Brainstem speech encoding is dynamically shaped online by fluctuations in cortical α state

Abstract

Experimental evidence in animals demonstrates cortical neurons innervate subcortex bilaterally to tune brainstem auditory coding. Yet, the role of the descending (corticofugal) auditory system in modulating earlier sound processing in humans during speech perception remains unclear. Here, we measured EEG activity as listeners performed speech identification tasks in different noise backgrounds designed to tax perceptual and attentional processing. Brainstem speech coding might be tied to attention and arousal states (indexed by cortical power) that actively modulate the interplay of brainstem-cortical signal processing. When speech-evoked brainstem frequency-following responses (FFRs) were categorized according to cortical states, low FFRs in noise were found to be weaker, correlated positively with behavioral response times, more "decodable" via classifiers, and associated indirectly with other signal-in-noise perceptual performance. Our data provide evidence for online corticofugal interplay in humans and establish that brainstem sensory representations are continuously yoked to the ebb and flow of cortical states to dynamically update perceptual processing.