Pro-ictal brain state marked by global critical slowing and local gamma power increase

Authors: Isa Dallmer-Zerbe, Jakub Kopal, Anna Pidnebesna, J. Curot, M. Denuelle, A. de Barros, J.-Ch. Sol, L. Valton, E. Barbeau, Jaroslav Hlinka
Publication year: 2024
Publication type: Abstrakt
Periodical: Epilepsia
Bibliographic citation: DALLMER-ZERBE, Isa, KOPAL, Jakub, PIDNEBESNA, Anna, CUROT, J., DENUELLE, M., DE BARROS, A., SOL, J.-Ch., VALTON, L., BARBEAU, E., HLINKA, Jaroslav. Pro-ictal brain state marked by global critical slowing and local gamma power increase. Epilepsia. 2024, 65(Special Issue Suppl. 1), 131-131), 192. ISSN 0013-9580. E-ISSN 1528-1167.
ID: 617859

Abstract

PURPOSE: The clinical workup during the pre-surgical evaluation for epilepsy relies on the electrophysiological recording of seizures. The interval until first seizure occurrence is characterised by an increase in seizure likelihood caused by progressive drug dose decreases, during which the epileptic brain transitions from a state of low to a state of high seizure likelihood, so-called pro-ictal state. This study aimed to identify and characterise the dynamic brain changes characteristic of this transition. METHOD: We analysed 386 10-min segments of intracranial EEG recordings of 29 patients with drug-refractory temporal lobe epilepsy, irregularly sampled between electrode implantation and first seizure. As measures of brain dynamics, we studied the mean phase coherence and the relative power in gamma frequency band, as well as the autocorrelation function width. We further investigate the interaction of those brain dynamics with various susceptibility factors, such as the rate of interictal spikes and high frequency oscillations, circadian and multi-day cycles, and clinical outcomes. RESULTS: We observe a significant increase in relative gamma power in the epileptogenic zone between the beginning and the end of the measured interval (Z = 2.998, pFDR = .008, Cohen's d = .678), and a network-wide critical slowing (epileptogenic zone: Z = 1.992, pFDR = .046, d = -. 545, healthy cortex: Z = 2.757, pFDR = .009, d = -. 680). These brain dynamic changes were linked with increases in spike and high frequency oscillations rate. While the brain dynamic changed on the slow time scale – from the beginning to the end of the multi-day interval – they did not change in the short-term during the pre-ictal interval. CONCLUSION: We highlight gamma power and critical slowing as markers of pro-ictal (as opposed to pre-ictal) brain states, as well as their potential to track the seizure-related brain mechanisms during the presurgical evaluation of epilepsy patients.