Welcome to brain Stuff production of I Heart Radio. Hey brain Stuff, Lauren Vogelbaum. Here, you're walking down a deserted street to all quiet in your thoughts, and suddenly you hear footsteps. Of course, your own footfalls. We're making noise too, So why is it so easy to ignore our own noises and so easy to hear others? Scientists have long known that we're capable of tuning out our own personal noises, but we're previously in the dark about how the brain
accomplishes this feat. The results of a new study published in the journal Nature aims to amp up our understanding of this phenomenon by focusing on footsteps. We spoke with lead researcher Dr David Schneider, an assistant professor with the Center for Neural Science at New York University. He explained, we wanted to understand how the individual cells in our
brains are neurons, work together to make that happen. To do that, we studied mouse brains, and we built an augmented reality system so that when mice ran, we could experimentally control the sounds they heard. We could give them a couple of days with their walking, making one sound then we could unexpectedly switch the sound. The research was
conducted at Duke University's School of Medicine. The scientists soon discovered that when the mice expected their walking to sound a particular way, the neurons and the auditory cortex, one of the main hearing centers of the brain, stopped responding to the noise. Schneider said. It was almost like they were wearing special headphones that could filter out the sound of their own movements. In contrast, when we played an unexpected sound, neurons and their auditory cortex had large responses.
The scientists soon realized that as the mice were becoming familiar with the sounds of their own walking, there were some important connections being changed between the auditory cortex and the motor cortex, which is the part of the brain responsible for moving. Schneider said the connections strengthen onto inhibitory neurons and the auditory cortex that are active when the
mouse heard the footsteps sound. The end result was that every time the mouse walked, a group of inhibitory neurons were active to create a photo negative of the sound the mouse expected, which could cancel out the expected sound when it was heard. The experience isn't limited to footsteps either. Schneider said, the heavy breather rarely knows that they're a heavy breather because it doesn't sound as loud to them, And I think the same is true of keystrokes as sure.
I can hear my own keystrokes when I'm typing, but I don't usually get annoyed by them. But if someone sitting next to me is typing heavily, it drives me batty. For any creature accustomed to being hunted, like mice, this ability to filter out one's own innocuous noises and focus on the more potentially dangerous ones is critical. This is also the same phenomenon at play when we sing, speak,
or play music. Schneider explained, we usually have an idea in our head for what sound would like to produce. When I sit down at the piano and strike the keys, for example, I know what music I want it to make, But when we're practicing, we often get it wrong. The mechanism that we've described in this paper, the ability to ignore the expected consequences of our movement, gives us the extra cool ability to detect when we've got it wrong. So if I play the piano just right, I hear it, sure,
but my auditory cortex is pretty silent. But when I play it wrong, I get a much larger response. As a result, the brain is able to interpret that response is hey, that didn't sound right. Maybe I should move my fingers a little different next time. That allows us to learn from our mistakes. Though the researchers are still trying to figure out exactly how such error signals are employed by the brain when learning language and music skills, they're hoping to use this information to shed light on
a couple of different areas next. For example, it's possible that the same brain circuits involved in ignoring and or detecting sounds malfunction in patients with diseases like schizophrenia. Schneider said they often vividly experienced phantom voices that aren't actually the air. It's been suggested that these hallucinations may be due to altered connectivity between motor and hearing centers of the brain, and we think the brain circuitry we've identified
might be involved. So I'd like to study mice who have similar genetic mutations to those that are associated with schizophrenia in humans. Today's episode was written by Alia Hoyt and produced by Tyler Klang. Brain Stuff is a production of iHeart Radio's How Stuff Works. For more in this and lots of other notable topics, visit our home planet,
how stuff Works dot com. And for more podcasts for my heart Radio, visit the iHeart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.