Abstracts

Rationale: In recent decades there have been many fundamental studies which have furthered our understanding of the mechanisms underlying epileptic activity and the resulting proposed biomarkers of epileptogenic regions may help to locate seizure onset zones. Surprisingly, however, we are still remarkable ignorant of how it is that a seizure starts. Unraveling the pathomechanisms that underlie the seizures initiation is challenging, and the complex correlations between different recorded frequency bands on EEGs are still not fully understood. In this study we aimed to investigate the relationship between different oscillations, and to test the hypothesis that a specific sequence of neuronal activity involving an interplay of high and low frequency oscillations is necessary for the initiation of a seizures. Such a sequence of events could serve as another biomarker of the seizure onset zone. Methods: In order to identify the characteristics of seizure initiation, we analyzed the seizures recorded from patients who underwent presurgical evaluation with intracranial electrodes. Patients were classified based on the site of their seizure generation. We primarily performed analysis on the seizures recorded from patients diagnosed with unilateral temporal lobe epilepsy. Local field potential recordings from these patients were carefully monitored to identify the changes in the low and high frequency bands in the seizure onset zones and the regions of secondary spread. Wavelet analysis was performed in an attempt to further elucidate the features of different frequency bands at the initiation of seizures in these regions. Results: Seizures recorded from 5 patients diagnosed with unilateral temporal lobe epilepsy were analyzed. Detailed analysis of the regions of interest (the seizure onset zone(s) and the regions of secondary spread) revealed that in the seizure onset zone(s), at the start of the seizure, there is an increase in the power of infraslow activity co-occurring with an increase in the power in the higher frequency band in 78% (21/27) of the seizures. The regions of secondary spread, however, showed lower power in these frequency bands. These findings suggest that accounting for activity in these widely different frequency bands and their correlations may provide additional information about how seizures start and how the seizure onset zone may be characterized. Conclusions: This analysis demonstrates the possibility of a correlation between low frequency and high frequency components at the start of the seizures. Changes in the pattern of different frequency oscillations occurring at seizure onset can reveal more information about the neuronal involvement underlying ictogenesis and the progression of the seizure. With the help of these analyses we may be able to pinpoint the involvement of different neuronal elements and networks in the generation of seizure onset. Funding: N/A