Static and Dynamic Functional Connectivity Alterations in Alzheimer's Disease and Neuropsychiatric Diseases.

Background: To date, numerous studies have documented various alterations in resting brain activity in Alzheimer's disease (AD) and other neuropsychiatric diseases. In particular, disease-related alterations of functional connectivity (FC) in the resting state networks (RSN) have been documented. Altered FC in RSN is useful not only for interpreting the phenotype of diseases but also for diagnosing the diseases. More recently, several studies proposed the dynamics of resting-brain activity as a useful marker for detecting altered RSNs related to AD and other diseases. Objectives: In this paper, we review recent studies exploring alterations of static and dynamic functional connectivity in AD and other neuropsychiatric diseases. We then discuss how to utilize and interpret dynamics of FC for studying resting brain activity in diseases. Results: In contrast to previous studies, which focused on FC calculated using an entire fMRI scan (static FC), newer studies focused on the temporal dynamics of FC within the scan (dynamic FC) to provide more sensitive measures to characterize RSNs. However, despite the increasing popularity of dynamic FC, several statistical investigations of dynamic FC cautioned that the results obtained in commonly used analyses for dynamic FC require careful interpretation. Conclusions: Although static and dynamic FC are likely to be a useful tool to detect altered RSN in patients affected by AD and other neuropsychiatric disorders, interpretation of altered dynamic FC in patients require special care.