A cochlear signal, the exact role of which has been unclear since its discovery about 70 years ago, probably gives the brain information about whether the ear is functioning normally or not. This is the conclusion of a study from Linköping University, Sweden.
Its findings are an important piece of the puzzle in explaining what happens to the ear in hearing damage caused by harmful noise, and may eventually contribute to diagnosing hearing damage caused by in the noise. The paper was published in the journal Cellular and Molecular Life Sciences.
When the ear is exposed to loud sounds, such as at a concert or when in a noisy environment, hearing can be temporarily damaged. Repeated exposure to loud sounds can cause permanent hearing damage.
There is research that shows that more than one billion young people are at risk of damaging their hearing by listening to loud music with headphones and in places. But although noise damage is a major cause of hearing loss, the exact mechanisms are largely unclear. Pierre Hakizimana of Linköping University is one of the researchers seeking to find out how these injuries occur and if they can be prevented.
The inner ear, or cochlea, contains about 15,000 hair cells. When hit by sound waves, the hair cells convert the vibrations into electric nerve signals. These signals are taken to the brain, which interprets them, and it is not until then that we hear the sound.
The hair cell signal consists of two parts, called AC and DC. AC signals are well researched. It gives the brain information about the loudness and frequency of the sound, ie how high or low the sound is. But the DC signal remains a mystery. Since its discovery about 70 years ago, researchers have wondered what it could do.
When the electrical signals from the hair cells of the cochlea are measured, the DC signal is detected because it causes a slight shift in the AC signal in the positive or negative direction. Different studies trying to characterize the DC signal have reached different conclusions about its polarity. In the current study, Pierre Hakizimana showed that the DC signal polarity changes from positive to negative when the cochlea is exposed to harmful noise. In other words, the signal can give an indication of the health status of the ear.
“It seems that this signal may be a way for the body to inform the brain whether the ear is healthy or not, and thus facilitate the brain’s ability to decode soft sounds. The brain can amplify a weak signal from the cochlea. If it is announced that the ear is not functioning normally, the brain does not need to spend resources to improve the signal to decode the sound from an injured ear,” said Pierre Hakizimana, chief research engineer at the Department of Biomedical and Clinical Sciences at Linköping University.
This discovery will hopefully contribute to new research on how the DC signal can be used to detect hearing loss caused by harmful noise. This has not been solved until now, because it is not yet known how to interpret this signal, or how to reliably separate and measure it in humans.
In his study, Pierre Hakizimana also showed that the DC signal is generated by potassium ion channels that release potassium ions through the hair cell membranes.
More information:
Pierre Hakizimana, Summating potential polarity encodes the health state of the ear, Cellular and Molecular Life Sciences (2023). DOI: 10.1007/s00018-023-04809-5
Provided by Linköping University
Citation: How the ear informs the brain when hearing is impaired (2023, July 4) retrieved 4 July 2023 from https://phys.org/news/2023-07-ear-brain-impaired.html
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