How Hearing Loss Can Change the Way Nerve Cells Are Wired

I agree! This kind of research may lead to better understanding of neo-neurogenesis.

But this may not be what you think it is. The synaptic and neural connections between SGNs and IHC/OHCs have not been lost here, as in neural hearing loss. What they did in this study is they looked at behavioral and structural changes of nerve cells following imposed conductive hearing loss. When this happens, they observed that the cells change behavior and structure, which ultimately changes the signaling to the brain. So it's not that here is loss of signaling, as in neural hearing loss, but the existing signaling changes in some respect.

They also observed that when they restore the normal sound conduction by removing the obstacle, such as ear infection or middle ear fluid, the nerve cells started to change back to their original structure and behavior.

"When you undo the treatment, the cells start to go back to what they were like before," Xu-Friedman says.

But they said they need to do more research to see if this is in fact what happens.

"However, it's not clear that they completely recover, so we need to do more research to see if that's the case."

So this is not about regenerating nerve cells, as we often refer to when talking about sensorineural hearing loss. This is about understanding the basic science behind existing and functional nerve cells in normal cochleas. This is an important part of the puzzle nevertheless, and we will need this basic understanding in our attempts at regenerating new nerve cells in cochleas that have been damaged.

 

This I don't understand!

I will try to dissect this. First of all, I don't understand what you mean by "quit surroundings or using earplugs". The way I see it, there is no difference between a blocked middle ear and lacking input. They mean the same thing. Do they not? If the middle ear is blocked there will be no input, or any external sound source entering the ear will be muffled. The lack of input may or may not mean a complete loss of input. It's all relative. Ultimately, it depends on what you mean by "input".

Can you please rephrase the question or post two separate questions? I'm not exactly sure how to answer this since I am not sure what you mean.

Again, I'm not sure what you mean by this. But generally speaking, the ear can receive sounds, even when your brain can't hear or interpret the sound! One such example is supersonic and infrasonic sounds! Sounds travel as mechanical waves and they hit your ears, regardless if you can hear them or not! The sense of hearing sits in the brain, not in the ears. Just like you perceive light with your brain, not with your eyes. Sound waves don't need to knock on the door and ask for your permission to enter your ear. They do this regardless, regardless of if you can hear them or not.

The inner ear, with the cochlea, the hair cells, and nerve cells, they are the most important components for hearing. Loose all of these and you won't be able to hear a thing. You become deaf! But hearing loss is a relative term. It's relative to what part of the ear is damaged, and also how severe the damage is. The easiest way to fix a bad ear is if the damage is in the outer ear or the middle ear and it's not too severe. The hardest part to fix is if the damage is in the inner ear, and especially if the damage is severe, which means you will have loss of sensory and neural cells. You are either deaf or nearly deaf. This is what biomedical researchers are up against, this is what they are trying to reverse. It's not an easy task.

Yes! This study showed that behavior and structure of nerve cells changed, following a conductive hearing loss in otherwise healthy ears. So yes, even a reversible conductive hearing loss can have a negative effect on otherwise healthy cochlea. That is what this study seems to suggest, yes.

This study doesn't say anything about damaged inner ear, i.e. damaged cochlea. But judging by what they have concluded so far about nerve cell behavioral and structural changes following middle ear obstructions, I would say yes! Yes, I think it's best not to understimulate damaged inner ears.

Damaged or not, it seems to me that inner ear needs sound stimulation for long term nerve survival, which should prolong the window of opportunity for future biological treatments. How effective sound stimulation is would depend on the severity of the synaptic and hair cell damage, I presume. I am also under impression that damaged inner ears need sound stimuli to help the central processing in the brain to recover, which seems to help recover from hyperacusis. I would say that overprotecting the ears following inner ear damage is not good.

 

Here is the study report:
http://www.jneurosci.org/content/early/2016/12/01/JNEUROSCI.0523-16.2016

In other words children growing up with frequent ear infections and other outer and middle ear obstructions may develop processing disorders, because unlike in an adult, their central auditory processing is not developed. Simply put, children need to hear sounds! Moreover, the sounds they hear need to be rich and unhindered! They need this more than adults! This is necessary for the young brains that are in the process of developing.

As I said, children don't just need to hear sounds, they need rich hearing! Otitis media and frequent ear infections are not helping to this end.

Now we go back on the lead researcher's comment on this topic:

Now we go back to the study report:

Occluding means closing or obstructing an opening, i.e. closing the ears. This leads to decrease of size in synapses, and increased likelihood of signaling rate. Likelihood! Which seems to suggest their method is based on statistics. So they haven't proven it yet. But they have found an interesting lead.

Reduced fidelity, reduced sound enrichment. Brain is understimulated during development, which is not good, etc, etc. So in conclusion, understiumlating the brain in children leads to hearing disorders, and in adults with damaged hearing it may lead to faster loss of nerve cells and a more narrow window of opportunity for future treatments.

 

Good question! Have you approached the researcher with this question? I think you should.

I see your point. Yes, this might be something worth looking into. It may be hard to overcome, but at least we would know what it is that causes tinnitus. That's always something. We would have a target to work against. Right now we don't even have a good target because we are not sure where tinnitus starts.

Indeed! It's still too early to make any definitive conclusion.

 

Interesting hypothesis... So this would mean that tinnitus is like a natural response to the lack of sound? Like a way to sense danger? Maybe that's why we get anxious about it?

I agree! There might be something to this. I know @MikeGreen talked about this idea where his tinnitus would go away for a moment just as he shut off his vacuum cleaner.

I must say I am impressed! Where are you getting all these fantastic ideas?

Is there anyone taking this seriously and researching these ideas to try to answer these question? Someone really should! The study you linked to is definitely on track of these ideas.

 

I'm not sure what it is you don't understand here. If you block the middle ear, by for example putting ear plugs in, less sound will enter the inner ear. No? The sounds need to be strong enough to get past the ear plugs. Just like you have to shout to someone who has bad hearing if you want to be heard.

The sound travels through the outer ear, via middle ear, and into the inner ear. Of course if you block sounds at the outer ear or middle ear, less sound will enter the inner ear. Another way sound enters the inner ear is also via bone conduction, so straight through your skull bone into the inner ear.

They are capable of adapting, and this is what this study shows. But they are working under the assumption that this is maladaption, that it's a bad kind of adaptation. One which may or may not be fully reversible, they don't know that yet.