Protect & Improve Your Hearing & Brain Health | Dr. Konstantina Stankovic

0:00:05 So now there’s mounting evidence for a strong link between hearing loss and dementia.
0:00:08 It’s not that everyone with hearing loss will develop dementia.
0:00:12 However, we are trying to identify who is at risk.
0:00:14 Hearing loss is a huge problem.
0:00:21 It currently affects one and a half billion people and disables half a billion of them.
0:00:28 And the World Health Organization estimates that another billion will be affected by 2050.
0:00:34 Welcome to the Huberman Lab Podcast, where we discuss science and science-based tools for everyday life.
0:00:44 I’m Andrew Huberman, and I’m a professor of neurobiology and ophthalmology at Stanford School of Medicine.
0:00:47 My guest today is Dr. Konstantina Stankovic.
0:00:55 She is a medical doctor and researcher and the chair of the Department of Autolaryngology Head and Neck Surgery at Stanford School of Medicine.
0:01:07 Today, we discuss hearing and how to protect yours, as well as how to deal with common problems related to hearing, like tinnitus or ringing of the ears, which is a very debilitating condition that many millions of people suffer from.
0:01:28 Most of us don’t think about our hearing very often unless it’s compromised, and yet we now know that our ability to hear clearly in many ways drives our ability to think and engage with the world, which is, of course, not to say that deaf people don’t have excellent cognition and the ability to engage with the world, but they, of course, compensate for that hearing loss with the use of sign language and lip reading.
0:01:40 Most people, of course, have the ability to hear, and yet don’t know that even subtle deficits in hearing can lead to focus issues, mild cognitive impairment, and more serious hearing loss is directly related to dementia.
0:01:56 And while until recently we thought about partial hearing loss as really something that accompanies aging, it turns out that for various reasons related to loud environments, the use of headphones, et cetera, progressive subtle hearing loss is occurring much earlier in people’s lives, even as early as childhood.
0:02:01 Today, you’re going to learn from one of the top experts in the world, how your auditory system works.
0:02:04 We’ll talk about how it works from the time you were in your mother’s womb.
0:02:10 Yes, indeed, you could hear quite well, even within your mother’s womb, all the way through adolescence and into old age.
0:02:14 And you’re going to learn the specific things that you can do to protect your hearing.
0:02:21 And I’m certain that you’ll realize that some or many of the things that you’re doing are subtly or not so subtly damaging your hearing.
0:02:24 And fortunately, you can remedy that very easily.
0:02:31 We talk about some of the behavioral protocols that are backed by science, as well as things like the use of magnesium to protect against hearing loss.
0:02:38 And, of course, we talk about tinnitus, this very common condition of ringing in the ears and how you can remedy it.
0:02:45 Dr. Stankovich, this is both a fascinating and incredibly important conversation relevant to people of all ages.
0:02:52 The information she shares is not covered in traditional public health announcements, but it absolutely should be, because it’s not just about protecting your ability to hear.
0:03:07 So today’s discussion is going to teach you about how your auditory system works, how to take care of it, how to remedy any partial hearing loss that you might have already experienced, and in doing so, how to take care of your brain health and cognition.
0:03:12 Before we begin, I’d like to emphasize that this podcast is separate from my teaching and research roles at Stanford.
0:03:19 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.
0:03:23 In keeping with that theme, today’s episode does include sponsors.
0:03:27 And now for my discussion with Dr. Konstantina Stankovich.
0:03:29 Dr. Konstantina Stankovich, welcome.
0:03:30 Thank you.
0:03:44 Most of us don’t think about our hearing often enough, except now everyone is using headphones or listening to things very loud, or most people are living in quite loud environments.
0:03:45 I was in New York last week.
0:03:48 I’ve been in Chicago, San Francisco.
0:03:50 These are really loud cities.
0:04:09 And even if one goes out into the countryside, you know, if you’re listening to music loudly, which can be fun, feels good, if you like loud music, classical or rock and roll or otherwise, I have a feeling you’re going to tell us that it’s not good for our hearing and that losing our hearing is not good for a bunch of other things.
0:04:10 Tell us about hearing loss.
0:04:11 How do we avoid it?
0:04:13 Absolutely.
0:04:15 So hearing loss is a huge problem.
0:04:22 It currently affects one and a half billion people and disables half a billion of them.
0:04:30 And the World Health Organization estimates that another billion will be affected by 2050.
0:04:33 So this is an enormous issue.
0:04:38 And it’s really underappreciated and stigmatized.
0:04:40 And lots of people live in silence.
0:04:46 For example, for those who have problems with their vision, they wear glasses.
0:04:52 And glasses can restore their vision back to normal to the point that people now wear glasses even if they don’t need them.
0:04:54 It’s a fashion statement.
0:04:57 However, that’s not the case for hearing loss.
0:05:02 And it’s because hearing aids are aids, like the name says.
0:05:05 They don’t restore hearing back to normal.
0:05:10 So to answer your question, I think we really should review how hearing works.
0:05:18 So the way we hear is when sound comes and travels down the ear canal, it vibrates the eardrum.
0:05:20 The fancy term for it is the tympanic membrane.
0:05:24 That sets in motion the smallest bones in the body.
0:05:30 They are called the malleus, incus, and stapes, which is Latin for the hammer, the anvil, and the stir bone.
0:05:36 As they vibrate, they set in motion fluids in the inner ear.
0:05:42 And this is where these incredibly delicate sensory cells reside.
0:05:45 They are called hair cells, but that has nothing to do with this hair.
0:06:05 And as they deflect their sensors on top of their surface, which are called stereocilia, that leads to flow of ionic current and release of neurotransmitter and excitation of the auditory nerve, which then sends signals all the way to the brain.
0:06:18 So in the inner ear occurs this, it’s called mechano-electrical transduction, because we are converting a mechanical stimulus into an electrical one.
0:06:22 And there are two broad categories of hearing loss.
0:06:28 One is the so-called conductive hearing loss, and the other is sensorineural hearing loss.
0:06:34 The conductive hearing loss affects the ability of sounds to be conducted to the inner ear.
0:06:42 That can be if there is a hole in the eardrum, or there is fluid behind the eardrum, or these hearing bones don’t vibrate.
0:06:45 They are frozen because of a disease process.
0:06:54 There are surgical treatment options for that type of hearing loss and non-surgicals, which include amplification with hearing aids.
0:07:03 So that’s an easier type of hearing loss to have, but the more common type of hearing loss is the sensorineural hearing loss.
0:07:06 It’s the one that originates from the inner ear.
0:07:15 And why it’s been so challenging to study and to crack that nut is because it’s tiny.
0:07:16 It’s a tiny organ.
0:07:22 It’s encased in the densest bone in the body, and it’s located deep in the base of the skull.
0:07:25 You may even ask, how tiny?
0:07:31 If you take a penny, then you’ll notice that Lincoln is on a penny.
0:07:42 So the human organ of hearing, which is called the cochlea, in cross-section is the size of Lincoln’s upper face on a penny.
0:07:44 Wow, that’s small.
0:07:45 Super small.
0:07:49 And that organ is filled with fluid.
0:07:51 How much fluid?
0:07:52 What’s your guess?
0:07:54 What’s the volume of this inner ear fluid?
0:07:56 It even has a fancy term.
0:07:58 It’s called perilymph and endolymph.
0:08:00 There are two types of fluid, but that doesn’t matter.
0:08:01 What matters is the scale.
0:08:04 So how much fluid do you think there is?
0:08:12 I’m guessing the equivalent of one, less than one drop out of an eyedropper.
0:08:14 That’s pretty close.
0:08:19 It’s actually the equivalent of three raindrops, so about 140 microliters.
0:08:22 So this is an organ that’s amazing.
0:08:26 It is the most sensitive sensory organ.
0:08:34 It can detect displacements that are on the order of the diameter of a hydrogen atom.
0:08:37 That’s astounding.
0:08:45 If you just think in terms of electronic chips, the traces are now on the order of one nanometer,
0:08:49 which is the size of five silicon atoms.
0:08:55 But the ear can detect displacements that are one-tenth of that.
0:08:57 So at the angstrom level.
0:08:58 Sub-angstrom level.
0:08:59 Sub-angstrom.
0:09:00 Sub-angstrom level.
0:09:01 It’s really phenomenal.
0:09:07 And another example to really highlight the sensitivity of this organ, if you have a trained
0:09:17 violinist, if they move their finger by only a micron, so that’s a millionth of a meter,
0:09:23 the ear can perceive that as a change in pitch.
0:09:23 Amazing.
0:09:27 You can see that with your naked eye, but the ear can perceive it.
0:09:33 So these examples really highlight how delicate this organ is.
0:09:38 And another absolutely stunning thing about the ear is that there are these cells, there
0:09:45 are sensory cells that we talked about, but they’re called inner and outer hair cells.
0:09:51 And what’s special about these outer hair cells, they actually move, but they move at audio frequencies.
0:09:53 So what does that mean?
0:10:00 To put it in perspective, let’s say that the heart beats at 60 beats per minute, which is
0:10:00 one hertz.
0:10:07 If the heart starts beating at two hertz, 120 beats per minute, that’s arrhythmia.
0:10:08 That could be life-threatening.
0:10:20 Well, these cells in the inner ear move in humans up to 20,000 hertz, and in bats up to 100,000
0:10:20 hertz.
0:10:26 So this is to tell you how incredible this system is.
0:10:29 And it’s designed to let us detect sounds.
0:10:36 And it’s evolved so that we can detect sounds at any point in a day or night.
0:10:38 Sound travels through any media.
0:10:41 Sound travels around obstacles.
0:10:43 It’s really essential for survival.
0:10:48 They’re a species that don’t even have vision.
0:10:54 They are blind, and they are surviving superbly well because of their incredibly astute sense
0:10:56 of hearing, like bats or moles.
0:10:59 May I just ask a question about sound waves themselves?
0:11:10 Could you differentiate for us how high versus low frequency sounds travel further or have a greater
0:11:17 propensity to impact the movement of the eardrum, which you beautifully explained is the consequence
0:11:23 of a bunch of mechanical features and the endo-lymph, and you said the other lymph?
0:11:24 Paralymp.
0:11:25 Paralymp.
0:11:30 So I want people to get this image in their mind that sound waves, not voices, not music,
0:11:37 but sound waves are traveling through space, arrive to the ear, and then there are converted
0:11:44 into a mechanical pressure that changes over time, like the beating of a drum, eardrum, that
0:11:50 then is converted into pressure within this lymph fluid, which then moves these little
0:11:56 hair, quote-unquote, hair cells, which then activates neuronal signals that go up to the
0:11:57 brain.
0:12:05 And remarkably, I mean, to this day, I’m a neuroscientist, and it still blows my mind that then we perceive
0:12:12 language, we perceive music, we recognize a cry versus laughter, and it all happens very,
0:12:13 very fast.
0:12:17 I think most people don’t think about hearing that way.
0:12:25 And so could you explain for us the elements within sound waves that create this incredible
0:12:27 architecture that we call the perception of hearing?
0:12:34 Sounds, as they set in motion, the tympanic membrane, the eardrum, and then lead to motion
0:12:36 of hearing bones.
0:12:43 There are different modes of vibration depending on both sound intensity and frequency.
0:12:51 Once they get transmitted to vibration within the inner ear, everything is tuned in the inner
0:12:52 ear.
0:12:55 So the cochlea is a coiled organ.
0:12:59 Cochlea even means snail in Greek.
0:13:02 So now if you uncoil it, then it’s a tube.
0:13:11 And high frequencies are encoded at the base, close to the middle ear, and low frequencies far
0:13:12 away at the apex.
0:13:21 And so when sound waves come in, if they’re of high frequency, they will cause primarily vibration
0:13:22 at the base of the cochlea.
0:13:26 If they’re of low frequency, they have to travel all the way up.
0:13:29 And this is where speech resides at higher frequencies.
0:13:36 It’s interesting that the high frequency end of the cochlea tends to be more vulnerable to
0:13:43 various insults like noise levels that you pointed out, certain drugs, and aging.
0:13:53 So now in terms of music being so essential for being human and our ability to communicate,
0:13:56 this is a podcast.
0:14:06 So it highlights how important our ability to communicate and hear that communication is essential.
0:14:08 It can create vivid experiences.
0:14:11 It can be very engaging, even without seeing people.
0:14:20 And looking at that throughout history, for example, Socrates in ancient Greece said,
0:14:24 speak so that I can see you.
0:14:34 And then in the medieval years, it was a French writer and physician, François Rabelais, who
0:14:42 said, of all the senses, hearing is the fittest for the reception of the arts, sciences, and
0:14:43 disciplines.
0:14:52 And then 500 years later, Helen Keller, who was both blind and deaf and is one of the most celebrated
0:15:01 people of the 20th century, said, deafness is a worse misfortune because it separates you from
0:15:04 people as opposed to things.
0:15:10 So that gets at your question of why is hearing important for us?
0:15:16 It’s important not only to communicate that’s direct relevance, but there are indirect major
0:15:24 effects on how we feel, on our emotional, relational, and cognitive well-being.
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0:18:46 I’d like to return to this close relationship between what we hear and how we feel, but before
0:18:53 we do that, let’s say I were in the wilderness, and I was lost, and I was trying to find my way
0:19:01 back, and I was out of water, and I spot somebody on the horizon, and I wanted to call out to
0:19:05 them with the greatest probability that they could hear me.
0:19:14 Would I call out in a higher pitched, lower pitched, or whatever my typical voice happened
0:19:20 to be, assuming that I’m going to call out at the greatest intensity in either case?
0:19:27 Which sound frequency is going to travel furthest and or have the greatest likelihood of reaching
0:19:28 somebody’s ears and having them perceive it?
0:19:35 You partly answered your question because sound intensity is the key, and as humans, we can
0:19:38 produce only sounds of certain frequencies.
0:19:42 And throughout history, people have used horns.
0:19:43 Horns really work.
0:19:49 And so that would be the first thing that you do, and you can even create it like this yourself.
0:19:51 Okay, put your hands on either side of your mouth.
0:19:54 Exactly, to project, but if you have a longer horn, use that.
0:19:55 That really works.
0:20:04 In terms of our human ability to detect tones, in every species, it’s a sensitivity curve.
0:20:13 So when we test hearing in clinic, we test it only up to 8 kilohertz, but we can hear up
0:20:14 to 20,000 hertz.
0:20:18 And it’s because most of speech really lives below that frequency.
0:20:23 Lots of speech lives between 250 hertz and 4,000 hertz.
0:20:32 And if you speak at those levels, which we do because that’s what we do as humans, women
0:20:37 can have more high-pitched voices, or children can have more high-pitched voices, but it’s
0:20:40 still in the range of optimal human hearing.
0:20:42 That’s what you would need to do.
0:20:48 So then all you have to do when you’re in a situation like that is speak as loudly as you
0:20:48 can.
0:20:51 And if you can, find a horn so that it amplifies.
0:20:55 And if you don’t have a horn, put your hand on either sides of your mouth, which we do
0:20:55 intuitively.
0:20:57 Intuitively, exactly.
