Thread by @schneiderneuro

1. Ever wonder why you don't usually hear your own footsteps? Why you're not surprised by the sound of your keyboard while typing? Or how you can (sometimes) ignore the sound of your keys jangling in your pocket?

Probably not. But @janani_ss and I did!

2. Why, you might ask? Well, because recognizing (and ignoring) the sounds you make -- while seemingly superficial -- is a key component in how we learn and maintain more complex behaviors, like speech or music.

3. Ignoring the irrelevant sounds you make requires your brain to do some cool computations.
(i) store a memory about the sound associated with an action
(ii) recall that memory during the next execution of that action
(iii) compare the expected with the experienced consequences

4. That last step is called a prediction! And we wanted to figure out how the brain does it.

So we created an augmented reality (AR) system where we could control the sounds mice heard while running. And we studied their brain before, during and after AR experience.

5. In our AR system, mice ran on a quiet treadmill but we monitored how fast they were running and played a series of tones with a tempo set by their speed. The faster the mice ran, the faster the tones were played; kinda like putting a baseball card in your bicycle spokes.

6. After a few days of running, neurons in the mouse's auditory cortex, her primary hearing center, stopped responding to the specific tone frequency associated with running, but only during running! It was like a notch filter was dynamically turned on whenever the mouse ran!

7. We were even able to watch this filter build up over time using 2p calcium imaging to monitor some of the same neurons over the course of several days.

8. How does the auditory cortex selectively turn off responses to a single sound frequency when a mouse is running? We thought that maybe a part of the brain that is active when the mouse runs (like motor cortex) might turn on inhibitory neurons in the auditory cortex.

9. In fact, we already knew it did that! But what we thought might be really cool is if, once the running-related sound was learned, the motor cortex ONLY turned on the inhibitory neurons that were tuned to this sound. That could create a photo-negative of the running sound.

10. And that seems to be what happens. Connections from motor cortex to auditory cortex appear to be strengthened with experience, specifically onto those inhibitory neurons that are tuned to the running sound.

11. Does all this action in the brain actually change what a mouse hears? We tested that too!

It turns out that once mice learn the sound associated with running, they become BETTER at detecting other, unexpected sounds.

12. For mice, who are prey animals, this ability to ignore the sounds they make probably allows them to better detect other sounds --- like a cat who might be stalking them while they're running over dried leaves.

13. That's our story! And what we've described is definitely way more simplified than what is ACTUALLY going on in the brain.

Neuromodulators are involved. Brainstem mechanisms are involved. Attention probably plays a role too.

14. But we think we've tapped into some key players that help us learn and recognize the sounds we make! And we think that studying these systems might help us learn a bit about how memories are formed and how they're used to predict the future.

15. If that sounds interesting to you, check out the full story nature.com/articles/s4158….

And if you're looking to start grad school or a PD, think about working with us @NYU_CNS. We're building next-gen versions of these experiments!

schneiderlaboratory.com

16. CREDITS:.
Co-1st author @janani_ss, an amazing grad student in the Mooney lab @DukeNeuro.

Supported by @NIDCD @BWFUND and Helen Hay Whitney Foundation/@HHMINEWS

And thank you to @marius10p for his amazing science-twitter abilities, which I'm humbly trying to emulate here.