The hearing brain and its connection to a ‘Sound Mind’

In her recent book “Of Sound Mind: How Our Brain Constructs a Meaningful Sonic World,” Northwestern University professor and neuroscientist Nina Kraus writes about the vastness of the hearing brain, explaining how the sounds of our lives shape our brains and help us build the sonic world we live in.

Exploring the power of music for healing as well as the destructive power of noise on the nervous system, the book traces decades of research to uncover what happens in the brain when we speak another language, have a language disorder, experience rhythm, listen to birdsong or suffer a concussion. 

In “Of Sound Mind,” Kraus encourages a holistic understanding of the biological consequences of our lives in sound — be those sounds sweet as neighborhood bird songs or trying like the din of the furnace cycling on and off.

“A holistic understanding of the biological consequences of our lives in sound positions us to make better choices for ourselves, education and medicine,” she said. “In a time when we are constantly running, our resources strained, and our sense of connection to others and the world ever more tenuous, this book invites the reader to slow down and consider how sound connects us all.”

Ingredients that make up sound

While the book is conversational in tone, the statements are rooted in the biological literature and the research conducted by Kraus and her colleagues at their Brainvolts Lab in Northwestern’s School of Communication.

Kraus writes lyrically in “Of Sound Mind” about auditory processing and the ingredients that make up sound.

“Like a visual object can be described in terms of color, texture, luminosity and movement, sound is made up of pitches, timbres, timing cues and movement,” said Kraus, who has discovered ways to measure these ingredients in the neural activity arising from hearing sounds like speech and music.

‘An ear is a cathedral’

A review of the book in the Wall Street Journal praised Kraus’s descriptions of the processes as “metaphorical imagery, giving us the sense that an ear is a cathedral with walls, roof and floor, with fountains of living (electrical) water.”

“Kraus’s greatest triumph,” the writer continues, “is in making the invisible visible in vividly rendering those vibrations of air through the medium of her words and reminding us to pause and listen.”

“Of Sound Mind” also explores the risk of being bombarded by meaningless noise.

The danger of loud sounds is broadly understood, but few people realize that noise can be dangerous even if it isn’t loud, said Kraus. The brain evolved to respond to changes in otherwise predictable sound patterns because our distant ancestors needed to be alerted to potential sources of danger.

Chronic exposure to meaningless noise requires the brain to sustain an exhausting state of alertness and ultimately dulls our perceptions.

Distinguishing signal from noise

“Overexposure to the background noise of life can blunt our ability to distinguish meaningful sounds and distinguish signal from noise, which is crucial to nearly everything we do, and the more noise that surrounds us, the less we are able to call our brains to attention when attention is warranted,” Kraus said.

Another topic Kraus addresses is noise in the brain itself, which has a baseline level of noise. If the noise level is too high, the neural activity that arises from the sounds you hear can be obscured. Because literacy skills so deeply depend on making sense of the sounds of language, a noisy brain can have a negative influence on learning to read.

A U.S. housing survey found that residents of low-income neighborhoods were more than twice as likely as others to report bothersome levels of neighborhood noise. Children raised in such environments often have a high level of neural noise in their brains, meaning that their auditory neurons are active even when the external world is quiet. The result is a noisy brain, processing sound less distinctly than it otherwise might.

“Imagine listening to a poorly tuned radio, with static noise getting in the way of hearing what the radio announcer has to say,” Kraus said. “The noise on the outside becomes noise on the inside, obscuring the subtle, yet important cues in spoken language.”

Kraus also studies the impact of concussions on the auditory system and the injured brain's ability to make sense of sound. In collaboration with Lurie Children’s Hospital sports medicine department and NU Athletics, Brainvolts Lab is developing a biological marker to aid concussion assessment and management.

“Of Sound Mind” also incorporates ongoing work involving Northwestern student athletes, where compared to their non-athlete classmates, elite Big Ten athletes have lower levels of noise in their brains.

In addition to praise Kraus has received by book reviewers, the Association of American Publishers Awards recently recognized “Of Sound Mind” with a 2021 PROSE Award for professional and scholarly excellence as best book in biomedicine.

“The sound mind engages how we think, feel, move and interpret our other senses. Not only does it shape our health, but it is deeply involved in forming memories and contributes in no small way to making us who we are,” Kraus said.