Exposing distinct subcortical components of the auditory brainstem response evoked by continuous naturalistic speech.

Melissa J Polonenko,Ross K Maddox

doi:10.7554/elife.62329

Abstract

Speech processing is built upon encoding by the auditory nerve and brainstem, yet we know very little about how these processes unfold in specific subcortical structures. These structures are deep and respond quickly, making them difficult to study during ongoing speech. Recent techniques have begun to address this problem, but yield temporally broad responses with consequently ambiguous neural origins. Here, we describe a method that pairs re-synthesized 'peaky' speech with deconvolution analysis of electroencephalography recordings. We show that in adults with normal hearing the method quickly yields robust responses whose component waves reflect activity from distinct subcortical structures spanning auditory nerve to rostral brainstem. We further demonstrate the versatility of peaky speech by simultaneously measuring bilateral and ear-specific responses across different frequency bands and discuss the important practical considerations such as talker choice. The peaky speech method holds promise as a tool for investigating speech encoding and processing, and for clinical applications.

Highlights

Understanding speech is an important, complex process that spans the auditory system from cochlea to cortex
This means that broadband peaky speech, unlike the unaltered speech, can be used to assess naturalistic speech processing at discrete parts of the subcortical auditory system, from the auditory nerve to rostral brainstem
Inter-wave latencies were 2.24 ± 0.06 ms (N = 19) for I–III, 1.68 ± 0.05 ms (N = 19) for III–V, and 4.00 ± 0.08 (N = 22) for I–V. These peak inter-wave latencies fall within a range expected for brainstem responses, but the absolute peak latencies were later than those reported for a click auditory brainstem response (ABR) at a level of 60 dB sensation level (SL) and rate between 50 and 100 Hz (Burkard and Hecox, 1983; Chiappa et al, 1979; Don et al, 1977)

Summary

Introduction

Understanding speech is an important, complex process that spans the auditory system from cochlea to cortex. Subcortical structures play a critical role in this process – they do not merely relay information from the periphery to the cortex, and perform important functions for speech understanding, such as localizing sound (e.g., Grothe and Pecka, 2014) and encoding vowels across different levels and in background noise (e.g., Carney et al, 2015). Given the complexity of speech processing, it is important to parse and understand contributions from different neural generators. These subcortical structures are deep and respond to stimuli with very short latencies, making them difficult to study during ecologically salient stimuli such as continuous and naturalistic speech. We created a novel paradigm aimed at elucidating the contributions from distinct subcortical structures to ongoing, naturalistic speech

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Conclusion