Abstracts

Surgical evaluation of intractable epilepsy often involves continuous intracranial subdural recording in which the goal is to determine the seizure onset zone. A difficulty with this approach is that the epileptologist must collect a sufficient number of seizures to evaluate if the patient is a candidate for resective surgery. Methods for interically identifying the seizure onset zone may shorten the phase 2 subdural monitoring and improve outcome. The goal of this research is to compare the interictal amplitude modulations of slow potentials, gamma, fast gamma, and neural ensemble activity for quantitatively locating the seizure onset zone., The subject participating in the study was undergoing extraoperative subdural grid evaluation for the treatment of intractable neocortical epilepsy. Multichannel subdural potentials were collected (IRB approved) while the patient was quietly awake. Neuronal activity indicated by the dashed box in Fig. 1 was recorded at 12kHz and bandpass filtered from 1-6 kHz. To compare the seizure onset zone identification in multiple frequency bands, we define the amplitude modulation as the sum of the power of the ECoG voltage signal during interictal segments of recording (compared 10s-60min). The seizure onset zone quantified was compared to the zone as determined independently by two certified pediatric epileptologists (PRC, ZL)., The amplitude modulations in the ECoG data indicates that the seizure onset zone demarcation is dependent upon the frequency band. Both the gamma bands presented similar regions of maximal amplitude modulations in electrodes 45, 46, and 47. The slow potential amplitude modulations were not as distinct but modulation was posterior and temporal to the gamma bands. Neural ensemble modulation indicating the activation of large neuronal networks presented in electrodes 49-52, 25-28, and were merging into the gamma onset zones., A direct correspondence was found between the quantitative analysis and the visually identified seizure onset zone. Clinically, this preliminary result indicates that analysis of brief (10s-30min) ECoG recordings could potentially be used to make efficient recommendations for epilepsy surgery and could shorten phase 2 monitoring. Neurophysiologically, the primary seizure onset zone was most clearly defined by gamma and fast gamma activity implicating the potential role of dendritic activiy in ictogenesis. However, the spread of epileptic activity was primarily identified by the neural ensemble activity corresponding to the axonal output of cortical neurons.[figure1], (Supported by Children[apos]s Miracle Network and Wilder ERC.)