Functional disorganization of small-world brain networks in mild Alzheimer's disease and amnestic Mild cognitive impairment: An EEG study using Relative Wavelet Entropy (RWE)

Christos A. Frantzidis, Ana B. Vivas, Anthoula Tsolaki, Manousos A. Klados, Magda Tsolaki, Panagiotis D. Bamidis*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Previous neuroscientific findings have linked Alzheimer's disease (AD) with less efficient information processing and brain network disorganization. However, pathological alterations of the brain networks during the preclinical phase of amnestic Mild Cognitive Impairment (aMCI) remain largely unknown. The present study aimed at comparing patterns of the detection of functional disorganization in MCI relative to Mild Dementia (MD). Participants consisted of 23 cognitively healthy adults, 17 aMCI and 24 mild AD patients who underwent electroencephalographic (EEG) data acquisition during a resting-state condition. Synchronization analysis through the Orthogonal Discrete Wavelet Transform (ODWT), and directional brain network analysis were applied on the EEG data. This computational model was performed for networks that have the same number of edges (N=500, 600, 700, 800 edges) across all participants and groups (fixed density values). All groups exhibited a small-world (SW) brain architecture. However, we found a significant reduction in the SW brain architecture in both aMCI and MD patients relative to the group of Healthy controls. This functional disorganization was also correlated with the participant's generic cognitive status. The deterioration of the network's organization was caused mainly by deficient local information processing as quantified by the mean cluster coefficient value. Functional hubs were identified through the normalized betweenness centrality metric. Analysis of the local characteristics showed relative hub preservation even with statistically significant reduced strength. Compensatory phenomena were also evident through the formation of additional hubs on left frontal and parietal regions. Our results indicate a declined functional network organization even during the prodromal phase. Degeneration is evident even in the preclinical phase and coexists with transient network reorganization due to compensation.

Original languageEnglish
Article number224
JournalFrontiers in Aging Neuroscience
Publication statusPublished - 2014

Bibliographical note

© 2014 Frantzidis, Vivas, Tsolaki, Klados, Tsolaki and Bamidis. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.


  • Alzheimer disease
  • Amnestic mild cognitive impairment
  • Electroencephalography
  • Graph analysis
  • Relative wavelet entropy


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