Study of neuroplasticity based on brain functional networks from neuroimaging

Abstract

The brain, as it is, is a complex network on multiple spatial and time scales, and, as it does, supports both segregated and distributed information processing. A small-world topology characterized by dense local clustering of connections between neighboring vertices has been proposed as an attractive model for brain networks. The organization of the brain can be changed as a result of experiences. This neuroplasticity is the lifelong ability of the brain, and has been known to support the basis for recovery after stroke. In this thesis, I focused on the study of neuroplasticity based on graph theoretical analysis of neuroimaging data. First, I investigated various types of normal subjects` brain networks and compared them: brain functional networks before and after brain stimulation, brain functional networks during the resting-state and the task-performing state, and brain functional networks and brain anatomical networks. As results, small-world properties of brain networks were confirmed, irrespective of modalities of the networks. Also, with respect to structural properties, brain functional networks were different from brain anatomical networks. Even in brain functional networks, there were differences in the task-performing state between before and after brain stimulation, and the resting-state was distinct from the task-performing state. As for stroke patients` brain functional networks, they were changeable during recovery from stroke. It is proposed that, in terms of normal subjects` brain functional networks, stroke patients` resting-state brain functional networks have structural properties like task-performing state brain functional networks, rather than resting-state brain functional networks, in normal subjects. Moreover, in an aspect of structural properties, the relation of resting-state brain functional networks in stroke patients with poor recovery to those in stroke patients with good recovery is analogous to the relation of brain functional...