Abstracts

Rationale: Understanding the electrophysiological milieu in which seizures develop is crucial to effective treatment and prevention. During sleep, epileptic seizures are primarily seen in slow wave sleep, in which delta frequency activity (reflecting neuronal synchrony) predominates. During wakefulness, increases in theta power correlate with drowsiness, decreased vigilance, and neuronal synchronization. We explored the hypothesis that epileptic seizures during wakefulness occur during periods of increased synchronization, as reflected by increases in theta power in the EEG. Methods: Continuous scalp EEG recordings were collected from patients with temporal lobe epilepsy who were admitted to the Epilepsy Monitoring Unit for presurgical evaluation or seizure classification. Segments of EEG containing artifact were manually rejected. Theta and delta power were calculated using Standard Fourier Transformation for channels C3 and C4. Results: Theta power increased during afternoon and evening hours. A preliminary analysis of seizure occurrence relative to theta power was performed in 3 patients. In two patients, there was an increase in theta power prior to a seizure. Postictally, theta power remained elevated for minutes to hours. Representative examples will be presented. Conclusions: Circadian variability in theta power can be demonstrated in the waking EEGs of patients in the Epilepsy Monitoring Unit. Theta power, reflecting level of vigilance and arousal, is increased prior to some epileptic seizures. Increases in theta power may reflect increasing neuronal synchrony, and may in part account for timing of epileptic seizures. Further analysis of larger numbers of patients and seizures will be needed to confirm this hypothesis.