et cetera, but if I'm taking off and my ears are plugged-

Dr. David Berson 1:00:44 Yeah.

Andrew Huberman 1:00:44 ... or I've recently ascended, plane took off, my ears are plugged, do I plug my nose and blow out or do I plug my nose and suck in?

Dr. David Berson 1:00:50 Right, so the basic idea is that if your ears feel bad because you're going into an area of higher pressure, so if they pressurize the cabin more than the pressure that you have on the surface of the planet, your eardrums will be bending in and they don't like that.

Andrew Huberman 1:01:07 Right.

Dr. David Berson 1:01:07 If you push them more, they'll hurt even more.

Andrew Huberman 1:01:08 That's a good description that they, you know, that pressure goes up, then they're going to bend in. Yep.

Dr. David Berson 1:01:12 Outside. Bend in. And the reverse would be true if you go into an area of low pressure. So, if, you know, you started to drive up the mountainside, you know, the pressure's getting lower and lower outside. Now, the inside, the air behind your eardrum is ballooning out.

Andrew Huberman 1:01:26 Yep.

Dr. David Berson 1:01:26 Right? So, it's just a question of, you know, are you trying to get more pressure or less pressure behind the eardrum? And there's a little tube that does that and comes down into your, you know, back of your throat there, and if you force pressure up that tube, you're going to be putting more air pressure into the compartment-

Andrew Huberman 1:01:41 ... to counter it.

Dr. David Berson 1:01:42 ... to, to, if, if it's, if it's not enough, and if you're sucking, you're going the other way. In reality, I think as long as you open the passageway, I think the diff- pressure differential is gonna solve your problem, so I think you could actually blow i- in when you're not, quote, "supposed to." Okay, so- I don't know.

Andrew Huberman 1:01:56 ... you could-

Dr. David Berson 1:01:58 Just breathe.

Andrew Huberman 1:01:58 ... hold your nose and blow air out, or hold your nose and suck in the-

Dr. David Berson 1:02:03 Right.

Andrew Huberman 1:02:03 ... effect? Either way is fine.

Dr. David Berson 1:02:05 I think so. I mean-

Andrew Huberman 1:02:05 Excellent. You just, I just won $100 from Harvey Karten.

Dr. David Berson 1:02:09 (laughs)

Andrew Huberman 1:02:09 Thank you very much. This is a lot. We, Harvey and I used to teach neuroanatomy together. And I'll say, I don't think it matters, but thank you ver- I'll, I'll split, I'll split that with you.

Dr. David Berson 1:02:16 Okay. (laughs)

Andrew Huberman 1:02:17 Um, this is, uh, this is important stuff. (laughs) Um, but, but it's true, you hear this, you know? So, so it doesn't matter either way.

Dr. David Berson 1:02:25 I-

Andrew Huberman 1:02:25 Okay?

Dr. David Berson 1:02:25 ... I'm no expert in this area. Don't-

Andrew Huberman 1:02:27 Don't worry.

Dr. David Berson 1:02:27 ... don't quote me. (laughs)

Andrew Huberman 1:02:27 ... he's, he's not gonna. Well, I'm going to quote you, but ... Okay, so we- we've talked about the inner ear and we've talked about the cerebellum. I want to talk about an

Andrew Huberman 1:02:35 area of the brain that is rarely discussed, which is the midbrain.

Dr. David Berson 1:02:39 Yeah.

Andrew Huberman 1:02:40 And for those that don't know, the midbrain is an area beneath the cortex. I guess we never really defined cortex. It was kind of the outer layers, or is, are the outer layers of the at least mammalian brain or human brain, uh, but the midbrain is super interesting, because it controls a lot of unconscious stuff, reflexes, et cetera. And then there's this phenomenon even called blindsight. So, could you please tell us about the midbrain, about what it does? And what in the world is blindsight? (laughs)

Dr. David Berson 1:03:15 Yeah, so this is a, there- there's a lot of pieces there. Um, I think the first thing to say is if you imagine the nervous system in your mind's eye, you see this big honking brain, and then there's this little s- thin, little, uh, wand that dangles down into your vertebral column, the spinal cord, and that's kind of your visual impression. Um, what you have to imagine is starting in the spinal cord and working your way up into this big, magnificent brain, and what you would do as you enter the skull is get into a little place where the spinal cord kind of thickens out. It still has that sort of long, skinny trunk-like feeling.

Andrew Huberman 1:03:54 Sort of like a paddle or a spoon shape.

