New research from Oregon Health & Science University and collaborating institutions reveals the complex orchestration of neurons in the brain that turns raw noise — the compression of airwaves and pressure on the inner ear — into the ability to, for instance, understand speech, enjoy music and discern train whistles from car horns.
The study is published in the journal Nature Communications.
"Our ability to understand the meaning of sounds depends on the ability of the brain to represent whether the sound is high- or low-pitched, loud or soft, near or far," said Laurence Trussell, Ph.D., professor of otolaryngology/head and neck surgery in the OHSU School of Medicine and scientist in OHSU's Vollum Institute. "All of that requires very specialized neurocircuitry and highly specialized types of neurons in the brain."
Researchers at OHSU, the Baylor College of Medicine and Texas Children's Hospital collaborated on the study. Using a technique developed by lead author Xiaolong Jiang, Ph.D., associate professor of neuroscience at Baylor, the study, which uses a mouse model, reveals the unique patterns of gene expression in specific neurons in the brain that process the signals of sound and enable communication.
This research builds on a previous discovery by Vollum Institute researchers, who in 2022 revealed the architecture of the inner ear in near-atomic detail. That study showed the physiology of the inner ear, which converts vibrations into electrical signals the brain translates as sound.
The study published reveals how the brain's cochlear nuclear complex processes those electrical signals from the ear, leading to the perception of sound.
"Those electrical signals don't have much meaning unless they're integrated over time and across the two ears," Trussell said. "The brain has to pull in all of this information and make sense of it. That requires a rich neural circuitry in the brain, with neurons that have very specific properties and jobs to fulfill.
"It's an amazing process, and now we know the genes that make that happen."
According to the Baylor researchers, some cells respond to sudden, sharp noises while others detect changes in pitch or fluctuating sounds, such as those found in speech or music. Knowing which cell types govern these different functions allows scientists to develop more targeted and effective treatments for hearing impairment.
"For some of these genetic forms of deafness, gene therapies that only treat the inner ear may not be sufficient," Trussell said. "Going forward, we're going to be able to take advantage of this information by looking at how these properties are altered during hearing loss."
The research was supported by various institutes of the National Institutes of Health under Award Numbers R01MH122169, R01MH120404, R01NS110767, R01DC004450, R35NS116798 and R01DC017797. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.
All research involving animal subjects at OHSU must be reviewed and approved by the university's Institutional Animal Care and Use Committee (IACUC). The IACUC's priority is to ensure the health and safety of animal research subjects. The IACUC also reviews procedures to ensure the health and safety of the people who work with the animals. The IACUC conducts a rigorous review of all animal research proposals to ensure they demonstrate scientific value and justify the use of live animals.
