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

1. 0:00 – 2:55

   Dr. David Berson

   1. AHAndrew Huberman0:00

      (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.

2. 2:55 – 8:02

   Sponsors: Athletic Greens, InsideTracker, Magic Spoon

   1. AHAndrew Huberman2:55

      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. Nowadays, there's a lot of data out there pointing to the fact that a healthy gut microbiome, literally little microbes that live in our gut that are good for us, is important to support our immune system, our nervous system, our endocrine system, and various aspects of our immediate and long-term health. With Athletic Greens, I get all the vitamins and minerals that I need, plus the probiotics ensure a healthy gut microbiome. It also tastes really good. I mix mine up with some water, a little bit of lemon juice. I'll have that early in the day and sometimes a second time later in the day as well. It's compatible with intermittent fasting, it's compatible with vegan diets, with, uh, keto diets, and essentially every diet that you could possibly imagine out there. It's also filled with adaptogens for recovery, it has digestive enzymes for gut health, and it has a number of other things that support the immune system. If you'd like to try Athletic Greens, you can go to athleticgreens.com/huberman to claim their special offer. They'll give you five free travel packs that make it really easy to mix up Athletic Greens while you're on the road, and they'll give you a year supply of vitamin D3 K2. There's now a lot of evidence that vitamin D3 supports a huge number of metabolic factors, immune system factors, endocrine factors. Basically, we need vitamin D3. We can get it from the sun, but many people are deficient in vitamin D3 even if they are getting what they think is sufficient sunlight. And K2 is important for cardiovascular health. So again, if you go to athleticgreens.com/huberman, you can claim their special offer, the five free travel packs, plus the year supply of vitamin D3 K2. Today's podcast is also brought to us by InsideTracker. InsideTracker is a personalized nutrition platform that analyzes data from your blood and DNA to help you better understand your body and help you reach your health goals. I've long been a believer in getting regular blood work done for the simple reason that many of the factors that impact your immediate and long-term health can only be analyzed from a quality blood test. And now with the advent of modern DNA tests, you can also get information about how your specific genes are impacting your immediate and long-term health. Now, the problem with a lot of blood tests and DNA tests out there is you get the numbers back, but you don't know what to do with those numbers. With InsideTracker, they make it very simple to figure out what to do to bring those numbers into the ranges that are right for you. They have a dashboard that's very easy to use. You can see the numbers from your blood and or DNA tests, and it will point to specific lifestyle factors, nutritional factors, as well as supplementation, maybe even prescription factors that would be right for you to bring the numbers into range that are ideal for your immediate and long-term health goals. Another feature that InsideTracker has is their InnerAge test. This test shows you what your biological age is and compares that to your chronological age and what you can do to improve your biological age, which of course is the important number. If you'd like to try InsideTracker, you can visit insidetracker.com/huberman to get 25% off any of InsideTracker's plans. Also, an interview I did with longevity research doctor and InsideTracker's founder, Dr. Gil Blander, is out now on their podcast, the Longevity By Design Podcast, and a link to that interview can be found in today's show notes.Today's episode is also brought to us by Magic Spoon. 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. They have a number of different flavors like cocoa, fruity, peanut butter, and frosted. I particularly like frosted. It tastes like donuts, and I really like donuts, although I try not to eat donuts too often, if ever. What I do lately is I take Magic Spoon, I put it in some Bulgarian yogurt, which is really good, and I mix that up. I put those in there, and sometimes I put some cinnamon on them. And as I'm describing this, I'm getting hungry for Magic Spoon. So if you want to try Magic Spoon, you can go to magicspoon.com/huberman to get their variety pack. Just use the promo code Huberman at checkout to get $5 off your order. Again, that's magicspoon.com/huberman and use the code Huberman to get $5 off. And now

3. 8:02 – 10:02

   How We See

   1. AHAndrew Huberman8:02

      for my discussion with Dr. David Berson. Welcome.

   2. DBDr. David Berson8:06

      Thank you.

