Auditory brainstem-cortical anatomy constrains the magnitude of frequency-following responses (FFRs) and event-related potentials (ERPs) coding speech-in-noise

Speech-evoked brain potentials provide a window into the neural encoding of speech, experience-dependent plasticity, and deficits in central auditory processing from communication disorders. Stronger and faster frequency-following responses (FFRs) and cortical event-related potentials (ERPs) have been interpreted as reflecting more robust and efficient auditory-sensory processing across brainstem and cortical levels. Importantly, these neural signatures relate to real-world listening skills like speech-in-noise (SIN) perception. Yet, how these speech-evoked FFRs/ERPs relate to underlying auditory anatomical structures is unknown. Using a multimodal imaging approach, we recorded FFRs and ERPs to clean and noise-degraded speech sounds to assess the strength of listeners' neural encoding of speech at brainstem (FFR) and cortical (ERP) levels. MRI volumetrics of midbrain and transverse temporal gyrus (Heschl's gyrus) quantified morphological variation in subcortical and cortical anatomy that underly these EEG potentials. The QuickSIN assessed behavioral SIN abilities. Results showed that larger and thicker right (but not left) Heschl's gyrus was related to listeners' SIN abilities as well as the size of their cortical ERPs. Structural and functional measures interacted at a subcortical level. For listeners with smaller midbrain volumes, larger speech FFRs were associated with better QuickSIN scores; whereas in individuals with larger midbrain volumes, larger FFRs were related to poorer QuickSIN. Our findings reveal common functional signatures of speech processing (FFRs, ERPs) are constrained by the anatomy of their underlying generators and suggest a complex interplay between auditory brain structure and function in accounting for perceptual SIN capacity.