Short Wave - Concussions: How A Mild Brain Injury Can Alter Our Perception Of Sound

Episode Date: December 13, 2021

Headaches, nausea, dizziness, and confusion are among the most common symptoms of a concussion. But researchers say a blow to the head can also make it hard to understand speech in a noisy room. Emily Kwong chats with science correspondent Jon Hamilton about concussions and how understanding its effects on our perception of sound might help improve treatment.For more of Jon's reporting, check out "After a concussion, the brain may no longer make sense of sounds."You can follow Emilly on Twitter @EmilyKwong1234 and Jon @NPRJonHamilton. Email Short Wave at [e-mail] pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Even in a room filled with voices, we can usually pick out the speech coming from one person. Sugar is very sweet. I mean, how else would you survive the holiday season, right? But after a concussion, those same words can be a lot harder to pick out. And to talk about that experience, I have neuro-nerd John Hamilton. here with me. Hey, John. Hey, Emily. So you cover neuroscience for NPR. When it comes to concussions, I thought I knew most of the symptoms, like it's headaches, dizziness, memory problems, confusion.

Now you're telling me it also affects your hearing. Well, yeah, I mean, sort of. Okay. What's different is that often these hearing problems we're talking about are in people whose ears work just fine. If you gave them a typical hearing test, they would pass. But if you tested their ability to pick out those words, sugar is very sweet from a lot of other conversations in a room, they would fail. That's because the trouble they're experiencing is in their brain. The concussion, which is also, by the way, known as a mild traumatic brain injury, is affecting the brain circuits that process sound. And one of the things those circuits do is filter out background noise so we can focus on a particular sound. So they can hear perfectly well, but their concussed brain can't

decipher and figure out what the sounds mean. Exactly. How often does this happen? It looks like sound processing problems affect maybe 15 to 20% of concussion patients. Of course, most of these, I mean, that's a lot of people, but most of them recover, of course. The thing is not all of them do. I talk to one of those researchers who is a pioneer in this field. Her name is Nina Krause. She's a neuroscientist at Northwestern University. Here's what she told me. Making sense of sound is one of the hardest jobs that we ask our brain to do.

So you can imagine that a concussion getting hit in the head really does disrupt sound processing. Yeah, I can't imagine that, but why have I never heard about this? Well, this is a pretty new idea, and scientists are only just beginning to understand what's going on. A lot of doctors aren't even aware of the symptom. They know that a concussion can cause, say, double vision or make somebody hypersensitive to light, but they may not know much about these auditory symptoms. It looks like that's changing, though, as more studies are showing that a hit injury really can't affect our ability to process sounds. So today on the show, how even a mild brain injury can affect our perception of sound.

And how understanding this problem might help improve the diagnosis and treatment of concussion. This is Shortwave, the Daily Science podcast from NPR. Back up, how does the brain process sound in someone who isn't recovering from a concussion? I learned a lot about that from Nina Krause's book, which is called Of Sound Mind, How Our Brain Constructs a Meaningful Sonic World. She has this long and very detailed description of how we perceive sound. I'll give you a highly condensed version. Okay. So let's say someone plays something on a bassoon.

The instrument creates pressure waves that travel through the air and into our ears. When the pressure waves reach the inner ear, they are converted into electrical signals that travel along nerve fire. that go to the brain. Then all kinds of sound processing takes place. There are areas of the brain that can tell whether the sound is loud, or soft. Whether the pitch is high and low. There's an area that compares the signals coming from the left ear and the right ear,

so you know where that bassoon sound is coming from. Another brain area interprets the harmonics and other characteristics of the sound, so you know it really is a bassoon. And these sound processing areas of the brain contain many cells that are specialized to recognize one specific property of a sound. So, for example, timbre, which is the quality produced by a unique combination of overtones. These specialized cells can distinguish the timbre of a bassoon, which uses two reeds, from the tamper of, say, a bass clarinet, which covers the same pitch range but uses a single read. And it's all these brain areas working together that create our perception of hearing sound. There's so much going on in a single sound, so much for our brains to chew on and figure out what it means.

Yes, so much. And that's just the path from the ear to the brain. The brain also sends all kinds of information back toward the ear to help us do things like turn down the volume of a really loud sound or track one sound while ignoring others. What's really remarkable is that all of this happens in a fraction of a second and that all of these brain circuits are able to work together with perfect timing. Yeah, it's like its own little orchestra inside the brain. It is. And when someone gets a concussion, how does this circuitry get messed up? In a concussion, the brain kind of slashes around inside the skull. And that can stretch or twist these nerve fibers that carry information from one area to another. When that happens, the circuits that process sound get slower.

Their timing is off. And the result can be the inability to do things like pick out a single voice in a noisy room or carry a on a conversation with someone who is speaking rapidly as I am right now. Another common problem is auditory hypersensitivity, where even quiet sounds can be overwhelming. Now, since scientists have discovered that a concussion can cause all of these auditory problems, will that make a difference to patients who've been diagnosed? Nina Krause thinks it could. Her lab is doing a five-year study of 500 elite college athletes, including football players.

