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Hidden Hearing Loss – the Problem and the Promise

Tuesday, June 14, 2016  
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Hidden Hearing Loss – the Problem and the Promise

 Sharon G. Kujawa and M. Charles Liberman


     Most adult hearing impairment is sensorineural in nature and arises from inner ear dysfunction.  Dogma has long held that hair cells are the most vulnerable cochlear elements and that cochlear neural loss typically occurs only after, and because of, hair cell degeneration. Work from our lab, and others, over the last 10 years has shown that this is not true for key etiologies of acquired sensorineural hearing loss, including noise, aging, and ototoxic drugs (Kujawa and Liberman 2015).  These insults can cause massive (>50%) loss of cochlear nerve peripheral synapses without any hair cell loss (see Figure).  This extensive cochlear synaptopathy has remained a “hidden hearing loss”, because 1) diffuse neural degeneration does not significantly elevate cochlear pure-tone thresholds, or the behavioral audiogram, until it reaches 80%, 2) the synaptic connections between cochlear neurons and hair cells are hard to see in routine histological material, and 3) the cell bodies and central axons of cochlear neurons,  survive for years to decades despite their loss of functional connection to the hair cells. Read more....


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