Brain Functional Organization Associated with Language Lateralization

Although it is well-established that human language functions are mostly lateralized to the left hemisphere of the brain, little is known about the functional mechanisms underlying such hemispheric dominance. The present study investigated intrinsic organization of the whole brain at rest, by means of functional connectivity and graph theoretical analysis, with the aim to characterize brain functional organization underlying typical and atypical language dominance. We included healthy left-handers, both those with typical left-lateralized language and those with atypical right-lateralized language. Results show that 1) differences between typical and atypical language lateralization are associated with functional connectivity within the language system, particularly with weakened connectivity between left inferior frontal gyrus and several other language-related areas; and 2) for participants with atypical language dominance, the degree of lateralization is linked with multiple functional connectivities and graph theoretical metrics of whole brain organization, including local efficiency and small-worldness. This is the first study, to our knowledge, that linked the degree of language lateralization to global topology of brain networks. These results reveal that typical and atypical language dominance mainly differ in functional connectivity within the language system, and that atypical language dominance is associated with whole-brain organization.