Dr. David Berson 1:03:56 Right, it starts to spread out a little bit, and that's 'cause your, you know, evolution has packed more interesting goodies in there for processing information and, and generating movement. So beyond that is this tween brain we were talking about-

Andrew Huberman 1:04:10 Tween?

Dr. David Berson 1:04:11 ... this link, this linker brain, with, diencephalon really means the, the between brain.

Andrew Huberman 1:04:14 Oh, I thought you said tween.

Dr. David Berson 1:04:16 Well, it is, yes, apostrophe-

Andrew Huberman 1:04:16 No, no, between.

Dr. David Berson 1:04:17 Between, yeah.

Andrew Huberman 1:04:18 I'm sorry, I said, said tween, T-

Dr. David Berson 1:04:19 Yeah, it's the between.

Andrew Huberman 1:04:20 Yeah, yeah, the, the between brain.

Dr. David Berson 1:04:22 It's the between brain is, is what the, the name means. It's the linker from the spinal cord and the periphery up to these grand centers of the cortex. But this midbrain you're talking about is the last bit of this enlarged sort of spinal cordy thing in your skull, which is really the brain stem is what we call it. The last bit of that before you get to this relay up to the cortex is the midbrain, and there's a really important visual center there. It's called the superior colliculus. Uh, there's a similar center in the brains of other vertebrate animals, a frog, for example, or a lizard would have this. It's called the optic tectum there. But it's, um, a center then in these n- non-mammalian, uh, vertebrates is really the main visual center. Uh, they don't really have what we would call a visual cortex, although there's something sort of like that. But this is where most of the action is in terms of interpreting visual input and, uh, organizing behavior around that. You can sort of think about the, this region of the brain stem as a reflex center that can reorient the animal's, uh, gaze, or body, or maybe even attention to particular regions of space out there around the animal, and that could be all, for all kinds of reasons. I mean, it might be a predator just showed up in one corner of the forest and you pick that up and you're trying to avoid it. Or just-

Andrew Huberman 1:05:50 Any movement.

Dr. David Berson 1:05:51 ... might be m- Any movement, right? It might be, you know, that suddenly, uh, y- you know, something splats on the page when you're reading a novel and, and your eye reflexively looks at it. You don't have to think about that. That's a reflex.

Andrew Huberman 1:06:04 What if you throw me a ball, but I'm not expecting it?

Dr. David Berson 1:06:07 Right.

Andrew Huberman 1:06:07 And I just reach up and, and try and grab it?

Dr. David Berson 1:06:09 Right.

Andrew Huberman 1:06:09 Catch it or not.

Dr. David Berson 1:06:10 Right.

Andrew Huberman 1:06:10 Is that handled by the midbrain?

Dr. David Berson 1:06:12 Well, that's probably not the midbrain, although it, I mean, by itself, because it's going to involve all these limb movements, this movement of your arm and body, uh, and-

Andrew Huberman 1:06:23 What about ducking-

Dr. David Berson 1:06:23 ... and sp- And probably-

Andrew Huberman 1:06:24 ... if something's suddenly thrown at my head?

Dr. David Berson 1:06:25 Yeah. Sure, right, things like that are, will certainly have a brain stem component, a midbrain component. You know, something looms and you duck. Um, it may not be the superior colliculus we're talking about now. It might be another part of the visual midbrain. But these are centers that e- emerged early in the evolution of brains like ours to handle complicated visual events that have significance for the animal in terms of space. Where is it in space? And in fact, this same center actually gets input from all kinds of other sensory systems that take information from the external world, from particular locations, and where you might want to either avoid or approach things according to their significance to you. So, you get input from the touch system. You get input from the auditory system. I worked for a while in rattlesnakes. They get input from a part of their, um, warm sensors on their face. They're in these little pits on the, on the face.

Andrew Huberman 1:07:20 You used to work on baby rattlesnakes, right?

Dr. David Berson 1:07:22 Well, they were, they were adults actually.

Andrew Huberman 1:07:23 Oh, I wasn't trying to diminish the danger.

Dr. David Berson 1:07:25 No, they-

Andrew Huberman 1:07:25 I thought for some reason they were little ones.

Dr. David Berson 1:07:27 No.

Andrew Huberman 1:07:27 Why in the world would you work on rattlesnakes?

