Abstracts

Rationale: During epileptogenesis, neural networks are formed that allow the propagation of electrical signals such that seizures can result. The process of epileptogenesis is poorly understood. It is our hypothesis that further insight into this process can be obtained by looking at the change in ictal EEG signal as more frequent seizures develop. Specifically, we consider the interspike interval at a fixed point during the seizure.Methods: Rats (n=5) were implanted with 3-channel radiotelemetry units. They were then treated with sufficient kainate to cause at least 10 convulsive seizures for 3 consecutive hours. For a 5 month period following implantation, these rats were monitored using video EEG. The EEG was processed using routines written in Visual Basic 6.0 (DClamp software) and reviewed by experts to locate seizures within the record. During the course of epileptogenesis, the rats were observed to have a sigmoidal rise in seizure frequency. Therefore, three phases of epileptogenesis were identified: (1) a slow increase with a low frequency of occurrence, (2) a rapid increase in occurrence, and, (3) a plateau phase. During each of these phases, five seizures were investigated. The sentinel spike, present for all seizures considered, was used as a reference. Spike frequency was determined 20 seconds following this spike by computing the time for 50 spikes to occur. The change in ictal EEG frequency during these phases is the subject of this abstract. Results: There is a significant change in the frequency of the ictal EEG. In the five rats studied, it increases significantly from the first phase of epileptogenesis (low seizure frequency) to the second phase (time of rapid frequency rise. Further, there is an increase in complexity of the ictal EEG with a greater number of spikes occurring on sharp waves.Conclusions: The ictal EEG shows progression during the process of epileptogenesis. This progression may be a result of a modification of the neural networks. Further study of this progression may lead to a greater understanding of epileptogenesis.