Note: This is a virtual presentation. Here is the link for where the presentation will be taking place.
Title: Transfer function models of cortico-cortical evoked potentials for the localization of seizures in medically refractory epilepsy patients
Abstract: Surgical resection of the seizure onset zone (SOZ) could potentially lead to seizure-freedom in medically refractory epilepsy (MRE) patients. However, localizing the SOZ is a time consuming, subjective process involving visual inspection of intracranial electroencephalographic (iEEG) recordings captured during invasive passive patient monitoring. Cortical stimulation is currently performed on patients undergoing invasive EEG monitoring for the main purpose of mapping functional brain networks such as language and motor networks. We hypothesized that the evoked responses from single pulse electrical stimulation (SPES) can be used to localize the SOZ as they may express the natural frequencies and connectivity of the iEEG network. We constructed patient specific transfer function models from evoked responses recorded from 22 MRE patients that underwent SPES evaluation and iEEG monitoring. We then computed the frequency and connectivity dependent “peak gain” of the system, as measured by the H_∞ norm from systems theory, and the corresponding “floor gain,” which is the gain at which the H_∞ dipped 3dB below the DC gain. In cases for which clinicians had high confidence in localizing the SOZ, the highest peak gain transfer functions with the smallest “floor gains” corresponded to when the clinically annotated SOZ and early spread regions were stimulated. In more complex cases, there was a large spread of the peak gains when the clinically annotated SOZ was stimulated. Interestingly for patients who had successful surgeries, our ratio of peak-to-floor (PF) gains, agreed with clinical localization, no matter the complexity of the case. For patients with failed surgeries, the PF ratio did not match clinical annotations. Our findings suggest that transfer function gains and their corresponding frequency responses computed from SPES evoked responses may improve SOZ localization and thus surgical outcomes.
Sridevi V. Sarma, Department of Biomedical Engineering
Joon Y. Kang, Department of Neurology
Archana Venkataraman, Department of Electrical and Computer Engineering
Nathan E. Crone, Department of Neurology