The Science of Hearing, Balance & Accelerated Learning

(music plays) 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, we're going to talk all about hearing and balance, and how you can use your ability to hear specific things and your balance system in order to learn anything faster. The auditory system, meaning the hearing system, and your balance system, which is called the vestibular system, interact with all the other systems of the brain and body, and used properly, can allow you to learn information more quickly, remember that information longer and with more ease, and you can also improve the way you can hear. You can improve your balance. We're going to talk about tools for all of that. This is one area of science where we understand a lot about the cells and the mechanisms in the ear and in the brain and so forth, so we're going to talk about that a little bit, and then we're going to get directly into protocols, meaning tools. We're also going to talk about ways in which the auditory and balance systems suffer. We're going to talk about tinnitus, which is this ringing of the ears that unfortunately, for people that suffer from it, they really suffer. It's very intrusive for them. We're going to talk about some treatments that can work in some circumstances and some of the more recent emerging treatments that I think many people aren't aware of. We're also going to talk about this what seems like kind of a weird fact, which is that 70% of people, all people, make what are called autoacoustic emissions. Their ears actually make noises. Chances are you- your ears are making noises right now, but you can't perceive them, and yet those can have an influence on other people and animals in your environment. It's a fascinating aspect to your biology. You're going to learn a lot about how your biology and brain and ears and the so-called inner ear that's associated with balance, you're going to learn a lot about how all those work. You're going to learn a lot of neuroscience. I'll even tell you what type of music to listen to, and if you listen to me, you can leverage that in order to learn faster. Before we begin talking about the science of hearing and balance and tools that leverage hearing and balance for learning faster, I want to provide some information about another way to learn much faster. There's a paper that was published recently. This is a paper that was published in Cell Reports, an excellent journal. It's a peer-reviewed paper from a really excellent group looking at skill learning. Now, previously, I've talked about how in the attempt to learn skills, the vital thing to do is to get lots of repetitions. You've heard of the 10,000 hours thing, you've heard of, uh, you know, lots of different strategies for learning faster, 80-20 rule and all that. The bottom line is you need to generate many, many repetitions of something that you're trying to learn, and the errors that you generate are also very important for learning. It also turns out that taking rest within the learning episode is very important. I want to be really clear what I'm referring to here. In earlier episodes, I've discussed how when you're trying to learn something, it's beneficial, it's been shown in scientific studies, that if you take a 20-minute shallow nap or you simply do nothing after a period of learning, that it enhances the rates of learning and the depth of learning, your ability to learn and remember that information. What I'm about to describe are new data that say that you actually should be- should be injecting rest within the learning episode. Now, I'm not talking about going to sleep while learning. This is the way that the study was done. The study involved having people learn sequences of numbers or keys on a piano. So let's use the keys on a piano example. I'm not a musician, but I think I'll get this correct. They asked people to practice a sequence of keys, G, D, F, E, G, G, D, F, E, G, G, D, F, E, G, and they would practice that either continually for a given amount of time or they would just do that for 10 seconds, they would play G, D, F, E, G, G, D, F, E, G, G, D, F, E, G, G, D, F, E, G for 10 seconds, and then they would take a 10-second pause, a rest. They would just space- sp- take a space or a period of time where they do nothing for 10 seconds, then they would go back to G, D, F, E, G, G, D, F, E, G. So the two conditions essentially were to have people practice continually, lots of repetitions, or to inject or insert these periods of- of 10 seconds idle time where they're not doing anything, they're not looking at their phone, they're not focusing on anything, they're just letting their mind drift wherever it wants to go, and they are not touching the keys on the keyboard. What they found was that the rates of learning, the skill acquisition, and the retention of the skills was significantly faster when they injected these short periods of rest, these 10-second rest periods, and the em- the rates of learning were, when I say significantly faster, were much, much faster. I'll reveal what that was in just a moment. But you might ask, why would this work? Why would it be that injecting these 10-second rest periods would enhance rates of learning? What they called them was micro offline gains because they're sort of taking their brain offline from the learning task for a moment. Well, it turns out the brain isn't going offline at all. You've probably heard of the hippocampus, the area of the brain involved in memory, and the neocortex, the area of the brain that's involved in processing sensory information. Well, it turns out that during these brief periods of rest, these 10-second rest periods, the hippocampus and the cortex are active in ways...... such that you get a 20 times repeat of the G-D-F-E-G. It's a temporal compression, as they say. So basically, the rehearsal continues while you rest, but at 20 times the speed. So if you were normally getting just, let's just say, five repetitions of G-D-F-E-G, G-D-F-E-G, G-D-F-E-G per 10 seconds, now you multiply that times 20. In the rest periods, you've practiced it 100 times. Your brain has practiced it. We know this because they were doing brain imaging, functional imaging of