Effective connectivity analysis of iEEG and accurate localization of the epileptogenic focus at the onset of operculo-insular seizures

Recognition of insular epilepsy may sometimes be challenging due to the rapid speed at which insular seizures can spread throughout the cortex via extensive connections to surrounding cortices. The spectrum weighted adaptive directed transfer function, a multivariate causality-based effective connectivity measure, was applied to intracranial electroencephalography recordings to identify generators of seizure activity. A non-parametric test based on surrogate data testing was used to validate statistical significance of causal relations. Outflow and inflow of seizure activity were extracted from the computed transfer matrix. Recorded data of 21 seizures from seven patients were analyzed including five who were rendered seizure-free after operculo-insular resection. Effective connectivity analysis of 7 s following electrical onset confirmed an operculo-insular seizure origin in 5 patients with a good post-operative seizure outcome, and for whom the resected region was sampled by intracranial electroencephalography contacts. Different or additional seizure foci were identified in 2 patients with a bad post-operative seizure outcome. Findings highlight the feasibility of accurate operculo-insular seizure foci localization based on quantitative approaches.