   3. AHAndrew Huberman8:06

      Yeah.

   4. DBDr. David Berson8:07

      So nice to be here.

   5. AHAndrew Huberman8:08

      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?

   6. DBDr. David Berson8:37

      Right.

   7. AHAndrew Huberman8:38

      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?

   8. DBDr. David Berson8:46

      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-

   9. AHAndrew Huberman9:03

      Mm-hmm.

   10. DBDr. David Berson9:04

       ... you're seeing things that aren't coming through your eyes.

   11. AHAndrew Huberman9:07

       Are those memories?

   12. DBDr. David Berson9:09

       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.

4. 10:02 – 13:47

   Color Vision

   1. DBDr. David Berson10:02

   2. AHAndrew Huberman10:02

      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?

   3. DBDr. David Berson10:13

      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-

   4. AHAndrew Huberman10:24

      When you say it's vibrating, it's oscillating, you mean that photons are actually moving?

   5. DBDr. David Berson10:28

      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.

   6. AHAndrew Huberman11:17

      So when, uh, a photon... So when a little bit of light hits my eye-

   7. DBDr. David Berson11:22

      Right.

   8. AHAndrew Huberman11:22

      ... goes in, the photoreceptors convert that into electrical signal.

   9. DBDr. David Berson11:26

      Right.

   10. AHAndrew Huberman11:27

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

   11. DBDr. David Berson11:35

       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.

   12. AHAndrew Huberman12:46

       Is it fair to assume that my perception of red is the same as your perception of red-

   13. DBDr. David Berson12:50

       Well, that's a great question.

   14. AHAndrew Huberman12:51

       ... and that mine is better?

   15. DBDr. David Berson12:52

       (laughs)

   16. AHAndrew Huberman12:52

       No, I'm just kid- I'm just kidding. (laughs)

   17. DBDr. David Berson12:55

       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.

   18. AHAndrew Huberman13:46

       You mentioned that there are five

5. 13:47 – 16:56

   “Strange” Vision

   1. AHAndrew Huberman13:47

      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.

   2. DBDr. David Berson14:05

      Right.

   3. AHAndrew Huberman14:05

      What are some of the more outrageous examples of that?

   4. DBDr. David Berson14:09

      Of seeing things that we can't?

   5. AHAndrew Huberman14:10

      Seeing things in, in, in the extreme.

   6. DBDr. David Berson14:12

      Right.

   7. AHAndrew Huberman14:12

      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.

   8. DBDr. David Berson14:22

      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.

   9. AHAndrew Huberman14:54

      I thought you were referring to, like, ultraviolet, and infrared, and, and things of that sort.

   10. DBDr. David Berson14:58

       Right, right.

   11. AHAndrew Huberman14:59

       Okay.

   12. DBDr. David Berson14:59

       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.

   13. AHAndrew Huberman15:40

       Do, uh, colorblind people suffer much as a consequence of being colorblind?

   14. DBDr. David Berson15:44

       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.

   15. AHAndrew Huberman16:26

       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-

   16. DBDr. David Berson16:33

       Right.

   17. AHAndrew Huberman16:33

       ... I'd certainly trade out color for clarity.

   18. DBDr. David Berson16:37

       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-

   19. AHAndrew Huberman16:48

       Yeah, because we take care of them. I spend most of my time-

   20. DBDr. David Berson16:50

       (laughs)

   21. AHAndrew Huberman16:50

       ... taking care of that dog. Uh, he took care of me too. Uh, let's talk about

6. 16:56 – 25:45

   How You Orient In Time

   1. AHAndrew Huberman16:56

      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-"

   2. DBDr. David Berson17:37

      (laughs)

   3. AHAndrew Huberman17:37

      "... in our eye."

   4. DBDr. David Berson17:38

      Yeah.

   5. AHAndrew Huberman17:38

      And you showed this slide of, like, a giant fly from a horror movie-

   6. DBDr. David Berson17:43

      Yeah.

