Speaker 1: Welcome to brain Stuff production of I Heart Radio. Hey
Speaker 1: brain Stuff, Lauren Vogelbaum. Here, you're walking down a deserted
Speaker 1: street to all quiet in your thoughts, and suddenly you
Speaker 1: hear footsteps. Of course, your own footfalls. We're making noise too,
Speaker 1: So why is it so easy to ignore our own
Speaker 1: noises and so easy to hear others? Scientists have long
Speaker 1: known that we're capable of tuning out our own personal noises,
Speaker 1: but we're previously in the dark about how the brain
Speaker 1: accomplishes this feat. The results of a new study published
Speaker 1: in the journal Nature aims to amp up our understanding
Speaker 1: of this phenomenon by focusing on footsteps. We spoke with
Speaker 1: lead researcher Dr David Schneider, an assistant professor with the
Speaker 1: Center for Neural Science at New York University. He explained,
Speaker 1: we wanted to understand how the individual cells in our
Speaker 1: brains are neurons, work together to make that happen. To
Speaker 1: do that, we studied mouse brains, and we built an
Speaker 1: augmented reality system so that when mice ran, we could
Speaker 1: experimentally control the sounds they heard. We could give them
Speaker 1: a couple of days with their walking, making one sound
Speaker 1: then we could unexpectedly switch the sound. The research was
Speaker 1: conducted at Duke University's School of Medicine. The scientists soon
Speaker 1: discovered that when the mice expected their walking to sound
Speaker 1: a particular way, the neurons and the auditory cortex, one
Speaker 1: of the main hearing centers of the brain, stopped responding
Speaker 1: to the noise. Schneider said. It was almost like they
Speaker 1: were wearing special headphones that could filter out the sound
Speaker 1: of their own movements. In contrast, when we played an
Speaker 1: unexpected sound, neurons and their auditory cortex had large responses.
Speaker 1: The scientists soon realized that as the mice were becoming
Speaker 1: familiar with the sounds of their own walking, there were
Speaker 1: some important connections being changed between the auditory cortex and
Speaker 1: the motor cortex, which is the part of the brain
Speaker 1: responsible for moving. Schneider said the connections strengthen onto inhibitory
Speaker 1: neurons and the auditory cortex that are active when the
Speaker 1: mouse heard the footsteps sound. The end result was that
Speaker 1: every time the mouse walked, a group of inhibitory neurons
Speaker 1: were active to create a photo negative of the sound
Speaker 1: the mouse expected, which could cancel out the expected sound
Speaker 1: when it was heard. The experience isn't limited to footsteps either.
Speaker 1: Schneider said, the heavy breather rarely knows that they're a
Speaker 1: heavy breather because it doesn't sound as loud to them,
Speaker 1: And I think the same is true of keystrokes as sure.
Speaker 1: I can hear my own keystrokes when I'm typing, but
Speaker 1: I don't usually get annoyed by them. But if someone
Speaker 1: sitting next to me is typing heavily, it drives me batty.
Speaker 1: For any creature accustomed to being hunted, like mice, this
Speaker 1: ability to filter out one's own innocuous noises and focus
Speaker 1: on the more potentially dangerous ones is critical. This is
Speaker 1: also the same phenomenon at play when we sing, speak,
Speaker 1: or play music. Schneider explained, we usually have an idea
Speaker 1: in our head for what sound would like to produce.
Speaker 1: When I sit down at the piano and strike the keys,
Speaker 1: for example, I know what music I want it to make,
Speaker 1: But when we're practicing, we often get it wrong. The
Speaker 1: mechanism that we've described in this paper, the ability to
Speaker 1: ignore the expected consequences of our movement, gives us the
Speaker 1: extra cool ability to detect when we've got it wrong.
Speaker 1: So if I play the piano just right, I hear it, sure,
Speaker 1: but my auditory cortex is pretty silent. But when I
Speaker 1: play it wrong, I get a much larger response. As
Speaker 1: a result, the brain is able to interpret that response
Speaker 1: is hey, that didn't sound right. Maybe I should move
Speaker 1: my fingers a little different next time. That allows us
Speaker 1: to learn from our mistakes. Though the researchers are still
Speaker 1: trying to figure out exactly how such error signals are
Speaker 1: employed by the brain when learning language and music skills,
Speaker 1: they're hoping to use this information to shed light on
Speaker 1: a couple of different areas next. For example, it's possible
Speaker 1: that the same brain circuits involved in ignoring and or
Speaker 1: detecting sounds malfunction in patients with diseases like schizophrenia. Schneider
Speaker 1: said they often vividly experienced phantom voices that aren't actually
Speaker 1: the air. It's been suggested that these hallucinations may be
Speaker 1: due to altered connectivity between motor and hearing centers of
Speaker 1: the brain, and we think the brain circuitry we've identified
Speaker 1: might be involved. So I'd like to study mice who
Speaker 1: have similar genetic mutations to those that are associated with
Speaker 1: schizophrenia in humans. Today's episode was written by Alia Hoyt
Speaker 1: and produced by Tyler Klang. Brain Stuff is a production
Speaker 1: of iHeart Radio's How Stuff Works. For more in this
Speaker 1: and lots of other notable topics, visit our home planet,
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