Interictal oscillations and focal epileptic disorders

Abstract

Neuronal network oscillations represent a main feature of the brain activity recorded in the EEG under normal and pathological conditions such as epilepsy. Specific oscillations occur between seizures in patients and in animal models of focal epilepsy, and thus, they are termed interictal. According to their shape and intrinsic signal frequency, interictal oscillations are classified as spikes and high-frequency oscillations (HFOs). Interictal spikes are recorded in the 'wideband' EEG signal and consist of large-amplitude events that usually last less than 1 s; HFOs, in contrast, are extracted by amplifying the appropriately filtered EEG signal and are usually categorized as ripples (80-200 Hz) and fast ripples (250-500 Hz). Interictal spikes and HFOs are used in clinical practice to localize the seizure onset zone in focal epileptic disorders, which is fundamental for performing successful surgical interventions in epileptic patients not responding to anti-epileptic drug therapy. Both types of interictal oscillations have been widely studied in animal models of focal epilepsy to identify the mechanisms underlying their generation as well as to establish their role in ictogenesis and epileptogenesis. In this review, we will address the cellular mechanisms underlying the generation of interictal spikes and HFOs in animal models of epileptiform synchronization and of focal epilepsy. Moreover, we will highlight in vitro and in vivo evidence indicating that these interictal oscillations mirror specific, dynamic changes in neuronal network excitability causing seizure generation (i.e. ictogenesis) and leading to a chronic epileptic condition (i.e. epileptogenesis).

Metastatic breast cancer cells induce altered microglial morphology and electrical excitability in vivo

“…The altered excitability and electrical signatures observed here resemble interictal-like epileptic wave forms that have been associated with poor cognitive performance and have been seen in electroencephalograms (EEGs) of patients presenting with epilepsy [56], suggesting that our model may recapitulate early stages of cortical disorganisation that could subsequently lead to tumour-associated epilepsy. Interictal activity can be caused by alterations in expression and/or activity of neurotransmitter receptors and ion channels [57] to promote glutamatergic transmission and decrease GABAergic activity. In addition, neuronal atrophy and/or altered connectivity can occur in the chronic phases of rodent epilepsy models [58].…”

Orchestration of brain oscillations: principles and functions

“…() provide a detailed review of research investigating the oscillatory markers underlying aberrant sleep patterns in schizophrenia patients, Levesque et al . () review the link between aberrant inter‐octal high‐frequency oscillations and epilepsy. A review contributed by Singh focuses on the various observations of aberrant oscillatory activity within the cortico‐basal ganglia‐thalamic (CBT) observed in patients with Parkinson Disease (Singh, ), and an empirical study by Pittman‐Polletta et al .…”

Deletion of calcineurin from astrocytes reproduces proteome signature of Alzheimer’s disease and epilepsy and predisposes to seizures

“…We thus, proceeded with registration of seizurefree mice. In all cases registered from ACN-KO mice there was a presence of aberrant electrical activity (100.8 ± 19.25 spikes/24h in ACN-KO vs 3.5 ± 0.50 spikes/24h in ACN-Ctr, p = 0.042, n = 5) resembling that of interictal spikes (Lévesque et al, 2018) (Fig. 5B).…”