Editor’s Note: From time to time The Hearing Blog presents guest articles for our Readers to consider. Today’s article is written by Peter Phua, M.D., a graduate of McMaster University’s medical program. This is Dr Phua’s third contribution on tinnitus to The Hearing Blog, his previous Guest Articles being Notched Sound Therapy as a Treatment for Tinnitus: A Guide for Hearing Professionals, and A Critical Review of the Evidence for Notched Sound Therapy as a Treatment for Tinnitus: A Summary.
I’ve been reading the literature on tinnitus for several years, and I have yet to come across a paper that provided data on what the distribution of tinnitus frequencies was among people who have tinnitus. Obviously there’s not a lot of money available to ask a question like this (since there’s no drug or treatment available). So I spoke to our CTO, Adrian Green, and we decided to mine the AudioNotch tinnitus treatment database to see if we could get an estimate of this data.
When people sign up for AudioNotch, their sound therapy is customized for their unique tinnitus frequency. They use our tinnitus tuner to match a computer generated tinnitus frequency with the tinnitus frequency that they hear inside of their head. Although it’s not perfect, and up to 50% of people can have a very difficult time determining their tinnitus frequency, it’s still a useful measure in the aggregate sense.
We took the information from our active accounts (to filter out people who were just playing around with the tuner), and then we took their most recently found tinnitus tone. We also cut out tones below 50Hz and above 20,000Hz (since that’s effectively the limit of human hearing). The data we received was as follows, with a total sample size of about 1,300 frequencies:
Some insights into the data:
- The tones are distributed roughly in a normal curve distribution. This is a bit unexpected since we’d think that the tinnitus tones would be clustered in higher frequency distributions, since most hearing loss is high frequency, and tinnitus tones seem to map onto regions of hearing loss. Then again, a lot of natural phenomenon seem to follow a normal distribution, so it’s not altogether that surprising.
- The sound energy of most environmental music (a huge driver of hearing loss) drops off rapidly around 8,000 hZ, so it’s interesting that so many tinnitus tones are still in the greater than 8,000 hZ region (for the aforementioned reason). That said, there’s a huge amount of tinnitus around that frequency range, which seems to match our expectations since there’s so much music in that region of sound.
- Limitations of the data were several: the tuning process is often inaccurate, the sample of people who matched their frequency was self-selected by individuals looking to pay for a treatment service and who were computer literate, and it doesn’t include the initial tinnitus tones from people whose tinnitus frequencies shifted. Still, I suspect the approximate normal distribution roughly tracks along the actual real-world population data.
- There’s a little uptick in tinnitus frequencies around the 20,000Hz region, making me wonder if people are hearing frequency tones beyond the range of perceptible hearing (perhaps there’s some sort of pathological neurological cause for this?).
This data can also be compared to our internal success rate data that we gleaned from e-mail surveys and published in December 2013.
In conclusion, it seems like tinnitus frequencies appear to track a normal distribution centered around approximately 8,000Hz. Let us know your thoughts in the comments below.
- In correspondence after his submission two years ago of Notched Sound Therapy as a Treatment for Tinnitus: A Guide for Hearing Professionals, Dr Phua pointed out there are some individuals who have “normal” audiograms which have no detectable hearing loss shown on them, yet these patients still have tinnitus. These individuals also typically do not have any identifiable cause for their tinnitus. However, this begs the question, what if people who present with normal audiograms have undetectable hearing loss? Two years ago, to his credit Phua points out the following theory on cochlear synaptopathy & spiral ganglion neurodegeneration by Sharon G Kujawa PhD and M Charles Liberman PhD, which in the intervening 23 months appears to be gaining traction: In February we published Uh Oh! Here Comes Noise-Induced Cochlear Synaptopathy …And It Just May Up-End Everything We Know About Hearing Conservation which updates the body of knowledge. At the time two years ago Dr Phua wrote:
Audiograms measure the “bottom” or “low” threshold of hearing by playing very quiet tones and then increasing the volume until they are detected. However, audiograms assume that hearing loss occurs in an upwards, step wise fashion. It turns out that there are different neurons that detect sound at a high volume threshold – and these are not tested in an audiogram.
From Adding Insult to Injury: Cochlear Nerve Degeneration after “Temporary” Noise-Induced Hearing Loss1, 2 in the Journal of Neuroscience, Phua highlighted from three paragraphs the following:
Overexposure to intense sound can cause temporary or permanent hearing loss. Postexposure recovery of threshold sensitivity has been assumed to indicate reversal of damage to delicate mechano-sensory and neural structures of the inner ear and no persistent or delayed consequences for auditory function.
Here, we show, using cochlear functional assays and confocal imaging of the inner ear in mouse, that acoustic overexposures causing moderate, but completely reversible, threshold elevation leave cochlear sensory cells intact, but cause acute loss of afferent nerve terminals and delayed degeneration of the cochlear nerve. Results suggest that noise-induced damage to the ear has progressive consequences that are considerably more widespread than are revealed by conventional threshold testing.
This primary neurodegeneration should add to difficulties hearing in noisy environments, and could contribute to tinnitus, hyperacusis, and other perceptual anomalies commonly associated with inner ear damage.
- The original article can be found here.
- A: Adding Insult to Injury: Cochlear Nerve Degeneration after “Temporary” Noise-Induced Hearing Loss, by Sharon G Kujawa, and M Charles Liberman; The Journal of Neuroscience, 11 November 2009, 29(45): 14077-14085; doi: 10.1523/JNEUROSCI.2845-09.2009 | Mirror copy of article
B: Mirror copy of Supplemental Data
- Adam C. Furman, Sharon G. Kujawa and M. Charles Liberman: Noise-induced cochlear neuropathy is selective for fibers with low spontaneous rates. Journal of Neurophysiology, AJP – JN Physiol August 1, 2013 vol. 110 no. 3 577-586
- Age-Related Cochlear Synaptopathy: An Early-Onset Contributor to Auditory Functional Decline, by Yevgeniya Sergeyenko, Kumud Lal, M Charles Liberman, and Sharon G Kujawa; The Journal of Neuroscience, 21 August 2013, 33(34): 13686-13694; doi: 10.1523/JNEUROSCI.1783-13.2013. | Mirror copy