As a child, Nina Kraus' world was shaped by sound. She grew up in a family that spoke two languages: both English and Italian.

As a kind of citizen of two countries, I feel much more like the intersection of these two languages and cultures than as an Italian or an American, because I feel like I belong at the intersection.

And Nina's family communicated in another way as well. Through the language of music...

Something that we did in our house is we sang together. You know, I learned to sing harmony. I don't really know to this day how I do it. Just like when a child learns language. So sound was was always important for me.

Nina still remembers playing with their toys underneath her family's piano as her mother practiced...

Yes, I still have that piano. I play it every day. My son played that piano when he was a little boy.

But when Nina got to college, she found a new love: science. So, she set out to find a way to combine her love of music, love of language and love of the brain.

And I thought, "Oh, I want to, I want to do this. Want more biology." So the idea even then, I realized that I can combine language and biology. And sound is at this intersection.

And, she did it! Today, Nina is one of the leading experts in the field of sound, and she leads a lab at Northwestern University called Brain Volts, where she studies how our brains make sense of all the sounds that surround us every day.

If you look at the home page of our website, which I hope people do, you will see that we research music, and rhythm, and bilingualism, reading, hearing loss, aging, concussion. And you might wonder, you know, "what are they even doing in this lab?" But it's all under the umbrella, you know, of sound and the brain. So sound and the brain is huge. It encompasses so many things that you and I care about.

And last year, Nina published a book all about sound and the brain. It's called 'Of Sound Mind: How Our Brain Constructs a Meaningful Sonic World.' But make no mistake, this isn't a dry academic text. It's beautifully written prose. She calls it her love letter to sound.

When I sent it off to the editor, I thought, "you know, why did I even write this book? Everything that I say is so obvious.".

Hmm.

And yet the resounding comments that I get from people all over the place is I had no idea sound is so important. And it really is. It really is. And we need to do what we can to to honor that.

I was so excited to speak to Nina for this episode because I've been familiar with her work for a while now, and the way she thinks of sound in the brain is really different than what we've been taught. You see, her focus isn't just on hearing. It's about how we make sense of sound and the way that each of our individual relationships with sound really is unique. At the end of the day, the way we experience sound is important because what we hear has an effect on our brains and our bodies. In fact, Nina says that when it comes to brain health, sound can be an invisible ally or an enemy.

Our experience matter, our choices of how we live, our world sonically really do matter.

So on today's episode, we're going to explore how our brains make sense of sound, sound's effect on the mind and the body and tips for intentionally building a healthier sonic world. So get ready. Listen up! I'm Dr. Sanjay Gupta, CNN's chief medical correspondent. And it's time to start Chasing Life.

Throughout this season of the podcast, one thing I've learned is that it's easy to take some of our senses for granted. I've had multiple experts tell me that we live in a really visual world, so we often underestimate the role that smell and taste and touch play in our lives. Nina says this rings true for hearing as well. That sound is under-recognized and underappreciated, especially because it's invisible. That really struck me. So I decided to start there by asking her: what role does sound play in our lives?

Helen Keller did a really good job, you know, having the experience of really not having either sense in the conventional way. But as she experienced it, she said that vision helps us connect with things and sound connects us to others.

Hmm.

I think one of the aspects of sound that is unique is the reciprocity, the back and forth. Sanjay, right now, you and I are having a conversation. We don't have a script. We are going back and forth. We are everyday improvisers. Sound let's us do that. I mean, have you ever talked to a baby? How do you go back-and-forth and back-and-forth? And, you know, you don't have to use words. It's this tremendous connection.

It's so interesting, Nina. You know, the the idea of sound, this sense being in some ways the most communal or the most connecting sense among humans. Are we always listening?

Yeah. Yeah. What is emblematic of of hearing is that our hearing is always on. You know, we can close our eyes, but we really can't close our ears. And that's important because sound is our alerting sense. And so we want to be able to be aware at all times of our sonic environment, 360 degrees around us, because, again, from an evolutionary standpoint, you know, the sound tells us, "am I going to be eaten? Can I mate with this?" These are important pieces of information that you were getting from your sonic self.

