Cochlear synaptopathy in acquired sensorineural hearing loss: Manifestations and mechanisms.

Summary

Noise exposure, ototoxic drugs, and aging are known to damage sensory hair cells, raising audiogram thresholds. This review describes a more insidious and likely more common process that happens well before overt hearing loss is visible: permanent interruption of synaptic communication between inner hair cells and subsets of cochlear nerve fibers. The silencing of these neurons alters auditory information processing, with or without threshold elevation, and is proposed as a contributor to speech-in-noise difficulty, tinnitus, and hyperacusis.

Key findings

• Cochlear synaptopathy can precede, and occur independently of, hair-cell loss and threshold elevation.
• Silenced (disconnected) auditory neurons persist for years but no longer transmit sound information.
• Reviews mechanisms across noise, ototoxic drugs, and aging as common causes.
• Frames synaptopathy as a likely contributor to speech-in-noise difficulty, tinnitus and hyperacusis.