0:21:02 And if we need to hear something at a distance, we put our hand to our ear in order to create
0:21:04 a temporarily larger ear.
0:21:05 And that works too.
0:21:07 It absolutely works.
0:21:08 Power patients tell us it works.
0:21:13 Sometimes in the clinic, if people don’t have a hearing aid and they’re really hard of hearing
0:21:18 and they don’t know how to lip read and they don’t want to be reading what’s being
0:21:20 written, that’s what they do.
0:21:22 And it really makes a difference.
0:21:25 Because it’s capturing the sound waves into a funnel.
0:21:26 Exactly.
0:21:35 Other animals, most famously the desert fox or the fennec fox, have these really cute tall
0:21:38 ears that they can direct independently.
0:21:43 Am I correct in thinking that some people can move their ears and other people can’t?
0:21:45 I don’t think I can do it.
0:21:46 I’ve never practiced it.
0:21:49 It didn’t seem like a worthwhile thing to try and generate that skill.
0:21:54 But I know people that can move their ears either together or independently a little bit.
0:22:00 Is this a vestigial thing from, I don’t know, from some other animal that we once were?
0:22:02 Yeah, it’s vestigial.
0:22:03 Some people indeed can do it.
0:22:04 It’s not common.
0:22:11 And as far as we know, it doesn’t convey any advantage in modern world to human hearing.
0:22:17 I know this might seem like a silly question, but based on the pure mechanics of everything we’re talking about,
0:22:23 especially ears, do people with larger ears hear better than people with smaller ears?
0:22:25 I don’t think that’s been studied.
0:22:30 I certainly haven’t come across data to support that.
0:22:35 In human body, things tend to be very proportional and they grow with time.
0:22:41 Children tend to reach their adult ear size around age 10.
0:22:48 So, for example, those who are born without the outer ear altogether, that’s called microtia, we can make it.
0:22:58 But the timing of surgery has to be conducted appropriately so that you don’t give them too small of an ear if you operate too early.
0:23:08 These days, there’s a lot of content online about how different sounds can impact the emotionality of kids,
0:23:16 independent of learning, sort of innate sound emotion relationships.
0:23:21 I actually don’t know whether or not these posts are ethical or not.
0:23:24 It’s hard for me to know because what they show is babies.
0:23:28 It’s typically a series of clips with babies where they’ll say something.
0:23:28 I forget what it is.
0:23:33 And it’s probably best that I forget so that people don’t do this and try it because I don’t know the ethics around it.
0:23:35 But they’ll say something to their kid.
0:23:37 And it’s not a word.
0:23:38 It’s a sound.
0:23:43 And the kid will suddenly either be terrified or will suddenly be really happy.
0:23:47 And there’s no indication that that sound is a scary sound or a happy sound.
0:23:50 It’s not like they’re screaming at the kid or barking at the kid.
0:23:55 So it seems to be that people have learned to tap into these frequencies and intensities.
0:24:00 But it tends to be pretty low intensity, at least by my listen of these things.
0:24:06 But very strong coupling of sound and emotion, independent of learning.
0:24:13 And I say independent of learning because, of course, I hear certain pieces of music and they really move me emotionally.
0:24:15 But I have a relationship to that music that I formed over time.
0:24:18 Or it’s similar to a different piece I heard over time.
0:24:23 What is known about the convergence of sound information and emotion?
0:24:33 And let’s leave outside, you know, big, loud bangs or, you know, high, shrill things that really, like, impact our pain system.
0:24:38 So is there something known about how different sounds impact emotionality?
0:24:39 Absolutely.
0:24:46 Really, the brain has evolved to perceive and manage sensory inputs.
0:24:49 And sound is one of these sensory inputs.
0:24:53 And it’s critical for emotional well-being.
0:25:01 We have thus far talked about the periphery, what happens in the inner ear and how those signals are then transmitted all the way to the brain.
0:25:06 Well, there are numerous relay stations from the ear to the brain, to the cortex.
0:25:12 And they are in the brainstem and midbrain all the way to the cortex.
0:25:19 And these auditory pathways have very strong links with emotional pathways and the limbic system.
0:25:24 And, in fact, that’s why music, hearing music, can really move us.
0:25:34 That’s why remarkable speeches of impressive leaders can get people aroused and motivated to do something.
0:25:46 So that link between hearing and emotion is really strong, well-established, and sometimes can be detrimental, for example, for people with tinnitus.
0:25:49 So tinnitus, it’s a phantom sound.
0:25:57 It’s produced by the brain, typically in response to reduced input to the brain.
0:26:00 So the brain makes up the sound that it’s normally not detecting.
0:26:12 It’s similar to phantom limb pain, where people don’t have an arm or a leg, but they can still perceive pain in the limb that they don’t have.
0:26:16 So now, some people with tinnitus can just put it in the background.
0:26:18 They can ignore it.
0:26:22 They are reassured by knowing that it’s not life-threatening and it’s fine.
0:26:25 But there are people who can’t handle it.
0:26:28 They are really severely disabled by it.
0:26:31 And some are suicidal, which is a huge spectrum.
0:26:33 And why is that?
0:26:39 So clearly, these circuits in the brain are differently connected for different people.
0:26:43 And in some, that emotional component is really amplified.
0:26:44 Interesting.
0:26:51 Many people have heard of ASMR, auditory sensory meridian reflex, I think it’s called.
0:26:59 This is something that, sure, there are accounts online where people will whisper or they’ll scratch or they’ll scratch a microphone.
0:26:59 I won’t do it here.
0:27:03 Some people find certain sounds extremely pleasant.
0:27:06 Other people find the same sounds extremely aversive.
0:27:11 Actually, I was thinking for a moment about fingers on a chalkboard.
0:27:14 And it’s enough to make me cringe.
0:27:15 Like, I tighten up.
0:27:18 It’s like, it’s as if I’m ready to get, you know, hit by something.
0:27:21 I think many people hearing this will imagine that sound.
0:27:22 It’s the same thing.
0:27:34 Is the relationship between our cringing, our physical cringing, and these high-frequency sounds, is that a pain offset mechanism?
0:27:41 You know, in other words, in the visual system, if you just show someone a really bright light, they’ll raise their hands, they’ll turn away.
0:27:42 It’s to protect their retinas.
0:27:43 And it’s a reflex.
0:27:45 It’s a hardwired reflex.
0:27:54 And when we’re sick, incidentally, there’s this incredible reflex pathway that sort of becomes unveiled that we always have, which gives us photophobia.
0:27:58 Bright light that we normally might like suddenly becomes aversive.
0:28:00 And it can give us headache, headaches, and this kind of thing.
0:28:03 Are there similar pathways in the auditory system?
0:28:04 There are.
0:28:08 There is this phenomenon of hyperacusis or even phonophobia.
0:28:17 And when it comes to hyperacusis, it frequently accompanies hearing loss.
0:28:26 And really what happens in people with hearing loss is that sounds have to be loud enough for them to hear them.
0:28:30 But if they are too loud, that can be painful, very uncomfortable.
0:28:33 So their dynamic range of hearing is reduced.
0:28:38 And pretty much everybody with hearing loss experiences that.
0:28:45 Now to have a real fear of sound, phonophobia, that’s not common.
0:28:50 And it’s usually linked with some underlying mental health condition.
0:28:57 It’s more common in people with obsessive-compulsive disorder or personality traits and other conditions.
0:29:04 So interesting how the timbre of somebody’s voice leaves a mark on us, pleasant or unpleasant.
0:29:05 Yes.
0:29:27 And going back to what you said earlier about hearing being so important and, you know, historically people really identifying that, I think we’re all familiar with something somebody said, perhaps by virtue of the way they said it and or what they said, kind of ringing in our ears, keeping, you know, it’s hard to forget those things.
0:29:32 Things we see, believe it or not, are pretty easy to unsee over time.
0:29:36 Some things that are very extreme can leave a, you know, a post-traumatic stress stamp.
0:29:42 But if you think about the number of violent and challenging images that we’re bombarded with all the time.
0:29:48 If you just go on X nowadays, I mean, it’s very hard to not see something you didn’t want to see.
0:29:51 But one, you can kind of suppress that over time.
0:29:52 It takes work.
0:29:59 But if you hear something that’s very disturbing, it’s very hard to unhear it.
0:30:03 It stays in our memory banks quite a long time.
0:30:05 You are correct.
0:30:10 And that can be true for both unpleasant and pleasant experiences.
0:30:14 And you are absolutely correct that it goes into our memory bank.
0:30:15 And how do we know that?
0:30:18 There are people who are profoundly deaf.
0:30:26 And if they have been profoundly deaf for many years, and now they are becoming a candidate for having cochlear implant surgery,
0:30:33 and that’s surgery that bypasses any cells in the inner ear that could be missing or non-functional,
0:30:37 and it directly electrically stimulates the auditory nerve,
0:30:42 before they have that cochlear implant surgery when they’ve been profoundly deaf,
0:30:48 they can have memories of music that they used to listen to.
0:30:51 So these are auditory hallucinations, but they are different.
0:30:53 They’re musical hallucinations.
0:30:57 They’re not like auditory hallucinations that people with schizophrenia have.
0:30:58 They’re not hearing voices.
0:31:04 They’re hearing symphonies and concerts in their head, whatever music they used to listen to.
0:31:09 And what’s fascinating is after they get the cochlear implant, and now they can hear a speech,
0:31:12 those musical hallucinations go away.
0:31:14 Amazing.
0:31:14 Yes.
0:31:15 Amazing.
0:31:19 We’ll get back to cochlear implants because I have a couple of friends in the deaf community.
0:31:25 And my understanding is there’s a very divergent stance on the cochlear implant within the deaf community.
0:31:26 Yes.
0:31:35 In part because the deaf community forms a lot of within community and outside of community bonds through lip reading and through sign language.
0:31:39 And the cochlear implant really transforms the way they interact with the world.
0:31:41 So we’ll get back to that a little bit later.
0:31:51 It’s an interesting and I must say I was about to say controversial topic, but I’ve been really positively surprised, actually,
0:31:59 how people in the deaf community are very open about talking about deafness and repair of deafness and whether or not they would want it or not want it.
0:32:10 Whereas from my work as a vision scientist, most of the people in the low vision, no vision community would say if they could get vision back or if they could get vision, they would take it.
0:32:17 Although right now the technologies don’t quite exist to go from completely blind throughout one’s life to seeing, although those may be coming.
0:32:22 In the meantime, let’s talk about hearing loss.
0:32:26 Let’s talk about what happens when we go to a loud concert.
0:32:28 I fear I’ve done this.
0:32:33 And you get too close to the speakers or they’re just turned up too loud.
0:32:38 And the acoustics of the room make it such that you have ringing in your ears the next day.
0:32:46 If you have ringing in your ears after a concert or some other auditory experience, does that mean that some level of permanent damage was done?
0:32:48 Possibly.
0:33:01 And why I say possibly is that until maybe 10 years ago, we thought that if you go to a concert like that, you have ringing in your ears.
0:33:03 You may even feel like your ear is clogged.
0:33:09 And then it goes away that that is temporary threshold shift.
0:33:15 But now we know that some forms of temporary threshold shift are, in fact, permanent.
0:33:23 Although your hearing may come back, and in fact, we can see it on audiometric testing,
0:33:33 we now know that the wheel has been set in motion where synapses that connect these sensory cells to neurons that contact them
0:33:37 have been damaged or destroyed by loud sound.
0:33:39 It takes them a long time to degenerate.
0:33:47 And in fact, it’s led to the concept of the so-called hidden hearing loss.
0:33:53 So there is obvious hearing loss that you can measure on audiograms.
0:33:59 But now we have a new appreciation for the type of hearing loss that you are describing, and it’s more common among young people.
0:34:04 And if they go through standard audiometric testing, it’ll be perfect.
0:34:06 All of their audiometric thresholds are fine.
0:34:15 However, they report that they cannot hear clearly in a noisy background, or they have this tinnitus that they didn’t have before.
0:34:26 So what’s now emerging from both animal and clinical data is that, indeed, there are anatomical correlates of this damage.
0:34:33 And it typically involves synapses between sensory cells and neurons, or it may even involve hair cells and neurons themselves.
0:34:38 So what is the loud noise level?
0:34:40 That was one of your questions.
0:34:48 For example, right now, we are speaking at about 60 decibel in terms of sound pressure level.
0:34:50 And what does that mean?
0:35:04 Decibel, it’s a logarithmic scale, because we had to compress an enormous scale that’s really million-fold from the softest sound to the loudest sound that we can hear.
0:35:08 We compressed it to a linear scale that looks linear.
0:35:10 It’s not, but it’s a logarithmic scale.
0:35:12 So that’s what dB is.
0:35:17 And we can hear anywhere between 0 to 120 decibel and louder.
0:35:21 We can even hear a jet engine, and that’s 140 decibel.
0:35:29 And to calibrate us, if I’m now speaking at around 60 decibel, to come here, I had to take a plane.
0:35:35 And the noise in the cabin is typically around 80 decibel.
0:35:40 If you drive a motorcycle, it’s about 100 decibel.
0:35:48 If you go to a concert that you have referred to, it’s not uncommon that it’s between 110 and 120 decibel.
0:35:53 And jet engine is around 140 decibel.
0:36:04 And the loudest noise level ever achieved at a football stadium was in Kansas City, and it was 142 decibel.
0:36:07 That is deafening.
0:36:09 Literally deafening?
0:36:10 Literally deafening.
0:36:15 Because it’s, again, a logarithmic scale.
0:36:24 So for every 3 decibel increase in sound intensity, you have to halve the time exposure that’s safe.
0:36:28 So now, back to your question, what is safe?
0:36:33 Roughly speaking, 80 decibel is fine for 8 hours.
0:36:40 But for any 3 decibel increase, you have to halve it, which means 83 decibel is okay for 4 hours.
0:36:43 86 for 2 hours.
0:36:45 89 for 1 hour.
0:36:48 92 for half an hour.
0:36:54 Well, most of music concerts that use amplified music are above 92 decibel.
0:37:03 But it’s not that everyone develops hearing loss, and it’s not that we have to stop enjoying music concerts at all.
0:37:05 It’s just that we have to take precautionary measures.
0:37:10 First of all, why does music have to be that loud?
0:37:15 It’s kind of a peer pressure phenomenon, because most people don’t even enjoy it when it’s that loud.
0:37:20 But they feel like they should, because somehow it’s a kind of being youthful.
0:37:21 I have an idea.
0:37:22 But it’s just a speculation.
0:37:27 Part of it, I think, is to drown out other sounds in the crowd.
0:37:44 In the same way that if you go to a party, and they dim the lights on the dance floor, partially because of people’s self-consciousness, but, you know, people are more likely to dance when not every, like, movement of the dance is being detected, right?
0:37:45 Than bright lights.
0:37:51 Like, when the lights come up at the end of a night of dancing, you’re going to feel like, okay, party’s over, right?
0:37:52 And that’s what they’re trying to signal.
0:37:57 So part of it is probably to drown out the micro-conversations going around.
