An electrographic analysis of the synchronous discharge patterns of GEPR-9s generalized seizures

Abstract

Previous results from our Laboratory have shown a synchronous discharge pattern (less than 1 ms apart) in monopolar recordings from electrodes placed in the cortex, inferior colliculus, and medulla of seizing GEPR-9s. However, the wave morphology of the ictal EEG is quite different for electrodes placed in different anatomical structures. These results lead us to hypothesize that wave morphology was indicative of neural circuitry involved in the GEPR9 seizure and that volume conduction was accounting for synchronous epileptiform EEG pattern. We decided to approach the problem by using a set of two experiments. Experiment 1: Perform a complete precollicular transection in GEPR-9s before inducing seizure in order to observe changes in EEG morphology after forebrain circuitry removal. Experiment 2: A novel methodological approach using a three-dimensional bipolar array enabled the reconstruction of a vector indicative of to which direction is voltage increasing. Such time-varying vector is indicative of the source direction of the high-amplitude epileptiform EEG signal. By placing such an array of electrodes, used to record the 3 bipolar EEGs, in the forebrain, midbrain, and hindbrain, we were able to use a simple intersection method to infer source localization. Our results suggest that the slow wave component of the GEPR9 epileptiform ictal EEG pattern is associated with a midbrain–forebrain circuit while the spike component is associated with a midbrain–hindbrain substrate. These results are supported by experiment 1 in which only the spike component of EEG remained after the precollicular transection.