these people with brain scanners while they were doing this. This is an absolutely staggering effect and it's one that, believe it or not, has been hypothesized or thought to exist for a very long time. This effect is called the spacing effect, and it was actually first proposed by Ebbington in 1885, and since then, it's been demonstrated for a huge number of different what they call domains. In the cognitive domain, so for learning languages, for in the physical domain, so for learning skills that involve a motor sequence. It's been demonstrated for a huge number of different categories of learning. If you want to learn all about the spacing effect and the categories of learning that it can impact, there's a wonderful review article. I'll provide a link to it. The title of the review article is Parallels Between Spacing Effects During Behavioral and Cellular Learning. What that review really does is it ties the behavioral learning and the improvement of skill to the underlying changes in neurons that can explain that learning. I should mention that the paper that I'm referring to, the more recent paper that injects these 10-second little micro offline games, uh, rest periods, is the work of the laboratory of Leonard Cohen, not the musician Leonard Cohen. He passed away. He was not a neuroscientist. A wonderful poet and musician, but not a neuroscientist. Again, the paper was published in Cell Reports, and we will provide a link to the full paper as well. So the takeaway is if you're trying to learn something, you need to get those reps in, but one way that you can get 20 times the number of reps in is by injecting these little 10-second periods of doing nothing. Again, during those rest periods, you really don't want to attend to anything else as much as possible. You could close your eyes if you want or you can just simply wait and then get right back into generating repetitions. I find these papers that Cell, uh, Reports and other journals have been publishing recently to be fascinating because they're really helping us understand what are the best protocols for learning anything, and they really, uh, leverage the fact that the brain is willing to generate repetitions for us provide- provided that we give it the rest that it needs. So inject rest throughout the learning period and, if you can, based on the scientific data, you would also want to take a 20-minute nap or a 20-minute decompress period where you're not doing anything after a period of learning. I think those could both synergize in order to enhance learning even further, although that hasn't been looked at yet. Before we begin talking about hearing and balance, I just want to mention 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 want to thank the sponsors of today's podcast and make it clear that we only work with sponsors whose products we absolutely love and that we think you will benefit from as well. Our first sponsor is ROKA. ROKA makes sunglasses and eyeglasses that, in my opinion, are the very highest quality available. The company was founded by two all-American swimmers from Stanford, and everything about their eyeglasses and sunglasses were created with performance in mind. These eyeglasses and sunglasses have a number of features that really make them unique. First of all, they're extremely lightweight. The optical clarity of the lenses is spectacular. 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But the dashboard at InsideTracker provides directives so that if you want to bring those numbers up or bring them down or if you want to keep them in the same range, it points to specific regimens related to nutrition, exercise, and other lifestyle factors so you can really move around those numbers to best suit your health goals and health status. If you want to try InsideTracker, you can go to insidetracker.com/huberman and you'll get 25% off any of InsideTracker's plans. Just use the code Huberman at checkout. Today's podcast is also brought to us by Headspace. Headspace is a meditation app that's backed by 25 published studies, and in addition to those, there are hundreds of studies showing that meditation is beneficial for our brain and for our body. One of the challenges, however, is maintaining a meditation practice. I started meditating a long time ago, but I found it very hard to keep that practice going. Then I discovered the Headspace meditation app, and what I found was that because they have meditations that are very short as well as some that are longer and some that are much longer, I could maintain my meditation practice. Sometimes I do a short five-minute meditation, sometimes I do 20-minute meditation. I try and meditate at least 20 minutes per day, but sometimes, some weeks, I only do it five times a week and I'll just meditate for longer. So with Headspace, you have the full palette of meditations to select from. If you want to try Headspace, you can go to headspace.com/specialoffer, and if you do that, you'll get a free one-month trial, so no cost whatsoever, with their full library of meditations. That's the best offer that they have. So again, if you want to try Headspace and you want to get access to all their meditations for free, go to headspace.com/specialoffer. Can you hear me? Can you hear me? Okay, well, if you can hear me, that's amazing because what it means is that my voice is causing little tiny changes in the airwaves wherever you happen to be and that your ears and whatever's contained in those ears and in your brain can take those sound waves and make sense of them, and that is an absolutely fantastic and staggering feat of biology, and yet we understand a lot about how that process works. So I'm going to teach it to you now in simple terms over the next few minutes. So what we call ears have a technical name. That techninal- technical name is auricles, but more often they're called pinna, the pinnas, P-I-N-N-A, pinna. And the pinnas of your ears, this outer part that is made of cartilage and stuff, is arranged such that it can capture sound in the best way for your head size. We're going to talk about ear size also 'cause it turns out that your ears change size across the lifespan and that how big your ears are, or rather