Summary: Researchers report subtle hearing loss during youth may pave the way to developing dementia later in life. The study reveals those with subtle hearing loss have altered activity in the right frontal cortex.
Source: Ohio State University.
Cranking up your headphones or scrambling for a front-row spot at rock shows could be damaging more than your hearing.
New research from The Ohio State University has found that young people with subtle hearing loss – the kind they aren’t even aware of – are putting demands on their brains that typically wouldn’t be seen until later in life.
“Hearing loss, even minor deficits, can take a toll in young people – they’re using cognitive resources that could be preserved until much later in life,” said lead researcher Yune Lee, an assistant professor of speech and hearing science at Ohio State. “Most concerning, this early hearing loss could pave the way for dementia.”
The study appears online in the journal eNeuro.
Lee and his collaborators recruited healthy men and women who were 18 to 41 years old so that they could monitor their brain activity while the subjects listened to various sentences. The structure of the sentences varied in difficulty because the researchers wanted the 35 participants’ brains to have to work harder to comprehend some of the messages.
The original study was designed to look just at brain differences when sentence complexity increased – something that is possible with use of functional magnetic resonance imaging (fMRI), technology that allows scientists to measure and map brain activity.
But the research team stumbled upon a surprising discovery. Before the fMRI tests, the researchers tested participants’ hearing to make sure there weren’t any problems that would interfere with the study. Some of the young people had subtle hearing deficits, but nothing serious enough to exclude them from the research.
As it turned out, those with minor hearing deficits had fMRI results that took an unexpected turn. Lee and his colleagues were expecting brain activity in the left hemisphere of the brain. But in the subjects with subtle hearing decline, the fMRI was showing activity in the right hemisphere as well – in the right frontal cortex, to be exact.
“This isn’t about the ear – it’s about the brain, the cognitive process, and it shouldn’t be happening until people are at least older than 50,” he said.
As part of the natural aging process, humans begin to use more of their right frontal brain to process language. But in healthy young people, the left side is wholly responsible for language comprehension.
“But in our study, young people with mild hearing decline were already experiencing this phenomenon,” Lee said. “Their brains already know that the perception of sound is not what it used to be and the right side starts compensating for the left.”
It’s unclear what this means for people as they age, but Lee said he is concerned that tapping into the right brain so early in life could mean worse hearing comprehension with age.
And he’s especially worried about the link between hearing loss and dementia.
“Previous research shows that people with mild hearing loss are twice as likely to have dementia. And those with moderate to severe hearing loss have three to five times the risk,” Lee said.
“We can’t be sure, but we suspect that what happens is you put so much effort into listening you drain your cognitive resources, and that has a negative effect on your thinking and memory and that can eventually lead to dementia.”
Lee said young people should take their hearing health seriously and understand that there could be serious repercussions down the road if they don’t. And it’s important to recognize that risks arise from routine exposures, such as listening to music on portable players and attending live music events, he said.
“Letting this process happen early in your life could be like spending your retirement money when you’re in your 30s,” Lee said. “You’re going to need that down the road.”
Source: Yune Lee – Ohio State University
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Original Research: Abstract for “Differences in Hearing Acuity among “Normal-Hearing” Young Adults Modulate the Neural Basis for Speech Comprehension” by Yune S. Lee, Arthur Wingfield, Nam-Eun Min, Ethan Kotloff, Murray Grossman and Jonathan E. Peelle in eNeuro. Published May 21 2018.
Differences in Hearing Acuity among “Normal-Hearing” Young Adults Modulate the Neural Basis for Speech Comprehension
In this paper, we investigate how subtle differences in hearing acuity affect the neural systems supporting speech processing in young adults. Auditory sentence comprehension requires perceiving a complex acoustic signal and performing linguistic operations to extract the correct meaning. We used fMRI to monitor human brain activity while adults aged 18–41 listened to spoken sentences. The sentences varied in their level of syntactic processing demands, containing either a subject-relative or object-relative center-embedded clause. All participants self-reported normal hearing, confirmed by audiometric testing, with some variation within a clinically normal range. We found that participants showed activity related to sentence processing in a left-lateralized frontotemporal network. Although accuracy was generally high, participants still made some errors, which were associated with increased activity in bilateral cingulo-opercular and frontoparietal attention networks. A whole-brain regression analysis revealed that activity in a right anterior middle frontal gyrus (aMFG) component of the frontoparietal attention network was related to individual differences in hearing acuity, such that listeners with poorer hearing showed greater recruitment of this region when successfully understanding a sentence. The activity in right aMFG’s for listeners with poor hearing did not differ as a function of sentence type, suggesting a general mechanism that is independent of linguistic processing demands. Our results suggest that even modest variations in hearing ability impact the systems supporting auditory speech comprehension, and that auditory sentence comprehension entails the coordination of a left perisylvian network that is sensitive to linguistic variation with an executive attention network that responds to acoustic challenge.
Significance Statement Hearing loss is associated with increased cognitive demand during speech comprehension. Here we used fMRI to measure brain activity while healthy adults with self-reported normal hearing listened to spoken sentences. We found that regions of right frontal cortex, outside of the traditional perisylvian language network, are more active for listeners with poorer hearing as measured with pure-tone audiometry. These findings suggest executive attention varies with hearing ability, even in the absence of clinical hearing loss, during successful auditory sentence comprehension.