   7. AHAndrew Huberman17:44

      ... uh, trying to attack this woman-

   8. DBDr. David Berson17:45

      Yeah.

   9. AHAndrew Huberman17:46

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

   10. DBDr. David Berson17:54

       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.

   11. AHAndrew Huberman18:39

       I like that. Never really thought of the photoreceptors as the film of the camera, but that makes sense.

   12. DBDr. David Berson18:42

       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.

   13. AHAndrew Huberman20:01

       So, and wh- what is the relationship to the fly eye?

   14. DBDr. David Berson20:05

       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.

   15. AHAndrew Huberman20:56

       I see.

   16. DBDr. David Berson20:56

       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.

   17. AHAndrew Huberman21:14

       So, it sounds like it's a very primitive part of, uh, primitive aspect of biology that we maintain.

   18. DBDr. David Berson21:20

       Exactly right. Exactly right.

   19. AHAndrew Huberman21:22

       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-

   20. DBDr. David Berson21:39

       Right.

   21. AHAndrew Huberman21:40

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

   22. DBDr. David Berson21:47

       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.

   23. AHAndrew Huberman22:02

       When you say brightness signal, you mean that it... Like right now, I have these cells. Do I have these cells?

   24. DBDr. David Berson22:06

       You do.

   25. AHAndrew Huberman22:06

       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.

   26. DBDr. David Berson22:16

       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.

   27. AHAndrew Huberman23:24

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

   28. DBDr. David Berson23:31

       Right.

   29. AHAndrew Huberman23:32

       So what, wh- wh- what are they doing on a day-to-day basis?

   30. DBDr. David Berson23:35

       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-
7. 25:45 – 34:45

   Body Rhythms, Pineal function, Light & Melatonin, Blueblockers

   1. AHAndrew Huberman25:45

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

   2. DBDr. David Berson25:53

      Right.

   3. AHAndrew Huberman25:54

      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-

   4. DBDr. David Berson26:12

      Right.

   5. AHAndrew Huberman26:12

      ... 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.

   6. DBDr. David Berson26:29

      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-

   7. AHAndrew Huberman26:37

      Yeah. We probably have, what, millions of clocks in our body.

   8. DBDr. David Berson26:40

      Yeah, I would say that's-

   9. AHAndrew Huberman26:40

      Yeah.

   10. DBDr. David Berson26:40

       ... 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-

   11. AHAndrew Huberman27:18

       The source of all our pleasures and all our problems.

   12. DBDr. David Berson27:20

       Right.

   13. AHAndrew Huberman27:21

       Or most our problems. (laughs)

   14. DBDr. David Berson27:22

       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.

   15. AHAndrew Huberman29:12

       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?

   16. DBDr. David Berson30:02

       Right. So there, there are pathways by which the suprachiasmatic nucleus can access both the parasympathetic and sympathetic nervous system.

   17. AHAndrew Huberman30:12

       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.

   18. DBDr. David Berson30:22

       Right.

   19. AHAndrew Huberman30:22

       In, in broad context.

   20. DBDr. David Berson30:23

       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.

   21. AHAndrew Huberman30:55

       The so-called third eye.

   22. DBDr. David Berson30:57

       Right.So this is the-

   23. AHAndrew Huberman30:58

       We'll have to get back to why it's called the third eye, because, yeah.

   24. DBDr. David Berson31:01

       That's an interesting history.

   25. AHAndrew Huberman31:02

       You can't call something the third eye and not, and just, you know.

   26. DBDr. David Berson31:05

       Just leave it there.

   27. AHAndrew Huberman31:05

       Just leave it there.

   28. DBDr. David Berson31:06

       Right.

   29. AHAndrew Huberman31:07

       Right.

   30. DBDr. David Berson31:08

       Anyway, this is the major source of melatonin in your body.
8. 34:45 – 36:20

   Spending Times Outdoors Improves Eyesight

   1. DBDr. David Berson34:45

      the incidence of myopia-

   2. AHAndrew Huberman34:47

      Near-sightedness.

