Measurable Transitions During Seizures in Intracranial EEG: A Stereo-EEG and SPECT Study
Abstract number :
2.094
Submission category :
3. Neurophysiology / 3G. Computational Analysis & Modeling of EEG
Year :
2023
Submission ID :
426
Source :
www.aesnet.org
Presentation date :
12/3/2023 12:00:00 AM
Published date :
Authors :
Presenting Author: Balu Krishnan, PhD – Cleveland Clinic Foundation
Simon Tousseyn, MD, PhD – Academic Center for Epileptology – Kempenhaeghe and Maastricht UMC+; Kenneth Taylor, PhD – Epilepsy Center – Cleveland Clinic Foundation; Demitre Serletis, MD, PHD – Epilepsy Center – Cleveland Clinic Foundation; Juan Bulacio, MD – Epilepsy Center – Cleveland Clinic Foundation; Andreas Alexopoulos, MD, MPH – Epilepsy Center – Cleveland Clinic Foundation
Rationale:
Ictal SPECT and stereo-EEG are two diagnostic techniques used for the management of patients with drug-resistant focal epilepsies. Hyperperfusion patterns observed in ictal SPECT studies reflect seizure onset and propagation pathways. However, the significance of ictal hypoperfusion is still not well understood. Our previous studies combining ictal SPECT with invasive or noninvasive electrophysiological techniques like stereo-EEG or magnetoencephalography have demonstrated that brain regions showing ictal hyperperfusion are interconnected, forming a network. On the other hand, brain regions experiencing hypoperfusion during seizures form a separate interconnected network. This study aims to systematically investigate how information flows between the epileptogenic zone (EZ) and brain regions with extreme changes in ictal SPECT perfusion. We hypothesize that there is a dynamic evolution of directional connectivity between the EZ and specific brain regions outside the area that undergoes surgical resection.
Methods:
We identified seizure-free patients after resective epilepsy surgery who had prior ictal SPECT and stereo-EEG investigations. Our first step was to align the ictal SPECT and CT images of the stereo-EEG electrodes. From there, we extracted the perfusion z-scores corresponding to each SEEG contact. For each patient, we identified a single SEEG contact that sampled the EZ as well as non-resected areas characterized by hyperperfusion, hypoperfusion, and baseline perfusion. Using directed transfer function, we then estimated the directional connectivity between these four brain regions during different periods, including interictal (background), preictal, ictal, and postictal phases.
Results:
Out of the initial fifteen patients, five were excluded due to a lack of SEEG contacts sampling hypoperfused areas outside the surgical resection. The analysis was conducted on the remaining ten patients, encompassing a total of 24 seizures (See Table 1). Compared to the background, we noted significant information out-degree (1) during the preictal period from the EZ to the non-resected baseline and hyperperfused regions, (2) during ictal onset from the EZ to all three groups of contacts, (3) during the period of seizure evolution from the area of hypoperfusion to all three groups of contacts, and (4) during the immediate postictal period from the area of hypoperfusion to the EZ (Fig. 1A-B). Furthermore, a significant inverse correlation was observed between seizure duration and net-degree (out-degree minus in-degree) from the hypoperfused area to brain regions not involved in the seizure (Fig. 1C).
Conclusions:
Our study provides unique insights into the dynamics of brain connectivity during seizures by analyzing changes in intracranial electrophysiology and brain perfusion. We highlight the dynamic interaction between the EZ and brain regions that experience both hyperperfusion and hypoperfusion during seizures. These findings have implications for understanding brain connectivity and network organization in epilepsy. We aim to inspire further research on the role of areas with ictal hypoperfusion and their connections in defining patient-specific epileptic networks.
Funding: None
Neurophysiology