High-rate Interictal Spike Sites Initiate More Propagation Outside the Seizure Onset Zone in Non-seizure Free Temporal Lobe Epilepsy Surgical Patients
Abstract number :
1.031
Submission category :
1. Basic Mechanisms / 1C. Electrophysiology/High frequency oscillations
Year :
2022
Submission ID :
2204378
Source :
www.aesnet.org
Presentation date :
12/3/2022 12:00:00 PM
Published date :
Nov 22, 2022, 05:24 AM
Authors :
Mohamad Shamas, PhD – UCLA; Hsiang Yeh, PhD – Neurology – UCLA; Itzhak Fried, MD, PhD – Director of the Epilepsy Surgery Program, Neurology, UCLA; Jerome Engel, MD, PhD – Director of the Seizure Disorder Center, Neurology, UCLA; Richard Staba, PhD – Professor in Neurology, Neurology, UCLA
Rationale: Recordings of interictal spikes are often used in combination with ictal recordings to plan epilepsy surgery to treat medication resistant seizures. However, evidence suggests high spike rates alone do not completely characterize the network, commonly referred to as the irritative zone (IZ), and unequivocally increase the likelihood of seizure freedom. Therefore, in addition to rates, this study analyzed the interactions of spikes between brain regions to better understand the IZ and how spike interactions could help inform the brain area responsible for generating seizures.
Methods: We retrospectively analyze interictal EEG recordings from 37 patients with focal seizures suspected to begin in limbic regions who required presurgical intracerebral studies. First, for all depth electrode contacts we computed the mean spike rate and power per contact. Next, we constructed the spike coupling matrices by computing the mean rate and power of nearly simultaneous spikes between every pair of contacts. Lastly, we quantified spike propagation or sequences, i.e. spikes detected within 50 msec of each other on all contacts. All measures were evaluated in relation to mesial (M) or lateral (L) temporal lobe or extratemporal (E) locations, and contacts labeled as seizure onset zone (SOZ) or non-SOZ, and in seizure free patients with (SF; n = 18) or without seizure-free outcome (not-SF; n = 19).
Results: Only when mesial temporal lobe was part of the SOZ, not-SF patients showed higher rates than SF patients (Anova p < 0.001 and η2 = 0.138). Considering the spiking coupling networks, not-SF patients showed more spiking connectivity segregation in all brain regions (M, L, E) when compared to SF (ANOVA p < 0.001 and η2 = 0.195, 0.113 and 0.102 respectively). Finally, Analysis of spike propagation and quantification of each spike sequence showed that: (1) average rate of sequences and average number of spikes per sequence are higher in not-SF patients (Wilcoxon p = 0.0202 and 0.0114 respectively), (2) the percentage of sites generating the highest 10% of spike rates and are also initiators of spike sequences in the SOZ is similar between SF and not-SF patients (Wilcoxon, p = 0.3416). By contrast, this percentage was significantly higher in the non-SOZ of not-SF than SF patients (Wilcoxon, p = 0.0172)._x000D_
Conclusions: Our results imply that brain regions with high rates of spikes localize with the SOZ, but provide little new information about the network generating seizures and how to treat it. Results with high rates of coupled spikes indicate brain regions are segregated, especially in non-SF patients. However, there are instances when these segregated regions interact through high-spike rate initiator sites, which occurs more frequently in non-SOZ of not-SF than SF-patients. These latter results could correspond with a mechanism of seizure spread, and if these sites are not removed or disconnected along with the SOZ, then this could contribute to seizure recurrence.
Funding: This study was supported by the NIH grant NS106957 (RS) and 033310 (JE).
Basic Mechanisms