Brain connectivity analysis in epilepsy for epileptogenic focus localization

Abnormal brain neural activities lead to abnormality and complexity of brain network connectivity in patients with epilepsy. The purpose of this research is to investigate the characteristics of brain connectivity and to explore more accurate localization methods of the epileptogenic foci in drug-resistant epilepsy. Brain connectivity measures based on synchronization were first evaluated on electroencephalogram data in healthy subjects to find different performance in detecting the synchronization dynamics in the brain network. Spatial and temporal phase-amplitude coupling characteristics between low and high frequency electrocorticogram data were then estimated in patients with temporal lobe epilepsy. The ‘fall-max’ phase-amplitude coupling pattern appeared in the middle period of seizure was suggested as a reliable biomarker of epileptogenic zone, which provides insight into the underlying neural dynamic between low and high frequency neural activities in the epileptic brain network. Effective connectivity and topology characteristics of the brain network were investigated as well in patients with temporal lobe epilepsy by adopting high temporal resolution effective connectivity measure combined with graph metrics on electrocorticogram data, which describes in detail the strength and direction of information transmission. The transient seizure onset effective connectivity network provides more accurate localization of seizure onset zone and epileptogenic zone. In addition, functional connectivity and source localization were studied on electroencephalogram data of a patients with reflex seizure, which provides insights on generation and propagation of epileptic activities, as well as the local and global topology characteristics on cortical level network. Overall, this research examined the performance of various brain connectivity measures by analyzing the functional connectivity and effective connectivity in healthy people and epilepsy patients, and explored more accurate methods for localization of epileptogenic foci. It provides insights into the underlying mechanism of epileptic brain network connectivity and an important reference for the preoperative evaluation of clinical epilepsy surgery, which can improve the localization accuracy of epileptogenic foci and reduce the probability of epileptic seizures. Keywords: brain connectivity, synchronization, epilepsy, epileptogenic focus, localization