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How the connections between the ear and the brain change with age

Andrew O’Connor is a PhD student in Professor Walter Marcotti’s lab at the University of Sheffield. His studentship began in 2019. The University of Sheffield are part-funding this studentship.


The cochlea is part of the inner ear. When sound enters the cochlea, it’s detected by inner hair cells, highly-specialised sound-sensing cells that convert sounds into electrical signals that the brain can interpret.

These inner hair cells are connected to sensory nerve cells, which receive the electrical signals and carry them to the brain. Information is also fed back from the brain to the cochlea via another system of nerve cells, known as the efferent system. This system feeds back to the inner ear when sounds are too loud and are damaging it tells outer hair cells (cells in the inner ear which act as sound amplifiers by making quiet sounds louder) to stop amplifying the sound, thus protecting the ear from noise-induced damage. 

Recent research in aged mice (that are used as a ‘model’ of early age-related hearing loss in people) has shown that, over time, the efferent nerve cells start communicating directly with inner hair cells, a configuration normally present only during pre-hearing developmental stages. There are many questions about this ‘re-wiring’ that need to be addressed, and that this project will help to answer. 


The aim of this project is to understand whether this re-wiring of the efferent system happens in mouse models of age-related hearing loss. It also aims to discover when these changes happen, and whether they protect against age-related hearing loss, or make it worse. 

To do this, the student will use a technique called electrophysiology, allowing them to measure the electrical currents produced by the inner hair cells as they convert sounds into electrical signals. The student will measure whether the re-wired efferent system cells actually communicate with inner hair cells, or whether the contacts they form are non-functional.  

The student will also use techniques to measure the hearing ability of the mice, similar to those used to diagnose hearing loss in people. They will also study whether molecules crucial for normal hearing are still present in the aged cochlea, using a technique called immunostaining. 


In order to prevent and treat age-related hearing loss, we need to understand what happens to the cells in our ears as our hearing declines with age.

This project will provide a better understanding of how communication between hair cells and nerve cells changes with age. This will help us to identify which cell types (and which biological processes inside them) are responsible for age-related hearing loss, and therefore which ones we should target when developing treatments to prevent age-related hearing loss and to protect the inner ear.

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