0:38:24 And I think the other part is that I do think that, like with highly palatable food, you know, there’s been this sort of drift of setting higher and higher thresholds of what’s normal, and that people many times go to concerts because they want to feel the music at the level of an intense sound wave, especially, you know, like, I mean, if you live in California, probably anywhere in the country, but you’re familiar with someone pulling up next to you and really blasting the bass in their car, and your whole car is shaking.
0:38:30 And they’re obviously enjoying it, and to you, it’s aversive, or you like it, depending on who you are.
0:38:39 But most of the time, we don’t want other people’s sound experiences encroaching on ours at that kind of, like, whole vehicle level.
0:38:47 So, yeah, I think it’s this notion that we can’t feel the music unless it’s very loud.
0:38:48 Again, it’s a speculation.
0:38:59 There is something to it, because it turns out that at loud enough sound intensities, the vestibular system is stimulated at all, as well.
0:39:04 And there are experiments in animals that have shown this unequivocally.
0:39:10 So, there are vestibular or balanced neurons that actually respond to loud sound.
0:39:14 So, yes, there is a component of that.
0:39:20 However, we talked about initially how delicate this organ is.
0:39:29 Again, it can detect sub-angstrom displacements, and now you are literally hammering it with this blast noise.
0:39:31 It’s like an elephant in a china shop.
0:39:34 And that is not good.
0:39:37 And that’s what contributes to some hearing loss.
0:39:43 So, what can you do to protect your hearing if you’re going to a loud concert like that?
0:39:45 Definitely wear earplugs.
0:39:51 You can even measure sound intensities if you want to be very quantitative about it, because now you have a rough formula.
0:39:55 You can get a dB app on your phone.
0:39:56 It’s free.
0:39:57 You can measure it.
0:40:05 And let’s say if it’s 120 decibel at the concert you’re using, then wear earplugs that provide at least 30 decibel of attenuation.
0:40:13 When you buy these earplugs in a store, it tells you what degree of attenuation they provide.
0:40:15 And it can be anywhere from 10 to 30.
0:40:21 Musicians’ earplugs usually provide about 14 decibel of attenuation.
0:40:25 So, clearly, that wouldn’t be good enough for this event.
0:40:32 And you have to put them in correctly, because if they don’t fit in, it doesn’t matter what the number says.
0:40:33 They’re not protecting you.
0:40:34 So, that’s one thing that you could do.
0:40:40 Another thing that you can do is take magnesium before going to a loud concert.
0:40:47 And this is because studies have shown that magnesium can protect against noise-induced hearing loss.
0:40:54 And the studies were done in countries where they have mandatory military service.
0:41:03 And they literally grouped people into those who received magnesium before those exercises and those who didn’t.
0:41:09 And everybody was exposed to the same artillery and explosions as a part of preparation.
0:41:13 Those who took magnesium beforehand had less hearing loss.
0:41:29 Also, what measurements have shown in animal models is that after noise trauma, it’s the levels of magnesium that changed the most in the cochlea, in the organ of hearing, more than any other ion that’s been studied.
0:41:43 And also, what large-scale human population studies have shown is that those with higher magnesium serum levels or higher magnesium intake tend to have better hearing.
0:41:52 However, that needs to be further studied and replicated because the precise dose is really not known or the formulation.
0:41:55 Because, as you know, there are many different kinds of magnesium.
0:41:57 And magnesium is good for your whole body.
0:42:03 But depending on the formulation, it may be better for the gut versus the musculoskeletal system versus the brain.
0:42:07 And different formulations have been studied in different scenarios.
0:42:14 What we now think is that magnesium threonate is most efficient in crossing the blood-brain barrier.
0:42:19 So we think it’s probably the best for hearing protection.
0:42:22 But that study is yet to be conducted.
0:42:24 Incredible.
0:42:34 I’ve been taking magnesium threonate for, gosh, well over a decade because I learned that it was the form that most readily crosses the blood-brain barrier.
0:42:37 I was interested in the cognitive-enhancing effects.
0:42:39 I take it about 30 or 60 minutes before sleep.
0:42:48 And it does seem to make me a little bit more drowsy and does seem to improve the architecture of my sleep, slow wave and REM sleep measured, et cetera.
0:42:53 I know a lot of people take magnesium bisglycinate as an alternative.
0:42:55 As far as I know, those are interchangeable.
0:42:58 I think it’s wonderful if people are getting enough magnesium from their diet.
0:43:01 And if they need to supplement, they think about that.
0:43:20 I’m struck by these studies on magnesium because, you know, in the visual system, the field of ophthalmology has been sort of reluctant to embrace supplementation with things, except for a few things.
0:43:24 Everyone knows you need enough vitamin A, you know, and carrots are good for your vision and this kind of thing.
0:43:26 But it’s a fat-soluble vitamin, so you don’t want to overdo it.
0:43:44 But nowadays there’s kind of an emerging sense from some of our colleagues in ophthalmology at Stanford that some of the things found in supplement form actually can help protect the retinal cells, which is a sort of correlate of the hair cells in the context of hearing loss.
0:43:48 So I’m curious as to why magnesium would do this.
0:43:56 Is it something about the lymph, the sort of the chemical architecture of the cochlear environment?
0:43:58 Is it happening at the level of the brain?
0:44:01 Maybe we don’t know, but it’s very interesting.
0:44:04 I think it’s probably both at both levels.
0:44:10 And by the way, going back to supplementation, really the best way is to have a healthy diet.
0:44:16 And numerous studies have shown is that what we absorb through a healthy diet is better than supplementation.
0:44:23 And supplements are not really strictly regulated in the way that other prescription medications are.
0:44:28 So what the label says on a box could be all over the map.
0:44:30 You need to go with a trusted brand.
0:44:39 Some companies get third-party testing, but I completely agree that the supplement industry is replete with all sorts of things, especially, for instance, melatonin.
0:44:53 You know, the great sleep scientist, Matt Walker, author of Why We Sleep, et cetera, has cited experiments where they look at bottles of melatonin labeled as one milligram, three milligrams, five milligrams, ten milligrams.
0:45:03 And the actual amount in one pillar capsule can be off by 85% in either direction, in either direction, either much less than you thought or much more.
0:45:12 Actually, that reminds me to ask, is there any evidence that taking magnesium can help slow, reverse, or prevent tinnitus?
0:45:17 Because I know many people are really struggling with tinnitus.
0:45:28 What is known is that for some people with tinnitus, in the setting of migraine, magnesium supplementation really helps.
0:45:40 As you know, magnesium can do magic for people with migraines, along with healthy diet and coenzyme Q10 and B-complex or at least B12 vitamins.
0:45:45 So that is the standard part of armamentarium to treat migraines.
0:45:54 And some people with migraines have tinnitus during their exacerbations, as well as auditory fluctuations.
0:45:56 And some people get really dizzy.
0:46:06 And this is where thorough evaluation is really key, because someone may assume that the problem is in the inner ear, but the problem is really in the brain.
0:46:23 And then going back to foods that are good for you, that are better than a supplement, given this unregulated nature of the supplements, they include seeds and nuts and fish, especially salmon, and then green leafy veggies like spinach.
0:46:27 They are all rich in magnesium, but it’s all common sense.
0:46:30 Basically, what’s good for your body is good for your hearing.
0:46:30 Yeah.
0:46:45 Although, you know, having done many episodes on nutrition and talked to experts in nutrition, the number of people that really go out of their way to make sure they get enough green leafy vegetables, fiber, and meet their protein quota per day.
0:46:52 Which, you know, nowadays there’s a kind of controversy about how much protein, but, you know, most people just don’t do the common sense thing.
0:47:02 So I think what I’ve learned is everyone, including myself, needs to be reminded to get sunlight, you know, set our circadian rhythm, not be on screens too late, get enough magnesium, ideally from food.
0:47:18 I completely agree that supplements are useful in the context of when you’re already doing things correctly with your nutrition, or sometimes it’s the case that when people are traveling or they’re overly busy, they’re just not paying enough attention to the foods they’re eating.
0:47:21 But that’s not a long-term solution.
0:47:23 So I completely agree.
0:47:26 Green leafy vegetables, fish.
0:47:30 And this information is now easy to find online, right, which forms of magnesium.
0:47:42 So for people that have tinnitus or that don’t want to get tinnitus, do you see any harm in them kind of emphasizing magnesium intake through food and or supplementation?
0:47:46 That really hasn’t been studied for any type of tinnitus.
0:47:50 It’s been studied in the context of migraine, and there it really helps.
0:47:56 And tinnitus, it’s an umbrella term, just like sensorineural hearing loss, it’s an umbrella term.
0:47:56 I see.
0:47:59 It encompasses lots of different conditions.
0:48:08 When it comes to hearing loss, there are already more than 200 genes identified to cause hearing loss, and that’s the genetic component.
0:48:16 But then there are environmental components to hearing loss, which includes noise trauma that we talked about, aging, infection.
0:48:33 Lots of different infectious diseases can cause hearing loss, not only viruses from the herpes family, like herpes simplex virus, which causes a cold sore, or cytomegalovirus, which is the most common congenital infectious cause of hearing loss.
0:48:35 CMV is very common.
0:48:35 CMV is very common, right?
0:48:36 Exactly.
0:48:41 Something like 80% to 90% of adults in the United States carry CMV.
0:48:41 Yes.
0:48:42 What does that mean?
0:48:49 That at one point they had the CMV virus in it, they felt it as a cold or a flu, but it was CMV?
0:48:49 Yes.
0:48:50 Indeed.
0:48:50 Indeed.
0:49:00 And some of these viruses, they stay dormant and live with us forever, and then when the immune system gets weakened, then they can wreak havoc.
0:49:11 And some of the other viruses from the herpes family, like Epstein-Barr virus, CBV, it’s actually linked to cancer, different cancer types, including nasopharyngeal cancer.
0:49:16 So that’s yet another cause of hearing loss, infectious hearing loss.
0:49:28 Then there is immunologic hearing loss, when there is no infection, but it’s an inflammation, such as people with celiac disease or rheumatoid arthritis.
0:49:41 They may have higher predisposition to developing hearing loss, not only because the little tiny joints in the middle ear become fixed and don’t vibrate as well, but also because the inner ear is injured.
0:49:51 So when we now say sensorineural hearing loss, we actually cannot specifically say exactly what’s wrong.
0:49:52 It’s like a fever.
0:49:54 It could come from any number of things.
0:49:55 Interesting.
0:50:17 And the reason for that really goes back to the tiny size of the inner ear to the point that if you image it using the current state-of-the-art imaging tools that include computer tomography or a CT scan or MRI, which is magnetic resonance imaging, you don’t see cells in the living human inner ear.
0:50:28 You just see a gray, and the organ is too small to be detectable by technologies of that resolution.
0:50:31 Another issue is that you cannot biopsy it.
0:50:36 It’s so tiny that if you did tissue biopsy, you would destroy it.
0:50:52 So that has really stimulated lots of very promising research in the area to improve diagnostics for hearing loss, which include both high-resolution imaging of the inner ear and liquid biopsy as opposed to tissue biopsy.
0:51:09 And we have shown that if you take as little as half a microliter of that fluid pair lymph, we can detect molecular differences between mice with or without hearing loss.
0:51:15 However, we have also collected this fluid from patients who undergo ear surgery.
0:51:33 It’s either when we perform cochlear implantation, for those who are profoundly deaf, or we literally have to drill through the inner ear to get to the brainstem because they have a tumor, such as a vestibular schwannoma or an acoustic neuroma, which is a tumor that causes hearing loss.
0:51:42 So in these two instances, we can actually get inner ear fluid, and we can study it, and we can see differences.
0:51:45 So I think that’s a promising direction on the horizon.
0:51:57 Another diagnostic possibility is genetic testing that’s relevant for people in whom there is a family history of hearing loss.
0:52:09 But today, when we test for known deafness-causing genes, it comes back with a definitive answer only in 50% of people.
0:52:17 And in another 50%, it often lists lots of variants of unknown significance.
0:52:21 They are so common that we even use an acronym, VUSs.
0:52:26 And some people will have tens, if not hundreds, of these variants of unknown significance.
0:52:28 So what do you make of that?
0:52:31 You just shrug your shoulders, and at this point, we say, well, we don’t know.
0:52:48 But now, one exciting research direction that we are pursuing with other investigators at Stanford and in collaboration with Google is to use AI to help us figure out which of these variants of unknown significance is actually significant.
0:52:53 And by using those tools, we can establish the diagnosis in 80% of people.
0:52:58 So now that’s for hearing loss.
0:53:00 And you really asked about tinnitus.
0:53:07 But this is really to tell you that both of these terms are huge umbrella terms.
0:53:15 And it’s been super frustrating not having the ability to establish precise diagnosis to guide therapy.
0:53:19 So tinnitus is an even bigger black box.
0:53:23 We’ve known for a long time that there are things that we can do to improve our sleep.
0:53:25 And that includes things that we can take.
0:53:30 Things like magnesium threonate, theanine, chamomile extract, and glycine.
0:53:33 Along with lesser known things like saffron and valerian root.
0:53:39 These are all clinically supported ingredients that can help you fall asleep, stay asleep, and wake up feeling more refreshed.
0:53:45 I’m excited to share that our longtime sponsor, AG1, just created a new product called AGZ.
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0:56:11 What you’re saying is extremely important, both by virtue of what you’re explaining in terms of the different types of hearing loss,
0:56:15 new novel ways to detect hearing loss and hopefully treat hearing loss,
0:56:23 but also that we lack subtyping of what we broadly call hearing loss or sensory hearing loss or tinnitus.
0:56:27 This is a ubiquitous problem in the health space.
0:56:33 I had our colleague Mike Snyder from the Department of Genetics on just recently.
0:56:40 That episode came out, and he said we have to stop talking about blood glucose responses.
0:56:42 Some people spike to potatoes.
0:56:43 Other people spike to grapes.
0:56:47 They actually have grape spikers versus potato spikers, and they need different things.
0:56:50 Same thing, we hear fiber is great for us, and I agree.
0:56:51 We need fiber.
0:56:57 Some people experience a profound reduction in inflammation when they eat certain types of fiber.
0:57:03 Some people experience significant inflammation, whole body inflammation when they eat other types of fiber.
0:57:13 This was actually studied by Justin Sonnenberg and Chris Gardner in their now-becoming classic study about the value of low-sugar fermented foods,
0:57:19 which were great for the microbiome, but the fiber group, actually, the inflammatome in some people show market increase.
0:57:21 Do we say fiber is bad?
0:57:23 No, it depends on the type of fiber.
0:57:23 You say fiber.
0:57:24 And on and on.
0:57:27 And we can talk about, it’s like when people say colorblindness, I would say, well, like, which kind?
0:57:29 I mean, there’s so many types of colorblindness.
0:57:32 So it’s very important that you’re highlighting this for vision as well.
0:57:38 I definitely want to ask something about tinnitus because I went into the literature, this was a while ago,
0:57:46 and just was trying to explore for what’s being done or what’s been tested in the nutrition and supplementation space,
0:57:48 just because that happened to be what I was looking at.
0:57:53 And it seems that there are a few studies, I don’t know how powerful these studies are,
0:57:58 but a few studies that suggest that perhaps low-dose melatonin might help.
