Constructing surrogate data to control for artifacts of volume conduction for functional connectivity measures

Abstract

Event Abstract Back to Event Constructing surrogate data to control for artifacts of volume conduction for functional connectivity measures Forooz S. Avarvand1*, Arne Ewald1, Andreas Ziehe1 and Guido Nolte1 1 Fraunhofer Institute FIRST IDA, Germany The major problem in examining interactions between sources of brain activity from MEG and EEG data are the ‘artifacts of volume conduction’ denoting the fact that the sensors measure a largely unknown superposition of brain activities. In this work we suggest a method to test for artifacts of volume conductions. The test is absolutely general: it is applicable to both linear and nonlinear methods and both on the sensor and source level. The idea of the method is to construct surrogate data which are statistically as close as possible to the original data but which are a superposition of independent sources. As a first step we decompose the data via Independent Component Analysis (ICA) resulting in signals which are as independent as possible. In a second step we destroy any remaining dependencies by shifting the n.th signal by a time (n-1)*T where T must be substantially larger than any autocorrelation time. Finally, these shifted signals are mixed again into sensors using the mixing matrix found by the ICA algorithm. Any interaction measure can now be calculated both for the original and the surrogate data. If a specific effect can be seen in both data sets we consider this effect as insufficient evidence for an observed brain interaction. We applied this method to real and imaginary parts of coherency (real EEG data), 1:2 phase locking (real EEG data) and Granger causality (simulated data). We found that the real part of coherency is almost perfectly consistent with mixtures of independent sources while the imaginary part cannot be explained with the surrogate data at all. Results for phase locking can only be explained partly by volume conductions. For true directional interactions Granger causality is attenuated but not removed in the surrogate data as compared to the original data. Conference: Biomag 2010 - 17th International Conference on Biomagnetism , Dubrovnik, Croatia, 28 Mar - 1 Apr, 2010. Presentation Type: Poster Presentation Topic: Signal proccessing Citation: Avarvand FS, Ewald A, Ziehe A and Nolte G (2010). Constructing surrogate data to control for artifacts of volume conduction for functional connectivity measures. Front. Neurosci. Conference Abstract: Biomag 2010 - 17th International Conference on Biomagnetism . doi: 10.3389/conf.fnins.2010.06.00130 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 24 Mar 2010; Published Online: 24 Mar 2010. * Correspondence: Forooz S Avarvand, Fraunhofer Institute FIRST IDA, Berlin, Germany, forooz.shahbazi@first.fraunhofer.de Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Forooz S Avarvand Arne Ewald Andreas Ziehe Guido Nolte Google Forooz S Avarvand Arne Ewald Andreas Ziehe Guido Nolte Google Scholar Forooz S Avarvand Arne Ewald Andreas Ziehe Guido Nolte PubMed Forooz S Avarvand Arne Ewald Andreas Ziehe Guido Nolte Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.