Journal
JOURNAL OF NEUROSCIENCE
Volume 39, Issue 48, Pages 9560-9569Publisher
SOC NEUROSCIENCE
DOI: 10.1523/JNEUROSCI.3004-18.2019
Keywords
aging; efferent; hearing
Categories
Funding
- Lauer Tinnitus Center [P50-015857, R01-DC-00188]
- National Institute on Deafness and Other Communication Disorders
- Department of Speech and Hearing Sciences at Vanderbilt University
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The mammalian cochlea is innervated by two cholinergic feedback systems called the medial olivocochlear (MOC) and lateral olivocochlear (LOC) pathways, which send control signals from the brainstem back to the outer hair cells and auditory-nerve fibers, respectively. Despite countless studies of the cochlear projections of these efferent fibers in animal models, comparable data for humans are almost completely lacking. Here, we immunostained the cochlear sensory epithelium from 23 normal-aging humans (14 males and 9 females), 0-86 years of age, with cholinergic markers to quantify the normal density of MOC and LOC projections, and the degree of age-related degeneration. In younger ears, the MOC density peaks in mid-cochlear regions and falls off both apically and basally, whereas the LOC innervation peaks near the apex. In older ears, MOC density decreases dramatically, whereas the LOC density does not. The loss of MOC feedback may contribute to the age-related decrease in word recognition in noise; however, even at its peak, the MOC density is lower than in other mammals, suggesting the MOC pathway is less important for human hearing.
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