چكيده انگليسي :
The human brain undergoes complex changes with age, which can lead to either improvements or declines in brain function. Investigating the normal and abnormal trajectory of brain development with age is crucial for identifying strategies to enhance brain function, early detection of functional disorders, and intervening to slow their progression. Resting-state functional MRI (rs-fMRI) allows for the examination of the functional organization of the brain. In rs-fMRI images, blood oxygen level-dependent (BOLD) signals are recorded for each brain region, reflecting its functional activity over time. Functional connectivity between two brain regions is obtained by calculating the statistical correlation between their BOLD signals. Brain function is characterized by multilateral interactions and functional connectivity among various brain regions. Therefore, conceptualizing brain organization as a graph with nodes representing brain regions and edges representing functional connections enables modeling of brain functional organization. The number of nodes, edges, and the pattern of connections between nodes determine the topology of the brain graph.The primary aim of this research is to investigate changes in brain function from a graph theory perspective in normal individuals. To this end, we examine how the topological features of brain functional graphs change with age in healthy individuals.The dataset for this research comprises rs-fMRI images from three datasets: ABIDE I, ABIDE II, and NKI, encompassing 1254 data from individuals aged 6 to 85 years. The ABIDE dataset includes images from several laboratories worldwide, each employing slightly different imaging devices and protocols. In this study, using GLM evaluation, the effects of age, age squared, gender, and differences in imaging centers on the topological features of brain functional graphs were examined. Moreover, only if the trends in changes of each topological feature with age were replicable across the entire dataset (ABIDE I, ABIDE II, and NKI) were they accepted as genuine age-related changes.This study revealed that the effect of differences in imaging centers prominently influences the topological features of brain functional graphs, and only after removing the effect of imaging center differences, the trends in changes of topological features with age across the entire dataset (ABIDE I, ABIDE II, and NKI) are replicable. The findings suggest that the human brain exhibits small-world and modular structures. After removing the effect of differences in imaging centers, characteristic path length increases, clustering coefficient, small-worldness, local efficiency, global efficiency, modularity, functional connectivity strength, mean within-network connectivity, and mean between-network connectivity decrease with age. Additionally, the characteristic path length is higher in females than males, while functional connectivity strength, mean within-network and between-network connectivity, global efficiency, and local efficiency are higher in males than females. However, modularity and small-worldness do not significantly differ between males and females, indicating that the balance between within-network and between-network connectivity, as well as between global and local efficiency, does not substantially differ between genders.