   3. DBDr. David Berson34:48

      Near-sightedness, right, is strongly related to the amount of time that kids spend outdoors.

   4. AHAndrew Huberman34:55

      H- in, in what direction of effect?

   5. DBDr. David Berson34:57

      The more they spend time outdoors, the less sh- near-sightedness they have. So this is all about-

   6. AHAndrew Huberman35:02

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

   7. DBDr. David Berson35:06

      This-

   8. AHAndrew Huberman35:06

      Uh, sunlight.

   9. DBDr. David Berson35:07

      ... 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-

   10. AHAndrew Huberman35:30

       Unless you're on your phone.

   11. DBDr. David Berson35:31

       Right, exactly.

   12. AHAndrew Huberman35:32

       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.

   13. DBDr. David Berson35:45

       Right.

   14. AHAndrew Huberman35:45

       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.

   15. DBDr. David Berson36:02

       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.

   16. AHAndrew Huberman36:11

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

9. 36:20 – 41:03

   Sensation, Mood, & Self-Image

   1. AHAndrew Huberman36:20

      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?

   2. DBDr. David Berson36:42

      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.

   3. AHAndrew Huberman37:30

      It's like a train station.

   4. DBDr. David Berson37:31

      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-

   5. AHAndrew Huberman37:45

      The, the eye, the ear, the nose...

   6. DBDr. David Berson37:47

      ... 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.

   7. AHAndrew Huberman38:32

      It's like a local, it's like a local train...

   8. DBDr. David Berson38:33

      Yeah.

   9. AHAndrew Huberman38:34

      ... from Grand Central to...

   10. DBDr. David Berson38:35

       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...

   11. AHAndrew Huberman38:57

       Self-image, literally how one thinks about themselves?

   12. DBDr. David Berson38:59

       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.

   13. AHAndrew Huberman39:23

       Mm-hmm. We didn't talk about this pathway though.

   14. DBDr. David Berson39:24

       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.

   15. AHAndrew Huberman39:57

       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-

   16. DBDr. David Berson40:26

       Right.

   17. AHAndrew Huberman40:26

       ... circadian clock, mood, hunger, the really kind of, um, vegetative stuff, if you will.

   18. DBDr. David Berson40:32

       Right. Right.

   19. AHAndrew Huberman40:32

       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.

   20. DBDr. David Berson40:42

       Right.

   21. AHAndrew Huberman40:42

       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.

   22. DBDr. David Berson41:01

       Right.

10. 41:03 – 50:43

    Sense of Balance

    1. AHAndrew Huberman41:03

       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.

    2. DBDr. David Berson41:21

       (laughs)

    3. AHAndrew Huberman41:22

       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.

    4. DBDr. David Berson41:37

       Right.

    5. AHAndrew Huberman41:37

       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?

    6. DBDr. David Berson41:47

       Right.

    7. AHAndrew Huberman41:47

       I realize this is a big question-

    8. DBDr. David Berson41:48

       It is.

    9. AHAndrew Huberman41:48

       ... because it involves eye movement, et cetera.

    10. DBDr. David Berson41:51

        Right.

    11. AHAndrew Huberman41:51

        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.

    12. DBDr. David Berson42:12

        (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-

    13. AHAndrew Huberman42:46

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

    14. DBDr. David Berson42:50

        Exactly.

    15. AHAndrew Huberman42:50

        ... as opposed to something outside you.

    16. DBDr. David Berson42:52

        Right. So vision-

    17. AHAndrew Huberman42:52

        But is it, is it a, it's a gravity sensing system?

    18. DBDr. David Berson42:55

        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.

    19. AHAndrew Huberman43:06

        All right, now you got to explain that.

    20. DBDr. David Berson43:08

        (laughs)

    21. AHAndrew Huberman43:08

        You got to explain that one to me.

    22. DBDr. David Berson43:10

        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.

    23. AHAndrew Huberman43:31

        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.

