How the ear can inform the brain of whether hearing is impaired

Date:
July 4, 2023
Source:
Linko"ping University
Summary:
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. These
new findings 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.


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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. This is the conclusion of
a study from Linko"ping University, Sweden. Its findings 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.

When the ear is exposed to loud sounds, as at a concert or when being in a noisy environment, hearing can be temporarily impaired. Being repeatedly exposed to loud sounds may cause permanent damage to hearing. There is
research to indicate that more than one billion young people are at risk
of damaging their hearing by listening to loud music with headphones
and at venues. But although noise damage is a major cause of impaired
hearing, the exact mechanisms are largely unclear. Pierre Hakizimana at Linko"ping University is one of the researchers aiming to find out how
these damages occur and whether they can be prevented.

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.

When measuring the electrical signals from the cochlea hair cells, the
DC signal is noticeable as it causes a slight shift in the AC signal
in either a positive or a negative direction. Various studies trying to characterise the DC signal have come to different conclusions as to its polarity. In the current study, Pierre Hakizimana shows that DC signal
polarity changes from positive to negative when the cochlea has been
exposed to harmful noise. In other words, the signal can provide an
indication of ear health status.

"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 Linko"ping 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.

The research was funded by Stiftelsen Tysta Skolan.

* RELATED_TOPICS
o Health_&_Medicine
# Hearing_Loss # Disability # Diseases_and_Conditions #
Nervous_System
o Mind_&_Brain
# Hearing_Impairment # Tinnitus # Perception #
Brain_Injury
* RELATED_TERMS
o Hearing_impairment o Auditory_system o Ear o Middle_ear o
Brain_damage o Eardrum o Ultrasound o Tinnitus

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Materials provided by Linko"ping_University. Original written by Karin So"derlund Leifler. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Pierre Hakizimana. The summating potential polarity encodes the ear
health condition. Cellular and Molecular Life Sciences, 2023; 80
(6) DOI: 10.1007/s00018-023-04809-5 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2023/07/230704110920.htm

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