Brain Network Research Of Alzheimer’s Disease And Mild Cognitive Impairment Based On Resting-state FMRI

Alzheimer’s disease(AD) is a central nervous system degenerative disease, which can seriously affect the elderly’s memory and cognitive system. Patients with AD couldn’t engage in normal social activities or even live independently without others’ help. Mild cognitive impairment(MCI) is a kind of intermediate state between normal ageing and dementia, which can lead to memory problems or other cognitive abnormalities, but haven’t meet the criterion of the dementia and have less effect on daily life. However, with the passage of time, patients with MCI will transfer to different disease states, such as AD or still maintain state of MCI or other dementia disease. Over the years, researchers have explored the pathological mechanism and the development of AD and MCI from the aspect of anatomy, nerve and imaging. By far, many important results have been obtained, however there is still a need for further study. The author’s major contributions are outlined as follows:1. Based on resting-state f MRI, this study applied brain image analysis methods independent component analysis(ICA) and Granger causal analysis(GCA) to explore the functional connectivity and effective connectivity of default mode network(DMN) in patients with AD and normal controls(NC). ICA is a totally data-driven method, which can extract the brain regions of DMN. Then, GCA was used to exploer the pattern of effective connectivity based on the DMN regions. After compared the statistical results of patients with AD and the normal controls, we find that:(i) connections in AD were decreased than those in NC, in terms of intensity and quantity. Posterior cingulated cortex(PCC) exhibited significant activity in NC as it connected with most of the other regions within the DMN. Besides, the PCC was the convergence center which only received interactions from other regions;(ii) right inferior temporal cortex(r ITC) in the NC exhibited stronger interactions with other regions within the DMN compared with AD patients; and(iii) interactions between medial prefrontal cortex(MPFC) and bilateral inferior parietal lobule(IPL) in the NC were weaker than those in AD patients. These findings may implicate a brain dysfunction in AD patients and reveal more pathophysiological characteristics of AD.2. In order to better understand the pathological mechanism of MCI with different follow-up disease state, firstly, we recruit two groups of participants, one is MCItransfer to AD and another is MCI remain MCI state. Afer that, we construct whole brain functional network of the two groups. Finally, we calculate the related measures of the network such as degree of connectivity, clustering coefficient and shortest path length, which can reflect the small-world networks properties of the network. Our results show that MCI transfer to AD group appear poor small-world network properties, compared with MCI remain MCI state.