Understanding the Consequences of Recreational Noise Exposure

The aim of this study is to determine whether measures derived from Magnetic Resonance Imaging (MRI) scans, and clinical and behavioural measures of hearing loss, in the peripheral and central auditory system (ranging from the cochlear nerve through the auditory brainstem to the auditory cortex) are associated with age and history of noise exposure in otherwise healthy adult humans.

Noise exposure is the main cause of preventable hearing loss worldwide. Noise exposure occurs in the workplace, such as in noisy factories, and recreationally through the use of personal music players and attendance at nightclubs and live music events.

Hearing loss is usually diagnosed using pure tone audiometry, which measures the sensitivity of the ear to quiet sounds by determining the levels of tones that can just be heard at several test frequencies. Until recently, it had been assumed that hearing loss results mainly from damage to the sensory hair cells in the cochlea, the part of the ear that converts acoustic vibrations into electrical impulses in the cochlear nerve (CN). However, recent results from animal studies suggest that even moderate noise exposure can cause substantial damage to the CN, without any noticeable damage to the hair cells. Crucially, these results suggest that such damage does not immediately affect sensitivity to quiet sounds, but may exacerbate the effects of ageing.

Hearing loss is a huge problem. Substantial numbers of people, millions in the United Kingdom (UK) alone, are routinely exposed to significant levels of occupational and/or recreational noise. A large UK study found that one in seven adults aged 17-30 years reported "great difficulty" hearing speech in noisy backgrounds, while only one in fifty had impaired sensitivity as measured by pure tone audiometry. Hearing loss can lead to social isolation, depression, and is likely to be predictive of more severe hearing loss in old age. Recent studies suggest that hearing loss also reduces quality of life and is a risk factor for dementia.

This study is part of a programme grant conducted from April 2021 to March 2026 by The University of Manchester and The University of Nottingham. The overall aim of the programme is to understand the consequences of recreational noise exposure through improvement of the understanding of the contribution of CN damage to listening difficulties and audiometric losses.

The primary research questions are:

1. How does auditory pathway integrity vary with noise exposure, audiometric / outer hair cell (OHC) loss, and age?
2. How do auditory pathway integrity, audiometric loss, and OHC loss relate to listening difficulties? The secondary research question is to address how MRI measures relate to electrophysiological measures of auditory pathway integrity.

All participants will undergo the following non-invasive examinations:

* Extended high frequency audiometry to 16 kHz.
* Distortion Product Otoacoustic Emissions (DPOAEs): DPOAEs to 10.5 kHz.
* Middle Ear Muscle Reflex (MEMR): using a broadband contralateral elicitor and a click probe.
* Auditory Brainstem Response (ABR) to assess cochlear synaptopathy and central neural function. The ABR will be elicited with high-pass clicks.
* Speech in noise: A masked speech test will comprise verbal stimuli presented through headphones. The signal-to-background ratio will be varied adaptively to determine reception threshold.
* The Auditory Digit Span test to assess both forward and backward recall as a measurement of short term memory and working memory.
* The Tinnitus Functional Index to assess the severity of tinnitus.
* The Noise Exposure Structured Interview (NESI) to assess the lifetime noise exposure.
* MR Neurography using structural Magnetic Resonance Imaging to visualise the cochlear nerve and measure the diameter/cross-sectional area.
* High-resolution diffusion tensor imaging (DTI) to determine the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in the cochlear nerve.
* Whole-brain DTI to measure the apparent diffusion coefficient (ADC) and fractional anisotropy (FA) in the ascending auditory pathway and auditory cortex.
* High spatial resolution quantitative T1 mapping will be used to assess myelination in the ascending auditory pathway and auditory cortex.
* High spatial resolution T1 weighted imaging will be used to assess morphometry in the ascending auditory pathway and auditory cortex.
* Resting State Functional MRI, lasting 15 minutes, with eyes open and relaxed fixation, will be used to assess the functional connectivity in the ascending auditory pathway and auditory cortex.

Eligibility Criteria:
Inclusion Criteria:

* Ability to give informed consent in English
* In the age range stipulated for the group, i.e. 18-19 inclusive for group 1 and 30-50 inclusive for groups 2 - 4.
* Audiometric thresholds in the range stipulated for the group, i.e. in the normal range for their age group for groups 1 - 3 and outside the normal range for their age group for group 4.
* Noise exposure in the range stipulated for the group, as determined by the NESI, i.e. less than 15 units for groups 1 - 2 and 15 or more units for groups 3 - 4.

Exclusion Criteria:

* Contraindications for MRI
* Motor impairment (for example, cerebral palsy)
* Cognitive impairment (for example, dementia or brain injury)
* Health conditions indicative of peripheral neuropathy (e.g. Type 1 diabetes).