Dr. David Berson 1:07:30 Well, because they have a version of an exteroceptive sensory system, that is they're looking out into the world using a completely different set of sensors. They're using the same sensors that would feel the warmth on your face if you stood in front of a bonfire, except-... evolution has given them this very nice specialized system that lets them image where the heat's coming from. You can sort of do that anyway, right? If you-

Andrew Huberman 1:07:54 Mm-hmm.

Dr. David Berson 1:07:54 ... walk around the fire, you can feel which, where the fire is from the, the, you know, the heat hitting your face. They've just-

Andrew Huberman 1:08:00 Is that the primary, uh, way in which they detect prey?

Dr. David Berson 1:08:04 It's one of, one of the major ways. And in fact, they use vision as well, and they bring these two systems together in the same place, in this tectum region, this brain stem midbrain region.

Andrew Huberman 1:08:15 So what's all the tongue jutting about when the snakes...

Dr. David Berson 1:08:17 That I don't know. That may be olfactory. There may be actually-

Andrew Huberman 1:08:20 They're sniffing the air with their tongue?

Dr. David Berson 1:08:22 ... they may be, yeah, there may be, uh, gustatory-

Andrew Huberman 1:08:23 Earlier in our drive, you told me that flies actually taste things with their feet.

Dr. David Berson 1:08:27 They do, yeah. Yeah.

Andrew Huberman 1:08:28 That's so weird.

Dr. David Berson 1:08:29 Yeah, they have, they have taste receptors in lots of funny places.

Andrew Huberman 1:08:33 I, uh, I want to pause here just for one second before we get back into the midbrain. I think what's so interesting, in all seriousness, about taste receptors on feet, heat sensors, tongues jutting out of snakes, and vision and all this integration, is that it really speaks to the fact that all these sensory neurons are trying to gather information-

Dr. David Berson 1:08:57 Right.

Andrew Huberman 1:08:57 ... and stuff it into a system-

Dr. David Berson 1:08:59 Right.

Andrew Huberman 1:08:59 ... that can make meaningful decisions and actions. And that it really doesn't matter whether or not it's coming from eyes, or ears, or nose, or bottoms of feet, because in the end, it's just electricity flowing in.

Dr. David Berson 1:09:11 Sure.

Andrew Huberman 1:09:11 And so it's b- it sounds like it's placed on each animal, this always feels weird to call a fly an animal, but they are-

Dr. David Berson 1:09:18 They are.

Andrew Huberman 1:09:18 ... creatures, uh, they are animals. Uh, it's placed in different locations on different animals depending on the particular needs of that animal.

Dr. David Berson 1:09:26 Right. But how much more powerful if the nervous systems can also cross-correlate across sensory systems? So if you've got a weak signal from one sensory system, you're not quite sure there's something there, and a weak signal from an- another sensory system that's telling you the same locations is, is a little bit interesting, there might be something there, if you've got those two together, you've got corroboration. Your brain now says, "It's much more likely that that's going to, you know, be something worth paying attention to."

Andrew Huberman 1:09:56 Right, so maybe I, I'm feeling some heat on one side of my face, um, and I also smell something baking in the oven.

Dr. David Berson 1:10:05 Right.

Andrew Huberman 1:10:05 So now there's, it's neither is particularly strong, but as you said, there's some corroboration.

Dr. David Berson 1:10:10 Right.

Andrew Huberman 1:10:10 And that corroboration is occurring in the midbrain.

Dr. David Berson 1:10:12 Right. And then if you throw things into conflict, now the brain is confused and that may be where your, your motion sickness comes from. So i- i- it's great to have, you know, as a, as a brain, it's great to have as many sources of information as you can have, just like if you're a, you know, you're, you're a spy or a journalist, you want as much information as you can get about what's out there. But if things conflict, that's problematic, right? Your sources are giving you different information about what's, what's going on, now you've got a problem on your hands. What do you publish?

Andrew Huberman 1:10:42 The midbrain is so fascinating. I, I

Andrew Huberman 1:10:44 don't want to eject us from the midbrain and go back to the vestibular system, but I do have a question that I forgot to ask about the vestibular system which is, why is it that for many people, including me, there's, despite my motion sickness in cabs, that there's a sense of pleasure in moving through space and getting tilted relative to the gravitational pull of the earth? For me growing up, it was skateboarding, but people like to corner in cars, corner on bikes, um, it may be for some people it's done running or dance, but, you know, what is it about moving through space and getting tilted, a lot of surfers around here, getting tilted that can tap into some of the pleasure centers? So is it, do we have any idea why that would feel good?

