Roles of Very Fast Ripple (500–1000Hz) in the Hippocampal Network During Status Epilepticus

Abstract

Very fast ripples (VFRs, 500–1000[Formula: see text]Hz) are considered more specific than high-frequency oscillations (80–500[Formula: see text]Hz) as biomarkers of epileptogenic zones. Although VFRs are frequent abnormal phenomena in epileptic seizures, their functional roles remain unclear. Here, we detected the VFRs in the hippocampal network and tracked their roles during status epilepticus (SE) in rats with pilocarpine-induced temporal lobe epilepsy (TLE). All regions in the hippocampal network exhibited VFRs in the baseline, preictal, ictal and postictal states, with the ictal state containing the most VFRs. Moreover, strong phase-locking couplings existed between VFRs and slow oscillations (1–12[Formula: see text]Hz) in the ictal and postictal states for all regions. Further investigation indicated that during VFRs, the build-up of slow oscillations in the ictal state began from the temporal lobe and then spread through the whole hippocampal network via two different pathways, which might be associated with the underlying propagation of epileptiform discharges in the hippocampal network. Overall, we provide a functional description of the emergence of VFRs in the hippocampal network during SE, and we also establish that VFRs may be the physiological representation of the pathological alterations in hippocampal network activity during SE in TLE.

Status epilepticus induces chronic silencing of burster and dominance of regular firing neurons during sharp wave-ripples in the mouse subiculum

“…Downregulated excitability of burster neurons might also explain why we did not observe an increased ripple frequency (within the frequency range of physiological ripples) in our recordings as a sign of hyperexcitability, as faster ripples can reflect in-phase synchronous bursting (>300 Hz) of individual burster cells or alternating out-of-phase firing of more than one cell at lower frequencies (100-200 Hz, Ibarz et al, 2010). Indeed, burster neurons in the CA1 from chronically epileptic rodents developed hyperexcitable features due to altered expression of sodium and calcium channels (Becker et al, 2008;Chen et al, 2011), consistent with the generation of fast ripples and their major role in the propagation of epileptic discharges (Hao et al, 2021). However, the present study in the subiculum did not reveal such hyperexcitability in burster neurons.…”

Status epilepticus induces chronic silencing of burster and dominance of regular firing neurons during sharp wave-ripples in the mouse subiculum

“…Downregulated excitability of burster neurons might also explain why we did not observe an increased ripple frequency (within the frequency range of physiological ripples) in our recordings as a sign of hyperexcitability, as faster ripples can reflect in-phase synchronous bursting (>300 Hz) of individual burster cells or alternating out-of-phase firing of more than one cell at lower frequencies (100-200 Hz, Ibarz et al, 2010). Indeed, burster neurons in the CA1 from chronically epileptic rodents developed hyperexcitable features due to altered expression of sodium and calcium channels (Becker et al, 2008; Chen et al, 2011), consistent with the generation of fast ripples and their major role in the propagation of epileptic discharges (Hao et al, 2021). However, the present study in the subiculum did not reveal such hyperexcitability in burster neurons.…”

Classification of the Epileptic Seizure Onset Zone Based on Partial Annotation

“… 2017 ; Hao et al. 2021 ). One of the datasets, the Bern-Barcelona, is already processed and band-pass filtered between 0.5 and 150 Hz.…”