Abstract
Studies of interictal EEG functional connectivity in the epileptic brain seek to identify abnormal interactions between brain regions involved in generating seizures, which clinically often is defined by the seizure onset zone (SOZ). However, there is evidence for abnormal connectivity outside the SOZ (NSOZ), and removal of the SOZ doesn’t always result in seizure control, suggesting in some cases, the extent of abnormal connectivity indicates a larger seizure network than the SOZ. To better understand the potential differences in interictal functional connectivity in relation to the seizure network and outcome, we computed event connectivity in the theta (4-8Hz, ThEC), low- (30-55Hz, LGEC) and high-gamma bands (65-95HZ, HGEC) from interictal depth EEG recorded in surgical patients with medication-resistant seizures suspected to begin in the temporal lobe. Analysis finds stronger LGEC and HGEC in SOZ than NSOZ of seizure free (SF) patients (p = 1.10e-9, 0.0217), but no difference in not seizure free (NSF) patients. There was stronger LGEC and HGEC between mesial and lateral temporal SOZ of SF than NSF patients (p = 0.00114, 0.00205), and stronger LGEC and ThEC in NSOZ of NSF than SF patients (p = 0.0089, 0.0111). These results show event connectivity is sensitive to differences in the interactions between regions in SOZ and NSOZ and SF and NSF patients. Patients with differential strengths in event connectivity could represent a well-localized seizure network, whereas an absence of differences could indicate a larger seizure network than the one localized by the SOZ and higher likelihood for seizure recurrence.
Significance Statement
In surgical patients with different forms of temporal lobe epilepsy, interictal event connectivity is a sensitive form of EEG functional connectivity that could be associated with synchrony of neuronal activity between brain regions. Differences in the strength of event connectivity or the lack thereof could indicate the extent of brain regions that are involved in generating seizures, which could be more numerous or larger than the clinically-defined brain area where seizures begin, and correspond with the likelihood for seizure control.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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