Abstracts

Sources, Sinks, and Spirals: Bridging the Micro and Macro Scales of Seizure Wave Dynamics

Abstract number : 3.227
Submission category : 2. Translational Research / 2C. Biomarkers
Year : 2024
Submission ID : 255
Source : www.aesnet.org
Presentation date : 12/9/2024 12:00:00 AM
Published date :

Authors :
Presenting Author: Trisha Mendoza, MS – University of California, Irvine

Marco Pinto Orellana, PhD – University of California Irvine
Joffre Olaya, MD – Children's Hospital of Orange County
Beth Lopour, PhD – University of California Irvine
Daniel Shrey, MD – Children's Hospital of Orange County

Rationale: In human seizures, rapidly traveling waves observed during epileptiform discharges (EDs) are believed to be associated with seizure sources. Investigations into this phenomenon, conducted on micro (80 μm diam.) and macro (2.4 mm diam.) spatial scales, has led to competing theories positing that waves could be emitted by static radial sources, a moving wavefront, or both (Schlafly et al. 2022). While microelectrodes provide excellent spatial resolution, they lack the ability to capture broader seizure spread. To bridge this gap, we recorded human seizure wave dynamics using a high-density (HD) subdural grid. We aim to quantify seizure onset and spread at an intermediate spatial scale to test the validity of existing theories.


Methods: Eight patients undergoing intracranial monitoring in preparation for epilepsy surgery were each implanted with an 8x8 HD- subdural grid (contacts with 1.17 mm diam., 3mm spacing). We recorded intracranial EEG during 23 seizures, with 17 of these seizures originating beneath the HD grid. To estimate the direction of the traveling waves associated with EDs we used the group delay method in 5x5 subgrids of electrodes. We then clustered the wave patterns using topological pattern matching on the subgrids. The occurrence of each pattern was compared at onset and termination using the Wilcoxon-Signed rank test. Finally, phase locked high gamma (PLHG) was calculated for each channel. PLHG channel recruitment was defined as the number of channels exceeding a threshold of three standard deviations above the mean PLHG.


Results: Consistent with prior studies, we find multiple stable planar wave directions in each seizure and an increase in planar waves at termination when recording from the SOZ (p< 0.05). Planar and source waves occurred most frequently (p< 0.01), followed by more complex wave dynamics (Figure 1A) including curves, sinks, spirals, and parallel waves. Both linear and radial source types were present, with significantly higher rates of linear sources (p< 0.01). These complex patterns evolved gradually over time (Figure 1B), but were consistent across seizures for several subjects. When the HD grid recorded seizure onset, this was associated with an increase in PLHG, which decreased at seizure termination. Outside the seizure onset zone, the increase in PLHG was delayed.


Conclusions: HD grid recordings revealed complex wave dynamics (sources, spirals, sinks) that have not previously been reported in human seizures. Multiple stable directions of planar wave activity could be consistent with multiple sources, as has been hypothesized. Finally, the presence of linear sources and an increase in PLHG at seizure onset may be evidence of seizure spread via an ictal wavefront.


Funding: NIH Diversity Supplement

Translational Research