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Improving our understanding of the way the cochlea processes sounds
[Small project grant: 2006-2010]
There are two types of sensory “hair cell” in the in the cochlea. Inner hair cells turn sounds into electrical signals that are passed on for the brain to interpret, while outer hair cells amplify the mechanical signals that drive the inner hair cells. In healthy ears, this mechanical process causes the ear to emit its own sounds, known as otoacoustic emissions.
This project has two main goals: to understand better how mechanical motion of the cochlea generates otoacoustic emissions, and to investigate the role of neural connections sent back from the brain to the outer hair cells. It is thought that the brain sends signals via these downward connections in order to control the way the outer hair cells amplify the incoming sounds. However, it is not yet fully understood just how this control is achieved.
The research team have successfully completed a number of difficult experiments to measure how the cochlea moves, both with and without the control signals from the brain, when stimulated by sound. They have also made measurements designed to distinguish between different theories of how sound travels inside the inner ear.
Initial results, published in the August 2008 edition of The Journal of the Acoustical Society of America, suggest that there are two distinct ways in which the downward neural connections affect cochlear motion.
“Our discovery of such distinct outer-hair-cell based effects opens up the possibility that each underlying mechanism has a separate function within the normal hearing process, and the search for this function is now on,” said Dr Cooper.
Results from the study will be relevant to millions of people in the UK and worldwide because problems with the way the cochlea processes sound underlie most forms of sensorineural or “nerve” deafness. Improvements in our understanding of how the cochlea functions should therefore lead to long-term benefits for substantial numbers of hearing-impaired people.
