Structural correlates of functional language dominance: a voxel-based morphometry study

Abstract

Background and purpose: The goal of this study was to explore the structural correlates of functional language dominance by directly comparing the brain morphology of healthy subjects with left- and right-hemisphere language dominance.

Methods: Twenty participants were selected based on their language dominance from a cohort of subjects with known language lateralization. Structural differences between both groups were assessed by voxel-based morphometry, a technique that automatically identifies differences in the local gray matter volume between groups using high-resolution T1-weighted magnetic resonance images.

Results: The main findings can be summarized as follows: (1) Subjects with right-hemisphere language dominance had significantly larger gray matter volume in the right hippocampus than subjects with left-hemisphere language dominance. (2) Leftward structural asymmetries in the posterior superior temporal cortex, including the planum temporale (PT), were observed in both groups.

Conclusions: Our study does not support the still prevalent view that asymmetries of the PT are related in a direct way to functional language lateralization. The structural differences found in the hippocampus underline the importance of the medial temporal lobe in the neural language network. They are discussed in the context of recent findings attributing a critical role of the hippocampus in the development of language lateralization.

Fig 1

Statistical parametric maps showing leftward PT asymmetry for subjects with (A) left- as well as those with (B) right-hemisphere language dominance. Structural differences are superimposed on the study-specific symmetrical gray matter template. Color scales bars indicate the T score. Please note that all results are presented in radiological convention (left = right).

Fig 2

Top: Statistical parametric map showing morphometric differences between subjects with left- and right-hemisphere language dominance, superimposed on the study-specific symmetrical gray matter template. Subjects with right-hemisphere language dominance have increased gray matter volume in the right hippocampus compared to subjects with left-hemisphere language dominance. Color scales bar indicates the T score. Please note that all results are presented in radiological convention (left = right). Bottom: Distribution of the voxel values extracted at the statistical peak in the right hippocampus (MNI coordinates 27–33–5) for both language dominance groups. The mean voxel value for each group is marked with a bold diamant. The scatter plot demonstrates that the hippocampus effect is not driven by outliers in the right-hemisphere dominance group. LHD = subjects with left hemisphere language dominance; RHD = subjects with right-hemisphere language dominance.