But, you know, here's the thing. Nina isn't only interested in studying how we hear. Her book is called 'Of Sound Mind' because it explores the bigger picture beyond just how our ears take in sound. It then untangles how our brains make sense of sound. And this may surprise you, but that is one of the hardest tasks we ask our brain to do.

A sound mind, in my view, is a mind that has been shaped by our life and sound by. Positive sound too, meaning connections. It has been shaped by learning that there are details in sound that connect us with what we do and with other people. So the sound mind inherently consists of our cognitive, sensory, motor and reward system. So it consists of how how we think, what we know, our attention, our memory, how we feel, how we integrate our other senses, how we move. All of that is part of the sound mind.

Nina says that we used to think that hearing moved in one direction. That sound would go into the ear and would then be transmitted to the brain where sense is extracted. But Nina believes that sound actually isn't a one way street. It's more like a feedback loop. She says the brain communicates back to the ear and teaches the ear, which sounds are important to remember and to listen out for. That means our memories and past experiences really do matter because they ultimately change our brain and then they shape how we hear sounds in the future.

My concept of the hearing brain is, I think, different from the typical idea of if you, you know, look up hearing you have the ear and then this classical auditory pathway. But no, the hearing brain, in my view, incorporates how we think and feel and move and integrate all of our senses. We know we are our memories and each one of us will have a different way of perceiving the world based on how we spend our time, which is why it is really important that we make good choices for ourselves, for our children, for our families, for education, for medicine. It matters. It matters because biologically we are what we do.

I want to make sure I can get my head around this. But the idea of I think when we think of our senses, we often think of them in a very functional way. Some sort of vision is in front of you. You're seeing that it's going into your eye, hitting your lens, going into your brain. Sound, you know, you hear something. But how you hear it can be really impacted by your previous experiences, your memories. I mean, listening to something is not just a sensation, it's an experience. And that experience is is affected by your previous experiences, your previous memories, all that stuff. I mean, you and I listen to the same thing objectively, let's say. Are we hearing the same thing?

No, we're not. Each one of our relationships with sound is different. We each have our own sound mind. And that sound mind, it is sculpted by our life in sound. And so it really matters how we spend our life in sound. For example, if you are a musician or you speak another language, you are making sound-to-meaning connections everyday that then enable you to automatically make sense of the world in a way that is different from someone else who has had a different experience.

Nina calls that unique relationship to sound our "sonic fingerprint." Now, you may be wondering, as I was, how different can our brain's interpretations of sound really be? Well, Nina has a remarkable way of studying this. She has created a way to essentially listen to the way that our brains listen.

So I can take your electrical response, and I can sonify it! We can listen to your brain. So as I'm talking to you now, the neurons in your brain that respond to sound are producing electricity. If I had scalp electrodes on your head, I would be picking up these electrical events. And so I pick up these events, and we have developed a way of measuring sound processing in the brain with with extraordinary precision. And we can capture the brain's response so that, you know, if you look at a sound wave and I say present a sound wave to you, the brain wave that I get from you actually physically resembles the sound wave.

I want to make sure you heard that right: you can actually see a sound wave of someone's brain processing sound. Yeah, that's pretty meta. I think there's no better way to demonstrate how this works than to let you hear it....

You know, we took the melody of 'A Hard Day's Night,' and then you can hear three healthy young adult brains listening and responding to that clip.

Here's brain number one [brainwave 1].brain number two [brainwaive 2]...and brain number three [brainwave 3]. You hear a difference?

You will recognize 'A Hard Day's Night' in all of the recordings. But each recording is different because each brain is different.

Hearing those three clips really made it make sense for me. It's so amazing. I mean, how often do you get the chance to listen to what's happening within the brain? I can't believe that there's actually a noticeable difference between how three perfectly healthy brains perceive sound. And here's the particularly exciting part: Nina then looks at the sound waves of these recordings, listens to them, and then actually measures and quantifies how well each brain is making sense of sound. She does this by analyzing our brains response to what she calls different sound ingredients. What's a sound ingredient? Well, think of this as being similar to the size or color or texture of something you see. What we hear also has specific attributes.

