Original Paper

Brain Topography

, Volume 26, Issue 2, pp 212-228

First online:

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

  • Benjamin LanferAffiliated withInstitute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster Email author 
  • , Christian RöerAffiliated withInstitute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster
  • , Michael SchergAffiliated withBESA GmbH
  • , Stefan RamppAffiliated withDepartment of Neurology, Epilepsy Center, University Hospital Erlangen
  • , Christoph KellinghausAffiliated withDepartment of Neurology, Klinikum Osnabrück
  • , Carsten WoltersAffiliated withInstitute for Biomagnetism and Biosignalanalysis, Westfälische Wilhelms-Universität Münster

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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