Envelope following responses (EFRs) are proposed as neural markers of cochlear synaptopathy in humans. However, it remains unclear whether EFRs are truly specific to synaptopathy or whether they are influenced by subtle cochlear dysfunction—such as elevated thresholds in the extended high-frequency (EHF) range (8 kHz). The present study investigated whether EHF hearing loss affects EFR metrics in adults with clinically normal audiograms. EFRs were recorded in 30 participants at three modulation depths (40%, 63%, and 100%) and analyzed using both fast Fourier transform (FFT) and wavelet-based approaches. Neural encoding was quantified using signal-to-noise ratio (SNR) and phase-locking value (PLV), modeled as a function of EHF thresholds while controlling for age, sex, and standard-frequency hearing thresholds. Elevated EHF thresholds were significantly associated with reduced EFR SNR at 40% modulation depth, but not at higher depths or for PLV measures. Wavelet analyses revealed additional timing-related EHF effects not captured by FFT. These findings suggest that subclinical cochlear damage or EHF hearing loss can compromise brainstem-level encoding of temporal envelopes—particularly under low modulation contrast. These results challenge the assumption that EFRs are entirely cochlear-independent and underscore the importance of accounting for EHF hearing status when using EFRs to assess synaptopathy.
Nair et al. (Wed,) studied this question.