Functional connectivity of interictal iEEG and the connectivity of high-frequency components in epilepsy

Epilepsy is a disease of altered brain networks. The monitoring and analysis of functional connectivity and network properties can yield a better understanding of the underlying pathology, and improve treatment and prognostics. Identifying hub network regions has been in the spotlight of network neuroscience studies in epilepsy, as monitoring these areas can provide a perspective of the network’s local and global organization. Functional network analysis can be especially useful in Medically Refractory Epilepsy (MRE) cases, where surgical intervention is necessary for seizure relief. In such cases, the delineation of the epileptogenic zone, which represents the surgical target, is a very crucial procedure, which can be enhanced by understanding the underlying network topology. In this review, we will explore the expanding body of literature on functional connectivity of interictal intracranial electrophysiologic data, focusing on the interpretation of network properties, global or local, for identifying epileptogenic tissue. We will emphasize functional connectivity at high frequencies (above 80 Hz), as during the past decade High-Frequency Oscillations (HFOs) have been increasingly recognized as a promising biomarker of the seizure onset zone. We will conclude the review with an assessment of current limitations and a discussion of future research paths.