Mapping The Human Lateral Parietal And Temporal Cortex Based On Different Connectivity Patterns

The human brain is one of the most complicated system in world. Efforts made to map its architecture and functions could greatly advance our understanding of the human brain. Recent studies have demonstrated that the human brain’s functions were determined by its external connectivity patterns. Thus, parcellation of human brain on the basis of different connectivity patterns could better characterize the functional segregation and integration. The current thesis mainly investigated the architecture of the lateral parietal cortex and temporal cortex based on its connectivity patterns and explored its application.A new clustering method called spectral clustering combined edge-weighted centroidal voronoi tessellations was firstly introduced to parcellate the inferior parietal lobule. Although the inferior parietal lobule is very complicated and participates in many different cognitive functions, the parcellation results of this region are consistent with previous cytoarchitectonic findings. In order to characterize the connectivity properties of each subregion, we proposed coordinate-based meta-analytical method to define the target brain areas to map the connectivity fingerprint of each subregion. In addition, resting-state functional connectivity analyses were used to identify the cortical network that each subregion participated in.Second, to define the precise anatomical boundary of Wernicke’s area, I first parcellated the traditional Wernicke’s area into component subregions on the basis of different anatomical connectivity patterns. Then, the resting-state functional connectivity analyses were used to establish the cortical network that each subregion participated in. Subsequently, the task-dependent coactivation connectivity pattern, behavioral domain analyses, and intraoperative electrical stimulation were used to validate the findings of resting-state functional connectivity analyses. These results revealed that the Wernicke’s area is primarily located on the posterior temporal gyrus but does not include the temporoparietal junction area which mainly participated in social cognition. For the first time, I redefined the posterior anatomical boundary of Wernicke, which has been debated for decades.Third, the previous studies investigated the consistency between structural connectivity and functional connectivity by establishing whether the functionally connected brain areas were also structurally connected or the relationship between the connectivity strength between structural connectivity and functional connectivity. In order to investigate the consistency of structure and function connectivity for specific brain area, in our study, different connectivity patterns including structural connectivity patterns, resting-state functional connectivity patterns and task-dependent coactivation were used to separately parcellate the human superior parietal lobule into component subregions to obtain a consistent parcellation results. In addition, our parcellation results were also consistent with cytoarchitectonic findings. Our finding revealed that superior parietal lobule has consistent functional and structural topography. Our results also indicated that a fundamental basis of superior parietal lobule determines its function and connectivity.Fourth, I applied the atlas constructed with connectivity-based parcellation approaches to explore the neurophysiological basis of cognitive neuroscience. in human brain, there are two predominant lateralized systems. One is language system, and the other is visuospatial attention system. To investigate the neurophysiological substrate of visuospatial attention, transcranial magnetic stimulation(TMS) technology was used to temporally inactivate the superior parietal lobule to assess the behavioral performances. Then, diffusion magnetic resonance imaging(MRI) was used to map the anatomical connectivity between posterior superior parietal lobule and the superior frontal gyrus, middle frontal gyrus, inferior frontal gyrus and contralateral posterior parietal cortex. Correlation analyses were performed to determine which connectivities were related to lateralized visuospatial attention and found that the unbalanced connectivities between posterior superior parietal lobule and middle frontal gyrus, inferior frontal gyrus and contralateral posterior parietal cortex were closely related to asymmetrical visuospatial attention. Our finding demonstrated the asymmetrical anatomical connectivity accommodates the lateralized visuospatial attention.Finally, many previous studies primarily focused on the interaction between higher cortical areas and ignored the interaction between higher cortical area and lower cortical area. Emerging evidence has demonstrated that the top-down bias signals will affect the perception of primary visual cortex, V1. These bias signals were mainly produced by higher cortical area, such as frontal and parietal cortex. However, the relationship between the top-down bias signals and asymmetric visuospatial attention remains unknown. To investigate the relationship between top-down connectivities and asymmetrical visuospatial attention. I used TMS to inactivate the superior parietal lobule to assess the behavioral performances and resting-state functional connectivity analyses were used to establish the relationship between top-down functional connectivity and behavioral performances. The resting-state functional connectivity analyses found that the top-down connectivity between superior parietal lobule and V1 was closely related to lateralization of visuospatial attention. We didn’t find the correlation between behavioral performances and connectivities between superior parietal lobule and V2, V3, V4. Our finding indicated that bias of top-down functional connectivity resulted in asymmetrical visuospatial attention and attention could directly modulate the activity of V1.Our study constructed the atlas of the human lateral parietal cortex and posterior temporal cortex. And we also applied the atlas to investigate the fundamental questions of cognitive neuroscience. Our finding will improve our understanding of the function and connectivity of brain and facilitate future studies in these areas at a finer-grained scale.