0:58:02 But then I realized it’s very difficult to separate those out from improvements in sleep
0:58:04 because the people were taking the melatonin before sleep.
0:58:08 And then we know that anytime you sleep less, your inflammation goes up,
0:58:11 you have a bunch of gut issues and whole body issues.
0:58:15 So is there any evidence that there’s anything that people could safely experiment with,
0:58:18 perhaps magnesium if they choose through diet or supplementation or both,
0:58:21 but is there any indication that people can take something,
0:58:28 or is it really the case that they need to go see a proper auditory neurophysiologist or clinician like you
0:58:29 and get treated for tinnitus?
0:58:34 Yeah, it’s the latter, that they need to really be evaluated.
0:58:39 And what studies have shown and systematic reviews and meta-analysis
0:58:44 that none of this supplementation makes a difference for tinnitus.
0:58:45 Because it’s a real shame.
0:58:46 It’s a shame.
0:58:54 And it’s also potentially a methodological issue because, again, everything was lumped under the same umbrella.
0:59:00 But it is conceivable that different subtypes may respond to certain interventions.
0:59:05 But because we don’t know how to identify these subtypes, we are lumping them all together.
0:59:10 So when you lump them all together and put all studies together that have ever been done
0:59:14 and perform meta-analysis, then it sounds like none of them make a difference.
0:59:20 So to the point that the American Academy of Otolaryngology Head and Neck Surgery
0:59:24 really endorses two main interventions.
0:59:28 One is amplification with a hearing aid for those who need it.
0:59:31 And two is cognitive behavioral therapy.
0:59:34 Those two interventions have actually shown to make a difference.
0:59:36 There are other things that have been tried.
0:59:38 Some people take things on their own.
0:59:42 There is anecdotal reports of potential benefit.
0:59:48 But that hasn’t panned out in large-scale epidemiologic studies that have had the appropriate control group.
0:59:50 Thank you for that.
0:59:55 When Michael Kilgard was a guest on this podcast, he’s an auditory – he’s a neuroplasticity guy,
1:00:02 but spent most of his time in the auditory system, now vagus nerve system, but he’s from Mike Merzenich lineage.
1:00:10 He emphasized that people who have tinnitus, the fact that they think about it and pay attention to it
1:00:12 tends to exacerbate the circuitry.
1:00:12 Yes.
1:00:18 And it sounds like a brush-off, but he really encouraged people to try and not think about it,
1:00:25 try to distract themselves, because that could help prevent some of the ramping up of the – what we call,
1:00:27 as you and I call, the gain of those circuits.
1:00:32 Because – and people don’t like that answer, and I can understand why they don’t like it,
1:00:35 because they’re like, well, you all want me to think about this loud ringing in my ears?
1:00:41 And he’s saying, yeah, until you get a treatment, a proper treatment, you need to try and not think about it,
1:00:44 because thinking about it makes it worse, which, of course, for some people makes it worse.
1:00:45 Yes.
1:00:49 But nonetheless, I think it’s a very important message that if you have tinnitus,
1:00:54 to do everything you possibly can to try and distract yourself from it and then pursue proper treatment.
1:00:55 Exactly.
1:00:58 And in fact, that’s what we recommend in the clinic as well.
1:01:03 Well, and lots of people find it reassuring, because we first have to do complete and thorough evaluation,
1:01:09 which includes examination of the ears, examination of the whole head and neck, hearing testing,
1:01:13 to make sure that there is no asymmetry or difference between the two ears.
1:01:19 If there is a significant asymmetry, that triggers imaging or additional testing,
1:01:21 like auditory brainstem evoked response testing.
1:01:28 And imaging, it’s typically MRI, and this is where we are looking for these tumors that could cause hearing loss.
1:01:33 They are super rare, so I don’t want people to be stressing out and thinking they have that.
1:01:36 But it’s important to rule out.
1:01:50 So indeed, once we find that there is no tumor, then we do try to reassure patients and explain
1:01:55 that tinnitus is indeed a phantom sound produced by the brain and why it makes it.
1:02:01 And the more you think about it, the more you reinforce that circuit, just like you said.
1:02:07 So if you are occupied by other things or you have background noise, it lessens it.
1:02:13 And we already know that this is true in terms of experiments that have been conducted
1:02:19 and that has been shown by electrophysiology, by imaging, even in people.
1:02:23 In people with tinnitus with normal audiometric thresholds,
1:02:27 you can see hyperactivity in auditory centers in the brain.
1:02:31 And in particular, the area that has been imaged is the inferior colliculus.
1:02:35 And so we know that there is hyperactivity.
1:02:39 Also, most of the brain works on the principle of inhibition.
1:02:50 Now, what has been shown in animal studies is that loud noise, which causes tinnitus, can lead to loss of that inhibition.
1:02:52 So that can lead to hyperactivity.
1:02:58 But tinnitus can also be due to increased synchrony.
1:03:02 And that informs different strategies going forward.
1:03:08 But at this day and age, really the best treatment option for tinnitus is a cochlear implant.
1:03:11 However, most people don’t need a cochlear implant.
1:03:12 And why do I say that?
1:03:23 Because we know that 75% of people with tinnitus who undergo cochlear implantation because they have severe or profound hearing loss get better.
1:03:27 And in 10% of those, it goes away altogether.
1:03:35 So it tells you that if you improve function at the periphery, the brain recalibrates and takes care of it.
1:03:36 Which is great.
1:03:38 Which is great, indeed.
1:03:49 And that’s why we are so enthusiastic about all the research that’s happening at Stanford and across the world to regenerate and restore function in the inner ear.
1:03:57 Because that then facilitates the brain’s adaptability to take care of itself.
1:03:59 The brain is so smart.
1:03:59 Yes.
1:04:01 I’ll never forget these studies.
1:04:05 You perhaps, maybe it was Thomas Poggio who authored these studies, I don’t recall.
1:04:07 But where people would wear inverting glasses.
1:04:11 So they put on glasses and then for a couple of days, the entire world looks upside down.
1:04:13 And you would think this would be very debilitating.
1:04:18 And you would think that people perhaps might learn how to, you know, pour water in a way that adjusts for that.
1:04:21 But actually, the brain just flips the image back.
1:04:21 Yeah.
1:04:29 It does a complete reversal, which is incredible because our eye actually inverts images coming into the brain.
1:04:30 And our brain does the same thing.
1:04:32 It does it all the time.
1:04:35 Our brain is incredible with respect to this ability.
1:04:44 I have to ask, with respect to headphones, how do I know if I’m listening to my headphones too loudly?
1:04:50 Because I used to assume that if I use, I use corded headphones.
1:04:56 I don’t like the Bluetooth headphones for reasons related to, anytime I use the Bluetooth headphones,
1:05:02 I get a swelling of the lymph behind my ear, not the sort of lymph that we’re talking about in the inner ear.
1:05:05 And it’s quite, quite consistent effect.
1:05:06 And I think it’s a heat effect.
1:05:09 Some people say, oh, it’s EMS, but I’m pretty sure it’s a heat effect.
1:05:10 So I don’t, and I don’t like them.
1:05:12 I don’t like having my ears plugged with those things.
1:05:15 It doesn’t sound as well to me as corded headphones.
1:05:18 And I also, it was always losing the non-corded ones.
1:05:26 I used to assume that there’s no way that the phone manufacturer would let me turn up my phone loud enough to cause damage to my ears.
1:05:28 How could that possibly be?
1:05:29 Everything’s regulated.
1:05:39 But I recently learned that it’s very easy to exceed the threshold of safety by going not even to the maximum volume of what I’m listening to.
1:05:41 Yes.
1:05:48 And it’s so interesting, that observation that you have made, because these regulations are different in different countries.
1:05:58 So even the same manufacturer of phones will set up the threshold at a lower level for the European market than for the American market.
1:05:59 Wild.
1:06:02 Because the assumption is that Americans like it louder.
1:06:07 They definitely talk louder than many, not all, but many areas of the world.
1:06:12 I was recently in Italy and I went to this farmer’s market and then I was indoors elsewhere.
1:06:15 The Italians talk a lot.
1:06:15 Yes.
1:06:17 And they gesticulate a lot.
1:06:18 And the noise level got up there.
1:06:21 But at one point I was like, wow, you know, it’s so pleasant.
1:06:23 It’s not super loud.
1:06:25 And then I landed in New York City, a city I love.
1:06:26 Yes.
1:06:30 And I was indoors in an environment shielded from outdoor sounds.
1:06:32 I was like, wow, people are super loud here.
1:06:35 And there are a couple other cities where I’ve really noticed that.
1:06:36 And this isn’t a knock on New York City.
1:06:40 But boy, Americans can be really loud.
1:06:45 And to your question, it’s not really the headphone style.
1:06:47 It’s really the sound level.
1:06:49 And you can measure it.
1:06:57 You can measure it on your dB meter that you can download on your phone if you don’t have it already.
1:07:02 And again, the safe rule of thumb is 80 decibel is safe for eight hours.
1:07:09 However, and then for every three decibel increase in sound level, you have to half it.
1:07:11 But what if I don’t use this decibel meter app?
1:07:13 What if I’m lazy and I…
1:07:22 So then if anyone can hear what you are listening to, who is standing by you, it’s too loud.
1:07:23 So that’s a good rule of thumb.
1:07:25 Great.
1:07:28 So parents, take note.
1:07:28 Exactly.
1:07:29 Take note.
1:07:36 If you can hear your child’s music or podcast that they are listening to through the headphones
1:07:37 that they are wearing, too loud.
1:07:46 Is there any detriment to listening in one ear, like setting up a strong asymmetry of sound input over time?
1:07:54 You know, a lot of people will go with one earbud or, you know, they’ll let one earbud dangle out.
1:07:58 Not earbud, but one headphone dangle out.
1:08:00 Is there any detriment to that?
1:08:04 Not really, as long as it’s at the safe sound levels.
1:08:08 It’s really all about what is the sound level that’s damaging.
1:08:10 And it’s not the same level for all.
1:08:20 In fact, if you have a construction worker and you have two of them being exposed to exactly the same levels of noise,
1:08:28 one may lose hearing very quickly and the other may work in that environment for 20 years and have really mild hearing loss.
1:08:35 So very roughly, we categorize them into those with tough versus tender ears.
1:08:37 That’s super simplification.
1:08:46 But it tells you that there must be a genetic predisposition to their vulnerability because they had the same environmental exposure.
1:08:51 And now we are uncovering genes that are contributing to this vulnerability.
1:08:53 And it’s not one.
1:09:00 It seems like it’s several different genes that are working together to orchestrate this sensitivity.
1:09:09 What we have also learned from both human and animal studies is that children are definitely more vulnerable.
1:09:12 So another take-home lesson for the parents.
1:09:16 What may be comfortable for an adult may be too loud for children.
1:09:25 And it’s another important message for how loud different events are in elementary schools or middle schools.
1:09:30 Because by the time they are high schoolers, auditory sensitivities are changing.
1:09:41 But there are numerous studies that have shown that younger adults, younger people or younger animals are more vulnerable to noise levels.
1:09:51 When I was in graduate school many moons ago, I took a great auditory neuroscience class from Irv Hafter, who’s one of the…
1:09:52 A legend.
1:09:57 A legend and a wonderful person and brilliant and just a wonderful person.
1:09:58 And he can move his ears.
1:09:59 He pointed that out.
1:10:00 Maybe he could move his ears.
1:10:07 And I recall him describing something called the two-hit model, which has parallels to concussion.
1:10:08 Where…
1:10:09 And I get asked this a lot.
1:10:12 You know, someone will say, you know, they had a bike accident or something.
1:10:16 Have they had a slip and a fall or maybe they played a sport and they had a concussion.
1:10:17 What should they do?
1:10:22 And the first thing I always say, based on my understanding of concussion, and all my colleagues,
1:10:29 our colleagues support this statement, is don’t get another concussion, especially not anytime soon.
1:10:33 Now, people don’t like that answer when it comes to a particular sport.
1:10:37 But oftentimes the advice is you got to stop playing the sport because if you get another
1:10:41 concussion soon, you’re going to have serious issues down the line, maybe even sooner.
1:10:46 But I recall Irv telling us about this notion that if you leave a concert and the next morning
1:10:52 you notice that your ears feel like they’re a little bit clout, like you have earplugs in
1:10:53 and you don’t.
1:10:57 Or if you hear a little bit of ringing in your ears, that you need to be especially careful
1:11:02 about getting another high threshold sound arriving at your ears because the vulnerability is there.
1:11:10 And two sub-threshold insults, as they’re called, right, to the cochlea, to the hair cells,
1:11:15 each of which is not sufficient to cause damage.
1:11:21 If they occur too closely together in time, you can get very potent damage that’s irreversible.
1:11:27 And so I wonder if it makes perfect sense in the context of like concussion, which we
1:11:28 raised as the parallel example.
1:11:31 And he had some interesting experiments.
1:11:33 I think these were done in guinea pigs, actually.
1:11:38 But you also see this in industrial workers where they have some ringing in their ears after
1:11:40 a long week of being on the construction site.
1:11:41 They’ll go to a concert.
1:11:45 And sure, they could have gone to the concert at another time and it wouldn’t have been an
1:11:46 issue.
1:11:48 They certainly could recover from their work week.
1:11:51 But you put those two things too close together in time and they end up death.
1:11:52 Yes.
1:11:54 It’s adding insult to injury.
1:11:59 And indeed, then the effect can be synergistic as opposed to additive.
1:12:00 Yeah.
1:12:03 I think about this a lot because I like going to concerts.
1:12:05 I also have friends that are musicians.
1:12:11 And I notice all the musicians wear earplugs because they’re very interested in keeping their
1:12:15 ears healthy to be able to create music and listen to the subtleties as they write music.
1:12:20 So I think that there’s this idea that wearing earplugs is kind of nerdy or not cool.
1:12:24 But the very people producing the music that people are listening to, these are rock and
1:12:28 roll musicians, they’re all very, very careful with their hearing.
1:12:29 They’re not messing around.
1:12:33 And some of the earplugs now actually go pretty far in.
1:12:37 So you don’t have to, you know, maybe other people don’t even know you have them in.
1:12:39 Do those work as well?
1:12:40 They do.
1:12:46 It really depends on whether they are fitted properly and how much attenuation they are
1:12:47 designed to provide.
1:12:54 Because some provide only 10 to 15 decibel of attenuation and others provide 30 decibel of
1:12:54 attenuation.
1:12:59 And depending on the ambient noise levels, one versus the other may work.
1:13:04 In the visual system, we know that if you’re in a dark environment or a dim environment
1:13:09 for a while, and you transition out of that environment, the eyes are particularly sensitive
1:13:11 for the first moments.
1:13:13 Is that also true for the auditory system?
1:13:17 So if I wear earplugs and then take them out, do I need to be especially careful about,
1:13:24 in other words, are my ears more susceptible than they normally would be if I’m coming from
1:13:28 a very quiet environment or a noise cancellation headphone environment?
1:13:29 They are.
1:13:34 And the way we know that is from people who have hyperacusis that we alluded to before.
1:13:42 And they are just so uncomfortable being in loud environments or even what we consider normal
1:13:46 auditor environments that they wear earplugs.
