Abstracts

Rationale: The delta (0.5-3 hz), theta (3-7 hz), alpha (8.5 -13 hz) and beta (15-30 hz)range human electroencephalographic (EEG) signals are known to be the basic synchronizing rhythms across the brain regions, and are known to play a role in effective communication across brain regions. In this study, we examined the changes in this synchronization between the scalp EEG and the hippocampal signals from normal and the epileptic side in patients undergoing intracranial depth electrode recordings as part of the epilepsy surgery evaluation. Methods: Methods: Scalp EEG and intracranial EEG simultaneously recorded from five epilepsy patients undergoing scalp and intracranial EEG monitoring for the epileptogenic zone localization were used in this study. Five, 10 second recording epochs obtained in resting alert state from each of the patients were used for this purpose. Periods of increased artifacts were avoided by visual inspection. The data was initially recorded in Nicvue system (Natus Medical inc.) and exported in the .edf format and was imported to Matlab (Mathworks) for analysis. The coherence between the signals from the scalp EEG and the 6 depth electrodes located on either hippocampi was analyzed for estimation of the synchrony. Results: Results: There was a significant reduction in the synchrony in alpha and theta range between the scalp EEG and the hippocampal signals from the side of epileptic focus. There was a mild increase in the synchrony between these signals in the beta range on the side of epilepsy. No significant change was noted in the delta range compared to the normal side Conclusions: Conclusion: Synchrony across brain regions in the EEG rhythms is suggested to be important in the effective communication across the brain regions. The significant reduction in the coherence between scalp EEG and the depth electrodes in the epileptic side suggest that there is a breakdown in the effective communication between the cortical processing and the hippocampus. Further studies are needed in exploring the significance of these results on the neuropsychological functions of the patient. Funding: University of Florida internal research support