how fast your ears are changing size, is a pretty good indication of how fast you're aging. So we'll get to that in a few minutes, but I want to talk about these things that we call ears and some of the stuff contained within them that allow us to hear. So the shape of these ears that we have is such that it amplifies high-frequency sounds. High-frequency sounds, as the name suggests, are the, is the squeakier stuff, right? So low-frequency sound, Costello snoring in the background, that's a low-frequency sound, or high-frequency sound. Okay? So we have low-frequency sounds and high-frequency sounds and everything in between. Now, those sound waves get captured by our ears and those sound waves, for those of you that don't maybe fully conceptualize sound waves, are literally just fluctuations or shifts in the way that air is moving toward your ear and through space. In the same way that water can have waves, s- air can have waves. Okay? So it's reverberation of air. Those come in through your ears and you have what's called your eardrum and on the inside of your eardrum, there's a little bony thing that's shaped like a little hammer. So attached to that eardrum, which can move back and forth like a drum, it's like a little membrane, you've got this hammer attached to it, and that hammer has three parts. For those of you that want to know, those three parts are called malleus, incus, and stapes. It's like a- but basically, you can just think about it as a hammer. So you've got this eardrum and then a hammer, and then that hammer has to hammer on something, and what it does is it hammers on a little coiled piece of tissue that we call the cochlea, sometimes called the cocklea, depending on where somebody lives in the country. So typically, in the Midwest, on the East Coast, they call them cocklea, and on the West Coast, we call them cochlea. Same thing. Okay? So this snail-shaped structure in your inner ear is where sound gets converted into electrical signals that the brain can understand, but I want to just bring your attention to that little hammer because that little hammer is really, really cool. What it means is that sound waves come in through your ears, that's what's happening right now, that eardrum that you have is like a- it's like the top of a drum, it's like a membrane or it can move back and forth, it's not super rigid, and it moves that little hammer and then the hammer goes (imitates sound) and hits this coil-shaped thing that we're calling the cochlea. Okay? Now, the cochlea, at one end, is more rigid than the other. So one part can move really easily and the other part doesn't move very easily, and that turns out to be very important for decoding or separating sounds that are of low frequency, like Costello's snoring, and sounds that are of high frequency, like a shriek or a shrill. And that's because within that little coiled thing we call the cochlea, you have all these tiny little, what are called hair cells-Now, they look like hairs, but they're not at all related to the hairs on your head or, uh, elsewhere on your body. They're just shaped like hairs, so we call them hair cells. Those hair cells, if they move, send signals into the brain that a particular sound is in our environment, and if those hair cells don't move, it means that particular sound is not in our environment. Okay? So just to give you the mental picture of this, sound waves are coming in because there's s- stuff out there making noises, like my voice, it's changing the patterns of air around you in very, very subtle ways, that information is getting funneled into your ears because your pinnaes are shaped in a particular way, the eardrum then moves this little hammer and the hammer bangs on this little snail-shaped thing, and because that snail-shaped thing at one end is very rigid, it doesn't want to move, and at the other end, it's very flexible, it can separate out high frequency and low frequency sounds. And the fact that this thing in your inner ear that we call the cochlea is coiled is actually really important to understand because along its length, it varies in how rigid or flexible it is, I already mentioned that before, and at the base, it's very rigid, and that's where the hair cells, if they move, will make high frequency sounds. And at the top, what's called the apex, it's very flexible and it's more like a bass drum. So basically, what happens is sound waves come into your ears and then at one end of this thing that we call the cochlea, at the top, it's essentially encoding or only responding to sounds that are like (imitates drum sound) whereas at the bottom, it responds to high frequency sounds, like a cymbal. (imitates cymbal sound) Okay? And everywhere in between, we have other frequencies, m- medium frequencies. Now, this should stagger your mind. If it doesn't already, it should, because what this means is that everything that's happening around us, whether or not it's music or voices or crying or screaming or screaming of delight from small children who are excited 'cause they're playing or 'cause they get cake, all of that is being broken down in- into its component parts, and then your brain is making sense of what it means. These things that I've been talking about, like the pinna of your ears and this little hammer and the cochlea, that's all purely mechanical. It has no mind of its own. It's just breaking things down into high frequencies, medium frequencies, and low frequencies. And if you don't understand sound frequency, it's really simple to understand. Just imagine ripples on a pond and if those ripples are very close together, that's high frequency. They occur at high frequency. If those ripples are further apart, it's low frequency. And obviously, medium frequency is in between. So just like you can have waves in water, you can have waves in air. So that's- that's really how it works. Now, we're all f- we are all familiar with light and how if you take a prism and put it in front of light, it will split that light into its different wavelengths, its different colors, red, green, blue, et cetera, right? Sort of like the Pink Floyd Dark Side of the Moon album I think has a prism and it's, uh, converting white light into all the