title: Reproducibility of functional connectivity and graph measures based on the phase lag index (PLI) and weighted phase lag index (wPLI) derived from high resolution EEG.
abstract: Functional connectivity (FC) and graph measures provide powerful means to analyze complex networks. The current study determines the inter-subject-variability using the coefficient of variation (CoV) and long-term test-retest-reliability (TRT) using the intra-class correlation coefficient (ICC) in 44 healthy subjects with 35 having a follow-up at years 1 and 2. FC was estimated from 256-channel-EEG by the phase-lag-index (PLI) and weighted PLI (wPLI) during an eyes-closed resting state condition. PLI quantifies the asymmetry of the distribution of instantaneous phase differences of two time-series and signifies, whether a consistent non-zero phase lag exists. WPLI extends the PLI by additionally accounting for the magnitude of the phase difference. Signal-space global and regional PLI/wPLI and weighted first-order graph measures, i.e. normalized clustering coefficient (gamma), normalized average path length (lambda), and the small-world-index (SWI) were calculated for theta-, alpha1-, alpha2- and beta-frequency bands. Inter-subject variability of global PLI was low to moderate over frequency bands (0.12<CoV<0.28), higher for wPLI (0.25<CoV<0.55) and very low for gamma, lambda and SWI (CoV<0.048). TRT was good to excellent for global PLI/wPLI (0.68<ICC<0.80), regional PLI/wPLI (0.58<ICC<0.77), and fair to good for graph measures (0.32<ICC<0.73) except wPLI-based lambda in alpha1 (ICC = 0.12). Inter-electrode distance correlated very weakly with inter-electrode PLI (-0.06<rho<0) and weakly with inter-electrode wPLI (-0.22<rho<-0.18). Global PLI/wPLI and topographic connectivity patterns differed between frequency bands, and all individual networks showed a small-world-configuration. PLI/wPLI based network characterization derived from high-resolution EEG has apparently good reliability, which is one important requirement for longitudinal studies exploring the effects of chronic brain diseases over several years.
authors.affiliation: Department of Neurology, Hospital of the University of Basel, Basel, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Hardmeier
authors.affiliation: Department of Neurology, Hospital of the University of Basel, Basel, Switzerland.
authors.forename: Florian
authors.initials: F
authors.lastname: Hatz
authors.affiliation: Department of Neurology, Hospital of the University of Basel, Basel, Switzerland; Swiss Tropical and Public Health Institute, University of Basel, Basel, Switzerland.
authors.forename: Habib
authors.initials: H
authors.lastname: Bousleiman
authors.affiliation: Swiss Tropical and Public Health Institute, University of Basel, Basel, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Schindler
authors.affiliation: Department of Clinical Neurophysiology and Magnetoencephalography, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Cornelis Jan
authors.initials: CJ
authors.lastname: Stam
authors.affiliation: Department of Neurology, Hospital of the University of Basel, Basel, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Fuhr
mesh_terms: D000328:Adult; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009415:Nerve Net / Q000502:physiology*; D015203:Reproducibility of Results; D013997:Time Factors; D055815:Young Adult