Abstracts

Rationale: We investigated preictal trends in change of broadband peri-ictal electrocorticographic activities determined automatically in 23 medically intractable epilepsy patients. Because gamma and ripples may signify synchronized inhibitory activities, there may exist preictal decrements.Methods: Included were 21 patients with medically intractable epilepsy who underwent chronic electrocorticography. There were 83 seizures. Mean age of patients were 28 years old (16-54). Investigated peri-ictal periods were -30 s to 15 s from the ictal onset. Prominent electrocorticographic activities were extracted in the wavelet transformed domain in 28 scales from 600Hz to 0.07Hz separately. Activities were detected by amplitude and duration thresholdings. Then we checked correlation between preictal time and amplitudes of detected activities. Thresholds were automatically optimized with the genetic algorithm to find out significant trend with the lowest p-value.Results: In high-frequency bands > 80 Hz, about 30% of patients had significant decreasing trend of high-frequency activities. However, these decreasing trends were not found in the other bands and data gap from harmonic artifacts at 200 Hz. 6 patients with this trend had generally good seizure outcomes, ILAE 1 or 2 except one patient. This phenomenon was usually found in 2nd or later seizures during invasive monitoring period. Locations may be within seizure onset zones or outside of seizure onset zones. This phenomenon was found in neocortical and lateral temporal lobes.Conclusions: Preictal decrement of high-frequency activities may exist. They may be related to inhibitory activities which may be preictally exhausted. This may signify partially preserved inhibitory network related with generally good seizure outcome. These acitivities may be more easily exhausted after the first seizure during invasive monitoring.