Differences in Click and Speech Auditory Brainstem Responses and Cortical Response Patterns: A Pilot Study

Abstract

Hearing loss has adverse developmental, cognitive and social impacts on individual’s lives. To improve its diagnosis and remediation outcomes, development of objective hearing methods offer new ways of optimizing care strategy. Complementary to the classical click-evoked brainstem and cortical responses, interest grows regarding the speech auditory brainstem responses, whose components, namely the onset and frequency following responses, are proposed as biomarkers of speech encoding at the brainstem level. To improve the understanding of auditory processing in the human brainstem and its effect on cortical processing, we used a multimodal set-up and recorded brainstem and cortical potentials in response to click stimuli and speech stimuli presented at different stimulation intensities in normal hearing adults. We hypothesized that even though click- and onset responses of the speechauditory brainstem responses share some similarities; their underlying mechanisms are in some point distinct. We also presumed that using a noninvasive method we could assess the generators underlying click, onset and frequency following responses and the time wise influence of brainstem encoding on cortical processing of click and speech stimuli. Results showed evidence regarding mechanisms underlying onset response and frequency following response components at the brainstem level. A direct time wise relationship between subcortical encoding and cortical encoding was revealed: cortical activity in the left cortex was related to the onset response latency at the brainstem level. These results highlight the potential use of new methods in speech processing electroencephalographic studies and provide qualitative and topographical data regarding subcortical and cortical auditory processing network.