From structure to function in the lateralized brain: how structural properties of the arcuate and uncinate fasciculus are associated with dichotic listening performance.

Structural asymmetries in white matter tracts within the language system have been suggested to be one of the factors underlying functional language lateralization. To test this assumption, the present study examined how performance in the dichotic listening task, a behavioral measure of language dominance, is affected by macro- and microstructural properties of the arcuate and uncinate fasciculus. To this end, whole brain tractography was performed on 29 diffusion tensor imaging datasets obtained from healthy adult participants. Mean tract volume and fractional anisotropy of the uncinate and arcuate fasciculus were linked to the individual extent of the right ear advantage in the dichotic listening task. On the macrostructural level, both arcuate and uncinate fasciculus had a larger tract volume in the left compared to the right hemisphere. In contrast, fractional anisotropy was higher in the right than in the left arcuate fasciculus. These structural asymmetries were linked to functional lateralization, that is, tract volume and fractional anisotropy of the left arcuate fasciculus were positively correlated to the strength of functional language lateralization, as was the volume of the right uncinate fasciculus. In conclusion, the results of the present study suggest that both micro- and macro-structural properties of language-relevant intrahemispheric white matter tracts modulate the behavioral correlates of language lateralization.