  Predicting post-operative seizure freedom using functional correlation
networks derived from interictal intracranial EEG has shown some success.
However, there are important challenges to consider. 1: electrodes physically
closer to each other naturally tend to be more correlated causing a spatial
bias. 2: implantation location and number of electrodes differ between
patients, making cross-subject comparisons difficult. 3: functional correlation
networks can vary over time but are currently assumed as static. In this study
we address these three substantial challenges using intracranial EEG data from
55 patients with intractable focal epilepsy. Patients additionally underwent
preoperative MR imaging, intra-operative CT, and post-operative MRI allowing
accurate localisation of electrodes and delineation of removed tissue. We show
that normalising for spatial proximity between nearby electrodes improves
prediction of post-surgery seizure outcomes. Moreover, patients with more
extensive electrode coverage were more likely to have their outcome predicted
correctly (ROC-AUC >0.9, p<<0.05), but not necessarily more likely to have a
better outcome. Finally, our predictions are robust regardless of the time
segment. Future studies should account for the spatial proximity of electrodes
in functional network construction to improve prediction of post-surgical
seizure outcomes. Greater coverage of both removed and spared tissue allows for
predictions with higher accuracy.
