Abstracts

Rationale: Not like anterior temporal lobectomy, extratemporal resective surgery would not provide sufficient control of neocortical seizures. Not only the ability to clearly define and completely resect the epileptogenic zone and the resectional limitation of eloquent regions, but also the unclear neurophysiology causes low average seizure-free rates of ~60% in extratemporal lobe epilepsy in comparison with over 90% seizure-free rate in mesial temporal lobe epilepsy. So in this study, we propose a method to show the seizure dynamics from burst frequency during a seizure that is more meaningful in neurophysiology and could be a useful tool to explore the seizure dynamics in clinical use. Methods: The digitalized incranial EEGs were extracted from 14 patients with intractable extratemporal epilepsies. The focus/foci of epileptogeneis was/were identified by the seizure activities from the implanted subdural electrodes (with a mesial temporal depth electrode if mesial temporal lobe seizure could not be excluded). By Hilbert Huang Transform (HHT), the complex ictal ECoG signals were decomposed into different Intrinsic Mode Functions (IMFs). The 1st to 3rd components of IMF modes as main activity of epileptic neurons were chosen. Then the IMF modes were enveloped and taken. The neural burst frequencies were enhanced by using the autocorrelation function. Results: The ictal stages over the seizure onset zone can be recognized and categorized into pre fast activity stage, fast spiking stage, phase transition stage, fast bursting stage and slow bursting stage. Over the region identified as seizure onset zone by visual assessment, a short train of high-frequency oscillation was unburied and the subsequent seizure stages were represented in the autocorrelogram remarkably. The adjacent recruited regions would also demonstrate similar periodic activity after seizure onset. No pre fast activity stage was found over the seizure propagated regions. Conclusions: Based on the simple functions of HHT and autocorrelation, our method demonstrated the temporospatial seizure dynamics from the burst frequency at seizure onset to the subsequent seizure propagation that is more meaningful in ictogenic neurophysiology. The overview of each electrode corresponding autocorrelogram throughout the seizure activity supported the scenario that a focal seizure is caused by an abrupt transition. The change of stages following ictal onset is very sudden as well.