ABSTRACT
The frequency-following response (FFR) is a scalp-recorded potential reflecting a mixture of phase-locked neural activity generated from several nuclei along the auditory pathway. FFRs have been widely used as a neural barometer of complex listening skills especially performance on speech-in noise (SIN) tasks: across listeners with various hearing profiles and ages, more robust speech-evoked FFRs are associated with improved SIN perception. Applying individually optimized source reconstruction to speech-FFRs recorded via EEG (FFREEG), we assessed the relative contributions of subcortical [auditory nerve (AN), brainstem (BS)] and cortical [bilateral primary auditory cortex, PAC] generators to the scalp response with the aim of identifying which source(s) drives the brain-behavior relation between FFRs and perceptual SIN skills. We found FFR strength declined precipitously from AN to PAC, consistent with the roll-off of phase-locking at progressively higher stages of the auditory neuroaxis. FFRs at the speech fundamental frequency (F0) were resistant to moderate noise interference across all sources, but FFRs were largest in BS relative to all other sources (BS > AN ≫ PAC). Cortical PAC FFRs were only weakly observed above the noise floor in a restricted bandwidth around the low pitch of speech stimuli (F0≈100 Hz). Brain-behavior regressions revealed (i) AN and BS FFRs were sufficient to describe listeners’ QuickSIN scores and (ii) contrary to neuromagnetic (MEG) FFRs, neither left nor right PAC FFREEG predicted SIN performance. Our findings suggest subcortical sources not only dominate the electrical FFR but also the link between speech-FFRs and SIN processing as observed in previous EEG studies.
New & Noteworthy The frequency-following responses (FFRs) is an auditory neurophonic brain response that correlates with complex listening skills including speech-in-noise perception. FFRs origin from phase-locked activity across the auditory pathway including sub- and neo- cortex. By recording speech-FFRs via EEG, we show that brainstem sources dominate FFRs measured at the scalp and are most predictive of behavior. Findings underscore the brainstem-centric view of the FFR and its relation to nascent auditory perceptual processing.