Purdue University

07/11/2019 | Press release | Distributed by Public on 07/11/2019 10:54

Now hear this: Study highlights the importance of avoiding noise-induced hearing loss

WEST LAFAYETTE, Ind. -Hearing loss is so common in today's society, especially in older individuals, that many people question the use of doing anything to protect their hearing from noise and loud sounds. But it turns out the source of hearing loss may have a large impact on a person's ability to understand speech and enjoy music.

That's the result of a new study from researchers at Purdue University and the University of Rochester that was recently published in The Journal of Neuroscience.

The study measured differences in neural processing of sound in chinchillas between the two most common sources of hearing difficulty: noise trauma and age-related metabolic loss. It was led by Kenneth Henry, who was a National Institutes of Health postdoctoral fellow at Purdue and is now an assistant professor in the University of Rochester Medical Center's Department of Otolaryngology; and Michael Heinz, a professor in speech, language and hearing sciences and biomedical engineering in Purdue University's colleges of Health and Human Sciences, and Engineering.

The researchers found that noise trauma causes substantially greater changes in neural processing of complex sounds compared with age-related metabolic loss, potentially explaining large differences in speech perception commonly seen between people with the same clinically defined degree of hearing loss based on an audiogram.

Metabolic loss is age-related deterioration of the electrochemical gradient - the ear's 'battery' - in the inner ear, and happens naturally as one gets older. NIHL is caused by physical trauma to various parts of the ear, causing scattered damage to and loss of delicate sensory hair cells within the cochlea. The trauma can be caused by a one-time event such as an explosion or a long-term event such as using heavy machinery without any ear protection.

'For complex sounds like speech or music, it is worse to get a hearing loss from noise exposure than from age; luckily noise exposure is preventable,' Heinz said. 'Although these two types of hearing loss are currently categorized together in clinical audiology, these results suggest the need to develop specific treatments, such as different hearing-aid amplification strategies, for each type of loss.'

There are several takeaways to the study, Heinz said, including minimizing noise overexposure, public health discussions on noise prevention strategies, and personalized or precision medicine approaches to audiological diagnosis and treatment in the future.

'Avoiding exposure to loud sounds is the best prevention, such as limiting the earbud volume with your smartphone to one-half to two-thirds of the maximum. If someone else can hear your music through your earbuds, it is way too loud,' Heinz said. 'Other simple strategies exist, such as wearing ear plugs when attending a sporting or music event or when mowing the lawn. Ear plugs or ear muffs are also easy solutions in loud work environments, which are regulated by federal guidelines for required hearing protection.'

Heinz's health research aligns with Purdue's Giant Leaps celebration, acknowledging the university's global advancements made in health, longevity and quality of life as part of Purdue's 150th anniversary. This is one of the four themes of the yearlong celebration's Ideas Festival, designed to showcase Purdue as an intellectual center solving real-world issues.

This research was supported by grants F32-DC012236 and R01-DC009838 from the National Institute on Deafness and Other Communication Disorders, the UK-US Fulbright Commission Scholarship Award funded by Action on Hearing Loss.

Writer: Matthew Oates, 765-496-2571, [email protected], @mo_oates

Sources: Michael G. Heinz, 765-496-6627, [email protected]

Kenneth S. Henry, 585-275-4851, [email protected]

Note to Journalists: For a copy of the research paper contact Matthew Oates at 765-496-2571 or [email protected]

ABSTRACT

Divergent auditory-nerve encoding deficits between two common etiologies of sensorineural hearing loss

Kenneth Henry, University of Rochester; Mark Sayles, Purdue University; Ann Hickox, Decibel Therapeutics; Michael Heinz, Purdue University

Speech intelligibility can vary dramatically between individuals with similar clinically defined severity of hearing loss based on the audiogram. These perceptual differences, despite equal audiometric-threshold elevation, are often assumed to reflect central-processing variations. Here, we compared peripheral-processing in auditory nerve (AN) fibers of male chinchillas between two prevalent hearing loss etiologies: metabolic hearing loss (MHL) and noise-induced hearing loss (NIHL). MHL results from age-related reduction of the endocochlear potential due to atrophy of the stria vascularis. MHL in the present study was induced using furosemide, which provides a validated model of age-related MHL in young animals by reversibly inhibiting the endocochlear potential. Effects of MHL on peripheral processing were assessed using Wiener-Kernel (system identification) analyses of single AN fiber responses to broadband noise, for direct comparison to previously published AN responses from animals with NIHL. Wiener-Kernel analyses show that even mild NIHL causes grossly abnormal coding of low-frequency stimulus components. In contrast, for MHL the same abnormal coding was only observed with moderate to severe loss. For equal sensitivity loss, coding impairment was substantially less severe with MHL than with NIHL, probably due to greater preservation of the tip-to-tail ratio of cochlear frequency tuning with MHL compared with NIHL rather than different intrinsic AN properties. Differences in peripheral neural coding between these two pathologies-the more severe of which, NIHL, is preventable-likely contribute to individual speech perception differences. Our results underscore the need to minimize noise overexposure and for strategies to personalize diagnosis and treatment for individuals with sensorineural hearing loss.

Significance Statement: Differences in speech perception ability between individuals with similar clinically defined severity of hearing loss are often assumed to reflect central neural-processing differences. Here, we demonstrate for the first time that peripheral neural processing of complex sounds differs dramatically between the two most common etiologies of hearing loss. Greater processing impairment with noise-induced compared with an age-related (metabolic) hearing loss etiology may explain heightened speech perception difficulties in people overexposed to loud environments. These results highlight the need for public policies to prevent noise- induced hearing loss, an entirely avoidable hearing loss etiology, and for personalized strategies to diagnose and treat sensorineural hearing loss.