Abstracts

Rationale: There are conflicting reports regarding epileptic networks and whether they are common amongst patients. Some intracranial EEG studies claim that networks can be generalized across patients.1,2,3 Other studies, mostly those using functional MRI (fMRI), have demonstrated variability and distinct patterns at a single patient level.4,7,9,10. To address these conflicting reports, we analyzed intracranial EEG onset and spread patterns and will compare these regions to those epileptic network regions identified by resting state fMRI. Improved knowledge of epileptic networks, and identifying whether fMRI can be used to delineate these non-invasively, will advance planning of intracranial EEG studies. Methods: All pediatric and adult patients who underwent intracranial electrode study at Yale New Haven Hospital between January 1, 2013, and March 31, 2019, were evaluated. Patients that did not have seizures captured during their intracranial EEG monitoring or who had hemispheric onset were excluded. Ictal EEG onset and propagation by anatomical region was determined by visual analysis. Ictal onset was defined as sustained low voltage fast activity > 0.5 seconds. Ictal spread was defined as the rhythm seen at onset or its evolution, that was present in another anatomical region. Slower rhythms such as periodic spiking or rhythmic slowing were excluded from ictal onset patterns and rhythmic alpha, theta and delta slowing were excluded as seizure spread patterns. Results: A total of 65 intracranial EEG studies were carried out in 62 patients between 2013 and 2019, including patients with mesial temporal, lateral temporal, frontal, parietal and occipital seizure onsets. Thirty patients were male. Three patients were pediatric. Six patients were excluded as their ictal onset was hemispheric, or because they did not have seizures during their study. We found that seizure onsets were distinct to and reproducible within individual patients. Commonalities in epileptic networks between patients with similar regions of seizure onset were not identified. For instance, patients with seizure onsets within the frontal lobe had a stereotyped onset and spread pattern between seizures, but this varied from patient to patient. Conclusions: There is conflicting information in the literature regarding the generalizability of epileptic networks amongst patients. We demonstrate that epileptic networks on intracranial EEG are stereotyped within but not amongst patients, even when seizures arise from the same regions. Further correlation with fMRI connectivity will allow for targeted intracranial EEG study design and better understanding of the network as a treatment target. Funding: No funding