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I recently stumbled upon an interesting online hearing test on YouTube, and it got me thinking about the root causes of hearing loss. I'm curious about the main contributing factors behind the loss of our hearing range as we age.

Is this degradation primarily linked to the loss of gray or white matter in our brains, indicating a neurological issue, or is it predominantly associated with the wear and tear of some other biological input mechanisms within our auditory system?

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  • $\begingroup$ Can you please link that hearing test, I am curious what it is. $\endgroup$
    – AliceD
    Commented May 27, 2023 at 15:19
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    $\begingroup$ @AliceD youtube.com/watch?v=zUmbmssqHOY $\endgroup$
    – GEP
    Commented May 27, 2023 at 15:35
  • $\begingroup$ Thanks for sharing! It guessed my age perfectly! $\endgroup$
    – AliceD
    Commented May 27, 2023 at 15:55

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Short answer
Age-related hearing loss is caused by the loss of hair cells in the inner ear, i.e., in the peripheral nervous system.

Background
Hearing declines with age and, typically, high frequencies are affected first (Kujawa & Liberman, 2006). Age-related hearing loss is progressive: it starts at the higher frequencies and progresses over the years to lower frequencies as a person ages. The decline in hearing sensitivity is mainly caused by the loss of hair cells. Hair cells are sensory cells in the inner ear that convert acoustic vibrations into electrical signals. These signals are transmitted to the brain via the auditory nerve. Because of this, age-related hearing loss is a type of sensorineural hearing loss.

Because of the tonotopic organization of the inner ear (the cochlea) one can conclude that age-related HL develops from the basal to apical region. The following schematic of the cochlea from Encyclopædia Britannica, Inc. nicely shows the cochlear tonotopy (i.e., high frequencies in the base, low frequencies in the apex);

cochlea

Why the basal regions are more sensitive is a topic of debate. It may be that sounds enter there first, or because toxins are more readily absorbed basally than apically.

If hearing loss persists over the course of years, the associated secondary neurons in the auditory nerve may slowly degenerate (Stronks et al., 2011) and accordingly, because of neural plasticity, the deafferented cortical areas may be recruited for other purposes (e.g. vision).

So in case of age-related hearing loss, it is the peripheral hair cells that are lost first. There are other types of hearing loss where the degenerative processes become apparent first in the auditory nerve, such as auditory neuropathy.

References
- Encyclopedia Brittanica The-analysis-of-sound-frequencies-by-the-basilar-membrane
- Kujawa & Liberman, J Neurosci 2006; 26:2115-23
- Stronks et al, Hear Res 2011; 272:95-107

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  • $\begingroup$ out of curiosity, is there any sound that sounds damaging to your ears, or at least activate the pain perception in your brain, but actually not really damage? A kind of sound illusion I guess? $\endgroup$
    – Ooker
    Commented May 28, 2023 at 8:45
  • $\begingroup$ @Ooker - the perception of sounds depends on physiological and psychological factors. What may sound disruptive to one may be fine for others. Misophonia comes to mind - a psychological dislike of certains sounds, such as chewing, and auditory recruitment, where people with severe hearing loss don't hear a thing and when you finally start screaming at them, they suddenly squirm away telling you you shouldn't be yelling at them so loudly. $\endgroup$
    – AliceD
    Commented May 28, 2023 at 9:14
  • $\begingroup$ This is a perfect textbook answer that I think no longer stands the test of time. Dubno (ncbi.nlm.nih.gov/pmc/articles/PMC3767874) has some nice work classifying audiograms and pure metabolic losses and combined metabolic and sensory losses are more common than pure sensory loss. $\endgroup$
    – StrongBad
    Commented May 29, 2023 at 2:35
  • $\begingroup$ @StrongBad the paper is based on animal studies and afaik its conclusions are not the current consensus on the causes of ARHL, at least in the clinic. $\endgroup$
    – AliceD
    Commented May 29, 2023 at 10:48

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