Distortion, High Frequencies and Hyperacusis: A Forensic Inquest

I had initially drafted this as a reply to another post, but in the end felt it deserved its own exclusive thread, as I feel this is something that has come up many times in our conversations as hyperacusis sufferers but has not been fully dissected as a point of interest. I would therefore like to make a start on this discussion.

This post was also prompted after reading again that not all hyperacusis sufferers experience relief from Gabapentin and other anticonvulsants, and has therefore made me think a little bit more about the type II afferent fibre theory, which I still believe to be the strongest out there. So let's begin.

The distortion and high frequency issue is something that I haven't been able to get my head around for a while. Why is it that many of us suffer disproportionately with distorted sounds and high frequencies compared to undistorted sounds and lower frequencies, regardless of volume? I have some audio engineering knowledge and what I do know is that, all other things being equal, smaller sound sources tend to produce a frequency spectrum that is more biased towards the high end, but why is this important?



A quick look at the cochlea diagram above shows that the stapes, which "push" into the cochlea after receiving a sound, are closest to the the cochlea base and furthest away from the cochlea apex. We know that the cochlea apex is responsible for low frequencies and the cochlea base is responsible for high frequencies. Now, let's look at the following diagram:



This diagram shows that, on a mechanical level, there is a membrane that displaces the stereocilia to the hair cells. This is the first time I have come across this mechanism. With this mechanism in mind, would it be reasonable to ask: given the distribution of frequency "responsibility" across the cochlea, does the apex of the cochlea, which is closest to the stapes, undergo a disproportionate amount of membrane displacement compared to the base of the cochlea? And I wonder: could this in any way give us some insight into the pathology of hyperacusis? Are the stereocilia of the high frequency OHCs overworked and overinflamed because they undergo excessive displacement compared to their low frequency OHC counterparts? Are they releasing a disproportionate amount of neurotransmitters, which may also play a role in how our brain perceives things? If so, one would imagine that this is also the case in people without hyperacusis, so why are we different? And while I remember, I also remember reading that higher frequencies carry more energy, and I wonder how that fits into the ATP leak theory, where ATP, of course, is the energy source of cells. I include another diagram below for reference with regards to what happens after the membrane displacement.



Moving on from the above, what I also know from my studio production days is that a distorted sound wave looks very different to a normal sound wave. A normal sound wave is usually a sine wave, but distorted waves have more 'square' edges. See diagram below:



A quick google search doesn't get many hits for 'sine waves' in relation to any kind of ear pathologies, but I would be interested to know how such information is processed in the auditory system. Intuitively, I don't see how stereocilia or OHCs could discriminate between a square wave or a sine wave, given that both waves induce a membrane displacement that releases neurotransmitters - a mechanical process, as far as I understand it. Indeed, my intuition would tell me that this distinction in quality of sound is made somewhere further along the auditory path - perhaps in the cochlea nucleus (brainstem) or the auditory cortex. I also know that there are efferent fibres carrying signals from the brain to the ear and am in the dark as to how these could fit into any kind of potential pathology model. I also know that hyperacusis is sometimes seen in children, some of whom grow out of it but others don't, and I wonder what role the brain plays here too. I wonder if in some of us hyperacusis sufferers, the brain or brainstem, for whatever reason I still haven't been able to establish (perhaps neuroinflammation, which has been shown to occur after noise exposure in this study) loses its capacity to process distorted or 'complicated' sounds (I know we also struggle with things like crunching plastic water bottles or scrap paper) and it sends some kind of faulty signal through the efferent fibres which then causes some kind of negative feedback loop where the afferent nerve fibres then come into play. At this point, I'm kind of thinking out loud, but I would very much welcome an open discussion on this @serendipity1996, @100Hz and others.

 

I'm bumping this thread because I've had a small setback from listening to a distorted audio source and I really think the issue of increased pain from artificial sources (phones/laptops etc) is not given enough attention by either us or the researchers. I know that this is something @serendipity1996 struggles with as well.

Why the hell do we struggle with these sources so much?

I've been toying back and forth as to whether the brain could be more at play here, but when I imagine my favourite rock songs and guitar solos playing back in my head, blasting them at full "brain volume", I don't get any pain, which would suggest that this is a peripheral phenomenon, but how the hell this fits into the type II fibre theory or increased synapses theory post-noise exposure I have no idea.

Can anyone shed any light on this?

 

For those out there who also suffer with distortion issues, this study may be of interest to you. I found this particular statement to be of interest:

"Accordingly, cochlear damage that destroys outer hair cells but leaves inner hair cells apparently intact abolishes distortion products in auditory-nerve responses"

In other words, one may infer that those with distortion issues have the opposite of the above: dead IHCs and intact OHCs, or alternatively, IHCs that have lost synapses to type 1 afferents and OHCs that have gained synapses to type II afferents. This could also explain then why most people with distortion issues also have hyperacusis, although it doesn't explain why not all those with hyperacusis have distortion issues.

