A voxel-based asymmetry study of the relationship between hemispheric asymmetry and language dominance in Wada tested patients.

Simon S Keller,Enis Cezayirli,Neil Roberts,Udo C Wieshmann,Anthony G Marson,Vanessa Sluming,Paul Eldridge,Andrew Mayes,Gus Baker

doi:10.1002/hbm.24058

Abstract

Determining the anatomical basis of hemispheric language dominance (HLD) remains an important scientific endeavor. The Wada test remains the gold standard test for HLD and provides a unique opportunity to determine the relationship between HLD and hemispheric structural asymmetries on MRI. In this study, we applied a whole‐brain voxel‐based asymmetry (VBA) approach to determine the relationship between interhemispheric structural asymmetries and HLD in a large consecutive sample of Wada tested patients. Of 135 patients, 114 (84.4%) had left HLD, 10 (7.4%) right HLD, and 11 (8.2%) bilateral language representation. Fifty‐four controls were also studied. Right‐handed controls and right‐handed patients with left HLD had comparable structural brain asymmetries in cortical, subcortical, and cerebellar regions that have previously been documented in healthy people. However, these patients and controls differed in structural asymmetry of the mesial temporal lobe and a circumscribed region in the superior temporal gyrus, suggesting that only asymmetries of these regions were due to brain alterations caused by epilepsy. Additional comparisons between patients with left and right HLD, matched for type and location of epilepsy, revealed that structural asymmetries of insula, pars triangularis, inferior temporal gyrus, orbitofrontal cortex, ventral temporo‐occipital cortex, mesial somatosensory cortex, and mesial cerebellum were significantly associated with the side of HLD. Patients with right HLD and bilateral language representation were significantly less right‐handed. These results suggest that structural asymmetries of an insular‐fronto‐temporal network may be related to HLD.

Highlights

IntroductionThe left cerebral hemisphere is dominant for Interhemispheric structural asymmetries of cortical regions known to language in up to 90% of right-handed people (Knecht et al, play an important role in language function have been considered as 2000a,2000b)
Foundas, Amunts, & Roberts, 2009a; Toga & Thompson, 2003; Witelson & Kigar, 1988)
We found that controls, who were all right handed, and righthanded patients with left hemispheric language dominance (HLD) had comparable leftward asymmetries in motor regions, insula, dorsal temporal lobe areas, supramarginal gyrus, temporo-occipital cortex, superior frontal gyrus, lateral cerebellum, and accumbens area, and rightward asymmetries in the banks of the superior temporal and cingulate sulci, mesial occipital cortices, precuneus, mesial cerebellum, frontal pole, temporal pole, and thalamus

Summary

Introduction

The left cerebral hemisphere is dominant for Interhemispheric structural asymmetries of cortical regions known to language in up to 90% of right-handed people (Knecht et al, play an important role in language function have been considered as 2000a,2000b). This figure decreases in people with left-handedness candidate regions representing an anatomical basis for hemispheric lan- (Knecht et al, 2000b; Pujol, Deus, Losilla, & Capdevila, 1999) and leftguage dominance (HLD), that is, the cerebral hemisphere most domi- sided brain insult (Brazdil, Zakopcan, Kuba, Fanfrdlova, & Rektor, 2003; nant for expressive and receptive language functions (Keller, Crow, Liegeois et al, 2004; Pahs et al, 2013).

Objectives

Methods

Findings

Discussion

Conclusion