How the brain detects unexpected sounds – a new study reveals

We all have experienced situations where something sounds off, such as a car door not closing properly, a football being kicked poorly, or a musical note being out of tune. But how does our brain know when a sound is wrong? A new study by neuroscientists from New York University has shed some light on this question.

The study, published in the journal JNeurosci on October 25, 2023, showed that the brain has a mechanism to make predictions about what sounds should happen and when they should happen. The researchers trained mice to push a lever with their paws and played a tone every time the lever reached a certain position. The mice learned to expect the tone and its timing.

How the brain detects unexpected sounds - a new study reveals
How the brain detects unexpected sounds – a new study reveals

The researchers then changed the sound or its timing and recorded the brain activity of the mice. They found that there were specific neurons in the auditory cortex, one of the brain’s hearing centers, that did not respond to the normal sound but only to the altered sound. These neurons signaled that something was different from what was expected.

The brain learns from mistakes

The researchers called these neurons “prediction error neurons” because they indicate when there is a mismatch between what the brain predicts and what actually happens. They suggested that these neurons are important for learning complex audio-motor tasks like speaking or playing music.

“Neurons like these might be vital in learning how to speak or how to play a musical instrument,” said Nicholas Audette, a postdoctoral fellow in NYU’s Center for Neural Science and the lead author of the paper. “Both of those behaviors involve lots of trial and error, lots of mistakes, and lots of learning from mistakes.”

David Schneider, an assistant professor at NYU and the senior author of the paper, added, “Do expert musicians have better prediction error neurons than novices? And in diseases in which speech is underdeveloped, are prediction error neurons malfunctioning?”

The brain adapts to different situations

The researchers also found that different prediction error neurons responded to different types of changes in the sound, such as its volume, pitch, or timing. This suggests that the brain can make precise predictions about various aspects of sound and adjust them according to different situations.

For example, when we listen to music, we expect certain notes to follow each other in a melody. But when we hear a note that does not fit, we notice it immediately. Similarly, when we speak, we expect our words to sound a certain way. But when we mispronounce something, we correct ourselves.

The study revealed how the brain works to distinguish “right” from “wrong” sounds and how it uses this information to learn and improve. It also opened up new questions about how the brain adapts to different environments and challenges.

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