Dr. David Berson 1:11:27 I have no clue.

Andrew Huberman 1:11:28 Is there dopaminergic input to this sy- system?

Dr. David Berson 1:11:31 Well, you know, the dopaminergic system gets a lot of places, you know? Uh, it's pretty much, to some extent, everywhere in the cortex, a lot more in the frontal lobe of course. But, you know, that's just for starters. I mean, there's basically dopaminergic innovation most places in the central nervous system, so there's the potential for dopaminergic involvement, but I really have no clue about the tilting phenomenon. I mean-

Andrew Huberman 1:11:55 People pay money to go on roller coasters.

Dr. David Berson 1:11:58 Right. Well, I think that may be as much about the thrill as anything else.

Andrew Huberman 1:12:01 Sure. And falling is, uh, the falling reflex is very robust in all of us.

Dr. David Berson 1:12:05 Right.

Andrew Huberman 1:12:05 When the visual world's going up very fast-

Dr. David Berson 1:12:07 Right.

Andrew Huberman 1:12:07 ... it usually means that we're falling.

Dr. David Berson 1:12:08 Right. Right.

Andrew Huberman 1:12:08 But, and some people are like that, some people don't.

Dr. David Berson 1:12:10 Right. And kids, kids tolerate a lot more, you know, sort of vestibular craziness, spinning around until they f- drop than adults will.

Andrew Huberman 1:12:18 Well, I've seen, I have friends that always, you know, it worries me a little bit that will, th- they throw their kids, I'm not recommending anyone do this, when they're little kids, you know, like throwing the kids really far back and forth. Um, kids, some kids seem to love it.

Dr. David Berson 1:12:30 Yeah. Yeah, our son loved being shaken up and down very, v- very, uh, vigorously. He, that was the only thing that would calm him down sometimes.

Andrew Huberman 1:12:39 Interesting. Yeah, so I'm guessing, we can, we can, uh, guess that maybe there's some activation of the reward systems from-

Dr. David Berson 1:12:48 Yeah.

Andrew Huberman 1:12:48 ... being move, moving through space.

Dr. David Berson 1:12:50 Well, I mean, if you think about it, you know, how rewarding it is to be able to move through space and how unhappy people are who are used to that who suddenly aren't able to do that, there is a, a sense of agency, right? If you g- you can choose to move through the world and to tilt, that's not only are you moving through the world, but you're doing it with a certain amount of finesse. Maybe that's what it is. You can feel like you're the master of your own movement-

Andrew Huberman 1:13:12 Mm-hmm.

Dr. David Berson 1:13:13 ... in a way that you wouldn't if you were going straight. I'm, I'm just blowing smoke here, right?

Andrew Huberman 1:13:17 Yeah. Well, we can speculate. That's fine. I, I couldn't help but ask the question. Okay, so if we, um, uh, move ourselves,

Andrew Huberman 1:13:24 um, pun intended, back into the midbrain, the midbrain's combining all these different signals for reflexive action. At what point does this become deliberate action? Because if I look at something I want and I want to pursue it, I'm going to go toward it, and many times that's a deliberate decision.

Dr. David Berson 1:13:42 Right. So this gets very slippery, I think, because what you have to try to imagine is all these different parts of the brain working on the problem of staying alive-... um, you know, and, and surviving in, in, in the world. Uh, they're working on the problem simultaneously, and there's not o- one right answer to h- how to do that. Um, but the, one way to think about it is that you have high levels of your nervous system that are very well designed to override an otherwise automatic movement if it's inappropriate. So, if you imagine you've been invited to tea with the queen and she hands you a, you know, very fancy Wedgwood, you know, teacup, very thin-

Andrew Huberman 1:14:29 Wedgwood teacup?

Dr. David Berson 1:14:30 Yes, with very hot tea in it and you're burning your hand, you probably will f- try to find a way to put that back down on the saucer rather than just dropping it on the floor, because you're with the queen. You, you know, you're trying to be appropriate to that. So, you have ways of reigning in automatic behaviors if they're going to be maladaptive, but you also want the reflex to work quickly if it's the only thing that's going to save you. The looming, you know, object coming at your head, you don't have time to think about that. So, this is the interplay in these hierarchically organized centers of the nervous system. At the lowest level, you've got the automatic sensors that, and centers and reflex, you know, uh, arcs that will keep you safe, even if you don't have time to think about it, and then you've got the higher center saying, "Well, maybe we could do this as well or maybe we shouldn't do that at all." Right? So, you have all of these different levels operating simultaneously and you need bidirectional communication between high level cognitive centers, decision-making on the one hand, and these low level, very helpful reflexive centers, but they're a little bit rigid.