 

I thought the same thing the other day.The thing is I don't even have an ounce of pain hyperacusis, it's just artificial audio of any type that's extremely distorted for me. 1 month and 1 day ago it started. It was MUCH worse the first few days but it improved a lot within 11 days. Then it stagnated since then. It's weird I can imagine my favorite songs sounding exactly like they should but then when I listen to them they don't sound like that anymore...

I should also add. one thing I dont understand is that the distortion issues are 100% symmetrical as far as the affected sounds and frequencies. However in one ear, my right ear, it's slightly worse than the rest and that ear has since developed pulsatile tinnitus. What could this be?

 

Time to destroy my OHCs I guess.

 

Yes this is something that puzzles me greatly too - it sort of feels like it must be to do with a certain frequency or pitch. Low-quality speakers tend to be very "trebly" I think? For me, artificial audio also induces reactive tinnitus too which makes me feel like there must be damage and/or hearing loss at a specific frequency.

 

Dear @Aaron91.

May you describe please what do you mean by distortions?

I am asking because I am dealing with a very difficult issue.

Thank you in advance.

@serendipity1996 as well.

 

Yeah I'm not sure why *I* have distortions though. Artificial audio is always distorted no matter the volume, and things like white noise, cars etc are too. The weird thing is the first 2 weeks or so I had this the distortions wildly fluctuated all over the place. Now it has flatlined since then with no improvement since. Granted I've only had this a month but I think this is a bit too intense for "hearing damage", but alas I cannot go on much longer with this. I don't even have "reactive tinnitus" either, but I used to.

 

Hello @__nico__.

Is it possible to describe your symptoms?

 

All I have is tinnitus and sound distortions/sensitivity.

 

Same here. Tinnitus, TTTS (I guess), sound sensitivity/hyperacusis, distortions that became DISTORTIONS 4 days ago and still getting worse. The hyperacusis and distortions are my big issues at the moment. I try to connect with people that have this. I've been dealing with the distortions for 2 years now. Somehow I've managed. They used to consist of mostly tones in the high frequency spectrum. Unfortunately since April my hyperacusis worsened and along with it, gradually my distortions worsened too. Now 4 days ago I developed a whole new spectrum of severe distortions. One of them sounds like a mid frequency sine wave that is killing me and it is triggered by most of the environmental sounds I perceive. Distance of the source that triggers the distortions is also a factor.

Did you find anything that helps? This worsening of mine happened literally out of the blue. No meds etc.

 

Steroids may have helped early on. Nothing else works. Hopefully Keppra will or else I'll probably catch the bus.

 

Do you think steroids could help about a week post worsening?

What about Keppra? Could you let me know please? As I can get that from the pharmacy. Are there any anecdotes?

 

Levetiracetam (Keppra) Worked for My Hyperacusis

 

Thank you @__nico__.
Not sure about the side effects/risks of Keppra.

Unfortunately @Danny Boy is not with us anymore. I remember I had a few talks with him over the phone in the past. We didn't discuss about Keppra at the time.

Have you purchased Keppra? Are you planning to proceed with it?

 

I am on it for about a week currently - it doesn't feel like anything right now. I'm not sure why everyone here thinks when they take a medication they have a 50/50 shot at instant death.

 

Dear @GBB,
Thank you for your reply.

That was not my point. My personal experience with medication has been bad, given that I got tinnitus from one and I try to be careful.

Are you on Keppra along with the help of a physician?

If it is ok with you, I would like to stay in touch and follow your updates. I am interested to try it as well.

Did you decide to proceed by the testimonies of Danny Boy?
I really wish for you to get benefit out of it.

 

I thought the high frequency issue could be due to the amplitude and latency of the sound waves they produce, but anyway it is only a guess... I lack technical expertise on acoustics; it seems a very complicated field.

 

I’ll up

I am on it under the supervision of a neurologist. I’ll post an update after a month.

 

When I get Keppra in a week or so I'll probably follow Danny Boy's dosage. I got nothing to lose. It cured him.

 

I do find benzos seems to help, I haven't tried them in a while though so maybe that magic is gonezos now.

I also tried a low salt diet, made me really fatigued but might have improved things a tad.

 

Sorry @vermillion, I think I may have confused you. I don't experience distortions myself - I've just noticed that I struggle more generally with artificial sources of sound as they're more likely to have distorted artifacts. I posted the study on distortion in the cochlea as I knew there were people out there who experience this to a terrible degree and figured it may be of interest.

Many hugs.