Biology

Discovery of new neurons in the ear could lead to treatments for tinnitus

Discovery of new neurons in th...
New types of neurons have been found in the auditory system
New types of neurons have been found in the auditory system
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From left Saida Hadjab, Haohao Wu, François Lallemend and Charles Petitpré, researchers on the new study
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From left Saida Hadjab, Haohao Wu, François Lallemend and Charles Petitpré, researchers on the new study
New types of neurons have been found in the auditory system
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New types of neurons have been found in the auditory system

It's estimated that there are 100 billion neurons in the human body, so it's no surprise that some of them have evaded detection by scientists. Now, a team of Swedish researchers have discovered three new types of neurons, which help carry auditory signals from the ear to the brain and may hold the secrets to treating hearing disorders like tinnitus.

Technically, these neurons have been known to science for a long time, but the finer nuances of their function have been mostly overlooked. What researchers from Karolinska Institutet have done in the new study is break down groups of these nerve cells into more accurate sub-classes, after realizing they had different roles. In that way, it's kind of like scientists dividing one species of animal into two on closer examination of differences between individuals.

Nerve cells in the cochlea are responsible for translating sound waves into electrical signals, which are then carried to the brain. It's long been thought that these cells generally fall into two categories dubbed type 1 and type 2 neurons, with the former handling most of the auditory information.

But the new study has identified no less than four types of neurons in the peripheral auditory system. Type 2 remains unchanged, but type 1, according to the team, actually comprises three different kinds of cells.

"We now know that there are three different routes into the central auditory system, instead of just one," says François Lallemend, lead researcher on the study. "This makes us better placed to understand the part played by the different neurons in hearing. We've also mapped out which genes are active in the individual cell types."

These new neurons appear to be involved in decoding the sonic intensity – in other words, the volume – of what we're hearing. That might make them responsible for the "cocktail party effect," where the brain is able to filter out loud background noise to focus on the voice of a friend. On the flipside, they might also play a part in developing hearing disorders like tinnitus and hyperacusis, which is an oversensitivity to sound. But, as the researchers say, identifying this might open up new ways to treat these conditions.

"Our study can open the way for the development of genetic tools that can be used for new treatments for different kinds of hearing disorders, such as tinnitus," says Lallemend. "Once we know which neurons cause hyperacusis we'll be able to start investigating new therapies to protect or repair them. The next step is to show what effect these individual nerve cells have on the auditory system, which can lead to the development of better auditory aids such as cochlear implants."

The team discovered the neurons in mice, using single-cell RNA sequencing. This technique allows researchers to understand the functions of individual cells by looking at which genes they express. The study also showed that these different neurons are all present at birth – at least in mice.

The research was published in the journal Nature Communications.

Source: Karolinska Institutet

2 comments
Daniel Gregory
Smh...sometimes scientists come at us with, "Leaves really are green", and you sit there and wonder how we got to this point. "Neurons only do one thing" -Scientists of yesteryear. "Now they do 4 or 5 things" -Albert Einstein. Aside from Tinnitus being the bane of my existence, working with audio and computers has taught me one thing: the universe is lazy. If nature can make one object serve several functions in a half-assed manner, it will, and it will call it "energy efficiency". If a neuron can send 4 electrical signals at once using COLORS instead of audio...that's what it will do.
marilyn29
This is a great article. I have suffered from T since March 7, 2018... it came on out of the blue one morning upon waking...it's very difficult to deal with at times. what I find interesting is knowing peripheral neves are effected. I have had genetic testing and have CMT type 1A as well as HNPP - this combo is very rare but I am proof it is possible to have both. They too affect peripheral nerves causing deterioration. Cant help but think this is playing a part with my condition.