Abstract
Purpose: To investigate the differences between interictal and ictal generalized spike-wave discharges (GSWDs) for insights on how epileptic activity propagates and the physiopathological mechanisms underlying childhood absence epilepsy (CAE).Methods: Twenty-five patients with CAE were studied using magnetoencephalography (MEG). MEG data were digitized at 6,000 Hz during the interictal and ictal GSWDs. GSWDs were analyzed at both neural magnetic source levels and functional connectivity (FC) in multifrequency bands: delta (1–4 Hz), theta (4–8 Hz), alpha (8–12 Hz), beta (12–30 Hz), gamma (30–80 Hz), ripple (80–250 Hz), and fast ripple (250–500 Hz). Brain FC was studied with the posterior cingulate cortex/precuneus (PCC/pC) as the seed region.Results: The magnetic source of interictal GSWDs mainly locates in the PCC/pC region at 4–8 and 8–12 Hz, while that of ictal GSWDs mainly locates in the medial frontal cortex (MFC) at 80–250 Hz. There were statistically significant differences between interictal and ictal GSWDs (p < 0.05). The FC network involving the PCC/pC showed strong connections in the anterior-posterior pathways (mainly with the frontal cortex) at 80–250 Hz during ictal GSWDs, while the interictal GSWDs FC were mostly limited to the posterior cortex region. There was no significant difference in the magnetic source strength among interictal and ictal GSWDs at all bandwidths.Conclusions: There are significant disparities in the source localization and FC between interictal and ictal GSWDs. Low-frequency activation in the PCC/pC during inhibition of seizures possibly relates to the maintenance of consciousness during interictal GSWDs. High-frequency oscillations (HFOs) of the MFC during CAE may associate with the inducing or occurrence of GSWDs. Weakened network connections may be in favor of preventing overexcitability and relates to the termination of GSWDs.
Highlights
Childhood absence epilepsy (CAE) is a type of idiopathic generalized epilepsy (IGE) characterized as episodes of unresponsiveness and generalized spike and wave discharges (GSWDs) on scalp electroencephalogram (EEG) of 3–4 Hz [1]
The present study aimed to investigate the difference of magnetic source localization and FC between the interictal and ictal GSWDs in various frequency bands in CAE patients using MEG, which has better spatial resolution comparing with EEG and higher temporal resolution than magnetic resonance imaging (MRI) [29]
Our findings have revealed that the magnetic source localization of interictal and ictal GSWDs differs at low and high bandwidths
Summary
Childhood absence epilepsy (CAE) is a type of idiopathic generalized epilepsy (IGE) characterized as episodes of unresponsiveness and generalized spike and wave discharges (GSWDs) on scalp electroencephalogram (EEG) of 3–4 Hz [1]. A subset of these localized in the medial frontal cortex (MFC), PCC/pC, and inferior temporal makes up the default mode network (DMN), a state of resting brain function [9]. These brain areas usually show decreased activity during attention-demanding tasks and become increasingly active during inattention to mental tasks or the external environment [10, 11]. The former assumes that the SWDs are closely related to the thalamocortical mechanism that generates sleep spindles [5, 12] The latter assumes that there is a focal area (pC, prefrontal and parietal cortex regions) active before occurrence of SWDs [13]. Disorders of consciousness may be caused by selective bilateral cortical and subcortical networks [5, 24] through abnormal patterns of neural activity [1]
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