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Understanding the impact of noise exposure on age-related hearing loss

This is a Discovery Research Grant awarded to Dr Stuart Johnson at the University of Sheffield in 2022.

Background

Our sense of hearing is susceptible to damage caused by loud noise or ageing. Both factors can cause hearing loss severe enough to affect communication, leading to isolation and depression. Despite the prevalence of hearing loss (it affects around 5% of the world’s population), we still do not have effective treatments. This is in part due to our lack of understanding of the full range of underlying causes.

Sound is detected by extremely sensitive sensory cells called hair cells. Hair cells are located inside a bony structure called the cochlea in the inner ear. Their name comes from hair-like elements (called stereocilia) that project from the top of the cell. When sound enters the inner ear, it causes the stereocilia to vibrate. These tiny vibrations trigger the hair cell to generate an electrical signal. The signal is then relayed to auditory nerve cells by way of specialized structures at the base of the hair cells called synapses. The electrical signals encode all the important features of sound, such as loudness and pitch. The auditory nerve then carries these signals into the brain, allowing us to perceive sounds such as speech and music.

Hair cells and their synapses with nerve cells are the main targets of damage caused by noise exposure and ageing. However, the cellular changes that underlie this damage, and how noise damage and damage from ageing impact on each other, are not well understood.

Aim

In this project, a team of researchers led by Dr Stuart Johnson will investigate how noise exposure affects the development of age-related hearing loss. They will determine if the damage caused by loud noise exposure is the same as the damage that normally occurs with ageing, or if it is different. This will help to explain whether damage from loud noise exposure worsens age-related hearing loss or instead makes it develop earlier.

The researchers will use a technique called electrophysiology to study these changes, measuring the tiny electrical currents produced by hair cells. They will also measure hearing in mice using techniques like those used to test hearing in people. Finally, they will use techniques such as electron microscopy to provide a visual understanding of the structure and molecules present in the hair cells.

Benefit

Currently, the only options available to treat hearing loss are hearing aids and cochlear implants. These devices benefit many people but do not restore natural hearing or prevent hearing loss from getting worse. Without a better understanding of why we lose our hearing after noise exposure and during ageing, we will not be able to develop effective treatments to either prevent hearing loss or restore hearing.