Auditory brainstem timing predicts cerebral asymmetry for speech

Abstract

The left hemisphere of the human cerebral cortex is dominant for processing rapid acoustic stimuli, including speech, and this specialized activity is preceded by processing in the auditory brainstem. It is not known to what extent the integrity of brainstem encoding of speech impacts patterns of asymmetry at cortex. Here, we demonstrate that the precision of temporal encoding of speech in auditory brainstem predicts cerebral asymmetry for speech sounds measured in a group of children spanning a range of language skills. Results provide strong evidence that timing deficits measured at the auditory brainstem negatively impact rapid acoustic processing by specialized structures of cortex, and demonstrate a delicate relationship between cortical activation patterns and the temporal integrity of cortical input.

Figure 1.

Grand average neurophysiologic responses. Bottom, Acoustic waveform of the synthesized speech stimulus /da/ (above) and grand average auditory brainstem responses to /da/ (below). The stimulus has been moved forward in time to the latency of onset responses (peak V) to enable direct comparisons with brainstem responses. Lower insets, First, third, and fifth quintile responses for waves V, A, and O. Top, Grand average cortical responses measured from left and right hemisphere temporal electrodes, grouped by latency of ABR responses.

Figure 2.

Brainstem responses and cortical asymmetry. The linear fit for the data in both plots is indicated by the central line and is flanked by dashed lines indicating the limits of the range for prediction of individual data points with 95% certainty. A, Brainstem onset/offset and cortical asymmetry. B, Brainstem frequency following and cortical asymmetry.

Figure 3.

Cortical asymmetry and measures of speech discrimination and academic achievement. Error bars indicate SEM.