    24. DBDr. David Berson43:36

        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.

    25. AHAndrew Huberman43:54

        Why'd they put it there?

    26. DBDr. David Berson43:56

        Uh, there's-

    27. AHAndrew Huberman43:57

        And I don't know who they is. (laughs)

    28. DBDr. David Berson43:58

        I don't really know. They're sort of derived. Derived from-

    29. AHAndrew Huberman44:00

        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-

    30. DBDr. David Berson44:06

        That's- that's a great line.
11. 50:43 – 1:00:03

    Why Pigeons Bob Their Heads, Motion Sickness

    1. DBDr. David Berson50:43

       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.

    2. AHAndrew Huberman50:54

       Is that why they're doing that? Really?

    3. DBDr. David Berson50:56

       Yes. And you- you've seen the funny chicken videos on YouTube, right?

    4. AHAndrew Huberman50:59

       Right.

    5. DBDr. David Berson50:59

       You take a chicken, move it up and down-

    6. AHAndrew Huberman51:01

       Yeah, the head stays.

    7. DBDr. David Berson51:01

       ... 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.

    8. AHAndrew Huberman51:15

       That's why the pigeons have their head back?

    9. DBDr. David Berson51:16

       It is, yeah.

    10. AHAndrew Huberman51:18

        Wow.

    11. DBDr. David Berson51:19

        Yeah. I mean, if you-

    12. AHAndrew Huberman51:20

        I think I just need to pause there for a second-

    13. DBDr. David Berson51:22

        (laughs)

    14. AHAndrew Huberman51:22

        ... 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.

    15. DBDr. David Berson51:50

        Right.

    16. AHAndrew Huberman51:50

        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.

    17. DBDr. David Berson51:57

        Right.

    18. AHAndrew Huberman51:58

        All right, so that gets us to this issue of motion sickness.

    19. DBDr. David Berson52:02

        Right.

    20. AHAndrew Huberman52:02

        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.

    21. DBDr. David Berson52:16

        Right.

    22. AHAndrew Huberman52:17

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

    23. DBDr. David Berson52:22

        Right.

    24. AHAndrew Huberman52:22

        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-

    25. DBDr. David Berson52:36

        (laughs) Yeah.

    26. AHAndrew Huberman52:36

        ... 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.

    27. DBDr. David Berson52:42

        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.

    28. AHAndrew Huberman53:33

        Or the motion is dis- or some other motion-

    29. DBDr. David Berson53:35

        Or some oth-

    30. AHAndrew Huberman53:35

        ... like a movie or, yeah.
12. 1:00:03 – 1:02:35

    Popping Ears

    1. AHAndrew Huberman1:00:03

       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.

    2. DBDr. David Berson1:00:26

       Right.

    3. AHAndrew Huberman1:00:27

       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-

    4. DBDr. David Berson1:00:44

       Yeah.

    5. AHAndrew Huberman1:00:44

       ... 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?

    6. DBDr. David Berson1:00:50

       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.

    7. AHAndrew Huberman1:01:07

       Right.

    8. DBDr. David Berson1:01:07

       If you push them more, they'll hurt even more.

    9. AHAndrew Huberman1:01:08

       That's a good description that they, you know, that pressure goes up, then they're going to bend in. Yep.

    10. DBDr. David Berson1:01:12

        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.

    11. AHAndrew Huberman1:01:26

        Yep.

    12. DBDr. David Berson1:01:26

        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-

    13. AHAndrew Huberman1:01:41

        ... to counter it.

    14. DBDr. David Berson1:01:42

        ... 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.

    15. AHAndrew Huberman1:01:56

        ... you could-

    16. DBDr. David Berson1:01:58

        Just breathe.

    17. AHAndrew Huberman1:01:58

        ... hold your nose and blow air out, or hold your nose and suck in the-

    18. DBDr. David Berson1:02:03

        Right.

    19. AHAndrew Huberman1:02:03

        ... effect? Either way is fine.

