Abstract
Background: Slow-wave activity (SWA) during non-rapid eye movement (NREM) sleep reflects synaptic potentiation during preceding wakefulness. Epileptic activity may induce increases in state-dependent SWA in human brains, therefore, localization of SWA may prove useful in the presurgical workup of epileptic patients. We analyzed high-density electroencephalography (HDEEG) data across vigilance states from a reflex epilepsy patient with a clearly localizable ictal symptomatogenic zone to provide a proof-of-concept for the testability of this hypothesis.Methods: Overnight HDEEG recordings were obtained in the patient during REM sleep, NREM sleep, wakefulness, and during a right facial motor seizure then compared to 10 controls. After preprocessing, SWA (i.e., delta power; 1–4 Hz) was calculated at each channel. Scalp level and source reconstruction analyses were computed. We assessed for statistical differences in maximum SWA between the patient and controls within REM sleep, NREM sleep, wakefulness, and seizure. Then, we completed an identical statistical comparison after first subtracting intrasubject REM sleep SWA from that of NREM sleep, wakefulness, and seizure SWA.Results: The topographical analysis revealed greater left hemispheric SWA in the patient vs. controls in all vigilance states except REM sleep (which showed a right hemispheric maximum). Source space analysis revealed increased SWA in the left inferior frontal cortex during NREM sleep and wakefulness. Ictal data displayed poor source-space localization. Comparing each state to REM sleep enhanced localization accuracy; the most clearly localizing results were observed when subtracting REM sleep from wakefulness.Conclusion: State-dependent SWA during NREM sleep and wakefulness may help to identify aspects of the potential epileptogenic zone. Future work in larger cohorts may assess the clinical value of sleep SWA to help presurgical planning.
Highlights
Epilepsy proves drug-refractory in 20–40% of cases (Liu et al, 2015)
Given that REM sleep is thought to suppress epileptic activity (Shouse et al, 2000; Ng and Pavlova, 2013; Lambert et al, 2018; Kang et al, 2020), state-dependent Slow-wave activity (SWA) may localize epileptic foci, especially when comparing non-rapid eye movement (NREM) sleep to REM sleep. This hypothesis is in line with our previous study where we reported no significant abnormality during REM sleep in patients’ High-density EEG (HDEEG) topographies but noted increases in SWA during NREM sleep compared to REM sleep (Boly et al, 2017)
The current study considers a patient with reflex epilepsy, providing an opportunity to test a proof-of-concept—that is, a pilot study to consider the feasibility of larger-scale analysis—for the localizing value of SWA across different vigilance states (Koepp et al, 2016)
Summary
Epilepsy proves drug-refractory in 20–40% of cases (Liu et al, 2015) In these patients, surgical resection represents the gold standard intervention (Ryvlin et al, 2014; Liu et al, 2015). High-density EEG (HDEEG; i.e., >64 electrodes) offers enhanced artifact rejection and source localization (Lantz et al, 2003; Puce and Hämäläinen, 2017). This technique is most commonly utilized to source-localize interictal spikes. We analyzed high-density electroencephalography (HDEEG) data across vigilance states from a reflex epilepsy patient with a clearly localizable ictal symptomatogenic zone to provide a proof-ofconcept for the testability of this hypothesis
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