From ECoG near fields to EEG and MEG far fields

ECoG source reconstruction is a relatively new field as compared to the well-established surface EEG or MEG source reconstruction techniques. The exact determination of the ECoG electrode positions requires post-implantation CT images. The cortical structures, which are needed for volume conductor modeling, source space constraints, and visualization purposes, are derived from pre-implantation MR images.Since there is increasing interest in mapping and source reconstruction from ECoG grid data and comparison to EEG and MEG evaluations of epileptic patients, we computed potential and field distributions and performed source reconstructions from measured and simulated ECoG, EEG, and MEG data. We used realistically shaped BEM volume conductor models derived from individual MR images with dipolar as well as cortically constrained current density source models.