Researchers have linked symptoms of cochlear synaptopathy, a “hidden” condition linked to the generation of tinnitus and hyperacusis, to difficulty understanding speech in noisy environments in college-age adults who regularly expose their ears to loud noises but who otherwise have normal hearing sensitivity, according to a new study from Massachusetts Eye and Ear.
Although all 34 participants passed a standard audiogram—indicating no hearing loss—those who self-reported that they did not regularly use hearing protection when exposed to loud sounds were more likely to perform poorly on a speech-in-noise test than participants who regularly use hearing protection. The researchers found that these results correlated with performance on an electrophysiological measurement of auditory nerve health.
“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,” says lead author Stéphane Maison, a researcher in the Eaton-Peabody Laboratories at Mass. Eye and Ear and assistant professor of otolaryngology at Harvard Medical School. The study was published in the journal PLOS ONE.
Cochlear synaptopathy, referred to as “hidden hearing loss,” is damage to the connections between auditory nerve fibers and sensory cells. This type of damage precedes loss of the sensory cells themselves in standard hearing loss that can be measured by an audiogram.
Testing patients with more sensitive measures that can detect cochlear synaptopathy could help clinicians see a fuller picture of noise-induced hearing loss, the authors note.
“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,” Maison says.
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