Mapping The Human Parietal Lobule And Its Applications

The brain is the most complex system in human body. Humans have explored architecture and function of the brain for a long time. As early as the 18 th century, some scholars developed theories about brain localization the function. These theories also became the prototype of brain atlas. By the early of the 20 th century, the Brodmann’s atlas was published in 1909 and it became the foundational result of brain atlas. Since then, there are more and more studies focused on brain atlas.Development of brain atlas has great significance for the neuroscience and clinical research. Brain atlas is an important tool for studying the brain architecture and function. We could define the region of interest from brain atlas. It can also be used to make functional localization for areas of activation. Additionally, brain atlas is useful in neuronavigational operations. In some sense, if we want to know how the brain works, we must know the organization of brain at first.In the present article, we investigated partition of the posteromedial cortex and the intraparietal sulcus. We selected appropriate parcellation method for each of the two regions and studied their functions and physiological significances from multiple perspectives.The posteromedial cortex is mainly located in the medial parietal lobule. Previous functional studies have revealed high heterogeneity of the posteromedial cortex and some recent studies have provided its functional partition. However, a consensus scheme has not yet developed, even though these studies are all based on functional image.Previous studies have indicated that function of the brain is determined by its connectivity patterns. In order to demonstrate architecture of the posteromedial cortex essentially, our study subdivided it by analyzing its anatomical connections. We used probabilistic fiber tracking to get connectivity patterns of the posteromedial cortex. Then a spectral clustering algorithm was used to group voxels with similar connectivity profiles together. We identified 5 subregions in the posteromedial cortex and this result was confirmed by another independent dataset.We also studied anatomical and functional connectivity for each of the posteromedial cortex. The dorsal-anterior subregion of the posteromedial cortex has rich connections with sensorimotor network. The dorsal-central subregion was involved in cognitive and associative functions. The dorsal-posterior subregion was mainly connected with visual related regions. The ventral part of the posteromedial cortex contained two subregions. The dorsal one was a transition region between precuneus and posterior cingulate cortex. The ventral one has strong connections with limbic system and was a core of the default mode network. Additionally, meta-analysis indicated that organization and connectivity patterns were similar between human and macaque, suggesting homology of the posteromedial cortex in the two species.We also studied the parcellation of the human intraparietal sulcus. The intraparietal sulcus is the main sulcus in the lateral parietal lobule. Because of the deep location and high individual differences, there is few report about the parcellation of sulcus previously. Considering the complexity and variability of the human intraparietal sulcus, we manually drew the seed region of the intraparietal sulcus for each individual, rather than defined the seed region in standard space and then registered into individual space. Additionally, the same method for parcellation was used on 3 independent datasets, then the parcellation with the highest consistency was selected as the partition of the human intraparietal sulcus. After that, we studied anatomical and functional differences between each subregion of the intraparietal sulcus. However, as an associative cortical region, the intraparietal sulcus was involved in multiple cognitive functions, which are difficult to be distinguished simply from its connectivity patterns. Thus we also assessed functions and behaviors for each subregion of the intraparietal sulcus by meta-analysis. Together with connectivity profiles, functions and behaviors demonstrated multi-aspect of the role for intraparietal sulcus subregions.At last, we studied the distinct functional alterations of subregions of the posteromedial cortex throughout the Alzheimer’s disease in a finer scale by using our new atlas. We recruited a group of healthy controls, a group of patients with mild cognitive impairment, a group of patients with mild Alzheimer’s disease and a group of patients with severe Alzheimer’s disease. The 5 subregions of the posteromedial cortex were used as seed regions. We studied the distinct changes of functional connectivity of these seed regions between the 3 patient groups and healthy controls respectively. Subregions of the posteromedial cortex that showed altered connectivity started with the transition region, and gradually expanded to the other subregions surrounded by. Connections between subregions of the posteromedial cortex and the episodic memory, default mode, syntactic, lexical-semantic, visual, and sensorimotor networks seem to be affected successively.