This article is more than 5 years old. Information may no longer be current.
Cochlear synaptopathy linked to speech comprehension deficits in college students
Click Here to Manage Email Alerts
Cochlear synaptopathy, or hidden hearing loss, was associated with college students’ difficulty in comprehending speech in challenging auditory environments, according to recent study findings.
“While hearing sensitivity and the ability to understand speech in quiet environments were the same across all subjects, we saw reduced responses from the auditory nerve in participants exposed to noise on a regular basis and, as expected, that loss was matched with difficulties understanding speech in noisy and reverberating environments,” Stéphane F. Maison, PhD, a researcher in the Eaton-Peabody Laboratories at Massachusetts Eye and Ear and assistant professor of otolaryngology at Harvard Medical School, said in a press release.
Maison and colleagues have had success, under some conditions, with restoring sensory cells and the auditory nerve using growth factors in animal models.
To assess cochlear synaptopathy in humans, the investigators recruited 34 young adults, aged 18 to 41 years, from surrounding colleges and universities into an observational study and performed behavioral threshold audiometry, electrophysiology and word recognition tests to determine cochlear function and hearing. Participants were divided into groups at either low-risk (n = 12; mean age, 24 years) or high-risk (n = 22; mean age, 25 years) for ear damage based on self-reports of noise exposure levels and hearing protection use. All participants had unremarkable otoscopic examinations with audiometric thresholds from 0.25 to 8 kHz in both ears. All testing was conducted at the Northeastern University Speech-Language and Hearing Center in a sound-treated booth.
Data analysis presented significant deficits in difficult word-recognition tests within noisy environments in the high-risk group vs. the low-risk group. High-risk participants demonstrated significant threshold tolerance at all frequencies above 8 kHz that grew to about 20 dB HL at 16 kHz (intergroup differences, .01 < P < .001). In addition, students in the high-risk group exhibited changes in auditory potentials defined by symptoms of cochlear synaptopathy.
“Establishing a reliable diagnosis of hidden hearing loss is key to progress in understanding inner ear disease,” Maison said in the release. “Not only may this change the way patients are tested in clinic, but it also opens the door to new research, including understanding the mechanisms underlying a number of hearing impairments such as tinnitus and hyperacusis.” – by Kate Sherrer
Disclosure: The researchers report no relevant financial disclosures.
Perspective
Back to Top
Lawrence R. Lustig, MD
We have always had these concepts of ‘temporary thresholds shifts’ and ‘permanent threshold shifts’ in response to noise exposure; for example, when you attend a concert and your ears are stuffy afterwards or you have a ringing in your ears that goes away within three days.
If you were to actually measure your hearing during that time period, you would be able to detect that your hearing was injured, but then later recovered. We call this a temporary threshold shift because the auditory threshold changed, but returned to normal, in contrast to permanent threshold shifts in which extreme noise exposure – like an explosion – causes a permanent change in the auditory threshold and results in permanent damage.
It was discovered a while ago that even in temporary threshold shifts – at least in animal models – there were some changes in the synaptic organization of the inner ear in hair cells which lead to long-term hearing loss. Studies of early noise exposure in animals have shown a more rapid age-related hearing loss than would otherwise be seen. This has been referred to as a 'hidden hearing loss,' because it is not seen but leads to long-term changes in hearing.
The problem that we have had in trying to determine what is happening in humans who have experienced noise exposure is that we do not really have any tests that can identify that a temporary threshold shift has occurred, after it recovers. Although the hearing tests show everything normalizes, we know from studying the inner ears of animals that the nerves are not normal. We have never had the tests to determine when patients have sustained temporary damage in response to noise exposure or what happens over time in those patients who have exhibited those changes.
This is what is so exciting about the study by Maison et al, which examined college-aged adolescents who were at risk for noise exposure. The researchers were, in fact, able to document there are some clinical tests that can be used to identify this so called “hidden hearing loss”, a hearing loss that occurs even though our traditional hearing tests do not capture it.
What the article doesn’t tell you – because it can’t – is what happens to those who have that hearing loss over time compared with those that don’t. However, we can suspect based on the data already demonstrated in animal models that this group will have more rapid age-related hearing loss and will have difficulty in complex listening environments, such as understanding speech. I think this study is terrific and will lead to some truly interesting longitudinal outcome studies that will finally allow us to determine what these noise exposures do in people over time.
Click Here to Manage Email Alerts