Abstracts

Rationale: Cortico-cortical evoked potentials (CCEPs) are responses elicited by single pulse electrical stimulation of intracranial electrodes. Stimulation of pairs of SEEG contacts can be employed to evoke measurable signals in both distant and nearby regions as a means of epileptic network analysis. Here we investigate and visualize the strength of connectivity per stimulation via a combination of root mean square (RMS) and statistical significance via a permutation test. Methods: We reviewed 30 patients with medically intractable epilepsy who were implanted with depth electrodes and subsequently underwent CCEPs stimulation as a part of their clinical evaluation prior to surgical intervention. All patients were classified as Engel Class IA, completely seizure free since surgery for at least 6 months. We illustrated the degree of connectivity between each stimulation pair and the other contacts within the array by first coloring the averaged responses according to RMS value, and separately by applying a permutation test to the early (10-60ms), late (60-250ms), and very late (250-600ms) periods of the response in order to identify periods of statistical significance. Areas within the surgical resection of each patient were then retroactively compared to these results. Results: The resulting visualizations identify regions of highest response in both near and distant connected regions. The permuted scores give insight into the time segments of significance on a per contact level. The results showed that higher thresholds for significance tend to primarily exclude very late responses. Conclusions: The CCEPs RMS and significance measures provide separate means of identifying periods of interest in averaged CCEPs data. We observe that contacts with relatively low RMS response in comparison to the largest observed responses may still test as significant. Funding: Research reported in this publication was supported in part by the National Institutes of Health under awards R01NS089212 and U01EB023820.