Subcortical rather than cortical sources of the frequency-following response (FFR) relate to speech-in-noise perception in normal-hearing listeners

Abstract

Scalp-recorded frequency-following responses (FFRs) reflect a mixture of phase-locked activity across the auditory pathway. FFRs have been widely used as a neural barometer of complex listening skills, especially speech-in noise (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/midbrain (BS)] and cortical [bilateral primary auditory cortex, PAC] source generators with the aim of identifying which source(s) drive the brain-behavior relation between FFRs and SIN listening skills. We found FFR strength declined precipitously from AN to PAC, consistent with diminishing phase-locking along the ascending auditory neuroaxis. FFRs to the speech fundamental (F0) were robust to noise across sources, but were largest in subcortical sources (BS\u2009>\u2009AN\u2009>\u2009PAC). PAC FFRs were only weakly observed above the noise floor and only at the low pitch of speech (F0≈100\u2009Hz). 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 related to SIN performance. Our findings suggest subcortical sources not only dominate the electrical FFR but also the link between speech-FFRs and SIN processing in normal-hearing adults as observed in previous EEG studies.