Have you ever noticed how you can suddenly hear the hum of your refrigerator in the background when you’re concentrating on it? Or how the sound of your name instantly draws your attention even in the middle of a noisy crowd?
The human brain is remarkably capable of adjusting what we hear based on contexts, such as our current environment or our priorities, but exactly how the brain helps us detect, filter, and react to sounds remains unknown.
Now, biologists at the University of Maryland are one step closer to solving that mystery. Using an animal model, the researchers discovered that the orbitofrontal cortex (OFC), a brain region associated with decision-making but not typically linked to hearing, plays a central role in helping the auditory cortex (a primary auditory center in the brain) adapt to changing contexts or situations. The team’s findings were published in the journal Neuroscience. Current biology July 11, 2024.
“Our hearing doesn’t depend solely on the sounds around us. It also depends heavily on what we’re doing and what’s important to us at the moment,” said UMD assistant professor of biology Melissa Caras, senior author on the paper. “Understanding the neural mechanisms responsible for these adjustments may also lead to better understanding and potential treatments for neurodevelopmental disorders such as autism, dyslexia or schizophrenia — conditions in which sensory regulation goes awry.”
To closely examine the brain circuits involved in the hearing process, the researchers turned to gerbils, small mammals whose basic auditory system is similar to that of humans. The animals were exposed to sound patterns in two different contexts. In one context, the animals listened to sounds passively without needing to do anything. In the other, the animals had to perform a specific action in response to the sounds they heard. By recording and manipulating the animals’ brain activity, the team found that the orbitofrontal cortex helped the animals switch between passive and active listening.
“In short, the ophthalmic cortex sends signals to the auditory cortex when it’s time to pay more attention to sounds,” Caras said. “It’s not clear whether the signals are sent directly or indirectly through an intermediary region of the brain, but we do know that the activity of the ophthalmic cortex is essential for the behavior of the gerbils in our experiments.”
When the ophthalmic auditory cortex was silenced, the animals’ auditory cortex did not switch between passive and active listening, which affected their ability to pay attention to and react to a behaviorally relevant sound.
“In terms of a more human-oriented analogy, it would be like if I told you to suddenly pay attention to the humming of your refrigerator in the background,” Caras explained. “If your orbitofrontal cortex was muted and you couldn’t send a signal to your auditory cortex, you might have a hard time doing so because the ability to rapidly alter your perception of sound would be impaired.”
Although this study was conducted in animals, Caras says the findings may have important implications for human health and well-being. The ability to quickly shift attention to important sounds is essential for many everyday activities, such as communicating with other people and navigating busy or dangerous environments.
“We are just beginning to understand how the brain adjusts hearing sensitivity in response to sudden changes in behavioral contexts. We plan to explore exactly how the ophthalmic auditory cortex communicates with the auditory cortex and see if it is possible to strengthen the connection and improve hearing ability,” Caras said. “This work is paving the way for researchers and health care professionals to develop better strategies to improve hearing in both healthy individuals and those with sensory impairments.”
This research was supported by the National Institutes of Health (award numbers R00DC016046 and R01DC020742).