So there's pitch, how high or low a note might be. There is timbre, which is the harmonics. And the timbre is what enables us to tell two instruments apart if they're playing the same note. The FM sweeps, so these are the very fast sweeps that are as you go from a consanant to a vowel or a vowel to a consanant. And they're all you know, if you record a sound wave, you can look at the sound wave and you can analyze the sound wave. You can see what are the pitch components, what are the timbre components? You can do an analysis of that. We can also listen to the brain's response to that and look at the brain's response to that.

Now, these may sound like musical terms, but Nina points out that factors like pitch and rhythm, they make a difference when we're speaking and communicating with each other as well. Think about it this way: if you're speaking quickly to convey, you're in a hurry, you're using rhythm and tempo to communicate. Or if your pitch goes up at the end of a sentence to signal, you're asking a question? You see what I mean?

And I like to use the metaphor of the brain as mixing board. So you have sound coming in to the brain. And then imagine a mixing board, right? So you've got the faders, and the faders will go up and down. Each fader is representing how well you process each one of these ingredients. So you have a fader for pitch, a fader for harmonic. And then you can see, based on the position of these faders, you can see how good a job an individual is doing at processing these particular ingredients. And we have learned a lot by thinking that way, you know, we know these are the strengths of this person and these are the bottlenecks.

Making sure the faders in your brain are working correctly is important. It's called auditory processing. And when your faders are out of balance, your brain can have trouble understanding what it hears. That can impact our ability to communicate with each other or even just move about the world. But here's the good news: Nina is studying the factors that make us better at making sense of sound. And she says we can all take steps to sharpen our sonic skills. And this can lead to changes for the better in our mental and physical health.

We often say, "I'm so stressed." Right? "I can't focus." Well, you know, sound is our alarm sense. So if you are constantly being bombarded with sounds that are not necessary, like every time you lock and unlock your car door or every time you get a text or some kind of notification, you're being distracted constantly.

After the break, Nina shares her tips for creating a sound mind. That's coming up in just a moment.

And now back to Chasing Life and my conversation with Professor Nina Kraus. Nina is an expert on sound and how it shapes our brains and really so many aspects of our lives, as we just heard, thanks to modern technology. Nina is able to record, to listen and even measure how our brains process sound. I found it so impressive. And that data is then incredibly valuable because it can help us identify some of the factors that help or hurt our ability to process sound. This information can be gathered on an individual basis so that we can help people with their sonic world. But the data also gives us information about groups of people and some of the environmental factors that can put large groups at risk.

One of the things that we notice in children who have not had a lot of linguistic stimulation and you know, these are often kids in low income areas - we've done a number of studies in gang reduction zones of L.A. and Chicago Public Schools - what we see is not only are the harmonics, for example, reduced in some of these kids, but there is excessive neural noise. So there's noise outside the head. You know, just the noise that you and I are familiar with, the subway and there is noise inside the head. Think of it as static. You know, our neurons are always firing. And so when they fire and if you listen to them, they kind of sound like and they there's a random pattern. And this random pattern is larger in kids who live in underserved areas.

On the other hand, there are some people who are particularly good at processing sound. As you might guess, musicians are good at this. People who speak different languages...and also athletes...

And we're following our division one athletes at Northwestern University, all 500 of the males and females across different sports for five years. And what we have learned is that the healthy athlete has an especially quiet brain, which enables them then to especially well interact with the world.

This particular point speaks to what Nina was mentioning earlier about how our sound mind involves more than just our brains and our ears. It's about how movement in our bodies can also help us process sound by increasing our focus. And you don't have to be a professional athlete or a musician to reap these sorts of benefits.

You know, you write in the book that sound can be an invisible ally and an enemy of brain health. When you describe these people who are living in very loud urban environments, typically, often lower socioeconomic class, as you said, "Okay. So you're in a loud environment." Your brain, as you said earlier, is pretty good at determining what is useful sound, what is not useful sound. Are people who live in those environments, are they able to tune it out? Like what is the what is the enemy of brain health here? Is it that you can't tune out that sound, that it's overwhelming or that you're spending so much energy to try and tune that out? Do they get better at being able to discern good sound versus not helpful sound?

