035-22 – Are inter-hemispheric shape asymmetries of white matter tracts related to language lateralization?

Interhemispheric anatomical asymmetries have long thought to be related to language lateralization. There have been some studies that have examined whether interhemispheric asymmetries of fundamental diffusion scalar metrics of white matter tracts known to be important for language are consistent with the side of language lateralization in healthy and brain damaged populations, with inconsistent results. In the present study, we examined whether asymmetric morphometric features of white matter tracts are related to the side of language lateralization in a large cohort of healthy individuals. We investigated 1049 healthy participants from the Human Connectome Project (HCP) database. All participants underwent diffusion and functional MRI. Functional activation associated with language comprehension was determined using a story-math contrast. Hemispheric language comprehension lateralisation was determined using a laterality index (LI) for each participant’s activated regions. The structural asymmetry index of the several shape metrics of the white matter tracts was calculated. The relationship between structural and functional asymmetry indices was assessed using linear regression model. The results demonstrated no significant associations between various tract characteristics along the white matter tract, indicating that interhemispheric shape asymmetries of white matter fibre tracts are not related to the lateralization of language comprehension functions. On the one hand, this is consistent with other studies that indicate no relationship between language lateralization and interhemispheric asymmetries of white matter and grey matter structure, suggesting that the lateralization of language functions may not have a gross morphological basis. On the other hand, it may be that such interhemispheric structure-function relationships exist in white matter not classically considered to comprise language neural networks.