Applicability of subcortical EEG metrics of synaptopathy to older listeners with impaired audiograms

Emerging evidence suggests that cochlear synaptopathy is a common feature of sensorineural hearing loss, but it is not known whether electrophysiological metrics targeting synaptopathy in animals can be applied to a broad range of people, such as those with impaired audiograms. This study investigates the applicability of subcortical electrophysiological measures associated with synaptopathy such as auditory brainstem responses (ABRs) and envelope following responses (EFRs) in older participants with high-frequency sloping audiograms. This is important for the development of reliable and sensitive synaptopathy diagnostics in people with normal or impaired outer-hair-cell function. Broadband click-ABRs at different sound pressure levels and EFRs to amplitude-modulated stimuli were recorded, as well as relative EFR and ABR metrics which reduce individual factors such as head size and noise floor level. Most tested metrics showed significant differences between the groups and did not always follow the trends expected from synaptopathy. Audiometric hearing loss and age-related hearing related deficits interacted to affect the electrophysiological metrics and complicated their interpretation in terms of synaptopathy. This study contributes to a better understanding of how electrophysiological synaptopathy metrics differ in ears with healthy and impaired audiograms, which is an important first step towards unravelling the perceptual consequences of synaptopathy.