The classification of Alzheimer's disease and mild cognitive impairment improved by dynamic functional network analysis

Brain network analysis using functional MRI has advanced our understanding of cortical activity and its changes in neurodegenerative disorders that cause dementia. Recently, research in brain connectivity has focused on dynamic (time-varying) brain networks that capture both spatial and temporal information on cortical, regional co-activity patterns. However, this approach has been largely unexplored within the Alzheimer's spectrum. We analysed age- and sex-matched static and dynamic fMRI brain networks from 315 individuals with Alzheimer's Disease (AD), Mild Cognitive Impairment (MCI), and cognitively-normal Healthy Elderly (HE), using data from the ADNI-3 protocol. We examined both similarities and differences between these groups, employing the Juelich brain atlas for network nodes, sliding-window correlations for time-varying network links, and non-parametric statistics to assess between-group differences at the link or the node centrality level. While the HE and MCI groups show similar static and dynamic networks at the link level, significant differences emerge compared to AD participants. We found stable (stationary) differences in patterns of functional connections between the white matter regions and the parietal lobe's, and somatosensory cortices, while metastable (temporal) networks' differences were consistently found between the amygdala and hippocampal formation. In addition, our node centrality analysis showed that the white matter connectivity patterns are local in nature. Our results highlight shared and unique functional connectivity patterns in both stationary and dynamic functional networks, emphasising the need to include dynamic information in brain network analysis in studies of Alzheimer's spectrum.