Abstracts

Rationale: High frequency (HF) activity represents a potential biomarker of the epileptogenic zone in epilepsy patients. Studies have shown that HF activity was strongly correlated with the seizure onset zone (SOZ) and the follow-up outcomes of epilepsy surgery. Scalp EEG is a noninvasive recording of electrophysiological brain activity and it has been widely used to help study functioning brain activity and pathological brain abnormalities. The aim of this study is to image the sources of HF activity using high-density scalp EEG and investigate the feasibility of noninvasive localization of the epileptogenic zone.Methods: Both computer simulation and patient data analysis were performed to image the sources of HF activity from noninvasive scalp EEG recordings. The computer simulations were tested by simulating dipolar sources with HF source activity. The pre-operative scalp EEG of patients was recorded from 76 electrodes placed according to the modified international 10-10 montage. The HF activity was identified from scalp recordings after high-pass filtering the data and the EEG segments with HF activity were concatenated together to form repetitive HF activity. Independent component analysis was utilized to extract the components corresponding to the HF activity. Noninvasive EEG source imaging using realistic geometric boundary element head modeling was then applied to image the sources of the pathological HF brain activity.Results: A series of computer simulations were tested and the results showed that the simulated high frequency dipolar sources can be correctly reconstructed from the noninvasive imaging approach. Five medically intractable focal epilepsy patients were also studied and the estimated sources were evaluated by comparing with the surgical resection or intracranial recordings of the patients. Four patients had surgical treatment and the locations of maximum estimated HF sources were concordant with the surgically resected regions of the patients. All the four patients had seizure-free outcome with at least one-year follow up after the surgery. Two patients had intracranial recordings available and the imaged HF sources were co-localized with the SOZ marked on the intracranial recording electrodes.Conclusions: We proposed a method to image the high frequency brain activity from scalp EEG of epilepsy patients. The results suggest that source imaging from the scalp HF activity could help to localize the SOZ and provide a novel noninvasive way of studying the epileptic brain. This study also indicates the potential application of studying HF activity in the pre-surgical planning of medically intractable epilepsy patients. (This work was supported in part by NIH EB006433, EB007920, and a grant from Minnesota Partnership on Biotechnology and Medical Genomics. Y. Lu was supported in part by the Doctoral Dissertation Fellowship of the University of Minnesota.)