    20. DBDr. David Berson1:02:05

        I think so. I mean-

    21. AHAndrew Huberman1:02:05

        Excellent. You just, I just won $100 from Harvey Karten.

    22. DBDr. David Berson1:02:09

        (laughs)

    23. AHAndrew Huberman1:02:09

        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.

    24. DBDr. David Berson1:02:16

        Okay. (laughs)

    25. AHAndrew Huberman1:02:17

        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.

    26. DBDr. David Berson1:02:25

        I-

    27. AHAndrew Huberman1:02:25

        Okay?

    28. DBDr. David Berson1:02:25

        ... I'm no expert in this area. Don't-

    29. AHAndrew Huberman1:02:27

        Don't worry.

    30. DBDr. David Berson1:02:27

        ... don't quote me. (laughs)
13. 1:02:35 – 1:10:44

    Midbrain & Blindsight

    1. AHAndrew Huberman1:02:35

       area of the brain that is rarely discussed, which is the midbrain.

    2. DBDr. David Berson1:02:39

       Yeah.

    3. AHAndrew Huberman1:02:40

       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)

    4. DBDr. David Berson1:03:15

       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.

    5. AHAndrew Huberman1:03:54

       Sort of like a paddle or a spoon shape.

    6. DBDr. David Berson1:03:56

       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-

    7. AHAndrew Huberman1:04:10

       Tween?

    8. DBDr. David Berson1:04:11

       ... this link, this linker brain, with, diencephalon really means the, the between brain.

    9. AHAndrew Huberman1:04:14

       Oh, I thought you said tween.

    10. DBDr. David Berson1:04:16

        Well, it is, yes, apostrophe-

    11. AHAndrew Huberman1:04:16

        No, no, between.

    12. DBDr. David Berson1:04:17

        Between, yeah.

    13. AHAndrew Huberman1:04:18

        I'm sorry, I said, said tween, T-

    14. DBDr. David Berson1:04:19

        Yeah, it's the between.

    15. AHAndrew Huberman1:04:20

        Yeah, yeah, the, the between brain.

    16. DBDr. David Berson1:04:22

        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-

    17. AHAndrew Huberman1:05:50

        Any movement.

    18. DBDr. David Berson1:05:51

        ... 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.

    19. AHAndrew Huberman1:06:04

        What if you throw me a ball, but I'm not expecting it?

    20. DBDr. David Berson1:06:07

        Right.

    21. AHAndrew Huberman1:06:07

        And I just reach up and, and try and grab it?

    22. DBDr. David Berson1:06:09

        Right.

    23. AHAndrew Huberman1:06:09

        Catch it or not.

    24. DBDr. David Berson1:06:10

        Right.

    25. AHAndrew Huberman1:06:10

        Is that handled by the midbrain?

    26. DBDr. David Berson1:06:12

        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-

    27. AHAndrew Huberman1:06:23

        What about ducking-

    28. DBDr. David Berson1:06:23

        ... and sp- And probably-

    29. AHAndrew Huberman1:06:24

        ... if something's suddenly thrown at my head?

    30. DBDr. David Berson1:06:25

        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.
14. 1:10:44 – 1:13:24

    Why Tilted Motion Feels Good

    1. AHAndrew Huberman1:10:44

       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?

    2. DBDr. David Berson1:11:27

       I have no clue.

    3. AHAndrew Huberman1:11:28

       Is there dopaminergic input to this sy- system?

    4. DBDr. David Berson1:11:31

       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-

    5. AHAndrew Huberman1:11:55

       People pay money to go on roller coasters.

    6. DBDr. David Berson1:11:58

       Right. Well, I think that may be as much about the thrill as anything else.

    7. AHAndrew Huberman1:12:01

       Sure. And falling is, uh, the falling reflex is very robust in all of us.

    8. DBDr. David Berson1:12:05

       Right.

    9. AHAndrew Huberman1:12:05

       When the visual world's going up very fast-

    10. DBDr. David Berson1:12:07

        Right.

