Cross-species experiments reveal widespread cochlear neural damage in normal hearing

Area of Science:

• Audiology
• Neuroscience
• Otolaryngology

Background:

• Animal models indicate cochlear afferent nerve endings are more susceptible to acoustic overexposure and aging than sensory hair cells.
• Neural degeneration without hair cell loss is undetectable by standard audiometry, making its occurrence in humans a subject of debate.

Purpose of the Study:

• To investigate the occurrence and patterns of cochlear neural damage in humans at risk for hearing loss.
• To determine if cochlear neuropathy is widespread, even in individuals with clinically normal hearing.

Main Methods:

• Co-ordinated experiments were conducted on at-risk humans and a wild-type chinchilla model.
• Wideband middle-ear muscle reflex measures were used to assess cochlear neuropathy in both species.
• Analysis included an independent public dataset and measurements using clinical equipment.

Main Results:

• Cochlear neuropathy in chinchillas caused significant reductions in the wideband middle-ear muscle reflex.
• Human wideband reflex measures showed distinct damage patterns in middle-aged individuals and young individuals with high acoustic exposure histories.
• Findings were corroborated by analysis of a large public dataset and clinical equipment measurements.

Conclusions:

• Cochlear neural damage is prevalent across various age groups and acoustic exposure levels.
• Wideband reflex measures can detect cochlear neuropathy, even when standard audiometry indicates normal hearing.
• The study provides strong evidence for widespread cochlear neural damage in the human population.