Brain Topography

, Volume 26, Issue 2, pp 212–228 | Cite as

Influence of a Silastic ECoG Grid on EEG/ECoG Based Source Analysis

  • Benjamin Lanfer
  • Christian Röer
  • Michael Scherg
  • Stefan Rampp
  • Christoph Kellinghaus
  • Carsten Wolters
Original Paper


The simultaneous evaluation of the local electrocorticogram (ECoG) and the more broadly distributed electroencephalogram (EEG) from humans undergoing evaluation for epilepsy surgery has been shown to further the understanding of how pathologies give rise to spontaneous seizures. However, a well-known problem is that the disruption of the conducting properties of the brain coverings can render simultaneous scalp and intracranial recordings unrepresentative of the habitual EEG. The ECoG electrodes for measuring the potential on the surface of the cortex are commonly embedded into one or more sheets of a silastic material. These highly resistive silastic sheets influence the volume conduction and might therefore also influence the scalp EEG and ECoG measurements. We carried out a computer simulation study to examine how the scalp EEG and the ECoG, as well as the source reconstruction therefrom, employing equivalent current dipole estimation methods, are affected by the insulating ECoG grids. The finite element method with high quality tetrahedral meshes, generated using a constrained Delaunay tetrahedralization meshing approach, was used to model the volume conductor that incorporates the very thin ECoG sheets. It is shown that the insulating silastic substrate of the ECoG grids can have a large impact on the scalp potential and on source reconstruction from scalp EEG data measured in the presence of the grids. The reconstruction errors are characterized with regard to the location of the source in the brain and the mislocalization tendency. In addition, we found a non-negligible influence of the insulating grids on ECoG based source analysis. We conclude, that the thin insulating ECoG sheets should be taken into account, when performing source analysis of simultaneously measured ECoG and scalp EEG data.


Finite element method FEM ECoG Presurgical epilepsy diagnosis Simultaneous EEG Constrained Delaunay tetrahedralization Dipole fitting method 



This work was supported by the Deutsche Forschungsgemeinschaft (WO1425/2-1, STE380/14-1). The authors would like to thank Chris Johnson, Tolga Tasdizen and Darby J. Van Uitert from the SCI Institute, University of Utah, Salt Lake City, USA, Gregory A. Worrell from the Department of Neurology and Division of Epilepsy, Mayo Clinic, Rochester, Minnesota, USA, and Scott Makeig from the Swartz Center for Computational Neuroscience, University of California San Diego, USA, for providing the necessary data for model construction and for their valuable help and the fruitful discussions with regard to this study. We would also like to thank the anonymous reviewers for their helpful critics and comments that significantly improved our manuscript.


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Copyright information

© Springer Science+Business Media, LLC 2012

Authors and Affiliations

  • Benjamin Lanfer
    • 1
  • Christian Röer
    • 1
  • Michael Scherg
    • 2
  • Stefan Rampp
    • 3
  • Christoph Kellinghaus
    • 4
  • Carsten Wolters
    • 1
  1. 1.Institute for Biomagnetism and BiosignalanalysisWestfälische Wilhelms-Universität MünsterMünsterGermany
  2. 2.BESA GmbHGräfelfingGermany
  3. 3.Department of Neurology, Epilepsy CenterUniversity Hospital ErlangenErlangenGermany
  4. 4.Department of NeurologyKlinikum OsnabrückOsnabrückGermany

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