Abteilung Prächirurgische Epilepsiediagnostik – EpilepsiezentrumKlinik für Neurochirurgie

Epileptic network characterization based on resting state interictal high-density EEG

The assessment of structural and functional networks applied in neurologic patients is used increasingly to understand the neuronal circuit dysfunction underlying epilepsy. Multiple studies have revealed disease-specific pattern of decreased and increased connectivity in the regions where seizures are generated. In this context, high density electroencephalography (HD-EEG), with 256 electrodes, offers the opportunity of exploring the network dynamics, allowing better spatial resolutions than conventional EEG.

The aims of this project is to validate a novel strategy for non-invasive characterization of the epileptic network based on analysis of Resting State directional connectivity using advanced signal processing of High Density EEG data. This approach is based on the premise that the epileptic network has abnormal information out/inflow and from neighboring neural structures during the recordings without any interictal or ictal abnormality.

1. Epileptic patients are measured at rest with eyes closed during 10 Minutes. The analysis comprises different steps:
2. The first step is projecting interactions between the signals at the electrodes to the structures towards anatomical brain structures by electric source imaging.
3. Directional connectivity between the brain structures is estimated by partial directed coherence.
4. Inflow and outflow are estimated for the single anatomical regions in standard EEG frequency bands.
5. A set of graph measures to characterize local and global properties of the networks are determined.

Finally, the results of the complete analysis are compared to a comprehensive set of electrophysiological and imaging results obtained during the pre-surgical work up of each patient (visual analysis of intracranial EEG, structural imaging and source localization based on HD-EEG).