Noise-Induced Hearing Loss: Permanent Versus Temporary Threshold Shifts and the Effects of Hair Cell Versus Neuronal Degeneration.

For decades, research on permanent noise-induced hearing loss has concentrated on the death of sensory hair cells and the associated threshold elevations. Recent work has shown that cochlear neurons are actually more vulnerable to noise, and even after exposures causing only temporary threshold elevation and no loss of hair cells, there is a rapid and irreversible loss of synaptic connections between cochlear neurons and hair cells followed by a slow degeneration of cochlear nerve cell bodies and central axons. Although this noise-induced neuropathy does not affect the audiogram, it likely reduces performance on more complex auditory tasks such as speech discrimination in noise.