Slow Electrographic Components at the Pre- and Postictal Transition at the Level of iEEG, LFP, and Single Units

Abstract-Text (inklusive Referenzen und Bildunterschriften)

Slow (DC) components in the electrographic seizure have been described at both seizure onset and offset, but their mechanisms and roles are still a matter of debate. DC-shifts have been proposed as potential biomarkers of seizure onset zone localization and slow-wave components have been described as postictal phenomena, such as spreading depolarization. Combined depth-electrode and microwire recordings in epilepsy patients provide a clear means for testing the involvement of these slow wave components in ictal events. Here we provide evidence of a DC-shift phenomenon detected at the pre- and postictal transition in epilepsy patients with implanted Behnke-Fried depth electrodes.

Data from 12 seizures (4 patients with medial temporal lobe epilepsy) were recorded using bilaterally implanted Behnke-Fried depth electrodes with 8 high-impedance platinum-iridium microwires protruding a few millimeters from their tips, allowing simultaneous recording of the local field potential (LFP) and unit data. We observed a DC-shift component recorded in hippocampal regions, the entorhinal cortex and the piriform cortex that was detected in 82% of the depth electrodes in which an ictal event was also noted. When observed at the ictal onset, the slow-wave component was only present in the LFP traces from microwires, and not the iEEG. Similarly, 15% (10 out of 144 channel recordings) of the LFP traces showed a high-amplitude DC-shift at seizure termination. Analysis in the frequency domain suggests a postictal power increase in the 0-1 Hz range when compared to baseline.

Our results show that slow wave electrographic components can be observed in human epilepsy patients using depth-electrode recordings. Additionally, these DC shifts have the potential to shed light upon the mechanisms involved in seizure initiation and termination. Moreover, we propose that the presence of an electrographic feature at the ictal onset, that is exclusively observable in the LFP scale, could provide a technical advantage for the use of microwires in clinical determination of the seizure onset zone and could lead to a mechanistic understanding of the ictal transition phase in human seizures.