Andrew Huberman 1:15:41 Mm-hmm.

Dr. David Berson 1:15:42 A little hardwired, so they need some nuance. So, there's, th- they're, both of these things are operating in tandem in real time all the time in our brains, and sometimes we listen more to one than the other. You've heard people in sports talking about messing up at the plate 'cause they overthought it, you know, thinking too hard about it. That's partly, you've already trained your cer- cerebellum how to hit a fastball right down the middle.

Andrew Huberman 1:16:05 Right, and if you start looking for, for something new or different-

Dr. David Berson 1:16:08 Right.

Andrew Huberman 1:16:08 ... you're going to mess up your-

Dr. David Berson 1:16:10 Right.

Andrew Huberman 1:16:10 ... your reflexive swing.

Dr. David Berson 1:16:11 Right, if you're trying to think about the physics of the ball as it's coming at you, you've already missed, right? You know, 'cause you, you're not using your, this, all those reps have built a kind of knowledge, this is what you want to rely on when you don't have enough time to, uh, contemplate.

Andrew Huberman 1:16:28 This is important and a great segue for what I'd like to discuss next, was it, which is the basal

Andrew Huberman 1:16:35 ganglia. This really interesting of the area of the brain that's involved in go type commands and behaviors, instructing us to do things, and no go, preventing us from doing things.

Dr. David Berson 1:16:47 Right.

Andrew Huberman 1:16:47 Because so much of motor learning and skill execution and, um, not saying the wrong thing or sitting still in class when, or as you used with the, you know, tea with the queen example, feeling discomfort involves suppressing behavior.

Dr. David Berson 1:17:03 Right.

Andrew Huberman 1:17:03 And sometimes it's activating behavior.

Dr. David Berson 1:17:05 Right.

Andrew Huberman 1:17:05 You know, a tremendous amount of online attention is devoted to, um, trying to get people motivated. You know, this isn't the main focus of our podcast. We touch on some of the underlying neural circuits of, of motivation, dopamine and so forth, but so much of what people struggle with out there are elements around failure to pay attention.

Dr. David Berson 1:17:26 Right.

Andrew Huberman 1:17:26 Or ch- challenges in paying attention, which is essentially like putting the blinders on nar-, you know, getting a soda straw view of the world and maintaining that for about a work or something of that sort, and trying to get into action. So, of course, this is carried out by many neural circuits, not just the basal ganglia, but what are the basal ganglia and what are their primary roles in controlling go type behavior and no go type behavior?

Dr. David Berson 1:17:52 Yeah, so I mean, the g- the basal ganglia are sitting deep in what you would call the forebrain. So, the highest levels of the brain, they are sort of cousins to the cerebral cortex, which we talked about as sort of the highest level of your brain that, the thing you're thinking with.

Andrew Huberman 1:18:09 Cerebral cortex being the refined cousins and then you've got the-

Dr. David Berson 1:18:12 Right.

Andrew Huberman 1:18:13 ... you know, the brutes that-

Dr. David Berson 1:18:14 Yeah.

Andrew Huberman 1:18:14 Yeah. All right.

Dr. David Berson 1:18:15 I mean, that's probably totally unfair, but the, the-

Andrew Huberman 1:18:18 It's all right.

Dr. David Berson 1:18:18 ... the point-

Andrew Huberman 1:18:18 I, I like the basal ganglia. I can relate to-

Dr. David Berson 1:18:20 (laughs)

Andrew Huberman 1:18:20 ... the brutish parts of the brain. A little bit of hypothalamus, a little bit of basal ganglia, sure.

Dr. David Berson 1:18:25 We need it all. We need it all. And, uh, y- you know, this area of the brain has gotten a lot bigger as the cortex has gotten bigger and it's deeply intertwined with cortical function. The cortex can't really do what it needs to do without the help of the basal ganglia and vice versa. So, they're really intertwined. Um, and in a way you can think about this logically as saying, you know, if, if you have the ability to withhold behavior or to execute it-

Andrew Huberman 1:18:57 Mm-hmm.

Dr. David Berson 1:18:57 ... how do you decide which to do? Well, the cortex is going to have to do that thinking for you. You have to be looking at all the contingencies of your situation to decide, is this a crazy move or is this a really smart investment right now