1:13:50 But then when they pull them out, everything is unbearably loud.
1:13:56 So in fact, the first thing in terms of counseling them, we say, well, take out your earplugs.
1:14:00 You have to get used to the normal listening environments.
1:14:03 And we already know that the brain is amazing.
1:14:06 It can get used to different stimuli.
1:14:11 And it’s important that it gets natural input so that it can work normally.
1:14:17 Otherwise, indeed, it can calibrate in ways that are unhealthy.
1:14:20 I know the fetus can hear.
1:14:21 Yes.
1:14:28 At what stage does the fetus begin to hear or sense mechanical waves at the level of the cochlea?
1:14:30 In the second trimester.
1:14:30 Wow.
1:14:36 And the organ of hearing is fully formed in utero, fully formed.
1:14:38 Babies coming to the world, ready to go.
1:14:39 Listening, ready to go.
1:14:42 And again, they hear in the womb.
1:14:43 It’s amazing.
1:14:44 Amazing.
1:14:53 So all this stuff about, you know, mothers talking to their unborn embryo and fathers too,
1:14:53 presumably.
1:14:53 That’s right.
1:14:54 But especially mothers.
1:14:55 They’re closer.
1:14:56 They have more opportunities for it.
1:14:58 What are the thresholds?
1:15:00 And the reason I ask is, I mean, can they hear a whisper?
1:15:03 Can they, or what can they hear?
1:15:06 As you can imagine, challenging experiments to perform.
1:15:09 And some are based on electrophysiologic data.
1:15:11 And others are done based on imaging.
1:15:16 And there’s only so much you can do to pregnant women for safety reasons.
1:15:19 So it’s actually hard to precisely answer your question.
1:15:24 But what is clear that the fetus can hear the mother’s voice.
1:15:29 So anything that’s of that same intensity, the fetus can hear.
1:15:35 For me, as somebody who’s long been interested in and worked on plasticity, it absolutely has
1:15:40 to be the case that the infant’s auditory cortex is tuned to the precise frequencies and
1:15:43 other aspects of mother’s voice in particular.
1:15:47 I mean, I think every mother would say, of course, but, but, you know, it, what’s intuitive
1:15:49 is not always scientifically supported.
1:15:51 And what’s scientifically supported is not always intuitive.
1:15:53 So it’s nice when the two things match.
1:15:53 Yes.
1:15:55 Fascinating.
1:15:57 Second trimester.
1:15:58 Wow.
1:16:04 This might seem like a bit of an unfair leap, but dogs have very sensitive ears.
1:16:08 Are we subjecting them to hearing damage?
1:16:12 I know this is more for the veterinary crowd, but I, I’m about to get another dog and I would,
1:16:16 my last dog, I, he always seemed to ignore me no matter what, he was a bulldog.
1:16:18 So that was part of his personality to pretend he couldn’t hear.
1:16:23 But should we be more thoughtful about the hearing of our cats and dogs and other animals?
1:16:24 Of all animals.
1:16:25 Absolutely.
1:16:32 And the most striking example is actually sea animals like whales and dolphins.
1:16:48 All of that noise generated by big ships and motorized vehicles that are in the water are damaging their hearing and modes of communication to astounding and scary ways.
1:16:52 It’s really unfair that we are doing that to the world around us.
1:17:02 So now whales are getting lost because they communicate by sending and receiving these sound waves really long distances, miles away.
1:17:04 And now you find them lost.
1:17:11 They can’t find their crew, the rest of their family, if you call it that.
1:17:21 And if they’re in a quiet environment, the way they used to communicate before the modern industrial world, they function completely differently.
1:17:22 Wow.
1:17:25 So sound pollution in the ocean is a very real thing.
1:17:26 Very real.
1:17:26 Yes.
1:17:29 It’s actually messing their navigation.
1:17:30 Wow.
1:17:39 It’s incredible because I think the paper was published a few weeks ago that light pollution is disrupting the duration over which songbirds are singing.
1:17:43 And it turns out they’re singing longer throughout the year than they normally would.
1:17:44 And everyone goes, oh, nice.
1:17:44 Songbirds sing.
1:17:48 But it’s screwing up all the mating patterns and the migration patterns.
1:17:59 I mean, we may see the eradication of many species, which I hope people realize is not just about being able to see them in a zoo or appreciate a photograph of them.
1:18:02 I mean, every animal impacts the ecosystem of another.
1:18:04 So I think it’s so important what you’re saying.
1:18:12 Are there any efforts being made to try and create limitations on where sound pollution or how much sound pollution can occur in the oceans?
1:18:13 I know it’s hard to regulate.
1:18:18 It’s hard because it’s not even tightly regulated for people on land.
1:18:19 Good point.
1:18:23 And there’s a lot of room for improvement.
1:18:26 For example, you have mentioned that you’ve traveled the world.
1:18:31 You have noticed that in Western Europe, amplified music is not allowed on the streets.
1:18:39 But in the United States, and you mentioned New York, you can have any artist amp up the volume to any level they want.
1:18:40 Or Venice Beach.
1:18:42 People bike around with speakers blasting.
1:18:43 Yes.
1:18:44 It’s completely unregulated.
1:18:52 And when I have approached some people about this topic, then I was told, well, this is a free country.
1:18:54 People should be allowed to do whatever they want.
1:18:59 And if they choose one behavior, then it’s up to them.
1:19:00 They know the consequences.
1:19:09 So there are pros and cons to that because as physicians and scientists, we also know what’s good for people.
1:19:24 And if that information is not widely disseminated or if it’s not widely accessible, which our conversation today clearly illustrates it’s not, then having some regulation in place to protect us all is a good thing.
1:19:33 Yeah, I mean, we don’t allow people to dump certain chemicals into the sewer, go down the drain, because we understand the toxicity of that.
1:19:39 What we’re talking about here is sensory-induced damage to the nervous system.
1:19:40 Yes.
1:19:41 I mean, which is no joke.
1:19:48 I mean, it’s just as serious to me as a chemical that somebody might put into, you know, the drinking water.
1:19:49 I mean, you don’t want that.
1:19:54 So I think it’s very important that we’re highlighting these topics.
1:20:07 That directly links to what you mentioned before, the importance of hearing for emotional communication, for relational well-being, and for cognition.
1:20:12 So now there’s mounting evidence for a strong link between hearing loss and dementia.
1:20:16 It’s not that everyone with hearing loss will develop dementia.
1:20:24 So I really want the listeners to feel reassured that they don’t need to run home and purchase hearing aids right away.
1:20:26 It’s just not the case.
1:20:30 However, we are trying to identify who is at risk.
1:20:45 And the standard tests are not that helpful in that regard, because if you get just the standard audiometric testing, where you’re in a sound booth and they play different tones and you raise your hand if you hear it, and then you have a plot generated,
1:20:53 And it turns out that you can have 90% of neurons gone, and your audiometric thresholds could be normal.
1:21:02 And it’s because the auditory system is so exquisitely sensitive that there is tremendous redundancy in it.
1:21:07 And we talked about sensory cells, how they are connected to the brain by the auditory nerve.
1:21:13 It turns out that 10 different nerve fibers contact a single sensory cell.
1:21:15 Do you need all 10 of them to perceive sound?
1:21:17 No, you need one.
1:21:22 However, you need all 10 of them if you are in a noisy environment.
1:21:35 So going back then to the link between hearing loss and cognitive decline, we are now using different tests to identify people who are at risk.
1:21:47 And studies such as testing speech in noise or the ability to understand words in a noisy environment as opposed to in a quiet environment turns out to be helpful.
1:21:59 It’s not so simple, it’s not that there is one test that has perfect sensitivity and specificity, but the field has recognized the need to develop better hearing tests, which are being developed.
1:22:10 I love hearing that because, no pun intended, because when I was a kid, I remember getting on, they would take you out of class, you’d get onto, it was typically a bus or a van, and you’d sit there and then you’d do the hearing test.
1:22:14 While that was appreciated, it was not very sophisticated.
1:22:16 I like to know that there’s been an evolution.
1:22:21 That brings up an interesting scientific phenomenon as well, which is the cocktail party effect.
1:22:22 Yes.
1:22:28 Here, you and I are sitting in a room that is essentially silent, except for a few noises around us from time to time.
1:22:37 But if we go to a loud environment, within a few moments, we can hold a conversation and essentially rule out all the other sounds.
1:22:39 Do we know where in the brain that occurs?
1:22:43 My guess is it’s a circuit or network-wide phenomenon, but that’s a brain thing.
1:22:44 It’s a brain thing.
1:22:45 It’s a circuit.
1:22:51 And it’s absolutely essential for understanding speech and noise.
1:22:57 In fact, people with hearing loss typically experience problems understanding speech and noise.
1:23:00 They have no problem in a quiet and facing you.
1:23:14 In fact, that’s a big message for everyone who is listening, that it’s more important to face someone and speak slowly if they have hearing loss than speaking loudly.
1:23:16 I mean, than yelling.
1:23:29 And so if someone has hearing loss and you are trying to talk to them with water running or TV on or you are trying to talk to them from a different room, forget about it.
1:23:34 You really have to face them and it has to be quiet and you have to slow down.
1:23:37 And then they can really understand so much more.
1:23:39 Thank you for that.
1:23:44 I have a family member who is suffering from some moderate hearing loss.
1:23:54 And I do notice that if there’s anything going on in the background while we’re on a phone call or even in person, it’s very – they get discombobulated.
1:23:55 And they’re very cognitively sharp.
1:24:05 But the relationship between hearing loss and loss of cognition, what we call age-related dementia, people normally hear the word dementia and they think, oh, Alzheimer’s.
1:24:13 But the reality is we’re all going to lose some cognition, speed or some other aspect of it with time.
1:24:19 And it seems that vision loss and hearing loss are profoundly linked to age-related dementia.
1:24:41 And I wonder if you could just speculate on whether you think that has to do with how hearing loss in this case changes our behaviors and then causes loss of neurons in other areas of the brain in the same way that, for instance, if I had chronic ankle pain on my left side, I’d probably take the stairs less.
1:24:44 I would at first probably push myself to do it.
1:24:46 But at some point, I would probably take the stairs less.
1:24:48 So then you say, we take the stairs less.
1:24:49 You get less fit.
1:24:51 Cardiovascular fitness declines over time.
1:25:05 And, you know, did the ankle actually cause the cardiovascular issue not directly but indirectly in the same way that if hearing is challenging, we’re less likely to interact socially, which also feeds back on dementia.
1:25:10 Is that how it works or is there a direct link to unplugging some of the auditory input?
1:25:12 We think that it’s both.
1:25:16 However, the direct link has not been established yet.
1:25:26 Lots of studies are being done, both in people and in animal models, trying to really establish the direct link.
1:25:30 So there are data supporting it and refuting it.
1:25:32 So that’s why it’s an active area of research.
1:25:43 The indirect link is super well established because we know that hearing loss leads to social isolation, to depression, and cognitive decline.
1:25:53 In fact, the cost of unaddressed hearing loss is the staggering nearly trillion dollars annually.
1:25:54 Trillion.
1:25:55 Trillion.
1:25:55 With a T.
1:25:56 Absolutely.
1:25:56 Whoa.
1:26:02 Yes, and it’s because people have issues getting employed.
1:26:08 They may not get the best jobs that they would like to be qualified for.
1:26:15 All of arrangements that have to be done to make them as fully functional as possible are very costly.
1:26:26 So, indeed, it’s an enormous problem that really needs more focus, more attention, and more research to develop new therapies.
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1:27:44 Do non-deaf, non-hearing impaired people lip-read?
1:27:48 Are we always lip-reading a little bit and we don’t realize it?
1:27:57 Some people are better than others, and as we’ve been discussing all along, it’s not that one size fits all.
1:28:07 All of us are a little different, and some people are better at some things than others, and people lip-read to different degrees depending on all sorts of things.
1:28:23 Their innate predisposition, their potential hearing loss that they may not even know, their artistic nature where they are analyzing a face all the time, their engagement and interest in what’s being said.
1:28:39 So going back to your question about the cocktail party environment, it’s a problem for standard hearing aids in an environment like that because they tend to amplify everything, including that background noise.
1:28:58 So that has led to a new generation of hearing aids that are AI-informed and really are performing auditory scene analysis in real time to pick up signal from noise and reduce amplification of the noise and reduce feedback.
1:29:01 So that’s an active area of research.
1:29:04 The latest data, very promising.
1:29:13 However, what’s still needed is large-scale controlled studies comparing traditional versus AI-enhanced hearing aids.
1:29:19 And indeed, that auditory scene analysis in a cocktail party environment is a problem.
1:29:24 For example, directional hearing aids can address it to a point.
1:29:31 I mean, hearing aids that have directional microphones, if you know who you want to be listening to because then you face them.
1:29:43 However, you may also want to be hearing someone who’s talking behind your back and you don’t realize it until you hear the first sentence or two that they have said.
1:29:47 So if you have purely directional microphones, you’re not even aware that that’s happening.
1:29:57 And that’s why hearing aids with directional microphones are loved by some and not by others.
1:30:12 So again, really all of this highlights that we are all a little different and it calls for personalized approaches that are tailored to a given individual’s makeup and needs and preferences.
1:30:17 I’m a big proponent of trying to get great sleep, enough sleep.
1:30:23 It’s a challenge for everybody, but it’s definitely worth striving towards because it’s really the foundation of mental and physical health, right?
1:30:26 I think everyone agrees on that nowadays.
1:30:38 Again, hat tip to Matt Walker for really being the first about 10 years ago to really bring it out of the scientific community because it was Dr. Dement at Stanford and others who did all this pioneering work.
1:30:50 And he himself was a physician and he was saying, you know, many deaths, sadly, of patients are due to sleep deprivation and fatigue of physicians and nurses.
1:30:52 And, you know, it’s a serious issue.
1:30:54 And that’s just leaving aside all the other health issues.
1:31:03 One of the things that I’ve done in really in the last six months to try and improve my sleep and it’s worked tremendously well is to use earplugs when I sleep.
1:31:16 And the motivation for this came from there’s this wild study published a couple of years ago in Nature Neuroscience that shows that people can actually answer simple math problems in their sleep in REM sleep.
1:31:20 And because you’re paralyzed in REM sleep, they have to answer a different way.
1:31:24 But we’re actually – we’re still hearing a lot in our sleep.
1:31:30 So many people with sleep disturbances actually could resolve those by wearing earplugs.
1:31:35 I’ve been using the wax earplugs that, you know, fill the space quite a lot.
1:31:39 And I noticed something that I put them in and for the first minute or two, I hear my heartbeat.
1:31:40 It’s very distracting.
1:31:42 But then it cancels out.
1:31:48 So I offer that if people are having trouble sleeping, you might try – the earplugs thing actually might help.
1:31:52 The other thing is that we don’t tend to hear our own voice.
1:31:54 We cancel it out.
1:31:56 I’m not listening to my voice in the room.
1:31:58 But, of course, I can hear it if I try.
1:32:05 So normally, how do we notch out our own voice given that our voice is encompassing a ton of different frequencies?
1:32:07 It has a dominant frequency.
