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Uncovering the hidden workings of the ear
13 September 2024
A few decades ago, the workings of the inner ear were something of a mystery. Professor Jonathan Ashmore from the UCL Ear Institute has devoted his research career to changing this.
Jonathan Ashmore has been a trailblazer in the field of hearing, and his ground-breaking discoveries have shaped how we understand hearing-related conditions like deafness and tinnitus today.听
He originally started out as a theoretical physicist and then moved into investigating the retina of the eye. He realised that a lot of the technologies developed for studying the eye could also be applied to understanding how the ear works.
There was a problem though. The ear contains a variety of cells, but compared to an organ like the eye there aren鈥檛 many of them. Consequently, when Ashmore became involved in the field in the 1980s, little was known about the workings of the inner ear. 鈥淭his seemed like a huge technical challenge and that's really how I got involved in it,鈥� Ashmore explains. 鈥淗ow do you look at something which doesn't have very many cells to play around with?鈥�
Top view of the rows of outer hair cells from inner ear. Image courtesy of Andrew Forge, UCL Ear Institute
From the beginning, Ashmore was involved in thinking about how the ear amplifies sound. He explains that the ear has a kind of 鈥渂iological hearing aid鈥� and the essential components of this are the so-called outer hair cells of the inner ear.
鈥淭he outer hair cells are a population of cells that start to disappear as you get old听and so you begin to get deafer. The outer hair cells were always the interesting cells to start looking at, and the techniques for looking at them in detail really only developed from about the mid-1980s,鈥� he says.
These outer hair cells behave like very fast muscles, amplifying sound mechanically. Up close they look as though they are dancing. Ashmore was one of the first people to show how fast these 鈥榙ancing鈥� outer hair cells work and the first to capture it on film, as part of a BBC documentary. He describes how they can move at frequencies way above 1,000 times per second, and possibly even up to 100,000 times per second in animals like whales or bats.
Nowadays, Professor Ashmore is focusing on understanding how animals hear at very high frequencies and investigating a research area known as cochlear mechanics. 鈥淭here are about 5000 mammals on the planet and most of them have a hearing range that extends way beyond what we can hear. I鈥檓 interested in understanding how this actually happens,鈥� he says.
He explains that one of the main challenges is that the inner ear is very inaccessible: it鈥檚 about the size of a pea in humans and about the size of a grain of rice in mice, and is buried inside a bone. To address this, he is synthesising data to try and build a theoretical model to show what鈥檚 happening when the ear processes high frequencies.
Professor Ashmore has some ideas that may explain what high frequency hearing is all about. He hopes that addressing these types of technical problems will ultimately enable new breakthroughs in tackling hearing loss. The ear may be an incredibly complex organ but there is no doubt that we鈥檙e getting closer to finally uncovering its hidden workings.