| The inferior parietal lobule,one of the high-order association cortices in the brain,is located near the center of the brain,receives and integrates information from somatomotor,auditory and visual modalities,and plays important roles in high-order cognitive functions such as language and tool use.These functions are not only humanspecific but also hemisphere-specific.In addition,the inferior parietal lobule is one of the most expanded areas in the cerebral cortex during evolution;the human postnatal cortical expansion during development shares similar patterns with the human evolutionary expansion.These high-expansion brain regions are typically the most latematuring and more vulnerable during development.Therefore,research on structural and connectivity asymmetries of the inferior parietal lobule during the course of evolution and development is crucial for understanding the origin and development of specific functions of the human brain.Focusing on the construction of the cross-species brain atlas of the inferior parietal lobule,this dissertation utilizes multimodal magnetic resonance imaging data to explore cross-species comparison methods,and to study the structural and connectivity asymmetries of the inferior parietal lobule from the perspective of evolution and development.The main achievements of this dissertation are as follows:1)We proposed a fiber bundle segmentation method and achieved a finer delineation of the superior longitudinal fasciculus/arcuate fasciculus.Using high quality diffusion-weighted imaging data from 30 healthy subjects aged 20?35 years,a new automatic segmentation method of white matter fiber bundles was proposed based on the connectivity profiles of the fiber bundles.The superior longitudinal fasciculus/arcuate fasciculus was then subdivided into ten distinct subtracts according to the consistency of the connectivity between the subtracts and the cortical regions.We provided detailed information about structural connectivity patterns,functions and behavioral phenotypes of the subtracts.We also applied this method to other major association fiber bundles and obtained their finer subtracts.These results contribute to a deeper understanding of the structure and connectivity of white matter fiber bundles,and also provide new insights into the evolution and development of human language pathways.2)We proposed a cross-species brain atlas of the inferior parietal lobule.Using diffusion-weighted imaging data from 40 humans,27 chimpanzees and 8 macaques,a surface-based cross-species parcellation method was developed to subdivide the human,chimpanzee and macaque inferior parietal lobule into four subregions,respectively,and then the cross-species brain atlas of the inferior parietal lobule was established.Specifically,the four subregions showed consistent,anterior-posterior topological patterns in all the three primates.In addition,structural connectivity profiles were identified for each subregion of the inferior parietal lobule for each species by using tractography.The cross-species brain atlas of the inferior parietal lobule provides insight into the evolution of functional units of the cerebral cortex.3)We revealed similarities and differences of the inferior parietal lobule and its subregions during evolution.Based on the established cross-species brain atlas of the inferior parietal lobule above,we investigated the evolutionary changes of the structural and connectivity asymmetries of the inferior parietal lobule.Structurally,the inferior parietal lobule and its subregions showed positive allometric scaling.In addition,the chimpanzee and human inferior parietal lobule shared the same and dichotomous asymmetric pattern,that is,leftward asymmetry in the anterior part and rightward asymmetry in the posterior part.In terms of structural connectivity,compared to chimpanzees and macaques,humans showed the most considerable asymmetric connections between the inferior parietal lobule and the frontal,parietal and temporal cortices,which may provide a structural basis for human-specific functions such as language and tool use.Species-specific differences in asymmetric connectivity between the inferior parietal lobule and superior parietal lobule in chimpanzees and humans may indicate the two species with different evolutionary trajectories.The unique asymmetry of the connectivity between the inferior parietal lobule and precentral gyrus may be related to specific behaviors of human handedness and hand skills.4)Using multimodal magnetic resonance imaging data from 284 healthy subjects,we revealed the asymmetries in the structure,structural connectivity,and functional connectivity of the inferior parietal lobule during development from 8 to 21 years.In terms of structure,the cortical volume,surface area and thickness of the inferior parietal lobule were asymmetric during development,while only the surface area of the subregion C3 of the inferior parietal lobule was shown a trend to be correlated with age.In terms of structural connectivity,structural connectivity of the inferior parietal lobule was asymmetric during development,and the asymmetric structural connectivity was weakly correlated with age.In terms of functional connectivity,the inferior parietal lobule showed leftward asymmetric functional connectivity mainly with brain regions associated with the default network at all the age groups.With increasing age,we found rightward asymmetric functional connectivity between the inferior parietal lobule and brain areas associated with the dorsal and ventral attention networks in the groups of11 years and older.In addition,age-related asymmetries were also found mainly in the functional connectivity between the inferior parietal lobule and brain regions related to the dorsal and ventral attention networks.These results suggest that,during development from 8 to 21 years,the asymmetries of the structure and structural connectivity of the inferior parietal lobule were showed fewer changes,while the functional connectivity was found to be prominently lateralized.The asymmetric directional reversal of functional connectivity indicates the maturation of the functional networks.Our findings are essential for understanding how cognitive and behavioral abilities are refined during human development. |
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