Nonlinear Dynamics, Psychology, and Life Sciences, Vol. 16, Iss. 1, January, 2012, pp. 5-22
@2012 Society for Chaos Theory in Psychology & Life Sciences


An EEG Study of Brain Connectivity Dynamics at the Resting State

Stavros I. Dimitriadis, University of Patras, Greece and Aristotle University, Thessaloniki, Greece
Nikolaos A. Laskaris, Aristotle University, Thessaloniki, Greece
Vasso Tsirka, University of Crete, Greece
Michael Vourkas, Technical High School of Crete, Greece
Sifis Micheloyannis, University of Crete, Greece

Abstract: We investigated the dynamical behavior of resting state functional connectivity using EEG signals. Employing a recently introduced methodology that considers the time variations of phase coupling among signals from different channels, a sequence of functional connectivity graphs (FCGs) was constructed for different frequency bands and analyzed based on graph theoretic tools. In the first stage of analysis, hubs were detected in the FCGs based on local and global efficiency. The probability of each node to be identified as a hub was estimated. This defined a topographic function that showed widespread distribution with prominence over the frontal brain regions for both local and global efficiency. Hubs consistent across time were identified via a summarization technique and found to locate over forehead. In the second stage of analysis, the modular structure of each single FCG was delineated. The derived time-dependent signatures of functional structure were compared in a systematic way revealing fluctuations modulated by frequency. Interestingly, the evolution of functional connectivity can be described via abrupt transitions between states, best described as short-lasting bimodal functional segregations. Based on a distance function that compares clusterings, we discovered that these segregations are recurrent. Entropic measures further revealed that the apparent fluctuations are subject to intrinsic constraints and that order emerges from spatially extended interactions.

Keywords: phase synchrony, evolving graphs, modularity, hubs, segregation motifs