Tinnitus --- Ear or Brain?
Ummmm... what was the good professor's opinion when all was said and done?
Now I ain't the sharpest tool in the box. My medical background or knowledge is very sparse, so my expertise on tinnitus is more from "below" as a sufferer/patient than from above as an academic or ENT.
One nugget of knowledge that I gleaned was that tinnitus starts in the inner ear -- at least noise induced tinnitus starts there. But later it is transposed to the brain.
How did the experts arrive at this? Which expert and when?
(No harm in keeping a history of this, but I recall reading some years ago that some researcher -- back in the 50s postulated that it was due to inner or outer hair-cell damage. This became widely accepted... why? Now due to the work of Liberman and what's her name, Jaruselski or some such name it could be due to ribbon ynapses from the hair cells being destroyed... or the stereocilia on the hair cells being destroyed or all three.
One piece of logic that kind of resonated with me was the following:
Back in the 80s or 90s a patient was suffering from such severe tinnitus that he asked that his hearing nerve be surgically severed. Well after the operation of course he was completely deaf -- couldn't hear at all --- except for one thing. You guessed it! Except for his tinnitus.
The fact that this procedure was repeated a few times with the same result on a few patients must excite your sympathy for the poor patients and also bring on your sense of exasperation that the ENTs don't network better.
But to my point: I came across this wonderful piece of logic in a paper from around 2005:
The fact that the above-mentioned patients could hear nothing except their tinnitus leads to the conclusion that the source of the tinnitus must be in their brain... at least not in their cochlea/ inner ear.
So far so good. Wonderful pristine logic. But I know that logic can be seductive.
My little question: Relate this above to the regeneration of hair-cells drive now taking place with Frequency Therapeutics, Hough Ear Institute, Auris Medical and some others.
It's in the ear and the brain is responding to the lack of signal. Further removing the signal wouldn't fix this but restoring it would.
That's obviously the million dollar question.
Is it a hearing disorder or a brain disorder?
Warning: long text trying to arrange my thoughts in regards to that question.
Some people having hearing damage, even profound damage, and do not have tinnitus at all.
This is usually counteracted by people who believe hearing regeneration will help reduce tinnitus, by saying that we had a traumatic cochlear event that generated the tinnitus signal, versus the other group which had a slow natural decline of their hearing which the brain can handle.
I believe however there are just too many cases of people who don't fit that scenario and had significant sudden sensorineural hearing loss and still did not develop tinnitus.
Others have no apparent hearing damage whatsoever and this is then explained by saying that the current hearing tests are archaic and that it must be hidden hearing loss. It is a valid argument. Hidden hearing loss is certainly something that will be clarified in the future.
So, the theory many believe in, is that due to hearing damage you end up having hair cell damage (and/or synapses) and therefore you have trouble with certain frequencies, which consequently leads to maladaptive neuroplasticity at the level of the auditory cortices (tonotopic rearrangement) and so the brain creates a constant auditory phantom perception. This is an often used explanation for tinnitus.
The hope that several people therefore have is that, once the damaged frequencies are restored, that the brain will reverse the maladaptive neuroplasticity and will effectively alleviate the tinnitus sound.
Several scientists however point out that there is likely something additional going on. Sure, there are very valid reasons to accept that hearing loss and tinnitus are linked. I don't doubt that. There is an overwhelming amount of anecdotal evidence of people with noise induced hearing loss or through exposure of ototoxic drugs that shortly after end up having (chronic) tinnitus.
However, when you dig deeper into the neurological level of tinnitus, you will come to see that tinnitus can probably only develop if there is also a brain malfunctioning present. I am referring to the hypothesis that there could be a problem at the level of the thalamus for people with tinnitus. The thalamus receives sensory input and relays that input through the paralimbic system (amygdala, nucleus accumbens) to undergo an evaluation of, in our case, sound. It is used to attribute an emotion to a particular sound (pleasant or danger for example) where there is a mechanism present to inhibit or excite that input signal back to the thalamic reticular nucleus in the thalamus which, depending on the signal being suppressed or not, sends it through to the auditory cortices.
Dr Rauschecker hypothesises that, in people with tinnitus, there is a malfunctioning at this level (Nucleus Accumbens to TRN) and therefore the central gating mechanism at the level of the thalamus in your brain is not working and is sending information to your consciousness that should not pass through. This would likely be due to a neurotransmission malfunctioning at that particular intersection of your brain.
So if there is somehow a tinnitus signal present, it will be sent through, if the filter does not work. If the filter works on the other hand, despite having hearing damage, no tinnitus signal will be sent to your consciousness.
Having said that, Dr Rauschecker did state that it is really rare to have tinnitus without some form of hearing damage. Due to that statement I would suspect that alleviating the hearing damage should have a positive effect on (reducing) tinnitus, even if your filtering mechanism is not working.
So, if that hypothesis is correct, it's likely both a hearing disorder and a brain disorder that results in tinnitus, but if the root cause for the initial generation of the tinnitus signal really is the inner ear malfunctioning, then solving either the hearing disorder or the brain disorder should solve tinnitus.
It is clear however that we know a lot more about the inner ear than our most complex organ, the brain, so it's likely that that particular route has the most chance to solve our problem.
Provided this reasoning is correct of course, because maybe not everyone is convinced of that. Perhaps some people suspect that it is possible that it is a pure brain malfunctioning where the brain may be picking up somatic brain sounds, rather than some signal being generated due to an issue with your inner ear. In that case our outlook would not be good at all.
That's where the argument comes in that cutting the auditory nerve did not resolve tinnitus for some people. This is well known, but if the initial reasoning would be correct, shouldn't this also result in maladaptive neuroplasticity and a nightmarish tinnitus that spans all frequencies and is very loud? Since all frequencies are gone and there is no more hearing left at any loudness level. It simply points to our brain being the source of our problem. Unless cutting the nerve does not create any maladaptive neuroplasticity, but I can't wrap my head around it, if that were true.
Our current technology is simply not advanced enough to look into deep detail what is going wrong in our brains. We will probably need 100 years to be able to see the neuronal pathways in such detail that we can reverse engineer the whole brain in nano detail and easily see on which exact level neurons are dead, dysfunctional, out of synch, misfiring or where there are erroneous loops, et cetera. The next step, to intervene and precisely fix the brain, would probably take another 100 years.
So our best hope is that hearing regeneration will indeed help to reduce tinnitus. Nobody knows however, but it does look like we are going to find out in the coming 5, 10 or 20 years when we can repair all elements of the non-neurological hearing system (cochlea,...). I hope it will help us all, but there are no clear signs yet that it will. Perhaps at best, it will mask the tinnitus a little better.
I just don't know at all. Although I'm fascinated by regenerative hearing medicine, I don't dare to bet on it for tinnitus. I believe this is also why many scientists don't dare to make any hard statements about hearing regeneration resolving tinnitus. They must have doubts as well.
I'd love to hear from others how they analyse this problem and if they believe that hearing regeneration will resolve tinnitus.
I've been thinking about this for many months now and it worries me a lot.
Especially when I look at my own condition (having VSS with tinnitus) everything points in the direction that there is a problem in or around the thalamus of my brain. It makes me very sad to think that it might not be a hearing issue. It would mean there is no hope for me and many others. I hope I'm wrong, but deep down inside... it scares me.
Member
Manager
