Analysis of functional connectivity of brain hierarchical structure using resting state fMRI and its application to Alzheimer's disease

Abstract

The information in the brain is known to be transmitted through hierarchical structuresin the brain.For example, sensory information flows from primary uni-modal area to secondary uni-modal area and then to multi-modal areas such as theparalimbic and limbic areas. The concept of structural and functional hierarchy comes from various histological, electrophysiological and functional neuroimaging studies in Macaque monkey and the human brain. These studies show that each hierarchy has different cytoarchitectonic patterns and also different anatomical or functional connection patterns. Functional connectivity using resting state fMRI (functional magnetic resonance imaging) shows endogenous and anatomically based network by spontaneous fluctuation of BOLD signal. Also, the characteristics of the network can be seen specifically through the graph theory analysis. In this research, I hypothesize that the unimodal region has more inter-hemispheric connections and high clustering, the heteromodal region has less inter-hemispheric connections, has many long distance connections and low clustering. Finally,that the limbic system has more inter-hemispheric connections and high clustering. I constructed the brain network using functional connectivity in resting state fMRI from 18 normal people and then the general characteristics of each hierarchical region in the network are identified by quantitatively comparing of graph theory parameters such as nodal strength, distance, betweenness centrality and clustering coefficient. I compared these measure among different hierarchy (unimodal, heteromodal, limbic, and subcortical) and different modalities (visual, auditory, somatosensory, and motor). Consequently, the results show thatunimodal region and limbic area have more inter-hemispheric connectionsthan heteromodal region, unimodal region has short-distant intra-hemispheric connections and heteromodal region has more and long-distant intra-hemispheric connections. Moreover, ...