1:32:09 Like, I guess, in your world, they call it what?
1:32:10 Like a frequency envelope, you know?
1:32:13 But, I mean, I can speak a little bit higher.
1:32:14 I can go a little bit lower.
1:32:17 So how does that work in real time?
1:32:18 That’s incredible.
1:32:19 It is incredible.
1:32:22 And you actually bring two really interesting points.
1:32:23 One about sleep.
1:32:30 So what studies have shown is that the ideal sleeping environment is what bears do when they hibernate.
1:32:32 It’s three things.
1:32:35 It has to be quiet, dark, and cold.
1:32:39 And that’s perfect for sleeping for months.
1:32:39 Love it.
1:32:46 But then when it comes to not hearing ourselves, actually, some people do.
1:32:48 And that’s very disturbing.
1:32:54 And that can occur if there are basically two things.
1:33:02 One, it can be that they are missing a part of the bone that covers the bony balance canal, one of the canals.
1:33:06 We have focused on talking about the hearing part of the inner ear.
1:33:11 But the inner ear has one organ of hearing and five organs of balance.
1:33:14 Two organs that detect linear acceleration.
1:33:18 One in a horizontal and the other in the vertical plane.
1:33:24 So either going forward, like imagine someone hitting the gas on a car versus bouncing on a trampoline.
1:33:25 Yeah, taking an elevator, bouncing on a trampoline.
1:33:31 And then there are three organs that detect angular acceleration.
1:33:33 And these are the three semicircular canals.
1:33:39 So the pitch of the, like the nod, the shaking the head, I guess it’s yaw, right?
1:33:41 Yaw and roll, right?
1:33:41 Exactly.
1:33:43 Which is the cute puppy thing.
1:33:44 Yes.
1:33:45 Yeah, okay, got it.
1:33:58 So what can happen is that over that superior semicircular canal, that bone can be missing partly and people can have superhuman hearing.
1:34:00 They can hear everything.
1:34:03 They can hear their eyeballs moving.
1:34:04 Whoa.
1:34:06 They can hear their footsteps.
1:34:10 If they’re taking a shower, it’s deafeningly loud.
1:34:11 They really can’t take it.
1:34:14 If an ambulance drives by, they start spinning.
1:34:19 If they are straining on the toilet, they start spinning and can pass out.
1:34:23 So that’s called superior semicircular canal dehiscence.
1:34:33 And it was actually discovered by our dean, dean of the School of Medicine, Lloyd Miner, when he was at Hopkins University.
1:34:34 Amazing.
1:34:37 Right on, Dean Miner.
1:34:39 Not just saying that because he’s our dean, but that’s…
1:34:45 But because he was such an astute physician where he listened to a patient.
1:34:52 Because before him, when patients like that would come to our office, I mean, what would be your knee-jerk reflex?
1:34:53 You’d be like, come on.
1:34:54 Come on.
1:34:55 Exactly.
1:34:55 Really?
1:34:58 Okay, like, you know, maybe we get someone from psych over here…
1:34:58 Exactly.
1:35:01 …to evaluate them, or maybe they’re a hypochondriac.
1:35:02 Exactly.
1:35:13 But what Lloyd heard and paid attention to is that the patient said, when I hear a loud sound, I feel that my eyes are moving and my vision becomes blurry.
1:35:16 And so Lloyd thought, really?
1:35:20 So let me put loud sound in your ear, which he did.
1:35:24 And he noticed that the patient’s eyes started moving in the vertical direction.
1:35:28 So there is this vestibular ocular reflex.
1:35:33 And he figured, well, then the superior semicircular canal must be involved.
1:35:39 And that led to imaging that had to be really developed so that it’s fine cuts through the appropriate plane.
1:35:42 And then you could really see the missing bone.
1:35:45 And then he developed surgery to fix the problem.
1:35:53 And now we can help people like that who actually do hear their bodily sounds that are too disturbing to them.
1:35:59 However, we don’t do that surgery lightly because clearly it has some risks like any surgery.
1:36:02 There are two ways of doing this.
1:36:09 One is through the middle cranial fossa, which entails lifting of the brain to identify the dehiscence,
1:36:14 and then plugging it or resurfacing it and then letting the brain fall down again.
1:36:20 Or we can approach it through the ear, so drilling from behind the ear.
1:36:27 But normally that surgery is really reserved for those with intractable vestibular symptoms.
1:36:34 They just can’t function in the normal world because if someone yells next to them or an ambulance drives by,
1:36:35 they just start spinning.
1:36:45 Awesome, awesome clinical work and science and discovery and description of this.
1:36:46 Incredible.
1:36:53 I knew Lloyd worked on the vestibular system and the hearing system, but I wasn’t aware of that.
1:36:55 So very, very cool.
1:36:58 I’m struck by a number of things.
1:37:04 You raised the relationship between the visual system and the balance system,
1:37:06 the vestibular system and the hearing system.
1:37:15 Do we have any idea why the auditory system and the vestibular system co-evolved in the inner ear, in the cochlea?
1:37:24 Is it just a function of neighborhood or is there something fundamental there that perhaps we can glean from other species
1:37:30 that tells us, oh, like, this is sort of like with the eye and the pineal?
1:37:35 You know, the human pineal is deep in the brain, almost certainly doesn’t have access to light,
1:37:41 but in birds the skull is thin, sunlight can go through the skull, and the pineal is a light-sensitive organ.
1:37:45 We have a light-sensitive pineal, but it gets light information indirectly through the eyes.
1:37:50 So over time, as we grew bigger, thicker brains, it just went deeper and deeper, and you need to do that.
1:37:59 So did the auditory system and the vestibular system start from the same origin and split?
1:38:09 They both sense vibration, and vibration is such a fundamental phenomenon.
1:38:15 If you think about it in terms of the universe, it’s these vibrations that are everywhere around us,
1:38:17 electromagnetic vibrations.
1:38:25 We’re talking about sound vibrations, but now we can even convert these electromagnetic vibrations
1:38:32 from the depths of the universe to sound so that we can hear gravitational waves, which is really interesting.
1:38:42 So this idea of being able to detect vibration is very deeply fundamental, and even bacteria can detect vibration.
1:38:46 They have those little flagella that allow them to move around.
1:38:55 And fish, for example, we talked about fish and other species that live in the seas and oceans.
1:39:07 They have this lateral line organ along their side that detects vibration, and it’s very similar to the sensory cells in the inner ear,
1:39:16 to the point that we sometimes use, for example, zebrafish as animal models because they are transparent.
1:39:26 You can see through them, and you can literally see these hair cells in the lateral line organ and test for drugs that may be toxic to the ear,
1:39:28 although they also have the ear.
1:39:40 So, yes, there is this profound, deep connectedness, and in the human auditory versus vestibular system, those cells look very similar.
1:39:46 We talked about inner versus outer hair cells in the auditory system.
1:39:55 Inner inner hair cells are flex-shaped, and outer hair cells are more like cylinder or cigar-shaped.
1:40:00 Similarly, in the vestibular system, there is type 1 and type 2 hair cells.
1:40:00 Beautiful.
1:40:04 And they detect vibration at different frequencies.
1:40:10 The vestibular system is a lower frequency system compared to the auditory system.
1:40:29 But what’s fascinating is that there are some data showing that even stimulation that’s non-auditory can still be very impactful on our functioning and perception.
1:40:38 And there are some data showing that people who live close to windmills have described some disturbances that they initially couldn’t really explain.
1:40:48 And then it turns out that that can stimulate stimulation of the vestibular system, and it’s all connected.
1:40:50 I mean, the whole body is connected.
1:41:02 Out of convenience, we have decided to sub-specialize in ear physiology and surgery versus eye versus liver.
1:41:05 But really, it’s all interconnected.
1:41:12 You know, you can’t live in Northern California, which is where I grew up for too long before somebody exposes you to sound therapy.
1:41:14 And at first, it seems a little silly, right?
1:41:18 They have the – if you’re not familiar with it, and I’m not about to say it’s silly.
1:41:19 I’m actually about to say the opposite.
1:41:21 You know, they’re doing these sound bowls.
1:41:27 And if I just take a step back from it, it’s like, of course, sound is going to impact the way I feel.
1:41:28 That’s why I listen to music that I love.
1:41:33 Sometimes it’s the lyrics in the music, but oftentimes it’s the components of the music.
1:41:39 And some years ago, I was very interested in kind of layers of sophistication within sensory systems.
1:41:43 Like we have aspects of our visual system that encode day and night, the circadian system.
1:41:46 We have aspects that relate to color vision, form, et cetera.
1:41:53 Likewise, in the auditory system, you have sort of more primitive reflex type things, like a really loud noise.
1:41:56 You orient towards it and away from – you want to know what – locate it.
1:41:57 You want to know where it is.
1:41:59 And you want to make sure it doesn’t damage you.
1:42:01 Same thing with a bright light.
1:42:03 You know, you shield yourself from it.
1:42:23 I find it very interesting – I would just love your thoughts on this – that music that has a lot of low-frequency bass tones tends to evoke people to dance with a lot of trunk and what we would call proximal musculature,
1:42:28 which is nerd speak for movement of the core muscles and then muscles closer to the midline.
1:42:36 Whereas high-frequency music, people, when they hear high-frequency music, will actually often raise a hand and start moving their fingers.
1:42:38 It’s as if they’re playing the music.
1:42:52 But if you look at different forms of dance – and I’ve been doing this in anticipation of a guest coming to the podcast who’s a world-renowned choreographer – you can see when low-frequency sounds are played, bass drums and things of that sort,
1:42:58 the movements tend to be very proximal musculature-dominated.
1:43:02 Whereas when high-frequency sounds are made, people actually lift themselves up.
1:43:09 You know, if you watch ballet, which I’ve been watching more and more ballet recently for this reason, and they’re moving the digits on their fingers.
1:43:11 It’s really incredible.
1:43:18 Like there’s almost like the sound frequency map is correlated with a body frequency map.
1:43:21 And you can look at hip-hop.
1:43:22 You can look at classical.
1:43:23 You can look at Gregorian chants.
1:43:29 I’ve been obsessed lately with Russian choir music because this Werner Herzog movie used it.
1:43:30 And I was like, this is beautiful.
1:43:32 And it encompasses a huge range of sound.
1:43:34 You know, oh my goodness.
1:43:36 Like our bodies have a frequency map.
1:43:37 Yes.
1:43:39 And it sounds crazy, but we’re neuroscientists.
1:43:44 So I can say this kind of thing with some degree of assuredness that I’m not crazy, at least not in this dimension.
1:43:45 Yes.
1:43:46 What are your thoughts about this?
1:43:51 It is fascinating because really vibration is around all of us.
1:43:54 We are exposed to vibration all the time.
1:43:59 Different things do happen at different time points.
1:44:05 And there seems to be this really fascinating frequency pattern to it.
1:44:09 We already know that circadian rhythm exists even in the inner ear.
1:44:16 We know that certain drugs are more effective if they are given at certain times of the day.
1:44:24 So, yeah, there is something to be studied even more.
1:44:39 But keeping within the realm of what’s manageable at this point in time, I will say that von Bekessy, who was a physicist, and he studied the auditory system because he worked for a telephone company.
1:44:50 And he was charged by making better devices for communication, and he said he reached a limit in terms of what he can do as a physicist.
1:44:52 So he needed to understand how the system worked.
1:44:58 And he started performing these experiments in human temporal bones.
1:45:05 So they are collected when people die of unrelated causes, and they donate their ears for study.
1:45:22 And he was playing sounds of different frequencies, and noticed that those of high frequencies stimulated the basal turn, the basal portion of the cochlea, and those of low frequencies stimulated the high end.
1:45:45 So because of his seminal contributions to understanding how the auditory system and description of this place frequency map, plus other things that he did, such as discovering that there is a biological battery in the inner ear where you have 100 millivolts of positive potential, which is really unheard of.
1:45:52 Everywhere else in the body, cells are bathed in fluid, and the potential of that fluid outside of them is typically around zero.
1:45:58 Yeah, we should explain for a second, sorry to interrupt, but just very briefly, when we’re talking about membrane potential, some people will know what that is.
1:46:01 We’re essentially talking about how charged a battery is.
1:46:06 Like, it’s an opportunity to create electricity of a given amplitude, essentially.
1:46:06 Yes.
1:46:07 Like, it’s a potential.
1:46:12 And you’re saying in the inner ear, the membrane potentials are very, very high.
1:46:13 Extracellular.
1:46:14 Extracellular.
1:46:15 Extracellular.
1:46:20 So normally cells have some resting potential, which is usually negative.
1:46:21 60, 80.
1:46:22 Exactly.
1:46:28 But now on top of it, you have 100 millivolts of extracellular potential.
1:46:37 So there’s a difference that really drives ionic current through these sensory cells is really large.
1:46:42 And that contributes to this exquisite sensitivity of the inner ear.
1:46:43 He discovered that, Von Beckes?
1:46:46 He discovered the endocochlear potential.
1:46:47 He was the first to measure it.
1:46:50 So for these contributions, he actually won a Nobel Prize.
1:47:10 So by studying frequency, because you started talking about frequency and how there may be a whole hearing-to-body frequency map, I think it’s a fascinating phenomenon because at least the auditory system is all functioning based on frequency.
1:47:22 And in fact, understanding that place frequency map has been essential for the introduction and success of cochlear implants because cochlear implants rely on that.
1:47:32 Cochlear implants pick up sound from the environment via a microphone and then process it into different frequency bands.
1:47:42 And then that is delivered to the intracochlear electrode that directly electrically stimulates the auditory nerve.
1:47:51 So if you’re hearing high frequencies, then it’s only the electrodes that are encoding high frequencies that are transmitting that information.
1:48:08 And so it all ties it together and really highlights how important it is to do fundamental research that is sometimes even curiosity-driven to really lead to major advancements in terms of therapies for people.
1:48:20 And many times that curiosity-driven research and its potential impact on therapies for humans is unknowable.
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1:49:54 Now, I completely agree.
1:50:01 I mean, much of what we know about how to treat strabismus and amblyopia and visual cataracts
1:50:07 and all this was born out of David Heuvel and Torrance and Weasel trying to figure out how the visual system works.
1:50:14 I guess that the crowd in the auditory system, it’s a little bit broader, but certainly von Beckese would be one.
1:50:16 David Corey’s done beautiful work.
1:50:22 I mean, these are names for the kind of inside ball of Hafter and others,
1:50:29 but I feel like the auditory system didn’t get as much attention as the visual system for a long time
1:50:35 because we are such visual creatures, but the more I learn about the auditory system from you
1:50:41 and the more I think about the incredible ways in which it shapes our emotionality at unconscious levels
1:50:47 as well as conscious levels, the more I’m convinced that it’s driving a lot of social development
1:50:53 and mental health and, in some cases, mental illness.
1:50:58 You know, we’ve talked before in this podcast about developmental challenges with social interactions.
1:51:01 Nowadays, the word autism is used too broadly.
1:51:02 Talk about subtyping, right?
1:51:06 So I’m going to set that aside, but I’m going to keep that kind of in reference for people
1:51:15 because what I’ve been learning is that many of the challenges that kids who have social interaction challenges have
1:51:22 relate to them feeling overwhelmed by the sensory environment, and some of it’s vestibular, and a lot of it’s auditory.
