Auditory Brainstem Response Altered in Humans With Noise Exposure Despite Normal Outer Hair Cell Function

Area of Science:

• Auditory Neuroscience
• Otoacoustic Emissions
• Neurophysiology

Background:

• Cochlear synaptopathy, a loss of synapses between inner hair cells and auditory nerve fibers, can occur after noise exposure without affecting hearing thresholds.
• Animal studies show noise-induced synaptopathy correlates with reduced auditory brainstem response (ABR) wave I amplitude.

Purpose of the Study:

• To investigate the association between lifetime noise exposure history and ABR wave I amplitudes in young adults with normal hearing thresholds.
• To determine if noise exposure impacts auditory nerve function even in the absence of threshold shifts.

Main Methods:

• Twenty-nine young military Veterans and 35 non-Veterans (19-35 years) with normal hearing were grouped by self-reported noise exposure.
• Suprathreshold ABRs and distortion product otoacoustic emissions (DPOAEs) were measured at 1, 3, 4, and 6 kHz.

Main Results:

• Higher self-reported noise exposure histories were associated with significantly smaller ABR wave I amplitudes across all tested frequencies.
• These findings persisted after controlling for sex and outer hair cell function (DPOAEs).

Conclusions:

• Reduced suprathreshold ABR wave I amplitudes in individuals with high noise exposure histories may indicate subclinical cochlear damage, potentially cochlear synaptopathy.
• This damage occurs independently of outer hair cell function and is consistent with animal models, though direct evidence of synaptopathy requires further study.