Brain Networks Of Language Lateralization

Studies on the neurophysiological basis of human language ability have consistently found that,for most individuals,the left ceberal hemisphere is the dominant hemisphere for language ability,that is,leftward language lateralization.Among current mainstream neurolinguistic models,the fundamental architecture of the language system is mainly based on links between left hemisphere brain areas involved in sub-functions of language(e.g.language production,comprehension,reading,and so on).It is worth noting that language lateralization is not homogeneous at the population level,but shows a continuous distribution from leftward to rightward lateralization.Therefore,this dissertation first investigated the question of "what is the relationship between the lateralization of language sub-functions and the architecture of the language system in the brain" from the perspective of individual differences in the lateralization of language sub-functions.Because the language system is part of the architecture of the whole-brain,this dissertation further investigated the question of "when the lateralization of language sub-functions changes,will the whole-brain architecture also change accordingly".In another aspect,from the perspective of the structure-function relationship,this dissertation also investigated the question of "whether the ubiquitous leftward language lateralization corresponds to any advantages of the brain mechanism in terms of language system or whole-brain architecture".The first part of the dissertation task fMRI and resting-state fMRI functional connectivity brain network approach to examine the relationship between brain network functional connectivity and the laterlization of three important language sub-functions,namely speech production(Study 1),speech perception and single word reading(Study 2).The results of Study 1 demonstrated that differences between leftward language lateralization and rightward language lateralization are associated with functional connectivity mostly within the language system.Additionallly,for participants with rightward language lateralization,the degree of lateralization is linked with functional network features at a larger scale compared to participants with leftward language lateralization.Study 2 showed that there is no obvious relationship between the lateralization of speech perception and single word reading,while the rightward lateralization of these two language sub-functions are also associated with functional network features at a larger scale.Moreover,individuals with rightward co-lateralization of speech perception and single word reading showed an advantage in language ability.The second part of the dissertation investigated the above-mentioned question of "whether the leftward language lateralization corresponds to any advantages in terms of system architecture",by using generative models of functional networks and DTI-based structural network approach.This part mainly examined the relationship between the lateralization of speech production and the wiring-rules of functional networks(Study 3),and the relationship between the lateralization of speech production and structural networks(Study 4).The results of Study 3 demonstrated that the lateralization of speech production is associated with the spatial distance(which is characterized by the wiring-rules of the generative models)of functional connectivity,while the results of Study 4 further revealed a structural sub-network related to the lateralization of speech production.In summary,the results of this dissertation revealed that when the side or the degree of lateralization of language sub-functions change,the functional architecture of the language system shows an alteration accordingly.Meanwhile changes in the functional architecture of the wholebrain is mainly associated with rightward language lateralization.The ubiquitous leftward language lateralization might be associated spatial distance features of brain networks,which is characterized by both the generative models of functional networks and structural networks.