You can be in a very noisy environment and as long as you are making good sound-to-meaning connections, you are training, you are shaping your brain to make good sense of sound and also to figure out what to listen to and what to ignore. It's a complicated picture. But if you know you live in New York City and you know you're reading to your kid a lot, you know, making music with him, taking his little feet. If he's an infant and tapping them together as you're singing a song to him and he's getting a lot of sound, too, meaning stimulation. You know, he's he's learning, okay, these are sounds that are important. They're meaningful to me. I feel good when when when we do this" and then you also get good at ignoring the background noise. So it's it's really a part of of the training that we do all the time in in our lives.

That's good. I think that a lot of people think of it as a binary thing. "This is the way I hear the world." But that's not necessarily the case.

Oh, no. And that's the whole point of of of the beauty of the sound mind and the hearing brain is that it changes and it learns for better and for worse, until we die.

It's comforting to hear that there are steps we can all take to sharpen our sonic health. But how exactly can we go about doing this? I wanted to know specifically how Nina cares for her sonic world.

As a preeminent sound scientist, what is your sound environment like? So you're preparing dinner or you're hanging out in the house? Are you listening to music? Is there always sound? Do you embrace quiet?

I'm married to a musician, so there's so much music going on. And that to me is beautiful sound. I really try to reduce what I call noise is unwanted sound, and it's typically manmade. We often say, "I'm so stressed." Right? "I can't focus." Well, you know, sound is our alarm sense. So if you are constantly being bombarded with sounds that are not necessary, like every time you lock and unlock your car door or every time you get a text or some kind of notification, you're being distracted constantly. But we have to first realize that it's happening when there's a truck outside my window, I don't know it's there. But when the guy cuts his ignition and suddenly it's quiet, we all go. So we didn't even realize that, you know, our body knows. Our brain knows. You know, there are things like that that we really can make a change in a difference in our world. And I try to do that personally as well as I possibly can.

Look, thank you, Nina, for a lovely conversation.

Well, thank you. Thanks for all your questions.

Maybe we'll do it in person sometimes. Maybe we can even jam a little bit. That'll be kind of fun.

I love that. We'll see what we could do together. That'd be fun. What do you play?

Piano mostly. Although I play an accordion. I learned the accordion when I was a child because, you know, I'm Indian, and my parents, when they moved to this country, they were all about Bollywood movies. And at that time, at least, accordion was the instrument to play.

So you're even cooler than I thought you were.

What a pleasure. Thank you, Professor.

Thank you.

As you can probably tell, I thoroughly enjoyed this conversation with Nina, and it made me think about sound and hearing in an entirely new way. And what better place to dive into all of this than on a podcast? This podcast, a solely sound-based medium. I really think being able to focus on just the sound of these conversations - no visuals, no graphics - it really makes a difference. I think the most important advice I heard from Nina is to just be aware, aware of the sounds that surround us, of the sounds that we allow into our lives. To look up from our phones every once in a while and just try listening, really listening to the world around us. And also to be vigilant about keeping out distracting, tiring and purposeless noise. And I also think we should try to be conscious of how we interact with those around us, because we all have a hand in shaping each other's sonic world. Next week, we wrap up the season all about the senses with a fascinating episode about synesthesia, a rare trait that melds the way that some people experience senses.

When I told my colleagues in neurology about this, they looked at me and said, "Oh, man, this is too weird, too New Age. You better drop this or it's going to ruin your career." But that just showed: why was everybody else so hostile to the notion that there could be like, say, colored hearing or taste and shape?

We'll be back next Tuesday. Thanks for listening.

Chasing Life is a production of CNN Audio. Our podcast is produced by Emily Liu, Grace Walker, Xavier Lopez, Eryn Mathewson and Andrea Kane. Our intern is Amber Alesawy. Haley Thomas is our senior producer and Abbie Fentress-Swanson is our executive producer. Tommy Bazarian is our engineer. And a special thanks to Ben Tinker, Amanda Sealy and Nadia Kounang of CNN Health.