Brain networks rewire to compensate for difficulty hearing speech in noisy environments, study finds

As they age, some people find it harder to understand speech in noisy environments. Now, University at Buffalo researchers have identified the area in the brain, called the insula, that shows significant changes in people who struggle with speech in noise.

The findings, published in the journal Brain and Language, contribute to the growing link between hearing loss and cognitive impairment leading to dementia. Previous research has separately established connections between hearing difficulties and dementia, as well as insula abnormalities and cognitive decline.

The insulae are two complicated structures that interact with the brain’s frontal lobe, which is responsible for higher-level cognitive function. The insulae integrate sensory, emotional and cognitive information.

The study involved 40 men and women aged 20–80. They underwent hearing testing first to determine who had difficulty hearing speech in noisy environments; they then underwent magnetic resonance imaging (MRI) tests of their brains at rest.

The brain at baseline

While task-based studies reveal what parts of the brain activate during specific activities, the researchers in this study wanted to see how difficulties hearing speech in noise might affect the brain at baseline, at rest.

According to David S. Wack, Ph.D., first author and associate professor of radiology in the Jacobs School of Medicine and Biomedical Sciences at UB, resting-state MRI reveals functional connections, showing how different brain regions work together even when not actively engaged in tasks.

The study found that the left insula shows stronger connectivity with auditory regions in people who struggle with speech in noise, suggesting a permanent rewiring of brain networks that persists even when they’re not actively listening to challenging speech.

“Your brain is always doing something,” Wack explains. “And when you have hearing loss, you are recruiting other areas of the brain to do more processing in order to decode what’s going on. What’s interesting is that we found the insula working harder when the brain was supposedly at rest, when there was no speech in noise.”

That finding, he says, has implications for how dementia may develop, since the insula is also associated with early dementia.

“Multiple studies have established correlations between hearing loss, speech-in-noise difficulties and dementia,” Wack explains. “Our findings show baseline brain connectivity changes that occur with poorer performance with speech in noise that may explain these connections.

“You have a bad signal coming (the sound or the seen object) and then the brain is left to interpret what it means,” he says. “Your brain fills in what works, what seems to make the most sense and it incorporates higher-level regions of the brain to do it.

He continues, “It’s not that hearing loss causes dementia, but if we could find a way to preserve the fidelity of the signal coming in, then the brain wouldn’t have to start compensating for that hearing loss.”

An unexpected finding

The researchers reported one unexpected and fascinating finding. “We had a subject who had relatively poor hearing for pure tones, but who achieved the highest score for speech-in-noise for one ear,” Wack says.

It turned out this person worked in an environment with high background noise.

“This suggests that people don’t have to just accept poor performance in noisy backgrounds,” says Wack. “It shows that you might be able to practice your way out of it.”

He hopes to further study the relationship between hearing loss and dementia. “By identifying shared neural networks at rest, our research adds to the understanding of why addressing hearing difficulties might help with cognitive function,” he says.