Age-related hearing loss is known as presbycusis. It is widely believed that this problem is caused by damage to the stria vascularis.
Stria vascularis is a cellular “battery” that powers the hair cell’s mechanical-to-electrical signal conversion.
But a new study has revealed something which is contrary to this widely held belief and which may probably lead to new understating of age-related hearing loss.
A team of scientists has demonstrated that age-related hearing loss is caused by damage to hair cells, the sensory cells in the inner ear that transform sound-induced vibrations into the electrical signals that are relayed to the brain by the auditory nerve.
This work is published in the Journal of Neuroscience in a paper titled, “Age-related hearing loss is dominated by damage to inner ear sensory cells, not the cellular battery that powers them.”
Age-related hearing loss arises from irreversible damage in the inner ear, where sound is transduced into electrical signals.
The inner ear, where most types of hearing impairment originate, cannot be biopsied, and its structures can only be resolved in specimens removed at autopsy.
Understanding the true cellular causes of age-related hearing loss impacts how future treatments are developed and how appropriate candidates will be identified, and can also suggest how to prevent or minimize this most common type of hearing damage, according to the study authors, led by Pei-zhe Wu, MD, a postdoctoral research fellow in otolaryngology head and neck surgery in the Eaton-Peabody Laboratories at Massachusetts Eye and Ear.
Researchers examined 120 inner ears collected at autopsy. They used multivariable statistical regression to compare data on the survival of hair cells, nerve fibers, and the stria vascularis with the patients’ audiograms to uncover the main predictor of the hearing loss in this aging population.
They found that the degree and location of hair cell death predicted the severity and pattern of the hearing loss, while stria vascularis damage did not.
Previous studies examined fewer ears, rarely attempted to combine data across cases and typically applied less quantitative approaches. Most importantly, prior studies greatly underestimated the loss of hair cells, because they didn’t use the state-of-the art microscopy techniques that allowed Wu and colleagues to see the tiny bundles of sensory hairs (> 200 times thinner than a typical human hair), that helped them identify and count the small number surviving hair cells. Prior studies scored hair cells as “present,” even if only one or two remained.