1:51:25 They’re not walking into a room and, you know, there’s too much black on the wall.
1:51:32 It’s uncomfortable, and I don’t know, it’s the noise, or what to other people isn’t noise, but to them is noise.
1:51:42 And, you know, and I feel like if we all spent a day listening to the experience of these kids, the way they experience life,
1:51:44 we would develop tremendous empathy for them.
1:51:45 Yes.
1:51:48 Right, in the same way that, and I’ve never done this experiment, I probably should,
1:51:53 but if you spend time with people in the low vision, no vision community, try and go about your day with no vision.
1:51:56 A seeing eye dog can help.
1:51:59 There are new technologies that additionally can help, but it’s very challenging.
1:52:03 Simple things for everybody else are made very, very challenging and time-consuming.
1:52:12 So I wonder what is known about the relationship between auditory development and social cognitive development and mental health?
1:52:16 There are really strong ties, and it’s a very active area of research.
1:52:29 And like you said, hearing is such an essential sense, and its hypersensitivity and sensory hypersensitivity or dysfunction beyond hearing
1:52:38 can be a part of both mental health disorders as well as, on the other end of the spectrum, developmental disorders.
1:52:45 And I think it really calls for, first of all, greater awareness.
1:52:54 And a part of what we are doing today is really bringing it up to the known, because so many people are really stigmatized,
1:52:59 because you don’t have a label on your forehead that you have hearing loss.
1:53:00 It’s invisible.
1:53:06 And people are afraid to admit that they have hearing loss because they are concerned about how they’ll be perceived.
1:53:11 And for a long time, it’s been linked automatically to losing your marbles.
1:53:20 And it’s a part of why people in a social situation where they don’t hear and they are having a gathering with friends,
1:53:25 and then they’re initially just nodding their head, and then they feel isolated because they’re just nodding their head,
1:53:31 and then they respond to what they think was said, and then it turns out it was something completely tangential.
1:53:34 And then they decide, I don’t even want to be a part of this anymore.
1:53:39 And that’s how they become withdrawn and isolated, at least a part of the reason.
1:53:46 And similarly, if you’re hypersensitive to everything around you, you want to avoid that kind of situation.
1:53:51 And I think we definitely need better education.
1:53:55 We need better ways to measure these things and quantify them.
1:53:57 We talked about tinnitus.
1:54:07 We don’t really have a way to quantify tinnitus, to measure it precisely, objectively, in a robust fashion.
1:54:21 We need these types of tests for all of sensory perceptions that we are discussing because senses are really essential for function of the brain.
1:54:26 And like I said before, the brain has really evolved to perceive and manage senses.
1:54:36 And it also provides a tremendous therapeutic potential because it’s easier to fix sensory dysfunction than to fix brain function.
1:54:40 But the brain will take care of it if it’s given corrected input.
1:54:49 And we already know that from the tremendous success of cochlear implants, which are the most successful neural prostheses out there.
1:54:54 There are more people with cochlear implants than all other neural prostheses combined.
1:54:56 Does insurance cover the cochlear implant?
1:54:57 It does.
1:54:59 It’s not an outpatient.
1:55:00 It is.
1:55:01 You can go in and out the same day?
1:55:02 And out the same day.
1:55:03 It takes only an hour or two.
1:55:05 By now, it’s become routine.
1:55:05 Really?
1:55:06 Yes.
1:55:08 I assume you are going under general anesthesia.
1:55:09 You are.
1:55:09 Okay.
1:55:09 You are.
1:55:10 But you’re up and back.
1:55:11 Yes, you’re up and back.
1:55:12 Excuse me, you’re down and back.
1:55:14 You’re down and back.
1:55:15 It’s very delicate.
1:55:16 It’s done under the microscope.
1:55:22 Relevantly, it was ear surgeons who were the first to introduce a microscope in the operating room.
1:55:23 Is that right?
1:55:24 And that was 100 years ago.
1:55:25 And it’s for a reason.
1:55:27 It was only 100 years ago?
1:55:27 Yes.
1:55:29 Before that, they were naked eyeballing it?
1:55:29 Exactly.
1:55:35 And in fact, you were kind of considered a lesser surgeon if you used a microscope when it was introduced
1:55:39 because the thinking was, well, your vision is not good enough or you are not good enough.
1:55:44 So interestingly enough, there was some backlash before widespread adoption.
1:55:57 And now, of course, you can’t imagine doing anything precise surgically without the use of a microscope, whether it’s ear surgery or brain surgery or microvascular tissue transfer.
1:56:07 Even my dermatologist has these things that I want my surgeon using a microscope or magnifier of some sort.
1:56:20 Do men or women, on average, these are always averages, hear better, meaning with more sensitivity, can detect either different frequencies or thresholds of sounds as compared to the other group?
1:56:30 What we know is that women tend to have better hearing premenopausally, but postmenopausally, they catch up to men.
1:56:36 So there are data showing that estrogen contributes to better hearing.
1:56:43 And now, larger-scale epidemiologic studies are being conducted.
1:56:48 As you know, for the longest time, women were not really studied in lots of clinical trials.
1:56:52 Most of clinical trials decades ago involved only men.
1:57:04 We already know from those studies that, for example, for a heart attack, how a woman presents with a heart attack could be very different than a man, where the classical description of a-
1:57:05 Pain down the left arm.
1:57:05 Down the left arm.
1:57:07 Elephant stepping on the chest type feeling.
1:57:08 What is it in women?
1:57:14 They may not have discomfort, but no elephant pressing, no pain in the arm.
1:57:28 And so we are only now starting to understand all these differences, how different diseases manifest in men versus women, and how they respond to different medications and different treatments.
1:57:33 And back to your question, what do we know about auditory sensitivity?
1:57:38 We do know that women tend to have better hearing premenopausally.
1:57:42 Now, does that have to do with environmental exposure?
1:57:56 That has to be factored in, because traditionally men have been more involved in occupations that entail large noise exposures, such as military or construction.
1:58:04 But these days, everybody is exposed to recreationally loud music and noise levels.
1:58:15 So I think these studies need to be conducted with proper controls and proper sample sizes to really answer some of the questions you’re asking.
1:58:24 If we were to look at the average adolescent males and females, they would have essentially equivalent hearing ability.
1:58:28 As they approach their 20s, 30s, 40s, those lines start to diverge.
1:58:29 Diverge, yeah.
1:58:31 Such that men have…
1:58:35 Higher thresholds, which means worse hearing.
1:58:35 Great.
1:58:36 On average.
1:58:36 Great.
1:58:37 Okay, thank you for that.
1:58:40 I mean, not great for me, I’m male, but great for the clarity.
1:58:48 And then at perimenopause menopause, women’s thresholds go up, which means their hearing gets worse.
1:58:49 Yes.
1:59:02 Which suggests, all other factors removed, that something about loss of estrogen or things in the estrogen-related pathways is causing that loss of hearing.
1:59:13 And presumably nowadays, with hormone replacement therapy becoming more prominent, the sort of recapture of hearing could be examined.
1:59:14 And hopefully that experiment is done.
1:59:21 That is now being studied because anything can be a treatment and a poison.
1:59:24 So whatever you are using, you have to look at pros and cons.
1:59:31 And hormone replacement therapy can be very helpful in certain situations and also carries risks in other situations.
1:59:37 And it’s having that discussion of what are the pros and cons for a given individual and does it make sense?
1:59:43 And the discussion that we are having really highlights the need for having more types of these studies.
1:59:51 However, the good news is that losing hearing as we age is not necessarily a given.
1:59:59 There are tribes in Africa where they’re not exposed to modern, loud environments.
2:00:13 So environment clearly plays a very important role, plus everything else that we take, which includes all sorts of drugs.
2:00:26 For example, we and others have shown that regular intake of non-steroidal anti-inflammatory medications like ibuprofen increases the likelihood of developing hearing loss.
2:00:29 And what is regular use is at least twice a week.
2:00:31 For all ages?
2:00:32 For all ages.
2:00:33 That’s been studied in men and women.
2:00:38 For younger people, it seems like they are a little more vulnerable.
2:00:41 The good news is that most of that hearing loss is reversible.
2:00:45 But there are other medications that affect our hearing.
2:00:45 Aspirin.
2:00:46 Aspirin.
2:00:47 In kids, right?
2:00:49 Don’t they warn against kids taking aspirin?
2:00:49 Yes.
2:00:50 For this very reason?
2:00:52 It’s for Rye syndrome.
2:00:53 How common is Rye syndrome?
2:00:55 It’s not common.
2:00:55 Okay.
2:00:58 And that’s different.
2:01:00 It’s not specifically for hearing loss.
2:01:06 However, in addition to these anti-inflammatory medications, there are others.
2:01:14 There are certain antibiotics that have increased risk of causing hearing loss, like gentamicin.
2:01:19 There are certain diuretics, like furosemide, that causes hearing loss.
2:01:25 There are drugs that are used to treat erectile dysfunction that can cause sudden hearing loss.
2:01:26 Most of the time that’s reversible.
2:01:29 Most of the time, that’s reversible if people stop taking them.
2:01:35 So what I’m saying is that there is, as always, genetic predisposition and then the environment.
2:01:47 And the environment can include what we take, what we eat, what our lifestyle is, what noise levels we’re exposed to, what drugs we take.
2:01:53 And all of that impacts our genetic predisposition.
2:01:57 What about environmental exposures to chemicals?
2:02:01 These days, there’s a lot of discussion about pesticides, which I think is an important discussion.
2:02:15 There’s a lot of discussion about food dyes, which, at least to my view, while I support a careful analysis of that, I think in terms of overall health there, if I were in charge and I’m not in charge, I perhaps would emphasize slightly different things first.
2:02:20 But, hey, you know, I’m not complaining if people are trying to clean up the food supply.
2:02:28 Just would hope that we would also pay attention to the kinds of environmental toxins that we know at low or moderate exposure can cause loss of neurons.
2:02:39 Because ultimately, you know, for the neuroscientists and for you, the clinical and researcher-oriented person, neurons don’t regenerate.
2:02:42 A couple in the nose regenerate, some in the dentate gyrus.
2:02:46 But, you know, unfortunately, so much has been made of so-called neurogenesis.
2:02:53 While an exciting topic, neurons in the adult brain and even in the adolescent brain, they don’t regenerate.
2:02:56 And so anything that kills neurons is bad.
2:02:58 It’s that simple.
2:03:12 So what do we know about, like, bus exhaust, car exhaust, any kind of environmental pollutants that could kill neurons, specifically in the auditory system?
2:03:13 Do we know?
2:03:14 Is there anything being done there?
2:03:16 Is the toxicology being done?
2:03:17 Some.
2:03:25 So, for example, heavy metals are known to be toxic to neurons in the ear, as well as other neurons through lead, mercury.
2:03:28 We talked about drugs.
2:03:41 So, for example, platinum-containing compounds, which are typically used to treat cancer, are toxic to the ear and auditory neurons in addition to other neurons throughout the body.
2:03:52 In terms of other environmental pollutants that are now gaining more and more interest, it’s plastic, micro and nanoplastics.
2:03:53 They are everywhere.
2:03:56 Long-term effects of that are unknown.
2:04:03 We have performed a study where we exposed sensory hair cells to micro and nanoplastics.
2:04:12 In fact, we exposed the entire inner ear, and it was striking to see that they were preferentially taken up by hair cells.
2:04:17 What that means for function, we don’t know, but it was striking.
2:04:22 So, we don’t even know what we are doing to ourselves, and it’s scary, because plastic is everywhere.
2:04:26 It’s released at very high levels, at extremes of temperature.
2:04:35 So, you definitely don’t want to put a food-containing plastic container into a microwave to heat it up, because then even more plastic gets released.
2:04:38 Or even cook hot food and then put it into plastic and then consume it.
2:04:50 You know, I sometimes will order food delivery, not that often, but oftentimes, excellent, you know, they’re doing all the right things with the foods in terms of, you know, organic sourcing and free-range meat and eggs.
2:04:55 And then, you know, and then it arrives hot in a plastic container.
2:04:56 Yes.
2:05:00 And, you know, you’re the second person to come on this podcast to emphasize this point.
2:05:08 The previous one was Dr. Shana Swan, who’s written about this extensively, as well as declining fertility rates and how it relates to endocrine disruptors.
2:05:15 You know, what used to be considered kind of like maybe or fringy type, like, analysis of this is becoming mainstream science.
2:05:17 I mean, she’s run a serious laboratory for a long time.
2:05:19 So, I’m so glad that you’re highlighting this point.
2:05:22 I make it a point to avoid drinking out of disposable plastic bottles.
2:05:28 I confess if I’m very, very thirsty, and it’s the only thing available, I’ll do it, but I really try to avoid it.
2:05:30 It’s also about generating less waste.
2:05:34 So, you know, it’s a twofer if you avoid those.
2:05:43 The micro and nanoplastics being taken up by hair cells is very interesting, concerning, but interesting.
2:05:54 And I have to wonder, given what you said before about the external environment of those cells when they’re in the body and how much charge there is there,
2:06:03 you kind of have to wonder if the neurons that are most metabolically active and most sensitive in the body are the ones that are most readily going to be taking up toxins because they’re the most active.
2:06:14 And auditory neurons are the most active because they have spontaneous firing rates that are really high, hundreds of spikes per second.
2:06:14 Really?
2:06:15 Yeah.
2:06:18 I always thought it was the visual cells, but I’m happy to know it’s the auditory cells.
2:06:35 They have to be active all the time because then it’s easier to respond quickly because if you are completely turned off and now a sound comes, it’s a higher activation energy than if you are always active and then sound comes in.
2:06:39 So the threshold of detecting that is lower.
2:06:40 Interesting.
2:06:46 We’ve talked a lot about the things that we can do to damage our auditory system, ways to avoid those.
2:06:57 Actually, before I move on, I should ask you, are there any other drugs or things that you might put into the absolutely avoid, maybe avoid it because we’re looking into it?
2:07:05 You know, people, we’re not trying to create hypochondriasis here, but I think people who listen to this podcast often are interested in things that they can do to take better care of themselves.
2:07:14 And if there are commonly used medications or environmental exposures that they should be thinking about, we’d want to highlight that.
2:07:15 So you said ibuprofen is one.
2:07:23 And all of those drugs in that category, non-steroidal, anti-inflammatory medications, that includes acetaminophen as well.
2:07:24 What are some good alternatives?
2:07:27 You’re a physician, so I mean…
2:07:32 So if you need to, if you need to take drugs, you take them.
2:07:37 It’s just not good to develop a habit of taking a drug on a regular basis if you don’t need it.
2:07:38 Got it.
2:07:40 And that has become sort of a norm.
2:07:50 For example, there’s this Tylenol PM where they put Benadryl into it so that it would help people sleep.
2:07:52 Well, that’s a bad habit.
2:07:55 Do you need Tylenol or do you need Benadryl?
2:07:55 What do you need?
2:07:56 Or do you need either?
2:08:02 And we talked about good diet, lifestyle, exercise.
