P372 Inference of intra and inter hippocampal directed causal relationships based on foramen ovale recordings

Abstract

Objectives The traditional method for seizure onset zone determination is based on the temporal order in the appearance of pathological waveforms. However, this method assumes, that the well observable pathological waveforms are really the first signs of those processes, which play important role in the seizure generation. Our objective is to develop and apply new mathematical methods to identify the causal relations between brain areas during epileptic activity. Methods The Convergent Cross Mapping method of Sugihara was modified to reveal temporal dynamics of causal connections, and applied to current source density distribution data calculated from multichannel foramen ovale electrode recordings. Results The causality analysis revealed directed connections between the two hippocampi and specific changes in intra and inter-hippocampal connections comparing interictal and ictal periods: intrahippocampal connections get stronger and spread away spatially, while inter-hippocampal connections show more complex temporal development patterns during the seizures: the functional connectivity decreases during initial phase of the seizures in some cases, while increases during the full blown seizures. Onset of the tonic phases accompanied by temporal increase of the causal connections between the two hippocampi as well. Conclusions New mathematical analysis method, such as Convergent Cross Mapping raise the possibility of objective determination the causal relationships at the initiation of the seizure, without specific assumptions about the waveforms. Significance Causality analysis can support more precise identification of seizure onset zones, thus results in better surgical outcome.