"It just sounds wrong" — new research sheds light on how our brains tell us when sounds are turned off

Whether it's a car door not closing properly, a kick in a football, or a misplaced note in music, our ears tell us what doesn't sound right
.
A team of neuroscientists recently discovered how the brain distinguishes between "right" and "wrong" sounds, and this research provides a deeper understanding
of how we learn complex auditory-motor tasks like speaking or playing music.

David M.
Schneider, an assistant professor at NYU's Center for Neuroscience, and senior author of the paper, published in the journal Current Biology, said, "We tell if we're making a mistake
by listening to the sounds produced by our movements.
This is most noticeable when musicians or talking, but our brains actually do it all the time, like when a golfer is listening to the sound of her club touching the ball
.
Our brains are always recording whether a sound meets or deviates from expectations
.
In our research, we found that the brain is able to predict precisely when sound should occur and what it should look like
.
”

The researchers' work focuses on better understanding everyday phenomena
.
For example, we know what a car door should sound like because we've closed
it countless times.
However, when we put the seat belt on the door frame and tried to close it, we heard a different sound - "dudang" instead of "bang"
.
It's like a baseball batsman hitting the ball squarely instead of crooked it — or a musician hearing a melody rather than a melody-breaking note
.

However, it's
unclear how the brain recognizes "right" and "wrong" sounds.
Understanding how it does this might give us an idea of how a healthy brain learns to speak and play music, and where neurological disorders like schizophrenia go
wrong.

To solve this problem, Schneider and his colleagues studied the neural activity
of rats when performing tasks similar to closing car doors.
The scientists trained rats to push levers with their paws — like closing a car door — and to play a tone
when the levers reach a specific position.
Eventually, the rats learned exactly what kind of sound
the lever should make.
If the researchers deleted sounds, played the wrong sounds, or played the right sounds at the wrong time, the rats adjusted their behavior, just as humans do when they did something unexpected in a car door
.

The scientists recorded how neurons in the auditory cortex responded
to the mice's brain activity during these behaviors—specifically, one of the brain's "auditory centers.
" Overall, when the rats pressed the lever and heard the expected sound, these neurons were only minimally active
.
However, if the researchers change the frequency of the sound to the wrong frequency — similar to the "clang" of a car door — or even slightly change the timing of the sound, the neurons respond
strongly.

Nicholas Audette, the study's first author and a postdoc in Schneider's lab, observed: "The auditory cortex doesn't seem to signal what is heard, but whether what is heard meets or goes against its expectations
.
" In addition, the researchers found that if they ignored sound altogether — similar to closing a door hard enough — they observed a selected set of neurons becoming active
when the sound was supposed to occur.

"Because if the sound actually plays, these neurons are also activated, as if the brain is recalling the memory of the sound it thinks it is going to hear
.
"

The brain circuits that Schneider and his colleagues are studying, in addition to playing a role in predicting self-generated sounds in everyday behavior, are thought to malfunction in disorders such as schizophrenia, causing people to perceive "phantom sounds"
that don't actually exist.
They hope that by understanding these brain circuits in a healthy brain, they can begin to understand what can go wrong
during illness.

Other authors of the study are Alessandro La Chioma, a postdoc at the Center for Neuroscience, and WenXi Zhou
, a doctoral student at New York University.

Nicholas J.
Audette, WenXi Zhou, Alessandro La Chioma, David M.
Schneider.
Precise movement-based predictions in the mouse auditory cortex.
Current Biology, 2022