Summary: A new study sheds light on the puzzling role of cochlear signals, suggesting they can inform the brain about the health status of the ear.
This research provides important insights for understanding the mechanisms of noise-induced hearing damage. DC signals, identified about 70 years ago, change polarity when the ear is exposed to noxious noise, indicating potential damage.
These findings may contribute to future diagnostic tools for noise-induced hearing loss.
Key Facts:
- DC signals in the ear, an old mystery, most likely tell the brain about the functioning state of the ear.
- A change in polarity of the DC signal occurs when the ear is exposed to noxious noise, indicating potential hearing damage.
- The study revealed that the DC signal is created by the release of potassium ions through the hair cell membrane.
Source: Linkoping University
Cochlear signals, whose exact role has been unclear since their discovery some 70 years ago, may provide information to the brain whether the ear is functioning normally or not.
This is the conclusion of a study from Linköping University, Sweden. Her findings are an important piece of the puzzle in explaining what happens in the ear in noxious noise-induced hearing loss, and in the long term may contribute to diagnosing noise-induced hearing injury.
When the ear is exposed to loud noises, such as at a concert or when in a noisy environment, hearing can be temporarily impaired. Repeated exposure to loud noises can cause permanent hearing damage.
There are studies showing that more than one billion young people risk damaging their hearing by listening to loud music with headphones and in public places. But although noise damage is a leading cause of hearing loss, the exact mechanism is largely unclear.
Pierre Hakizimana at Linköping University is one of the researchers whose aim is to find out how this damage occurs and whether it can be prevented.
The inner ear, or cochlea, has about 15,000 hair cells. When exposed to sound waves, hair cells convert the vibrations into electrical nerve signals. These signals are carried to the brain, which interprets them, and only then can we hear the sound. The hair cell signal consists of two parts, called AC and DC.
AC signal is well researched. This gives the brain information about the loudness and frequency of the sound, i.e. how high or low the pitch of the sound is. But the DC signal remains a mystery. Since its discovery some 70 years ago, researchers have wondered what it does.
When measuring the electrical signal from the cochlear hair cells, the DC signal is visible because it causes a slight shift in the AC signal in either the positive or negative direction. Various studies trying to characterize DC signals have come to different conclusions regarding their polarity.
In the current study, Pierre Hakizimana demonstrated that the polarity of the DC signal changes from positive to negative when the cochlea is exposed to noxious noise. In other words, these signals can provide an indication of ear health status.
“It seems like this signal could be a way for the body to tell the brain whether the ear is healthy or not, and in that way facilitate the brain’s ability to decode weak sounds. The brain can amplify weak signals from the cochlea.
“If it is told that the ear is not functioning normally, the brain does not need to spend resources trying to fix the signal to decode the sound from the injured ear,” said Pierre Hakizimana, principal research engineer in the Department of Biomedical and Clinical Sciences. at Linkoping University.
It is hoped that this discovery will contribute to new research into how DC signals can be used to diagnose hearing loss caused by noxious noise. So far unsolved, because it is not yet known how to interpret these signals, or how to isolate and reliably measure them in humans.
In his study, Pierre Hakizimana also showed that DC signals are created by potassium ion channels that release potassium ions through the hair cell membrane.
Funding: This research was funded by Stiftelsen Tysta Skolan.
About this hearing neuroscience research news
Author: Karin Söderlund Leifler
Source: Linkoping University
Contact: Karin Söderlund Leifler – Linkoping University
Picture: The image is credited to Neuroscience News
Original Research: Open access.
“Polarity of sum potential encodes ear health condition” by Pierre Hakizimana. Cellular and Molecular Life Sciences
Abstract
The polarity of the sum potential encodes the health condition of the ear
The sum potential (SP), the DC potential that, along with the AC response, is generated when the hair cells convert the mechanical energy of sound vibrations into an electrical signal, is the most confusing potential of the cochlea because of its polarity and function. elusive for more than seven decades.
Despite the tremendous socioeconomic consequences of noise-induced hearing loss and its deep physiological importance for understanding how exposure to loud noise impairs hair cell receptor activation, the relationship between SP and noise-induced hearing loss remains of a poor character.
Here, I show that in the normally hearing ear, the SP polarity is positive and its amplitude relative to the AC response grows exponentially across frequencies, and becomes negative and decreases exponentially across frequencies after noise-induced hearing injury.
Since SP is assumed to be generated by K+ outflow down gradient through K basolateral hair cells+ channel, the SP polarity switches to a negative value consistent with a noise-induced shift at the hair cell operating point.
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