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, researchers from Bergen, Norway, and the biopsychology lab in Bochum examined how performance in the dichotic listening task is affected the structure of the arcuate and uncinate fasciculus, assessed with DTI. Both arcuate and uncinate fasciculus had a larger tract volume in the left compared to the right hemisphere, but fractional anisotropy was higher in the right than in the left arcuate fasciculus. Interestingly, 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. These results suggest that both micro- and macro-structural properties of language-relevant intrahemispheric white matter tracts modulate the behavioral correlates of language lateralization.

Ocklenburg, S., Schlaffke, L., Hugdahl, K., Westerhausen, R. (2014). From structure to function in the lateralized brain: How structural properties of the arcuate and uncinate fasciculus are associated with dichotic listening performance. Neuroscience Letters, 580: 32-36.