2:08:05 If you exercise during the day, you’ll sleep better.
2:08:10 So you don’t need these other Band-Aids, really.
2:08:12 I totally agree, by the way.
2:08:25 So then it’s considering the whole patient, their needs, their priorities, their lifestyle, and helping them understand how to manage that in the healthiest way possible.
2:08:39 Because we really aim to keep people healthy as opposed to letting them get sick and that sickness getting out of control and then trying to fix the problem because then it’s a much more challenging problem to fix.
2:08:41 Even we’re talking about the auditory system.
2:08:48 It’s much easier to intervene if these cells are still there as opposed to if they are gone.
2:08:53 If they are gone, they do not spontaneously regenerate in mammals.
2:08:57 However, in birds, and you talked about birds and songbirds.
2:08:59 This is Ed Rubel’s work, right?
2:09:00 Yes, indeed.
2:09:08 And numerous studies have shown that birds really regenerate their hair cells.
2:09:20 And one of our investigators at Stanford, Stefan Heller, recently published a paper describing the specific pathways that are absolutely essential for this in birds.
2:09:25 So in birds, we really have nailed it in terms of understanding the specifics.
2:09:26 And birds do it quickly.
2:09:28 They regenerate their hair cells within days.
2:09:30 Within a month, they’re done.
2:09:33 But humans don’t.
2:09:46 However, by understanding how birds do it, we can now start to think, can we reawaken these pathways in mammals, in humans?
2:09:55 And can we do it in a very precise fashion so that we turn them on when needed and turn them off afterwards?
2:09:59 Because cancer is regeneration gone awry.
2:10:07 So if we let these cells continue to divide and generate more cells in an uncontrollable fashion, that’s a problem.
2:10:14 What’s also really interesting is that there isn’t a primary cancer of the inner ear.
2:10:17 And that’s really cool.
2:10:28 That’s another fascinating thing that could be used to potentially even develop new cancer therapies, since there is an organ that doesn’t get it.
2:10:32 I think most people heard at some point that sharks don’t get cancer.
2:10:33 Everyone was obsessed with shark cartilage.
2:10:36 That’s not the direction to go to avoid cancer, folks.
2:10:40 Very interesting that the ear doesn’t develop cancers.
2:10:46 I feel like there are two areas, at least from the neck up, that are so fascinating that we need to understand.
2:10:51 One is this, the inability of cancers to develop in the ear.
2:10:51 So interesting.
2:10:53 And the other is someone pointed this out.
2:10:59 I think this was a lab at Stanford, that our mouth is open a lot of the day and exposed to the environment.
2:11:02 It’s a moist, warm environment.
2:11:08 That combination of features means that it should be filled with infections all the time.
2:11:18 And yet, if we get a cut in our mouth, we bite down on our lip or something, it hurts, it heals very fast with often, not always, no infection.
2:11:19 It’s an incredible area.
2:11:22 And it’s our gut exposed to the world.
2:11:26 We don’t like to think about it as the top part of our gut pathway exposed to the world.
2:11:30 And it doesn’t tend to collect infections nearly as easily as other areas of the body.
2:11:35 And wounds heal often with minimal or no scar.
2:11:36 Fascinating.
2:11:39 I know this is a discussion about the auditory system.
2:11:45 I feel like here we’re sort of getting into the fascination about science and medicine and what we don’t know.
2:11:52 And it’s so important that we parse this because there may be molecules within the mouth that could lead to robust wound healing for people with burns,
2:11:55 for people with deformities, you know, repair of neural tissues.
2:12:02 I mean, there’s, I have a feeling there’s an immense number of important discoveries to be made there.
2:12:02 Yes.
2:12:09 And before I comment on that, I’ll just clarify that there is no cancer of the inner ear.
2:12:13 There can be cancer of the outer ear, which is the oracle or the ear canal.
2:12:15 But we are really talking about the inner ear.
2:12:24 In terms of this remarkable microenvironment within the head and neck region, yes, it’s one of a kind.
2:12:32 And at least in part, it has to do with the remarkable blood supply to the area and the lymphatic system.
2:12:37 There is a very dense lymphatic system in the head and neck region.
2:12:38 We even call it a walled eye ring.
2:12:46 It includes the adenoid, which is the gland that sits at the back of the nose, plus the tonsils that sit at the back of your throat,
2:13:01 And indeed, in reconstructive surgery of the head and neck, we capitalize on that ability to heal quickly without an infection.
2:13:12 Because sometimes people develop cancer of their jaw or of their tongue, and a part of the jaw or the whole jaw has to be removed,
2:13:16 or the tongue has to be removed, a part or a whole tongue.
2:13:18 So how do you reconstruct that?
2:13:21 We reconstruct that by borrowing tissue from somewhere else.
2:13:30 We can use tissue from the leg that’s called fibular free flap or from the radial forearm or any other part of the body, and we bring it in.
2:13:40 So now you are bringing sterile tissue into a super dirty environment that you are describing that’s rich in these microbes.
2:13:45 You sew it all together, artery to artery, vein to vein, nerve to nerve.
2:13:50 You close it up, and it heals beautifully most of the time.
2:13:59 And people do not need extra antibiotics than what’s typically prescribed for every surgery, just a short perioperative course.
2:14:09 So indeed, this area of the body, the head and neck, which is in our turf, that’s what otolaryngology, head and neck surgery is,
2:14:23 is super inspiring and really motivating to understand and really ripe for even deeper discoveries than what have been done to accelerate progress,
2:14:26 not only in the head and neck region, but throughout the body.
2:14:27 Fantastic.
2:14:28 I love it.
2:14:38 And we are not here to beat the drum again, no pun intended, for support of basic research to fund important treatments for disease.
2:14:44 But there’s just so much to discover that we clearly, clearly need to discover.
2:14:52 I want to ask about plasticity of the auditory system in the other direction, meaning in the direction of positive change.
2:15:03 Let’s say, let’s say, as an adult, or a young person, we decide to start listening to a new form of music, but really paying attention.
2:15:06 Or we learn a new language.
2:15:15 Or we just expose ourselves to some healthy, appropriate volume levels of sound and type of sound.
2:15:19 How much plasticity is there in the auditory system?
2:15:23 And can that be beneficial for cognition?
2:15:23 Yes.
2:15:30 I mean, there are a lot of nice studies showing that, you know, people who play music or people, especially who play music with others, where you need to coordinate action,
2:15:34 brain plasticity is more, is sort of opened up, if you will.
2:15:38 What’s known about shaping of the auditory system?
2:15:42 And here, I might even just go a step further and ask you, if you’re willing.
2:15:46 I’m sure you do all the things to take care of your auditory system.
2:15:50 And I’m sure you tell the people in your life to take care of their auditory system.
2:15:54 But what sorts of things do you do to enrich your auditory system?
2:15:56 That’s a great question.
2:15:57 And I agree with you.
2:16:00 I love to listen to music like you.
2:16:02 I also love to sing.
2:16:04 I used to play the piano.
2:16:06 I hope to get back to it.
2:16:12 It’s been a very busy life, but I really love being immersed in music.
2:16:16 In fact, that’s one of the main reasons that I pursued this field.
2:16:21 It was my love of music and the appreciation of how important it is for human connection.
2:16:28 And it’s for a reason that no culture has ever existed without music.
2:16:30 And that dates back to 40 millennia.
2:16:38 So music perception and language have been so essential for us as humans.
2:16:40 That’s unique to us.
2:16:47 And we, as clinicians, know that auditory training is very helpful.
2:16:52 For example, we talked about people sometimes needing cochlear implants.
2:17:02 Well, those who are musically trained, they tend to do better in terms of their appreciation of music after cochlear implantation.
2:17:08 On average, people cannot really appreciate music after cochlear implantation on average.
2:17:12 They can appreciate rhythm, but not tonality of it.
2:17:15 But there are those who can.
2:17:19 They can actually go back to playing the instruments they were playing.
2:17:36 And we definitely now have growing evidence that the more you train your brain to be sensitive to different inputs, which in this case includes music, the better it responds when challenged.
2:17:38 It’s incredible.
2:17:49 In the last couple of years, I’ve been asked a lot about, and I’ve experimented a bit with things like binaural beats for focus during learning and things of that sort.
2:17:57 My read of the literature is that certain sounds, white noise, brown noise, pink noise, people wonder what is brown noise, but different frequencies added or deleted.
2:18:04 But white noise, essentially, all the sound frequencies played at an appropriate volume to not damage your ears, binaural beats, et cetera.
2:18:06 There’s some modest effects in some studies.
2:18:16 But I’m curious what your take is on just auditory environments and learning at the social level.
2:18:18 So nowadays, people text a lot.
2:18:21 That’s devoid of auditory information.
2:18:26 I grew up in the era of people actually having phone calls, but there you don’t see the mouth move.
2:18:30 So, you know, probably my grandparents probably would have said, oh, you’re not actually interacting with people.
2:18:31 You’re just talking on the phone.
2:18:34 And now I’m saying, you’re not even talking on the phone.
2:18:34 You’re just texting.
2:18:39 But we do seem to be separating the different senses from one another more and more.
2:18:53 Do you think with AI there’s an opportunity for people to, at some point soon, perhaps, to receive a text from someone and see a video of them actually talking in a way that’s very realistic, even though they didn’t take a video of themselves, right?
2:18:59 Like there’s actually a company out there where you can give them 10 minutes of video and then you authorize them.
2:19:06 And then after that, they will generate a very accurate video of you saying anything you want in Word document form or whatever.
2:19:07 And you can use that.
2:19:08 It would look just like this.
2:19:11 You have pupil dilation and inflection and everything.
2:19:14 It’s not perfect, but it’s pretty darn close.
2:19:18 So I imagine pretty soon text messages will be your son or daughter or spouse.
2:19:19 You go, hey, how’s it going?
2:19:23 And they’re like, hey, can you pick up some milk or eggs at the store after what time are you going to be home?
2:19:30 And they will have written that or spoken that, but it will look as if it’s a video of them.
2:19:33 Do you think that’s going to be better than where we’re at now?
2:19:36 Because right now there’s a lot of splitting of the different senses.
2:19:40 I think it’s a really interesting question.
2:19:42 There is a splitting of the senses.
2:19:46 I think integrating senses is really important.
2:19:47 And we already know that.
2:19:52 There are people who, if they lose their hearing, they are devastated.
2:19:54 They really can’t function.
2:19:56 And there are others who adopt to it.
2:19:59 We think that it has to do with sensory integration.
2:20:05 Those who are really reliant on one sense, if they lose it, then they can’t function well.
2:20:12 But those who have exercised various senses, then the other senses can pitch in to provide, to fill the gap.
2:20:20 So, I think it’s going to be a fascinating world.
2:20:27 And the popularity of podcasts highlights the growing interest in the auditory system.
2:20:31 And in fact, I was talking to a colleague whose son is now applying to colleges.
2:20:36 And the colleague was really concerned because he never saw his son studying and said, I don’t know how you’ll do.
2:20:38 And the son nailed the exam.
2:20:41 And so, the question was, when did you study?
2:20:43 I’ve never seen you read a book.
2:20:47 And the son just said, well, who reads books these days?
2:20:48 You just listen to the stuff.
2:20:54 So, he was studying all the material through podcasts and prepared for the tests really well.
2:20:58 So, as human species, we are adaptable.
2:21:05 I think when you mention AI, we now are at an inflection point.
2:21:21 And in fact, an essay was written that actually won the New York Times Essay Award last year by Ashen Brenner, who talked about AI and its transformative impact on humankind.
2:21:35 And one of the graphs talked about how long does it take for something to double the economy.
2:21:38 So, he looked at hunting, for example.
2:21:44 For hunting, it took a quarter of a millennium to double the economic impact.
2:21:48 But then, as new and new technology was introduced, it took less and less.
2:21:53 So, when you look at scientific discoveries, it takes about 60 years.
2:21:55 So, that’s on the order of a lifespan.
2:22:01 For technological advances, it takes only 15 years to double the economy.
2:22:16 And now, with AI and super intelligence on the horizon, the question is, are we really at this inflection point where the growth of human progress has been increasing at a steady pace?
2:22:20 And now, it’s about to take off in ways that we can’t even imagine.
2:22:22 Super exciting.
2:22:30 Well, before we wrap here, I want to just toss out a couple of things that I heard.
2:22:31 And I want to make sure that I have this correctly.
2:22:33 But also, I just want to highlight them.
2:22:38 Because there are things that I’m going to definitely change in my behavior.
2:22:44 One is to really be thoughtful about the level of volume I use with headphones and just noise pollution around me in general.
2:22:47 This isn’t just a function of age.
2:22:49 I turn 50 in a couple of weeks.
2:22:53 But just because hearing is so fundamental to how we experience life.
2:23:01 And I think unlike vision loss, people don’t really conceptualize just how detrimental hearing loss can be.
2:23:04 And so I’m going to do that.
2:23:16 I also really took note of the fact that you said when you talk to somebody who has difficulty hearing, the point is not to talk louder and certainly not to gesticulate more or something.
2:23:22 But the idea is to slow down and try as much as one can to eliminate background noises.
2:23:23 Great.
2:23:24 That’s going to help a lot of interactions.
2:23:36 The other one is I think I know I have developed a much greater appreciation for the auditory system as a consequence of this conversation.
2:23:38 I mean, I always loved the auditory system.
2:23:43 I have to admit part of it is Irv Hafter because we’re talking here about somebody that nobody knows who he is.
2:23:47 He’s just a very colorful and very kind character and has immense amounts of enthusiasm.
2:23:51 And so I was intrigued by the auditory system.
2:23:53 Maybe in a different lifetime, I would have worked on it.
2:24:01 But I think until this discussion with you today, I didn’t appreciate the incredible richness within it that it offers, especially every domain of life.
2:24:05 I mean, from the second trimester, we’re listening to stuff, mostly our mom.
2:24:07 OK, we’re hearing stuff.
2:24:13 I intentionally did not ask you to comment on whether or not men or women listen better as opposed to hear better.
2:24:15 We’ll leave that for another time.
2:24:21 But then we enter the world and we’re exposed to all these auditory environments which shape our brain.
2:24:31 And you’ve just beautifully illustrated the functioning of the auditory system, the structure of the auditory system, the things that we can do to protect it, the things that we can do to enrich it.
2:24:34 And as you pointed out, this is an evolving field.
2:24:40 So first of all, thank you so much for coming here today to share this immense and valuable knowledge with us.
2:24:44 Please come back and update us on the discoveries coming soon.
2:24:48 And also, we will highlight your work and the ongoing work.
2:24:51 This is super important clinically at every level.
2:24:52 Mental health.
2:24:53 We talked about cancers.
2:24:58 I mean, it’s incredible the number of different areas of health and well-being.
2:25:02 We talked about nutrition even that intersect with the auditory system.
2:25:04 So thank you so much.
2:25:04 It’s been wonderful.
2:25:06 Thank you so much for having me.
2:25:07 What a pleasure.
2:25:09 And I look forward to staying in touch.
2:25:09 Great.
2:25:10 Will do.
2:25:14 Thank you for joining me for today’s discussion with Dr. Konstantina Stankovic.
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