Relations between hemispheric asymmetries of grey matter and auditory processing of spoken syllables in 281 healthy adults

Abstract

Most people have a right-ear advantage for the perception of spoken syllables, consistent with left hemisphere dominance for speech processing. However, there is considerable variation, with some people showing left-ear advantage. The extent to which this variation is reflected in brain structure remains unclear. We tested for relations between hemispheric asymmetries of auditory processing and of grey matter in 281 adults, using dichotic listening and voxel-based morphometry. This was the largest study of this issue to date. Per-voxel asymmetry indexes were derived for each participant following registration of brain magnetic resonance images to a template that was symmetrized. The asymmetry index derived from dichotic listening was related to grey matter asymmetry in clusters of voxels corresponding to the amygdala and cerebellum lobule VI. There was also a smaller, non-significant cluster in the posterior superior temporal gyrus, a region of auditory cortex. These findings contribute to the mapping of asymmetrical structure-function links in the human brain and suggest that subcortical structures should be investigated in relation to hemispheric dominance for speech processing, in addition to auditory cortex.

Keywords: Brain asymmetry; Brain laterality; Dichotic listening; Hemispheric language dominance; Speech processing; Voxel-based morphometry.

Fig. 1

Mean correct responses for the four different presentation categories by voice onset time (VOT) category. LL  long to both ears, SS short to both ears, LS  long to left, short to right, SL  short to left, long to right. 95% confidence intervals (plus and minus two standard errors) are shown on each bar

Fig. 2

Frequency distribution of the dichotic listening laterality index. Negative values indicate left-ear advantage, positive values indicate right-ear advantage. Right-handers and left-handers are indicated by different shading

Fig. 3

a Two significant clusters associated with the dichotic listening laterality index, in voxel-wise grey matter asymmetry analysis; one in the amygdala, the other in cerebellum lobule VI. Both associations were in a positive direction (red-yellow indicates the association Z score). b Region-of-interest analysis of voxel-wise grey matter volume asymmetry in relation to the dichotic listening laterality index. The posterior superior temporal region of interest is shown in green (voxels with at least 50% probability of belonging to the region according to the Harvard–Oxford atlas), and a tentative cluster showing positive association is mapped in red-yellow (indicating the association Z score). c Correlations between the dichotic listening laterality index and peak coordinate measures of grey matter volume, for the amygdala cluster (top), the cerebellum lobule VI cluster (middle), and the posterior superior temporal gyrus (pSTG) cluster (bottom). For each peak coordinate, correlations for voxel-wise grey matter asymmetry indexes (AI) as well as the corresponding unilateral left and right volume data are shown. Note that the primary analysis of AIs was based on General Linear Modelling including confound variables (see “Methods” section), but that correlations at the peak voxels are shown here for visualization