Our ears can tell the brain when hearing is impaired

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Summary: A recent study sheds light on the longstanding mystery of the DC signal in the cochlea, suggesting that it informs the brain about ear health. Understanding its role can help diagnose noise-induced hearing damage and decode quiet sounds. The DC signal is generated by potassium ion channels in hair cell membranes.

Key points to remember:

A cochlear signal, whose exact role has been unclear since its discovery around 70 years ago, probably gives the brain information about whether or not the ear is working normally. The results of a new study are an important piece of the puzzle in explaining what happens in the ear when hearing loss is caused by harmful noise, and may in the long term help in the diagnosis of noise-induced hearing damage.

The inner ear, or cochlea, has about 15,000 hair cells. When struck by sound waves, hair cells transform the vibrations into electrical nerve signals. These signals are directed 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. The AC signal is well studied. It gives the brain information about the intensity and frequency of the sound, i.e. the pitch or gravity of the sound. But the DC signal remained a mystery. Since its discovery around 70 years ago, researchers have wondered what its function might be.

elusive signal

“It seems that this signal could 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 informed that the ear is not functioning normally, the brain does not have to expend resources trying to improve the signal to decode the sound of an injured ear,” explains Pierre Hakizimana, Senior Research Engineer at the Department of Biomedical and Clinical Sciences of Linköping University.

This finding could hopefully contribute to further research into how the DC signal could be used to diagnose hearing loss caused by harmful noise. This has so far remained unresolved, as it is unclear 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 the membranes of hair cells.

Reference: Hakizimana P. Summation potential polarity encodes ear health status. Cell Mol Life Sci. 2023;80(6):163. do I: 10.1007/s00018-023-04809-5

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