Ghost interactions in MEG/EEG source space: A note of caution on inter-areal coupling measures


When combined with source modeling, magneto- (MEG) and electroencephalography (EEG) can be used to study long-range interactions among cortical processes non-invasively. Estimation of such inter-areal connectivity is nevertheless hindered by instantaneous field spread and volume conduction, which artificially introduce linear correlations and impair source separability in cortical current estimates. To overcome the inflating effects of linear source mixing inherent to standard interaction measures, alternative phase- and amplitude-correlation based connectivity measures, such as imaginary coherence and orthogonalized amplitude correlation have been proposed. Being by definition insensitive to zero-lag correlations, these techniques have become increasingly popular in the identification of correlations that cannot be attributed to field spread or volume conduction. We show here, however, that while these measures are immune to the direct effects of linear mixing, they may still reveal large numbers of spurious false positive connections through field spread in the vicinity of true interactions. This fundamental problem affects both region-of-interest-based analyses and all-to-all connectome mappings. Most importantly, beyond defining and illustrating the problem of spurious, or “ghost” interactions, we provide a rigorous quantification of this effect through extensive simulations. Additionally, we further show that signal mixing also significantly limits the separability of neuronal phase and amplitude correlations. We conclude that spurious correlations must be carefully considered in connectivity analyses in MEG/EEG source space even when using measures that are immune to zero-lag correlations.

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Divisions: College of Engineering & Physical Sciences > School of Engineering and Technology > Mechanical, Biomedical & Design
College of Engineering & Physical Sciences > School of Engineering and Technology
Additional Information: © 2018 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY-NC-ND license ( Funding information: This study was supported by the Academy of Finland Grants 253130 and 256472 to J.M.P. and 1126967 to S.P., and by the Helsinki University Research Funds. MJB was funded by a Medical Research Council New Investigator Research Grant (MR/M006301/1). KJ acknowledges funding from the Canada Research Chairs program, IVADO (UdeM), NSERC Discovery Grant (RGPIN-2015-04854) and FRQNT New Researcher Grant (RQT00121). JMS was supported by the Dutch Organisation for Scientific Research (NWO-VIDI grant 864.14.011).
Uncontrolled Keywords: Connectivity,MEG,EEG,Phase synchrony,Orthogonalized amplitude correlation,Signal mixing,Secondary leakage
Publication ISSN: 1095-9572
Last Modified: 22 Feb 2024 08:14
Date Deposited: 14 Jun 2023 08:50
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Related URLs: https://www.sci ... 1290?via%3Dihub (Publisher URL)
PURE Output Type: Article
Published Date: 2018-06
Published Online Date: 2018-02-22
Accepted Date: 2018-02-16
Authors: Palva, JM
Wang, S. H.
Palva, S
Zhigalov, Alexander (ORCID Profile 0000-0002-3359-5093)
Monto, S
Brookes, Matthew J.
Schoffelen, JM
Jerbi, K

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