Abstract
BackgroundSome evidence suggests that young adults exhibit a selective laterality of auditory brainstem response (ABR) elicited with speech stimuli. Little is known about such an auditory laterality in older adults.ObjectiveThe aim of this study was to investigate possible asymmetric auditory brainstem processing between right and left ear presentation in older adults.MethodsSixty-two older adults presenting with normal hearing thresholds according to their age and who were native speakers of Quebec French participated in this study. ABR was recorded using click and a 40-ms /da/ syllable. ABR was elicited through monaural right and monaural left stimulation. Latency and amplitude for click-and speech-ABR components were compared between right and left ear presentations. In addition, for the /da/ syllable, a fast Fourier transform analysis of the sustained frequency-following response (FFR) of the vowel was performed along with stimulus-to-response and right-left ear correlation analyses.ResultsNo significant differences between right and left ear presentation were found for amplitudes and latencies of the click-ABR components. Significantly shorter latencies for right ear presentation as compared to left ear presentation were observed for onset and offset transient components (V, A and O), sustained components (D and E), and voiced transition components (C) of the speech-ABR. In addition, the spectral amplitude of the fundamental frequency (F0) was significantly larger for the left ear presentation than the right ear presentation.ConclusionsResults of this study show that older adults with normal hearing exhibit symmetric encoding for click stimuli at the brainstem level between the right and left ear presentation. However, they present with brainstem asymmetries for the encoding of selective stimulus components of the speech-ABR between the right and left ear presentation. The right ear presentation of a /da/ syllable elicited reduced neural timing for both transient and sustained components compared to the left ear. Conversely, a stronger left ear F0 encoding was observed. These findings suggest that at a preattentive, sensory stage of auditory processing, older adults lateralize speech stimuli similarly to young adults.
Highlights
Subcortical asymmetries between the right and left auditory pathways have been reported in newborns [1,2,3] and young adults [4,5,6,7,8,9,10]
No significant differences between right and left ear presentation were found for amplitudes and latencies of the click-auditory brainstem response (ABR) components
Shorter latencies for right ear presentation as compared to left ear presentation were observed for onset and offset transient components (V, A and O), sustained components (D and E), and voiced transition components (C) of the speech-ABR
Summary
Subcortical asymmetries between the right and left auditory pathways have been reported in newborns [1,2,3] and young adults [4,5,6,7,8,9,10]. Studies conducted in samples of young adults have found that click stimuli seem to produce similar responses (i.e. amplitude and latency) for the auditory brainstem response (ABR) between right and left ear presentation. It has been suggested that hemispheric lateralization is associated with lateralization of the entire auditory pathway [15, 16] and speech-like stimuli are more efficiently processed when presented to the right ear [17, 18]. Little is known about such an auditory laterality in older adults
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