Initiation, Propagation, and Termination of Partial (Focal) Seizures

Abstract

The neurophysiological patterns that correlate with partial (focal) seizures are well defined in humans by standard electroencephalogram (EEG) and presurgical depth electrode recordings. Seizure patterns with similar features are reproduced in animal models of partial seizures and epilepsy. However, the network determinants that support interictal spikes, as well as the initiation, progression, and termination of seizures, are still elusive. Recent findings show that inhibitory networks are prominently involved at the onset of these seizures, and that extracellular changes in potassium contribute to initiate and sustain seizure progression. The end of a partial seizure correlates with an increase in network synchronization, which possibly involves both excitatory and inhibitory mechanisms.

Low‐voltage fast seizures in humans begin with increased interneuron firing

“…8,9 Findings obtained in vitro from entorhinal cortex and hippocampal tissue slices and from isolated guinea pig preparation show that 4-aminopyridine or bicuculline application induces LVF seizurelike discharges that coincide with sustained interneuron discharges and robust inhibitory postsynaptic events in principal (glutamatergic) neurons. 4,[10][11][12][13][14] In line with these findings, optogenetic stimulation of parvalbumin-or somatostatin-positive interneurons can initiate ictallike LVF onset events similar to those occurring spontaneously. [15][16][17] Experimentally, LVF onset seizures are also recorded in status epilepticusinduced models of mesial-temporal lobe epilepsy.…”

“…4,10–14 In line with these findings, optogenetic stimulation of parvalbumin- or somatostatin-positive interneurons can initiate ictallike LVF onset events similar to those occurring spontaneously. 15–17 Experimentally, LVF onset seizures are also recorded in status epilepticus-induced models of mesial–temporal lobe epilepsy.…”

“…by synchronous inhibitory cell spike firing (see for review: Avoli et al, 3 de Curtis and Avoli 4 . LVF seizures, which are often heralded by an electroencephalographic (EEG) spike and immediately followed by beta-gamma frequency activity, have a regional onset and frequently involve mesial and lateral temporal lobe structures.…”

Adult-born granule cells support pathological microcircuits in the chronically epileptic dentate gyrus

“…This model represents the first application of Bayesian topic modeling to in vivo two-photon calcium imaging data, as well as a novel conceptual framework for relating interictal events to ictogenic circuits: each micro-level population event represents a "snapshot" of a much wider macro-level network, whose functional or synaptic organization is not directly observable, yet whose micro-level calcium response at each time point is. Each one of these snapshots reveals some information about the underlying network, which is hypothesized to be structured on multiple scales to support seizure initiation and propagation (Paz andHuguenard, 2015, de Curtis andAvoli, 2015). While each individual event is relatively uninformative on its own, by accumulating these snapshots in an unsupervised way, it is possible to reconstruct a more complete picture of the underlying macro network structure.…”

A companion to the preclinical common data elements and case report forms for rodent EEG studies. A report of the TASK3 EEG Working Group of the ILAE/AES Joint Translational Task Force

“…Ictal EEG patterns can be reported here for each seizure event (or for the characteristic seizure event(s), if so chosen by the experimental design, if seizures are very frequent) describing the onset, propagation/evolution, and postictal phases. 37 The onset pattern is classified into rhythmic discharges, electrical attenuation, polymorphic slowing, and other patterns, which the investigator can fill in using free text form. Rhythmic discharges are further divided into slow waves, fast activity, and spikes/spike-waves burst, and their frequencies and bandwidths are additionally reported.…”