Interictal Epileptic Spiking during Sleep and Wakefulness in Mesial Temporal Lobe Epilepsy: A Comparative Study of Scalp and Foramen Ovale Electrodes

PURPOSE: To assess distribution of temporal lobe spikes across different states of sleep and wakefulness in simultaneous scalp and foramen ovale (Fo) recordings. METHODS: The study included 12 patients with mesial temporal lobe epilepsy (MTLE). As part of their presurgical evaluation, patients underwent long-term video-EEG monitoring with combined scalp and foramen ovale electrodes (FoEs). In addition to traditional sleep scoring, waking was subdivided into eyes-opened and eyes-closed states, and rapid-eye-movement (REM) sleep was divided into phasic and tonic states. Spike counts were carried out visually for scalp and FoEs, and spiking rates were determined for each state. A ratio between FoE and scalp spiking rates also was calculated for each state. RESULTS: Scalp spiking showed a significant increase during NREM3,4, whereas FoE spiking increased during NREM2. The scalp/FoE ratio significantly increased during NREM3,4. A significant difference in spiking rate also was found between phasic and tonic REM states as well as between waking with eyes opened and closed in FoE recordings. CONCLUSIONS: Our data provide evidence of a discrepancy in spike distribution across different states of sleep and waking monitored by scalp and FoE recordings. We suggest that these discrepancies may reflect differences in archicortical and neocortical spike synchronization.