colors, all the wavelengths that are contained in white light. Your cochlea essentially acts as a prism. It takes all the sound in your environment and it splits up those sounds into different frequencies. So you can think of the cochlea of your ear sort of like a prism and then the brain takes that information and puts it back together and makes sense of it. So those hair cells in each of your two cochlea, 'cause you have two ears, you also have two cochlea, send little wires, what we call axons, that convey their patterns of activity into the brain and there are a number of different stations within the brain that information arrives at before it gets up to the parts of your brain where you are consciously aware. And because some of you have asked for more names and nomenclature, I'll give that to you. If you don't want a lot of detailed names, you can just ignore what I'm about to say, but basically, the cochlea send information to what's called the spiral ganglion. The spiral gang- a ganglion, by the way, if you're going to learn any neuroscience, just know that anytime you hear "ganglion", a ganglion is just a clump, so it means a bunch of neurons. So a clump of cells. So the spiral ganglion is a bunch of neurons that the information then goes off to what are called the cochlear nuclei in the brain stem, brain stem is kind of down near your neck, then up to a structure that has a really cool name called the superior olive, because it, uh, you have one on each side of your brain, um, and if I were to bring you to my lab and show you the superior olives in your brain or anyone else's brain, they look like little olives. They even have a little divot in them that, to me, looks like a pimiento, but they just call them the super- the superior olive. And then the- the neurons in the superior olive, then they send information up to what's called the inferior colliculus, only called inferior because it sits below a structure called the superior colliculus, and then the information goes up to what's called the medial geniculate nucleus, and then up to your neocortex where you make sense of it all. Now, you don't have to remember all that, but you should know that there are a lot of stations in which auditory information is processed before it gets up to our conscious detection and there is a good reason for that, which is that more important than knowing what you're hearing, you need to know where it's coming from. It's vital to our survival that if something, for instance, is falling toward us, that we know if it's coming to our right side, if it's going to hit us from behind, we have to know, for instance, if a car is- is coming at us from our left or from our right, and our visual system can help with that, but our auditory and our visual system collaborate to help us find and locate...... the position of things in space. That should come as no surprise. If you hear somebody talking off to your right, you tend to turn to your right, not to your left. If you see somebody's mouth moving in front of you, you tend to assume that the sound is going to come from right in front of you. Disruptions in this auditory, hearing, and visual matching are actually the basis of what's called the ventriloquism effect, which we'll talk about in a few minutes in more depth. But the, but the ventriloquism effect can basically be described in simple terms as when you essentially think that a sound is coming from a location that it's not actually coming from. We'll talk about that in a moment, but what I'd like you to realize is that one of these stations deep in your brain stem is responsible for helping you identify where sounds are coming from through a process that's called interaural time differences. And that sounds fancy, but really, the way you know (laughs) where things are coming from, what direction a car or a bus or a person is coming from, is because the sound lands in one ear before the other, and you have stations in your brain and y- meaning you have neurons in your brain that calculate the difference in time of arrival for those sound waves in your right versus your left ear. And if they arrive at the same time, you assume that thing is making noise right in front of you. If it's off to your right, you assume it's over on your right, and if the sound arrives first to your left ear, you assume, quite correctly, that the thing is coming toward your left ear. So it's a very simple and kind of mechanical system at the level of sound localization, but what about up and down? If you think about it, a sound coming from above is going to land on your right ear and your left ear at the same time. A sound from below is going to land on your right ear and your left ear at the same time. So the way that we know where things are in terms of what's called elevation, where they are in the up and down plane, is by the frequencies. The shape of your ears actually modifies the sound depending on whether or not it's coming straight at you, from the floor, or from high above. And so already at the level of your ears, you are taking information about the outside world and determining where that information is coming from. Now, this all happens very, very fast in the subconscious, but now you know why if people really want to hear something, they make a cup around their ear, they essentially make their ear into more of a fennec fox-type ear, if you've ever seen those cute little fennec fox things. They have these big, spiky ears. They kind of look like a French Bulldog, although they're kind of the fox versi- version of the French Bulldog with these big s- big, tall ears, and they have excellent sound localization. And so p- when people lean in with their ear like thi- with their hand like this, if you're listening to this, I'm just cupping my hand at my ear, I'm giving myself a bigger pinna, okay? And if I do it on the left side, and I do this side, and if I really want to hear something, I do it on both sides. Okay? So this isn't just gesturing. This actually serves a mechanical role. And actually, if you want to hear where things are coming from with a much greater degree of accuracy, this can actually help because you're capturing sound waves and funneling them better.