Directed Functional Connectivity of Posterior Cingulate Cortex and Whole Brain in Alzheimer's Disease and Mild Cognitive Impairment

Background: Impaired functional connectivity in the default mode network (DMN) is supposedly involved in Alzheimer's disease (AD) progression. The posterior cingulate cortex (PCC) might be an imaging marker for monitoring AD progression. Objective: To investigate the alterations in the directed functional connectivity between the PCC and whole brain in patients with AD, patients with mild cognitive impairment (MCI), and healthy controls. Methods: A total of 116 enrolled participants were divided into three groups: AD (n(-) 32), MCI (n(-) 26), and controls (n= 58). Using resting-state functional magnetic resonance imaging (rs-fMRI), the directed functional connectivity was studied using Granger causality analysis (GCA). Results: Almost all of the directed functional connections with significant differences were unidirectional. Compared with the NC group, the AD group showed enhanced directed connectivity from the whole brain to the PCC mainly for regions outside the DMN, and reduced connectivity from the PCC to the whole brain mainly for regions inside the DMN. Compared with the NC group, the MCI group showed enhanced directed connectivity from the PCC to the whole brain for the bilateral precuneus and postcentralgyrus, and reduced connectivity from the whole brain to the PCC for regions outside the DMN. Compared with the MCI group, the abnormal directed connectivity in the AD group was predominantly in the left hemisphere, possibly suggesting asymmetric characteristics. Conclusion: In patients with AD, the PCC in the DMN shows disorders in receiving and transmitting information, and these abnormalities are directional.