All of these athletes take a hearing test when they enter the study. then they also take a brain test to see how well their brain processes sounds. So if something happens to them on the field, the scientists can then look to see what has changed. The research has shown that when a player experiences a concussion, it can change the electrical signals coming from areas of the brain that process sounds. And the change in these electrical signals correlates with these symptoms an athlete is experiencing. John, that is huge as far as discoveries go. Because with a concussion, it's usually an invisible injury. You can't detect it with a brain scan or a blood test, at least not at the moment it happens.

This sounds like it would provide more conclusive evidence. I mean, it might because measuring electrical activity could become a way to objectively assess a brain injury. You know, that could help with getting a diagnosis quickly. It could also help, you know, coaches and doctors know when a player is ready to play again. Here's what Nina Krause told me. One of the beauties of this is that you can. just put on the scalp electrodes and play some sounds. And without the athlete having to actively communicate anything, you can get a really good measure of their brain health.

Absolutely. That's really groundbreaking. So what do athletes think about this? I have to confess, I didn't do a survey, but I did speak with one guy who was part of the study. My name's Emmett Clary. I'm a medical student at USC. former NFL player. So Cleary was an offensive tackle who played for seven different NFL teams. Then he worked in Krause's lab before he headed to medical school. So that's how he ended up in the study. Cleary told me that at the beginning of his career, some players and coaches tended to think that concussion symptoms were just a sign of, you know, weakness. Things are changing, he says, and now there's more awareness that it is a physical injury. But players are still pretty reluctant to report that they have had symptoms of a concussion. So Cleary told me that testing a player's auditory brain circuits might solve a really big problem.

If you give an athlete an objective test, that kind of removes some of the burden from them of wanting it to be a certain way. And so this could represent a valuable tool and potentially help a lot of people. Yeah, and it's not just athletes who get concussions. Like what other populations could benefit from this? Pretty much everybody. I mean, Krause has studied concussions in children and other non-athletes, and she says the sound processing problem seemed to work the same way. Also, the military has been studying this phenomenon in troops. Yes, I imagine this is a huge area of study and concern. With the wars in Iraq and Afghanistan, there's serious need to look at concussions and military personnel. How is the focus on sound processing changing that work?

Well, so regular hearing loss has always been a big problem for people who served in the military. You know, even with the ear protection guidelines and all this kind of stuff, they have a lot of exposure to loud weapons, explosions, stuff like that. So audiologists who see veterans or active duty service members, they're used to encountering significant hearing loss. But around 2005, audiologists began to see something that was a lot harder to explain. Here's how Melissa Pappish described it. She's a research investigator at the Veterans Affairs National Center for Rehabilitative Auditorial Research in Portland. We have all of a sudden this large influx of relatively young and middle-aged people. They're coming into our audiology clinics and saying, hey, I'm having problems hearing.

We test their hearing, and their hearing essentially looks normal. But their ability to process sounds, wasn't. Remember that speech and noise test we heard at the top of the episode, you know, the one where you'd try to pick out one voice at a noisy party? Sugar is very sweet. They usually failed that. And Pappish told me many of them also had trouble understanding someone who was speaking quickly. And when we started looking into some of those cases, it definitely seemed like brain injury and in particular blast exposure was really the main thing that was linking those things together. Blast exposure, that's something you've been reporting on for a long time now.

I have. The military has done a bunch of studies now showing that the blast wave from an explosion, you know, like a roadside bomb, it can cause a concussion without leaving a. scratch. And now scientists like Pappish are trying to learn more about how this sort of concussion disrupts the brain areas that process sounds. One thing they've learned so far is that the damage includes the brain stem. So this is the same part of the brain that controls basic functions like your heart rate, breathing, sleep. Pappish says they've also learned that this can be a very long-term disability. They've talked to some patients who are still having auditory problems more than 13 years after they were exposed to a bomb blast. Yeah, it sounds like the auditory consequences of a concussion are pretty serious. So outside of the military and experts like Nina Krause, are doctors and audiologists aware of this aspect of concussions?

Really? Not so much, at least not yet. Wow. Okay. But the thing is, as more and more studies are coming along that show what is happening in the brain, the word is beginning to reach more of these audiologists and neurologists for them. matter. Yeah. Before we go, let's talk about treatment. Is there anything people can do to improve their sound processing if they've had a concussion? It looks like there might be. So both Nina Krause's lab and the Department of Veterans Affairs are using some experimental treatments. Okay. Krause has been trying something she calls rhythm therapy, which sounds like fun. It's based on dance. The idea is that exercises that train the body to stay in sync with a specific rhythm can strengthen the brain pathways that process out. The VA has also been working on stuff. They've been using several computer-based training programs that let people practice listening to very fast speech or picking out a single voice in the crowd in the hopes that they get better at it.

And does that basically help the brain repair some of that circuitry? Repairing or finding an alternative. Usually what the brain does when it's been injured is it finds a way to rewire around the problem. So the problem may still be there, but the brain does a better job doing the same function. Gotcha. Well, John, thank you so much for bringing us this new science and just an update on concussion research. Always a pleasure, Emily. This episode was produced by Thomas Liu, edited by Sarah Saracen, and fact-checked by Margaret Serrino. The audio engineer for this episode was Gilly Moon.

I am Emily Kwong. Thank you for listening to Shortwave, the Daily Science Podcast from NPR.