    11. AHAndrew Huberman1:12:07

        ... it usually means that we're falling.

    12. DBDr. David Berson1:12:08

        Right. Right.

    13. AHAndrew Huberman1:12:08

        But, and some people are like that, some people don't.

    14. DBDr. David Berson1:12:10

        Right. And kids, kids tolerate a lot more, you know, sort of vestibular craziness, spinning around until they f- drop than adults will.

    15. AHAndrew Huberman1:12:18

        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.

    16. DBDr. David Berson1:12:30

        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.

    17. AHAndrew Huberman1:12:39

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

    18. DBDr. David Berson1:12:48

        Yeah.

    19. AHAndrew Huberman1:12:48

        ... being move, moving through space.

    20. DBDr. David Berson1:12:50

        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-

    21. AHAndrew Huberman1:13:12

        Mm-hmm.

    22. DBDr. David Berson1:13:13

        ... in a way that you wouldn't if you were going straight. I'm, I'm just blowing smoke here, right?

    23. AHAndrew Huberman1:13:17

        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,

15. 1:13:24 – 1:16:35

    Reflexes vs. Deliberate Actions

    1. AHAndrew Huberman1:13:24

       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.

    2. DBDr. David Berson1:13:42

       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-

    3. AHAndrew Huberman1:14:29

       Wedgwood teacup?

    4. DBDr. David Berson1:14:30

       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.

    5. AHAndrew Huberman1:15:41

       Mm-hmm.

    6. DBDr. David Berson1:15:42

       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.

    7. AHAndrew Huberman1:16:05

       Right, and if you start looking for, for something new or different-

    8. DBDr. David Berson1:16:08

       Right.

    9. AHAndrew Huberman1:16:08

       ... you're going to mess up your-

    10. DBDr. David Berson1:16:10

        Right.

    11. AHAndrew Huberman1:16:10

        ... your reflexive swing.

    12. DBDr. David Berson1:16:11

        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.

    13. AHAndrew Huberman1:16:28

        This is important and a great segue for what I'd like to discuss next, was it, which is the basal

16. 1:16:35 – 1:24:40

    Basal Ganglia & the “2 Marshmallow Test”

    1. AHAndrew Huberman1:16:35

       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.

    2. DBDr. David Berson1:16:47

       Right.

    3. AHAndrew Huberman1:16:47

       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.

    4. DBDr. David Berson1:17:03

       Right.

    5. AHAndrew Huberman1:17:03

       And sometimes it's activating behavior.

    6. DBDr. David Berson1:17:05

       Right.

    7. AHAndrew Huberman1:17:05

       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.

    8. DBDr. David Berson1:17:26

       Right.

    9. AHAndrew Huberman1:17:26

       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?

    10. DBDr. David Berson1:17:52

        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.

    11. AHAndrew Huberman1:18:09

        Cerebral cortex being the refined cousins and then you've got the-

    12. DBDr. David Berson1:18:12

        Right.

    13. AHAndrew Huberman1:18:13

        ... you know, the brutes that-

    14. DBDr. David Berson1:18:14

        Yeah.

    15. AHAndrew Huberman1:18:14

        Yeah. All right.

    16. DBDr. David Berson1:18:15

        I mean, that's probably totally unfair, but the, the-

    17. AHAndrew Huberman1:18:18

        It's all right.

    18. DBDr. David Berson1:18:18

        ... the point-

    19. AHAndrew Huberman1:18:18

        I, I like the basal ganglia. I can relate to-

    20. DBDr. David Berson1:18:20

        (laughs)

    21. AHAndrew Huberman1:18:20

        ... the brutish parts of the brain. A little bit of hypothalamus, a little bit of basal ganglia, sure.

    22. DBDr. David Berson1:18:25

        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-

    23. AHAndrew Huberman1:18:57

        Mm-hmm.

    24. DBDr. David Berson1:18:57

        ... 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 or, you know, what?

Episode duration: 1:52:47