Our Ears Can Tell the Brain When Hearing Is Impaired
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A recent study sheds light on the long-standing mystery of the DC signal in the cochlea, suggesting it informs the brain about the ear's health. Understanding its role may aid in diagnosing noise-induced hearing injuries and decoding faint sounds. The DC signal is generated by potassium ion channels in hair cell membranes.
A cochlear signal, the exact role of which has been unclear since its discovery around 70 years ago, probably gives the brain information on whether the ear is functioning normally or not. Findings from a new study are an important piece of the puzzle in explaining what happens in the ear in hearing impairment caused by harmful noise, and may in the long run contribute to diagnosing noise-induced hearing injury.
The inner ear, or cochlea, has around 15,000 hair cells. When hit by sound waves, the hair cells transform the vibrations to electric nerve signals. These signals are led to the brain, which interprets them, and not until then can we hear the sound. The hair cell signal consists of two parts, called AC and DC. The AC signal is well researched. It gives the brain information on sound loudness and frequency, i.e. how high or low pitched the sound is. But the DC signal has remained something of a mystery. Ever since its discovery some 70 years ago, researchers have been wondering what its function could be.
“It seems like this signal could be a way for the body to inform the brain whether the ear is healthy or not, and in that way facilitate the brain’s ability to decode faint sounds. The brain can amplify a weak signal from the cochlea. If informed that the ear isn’t functioning normally, the brain doesn’t have to spend resources trying to improve the signal to decode sound from an injured ear,” says Pierre Hakizimana, principal research engineer in the Department of Biomedical and Clinical Sciences at Linköping University.
This discovery may hopefully contribute to new research on how the DC signal could be used to diagnose hearing loss caused by harmful noise. This has so far not been solved, as it has not been known how to interpret this signal, or how to reliably isolate and measure it in humans.
In his study, Pierre Hakizimana also shows that the DC signal is created by potassium ion channels releasing potassium ions through hair cell membranes.
Reference: Hakizimana P. The summating potential polarity encodes the ear health condition. Cell Mol Life Sci. 2023;80(6):163. doi: 10.1007/s00018-023-04809-5
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