Understanding the Consequences of Recreational Noise Exposure

Hearing loss is the most common sensory deficit and the third leading cause of long-term disability, higher than diabetes and dementia. Yet just 0.6% of UK health research spending is on hearing health. Noise exposure is the main cause of preventable hearing loss worldwide. In particular, there is much concern in the academic and clinical communities, and in the popular media, that young people are damaging their hearing by exposure to intense recreational noise, through the use of personal music players and attendance at nightclubs and live music events. In the clinic, hearing loss is diagnosed using pure tone audiometry, which measures the sensitivity of the ear by determining the softest tones that can be heard at several test frequencies, plotted as an audiogram. However, pure tone audiometry is relatively insensitive to the earliest effects of noise damage: damage to the hair cells in the inner ear can occur without affecting the audiogram; hearing loss may occur at high frequencies, beyond the standard range that is tested in the clinic; and evidence from experiments in rodents and monkeys suggest that noise exposure can disconnect the nerve fibres that carry information from the ear to the brain, again without affecting sensitivity to quiet sounds.

It is important that we understand the full effects of recreational noise exposure, beyond the pure tone audiogram, because:

1. "Sub-clinical" deficits may contribute to listening difficulties, such as understanding speech in noisy environments, and may be a cause of tinnitus ("ringing in the ear").
2. These deficits will likely be exacerbated by the effects of age, which is also associated with hair cell and nerve deficits. Hence, noise damage in early life, even if it doesn't cause listening difficulties at the time, may contribute to listening difficulties in later years, affecting employability, reducing quality of life, and possibly increasing the risk of dementia.
3. The presence of sub-clinical deficits may be an early warning that continued exposure will lead to future, more substantial, clinical hearing loss and chronic tinnitus.

In this five-year grant we aim to determine the true impact of recreational noise exposure on hearing health. We will test a large cohort of teenagers before and after their first years of exposure to potentially harmful recreational noise, using advanced tests sensitive to subtle hair cell and neural deficits. We will also investigate listening habits and relation to hearing ability and tinnitus in a large number of young adults using an internet survey, and we will investigate the factors affecting temporary hearing loss in a laboratory-based study, in particular whether ears can be "toughened" by prior noise exposure. We will use these results to determine the early signs of noise damage and the risk factors involved. Finally, we will use advanced brain imaging and electrophysiological techniques to help detect sub-clinical damage to the auditory nervous system in younger and older adults. We will determine the relative contributions of the sub-clinical and clinical deficits to listening ability.

Our research has a number of potential benefits. Being able to detect the early signs of noise damage, and characterise the circumstances and individual characteristics that are associated with damage, will help identify young people who are at risk, and provide targeted healthcare advice to prevent further hearing loss. Understanding the true impact of noise exposure will also inform noise exposure regulations, particularly in recreational situations for which current regulations are weak. For people experiencing listening difficulties, our results may lead to more sensitive clinical tests that will improve management options, such as fitting characteristics for hearing aids and behavioural changes. Overall, our findings will help to reduce the huge societal burden of hearing loss and tinnitus.

There is increasing concern that young people are damaging their hearing by exposure to recreational noise. The scale of the problem is unclear because exposure can cause damage that is undetectable by conventional audiometry, including: hair cell damage, particularly at high frequencies; cochlear synaptopathy; and retro-cochlear deficits including neural loss and demyelination. It is important to identify the full impact of recreational noise exposure so that we can:

1. Identify at-risk individuals and provide personalised healthcare advice
2. Re-evaluate recreational noise-exposure regulations
3. Adequately assess hearing ability, and provide appropriate treatments

The main work package, led by Manchester, will be a longitudinal study on a large cohort of teenagers before and after their first years of potentially harmful exposure. Electrophysiological and listening tests will detect the early signs of damage, and their relation to listening habits. We will also investigate listening habits and relation to tinnitus and hearing ability in a large number of young adults using an internet survey, and we will measure the factors influencing temporary hearing loss in a laboratory-based study. These results will identify the individual factors associated with noise damage, including sex, skin tone, and prior exposure. The fourth work package capitalises on the outstanding facilities at the Sir Peter Mansfield Imaging Centre, University of Nottingham. We will optimise advanced structural MRI to detect damage to the auditory nerve and central auditory pathways, and also study alterations in resting state network connectivity. We will determine the contributions of sub-clinical and clinical deficits to listening ability.

Our programme is unique in combining a world-leading audiology research group with a world-leading MRI group. The multidisciplinary approach has great potential to deliver new insights into the consequences of recreational noise exposure.