A seizure is an episode of increased or irregular electrical activity in the brain. Seizures can happen in both humans and other animals, of all ages, and can be due to a variety of factors; including but not limited to, chronic early life stress (Dubé et al,. 2015), a genetic predisposition, developmental disorders, infectious disease, injury or nerve agent exposure. In many cases the cause is of unknown origins. Seizures can occur throughout the brain (generalized) or only in a single hemisphere or location (partial or focal). They can present as a single event or exhibit recurrent characteristics (epilepsy). The symptoms can vary, depending on type, location and severity. Some of these signs can include a strange feeling or sensation as precursory (prodromal) symptoms, freezing or zoning out, loss of consciousness and violent or rhythmic muscle contractions. The long term effects can include histopathological alterations in various brain regions (Curia et al., 2008), abnormalities in sleep (Suntsova et al., 2009) and neuropsychiatric disorders (Loughman et al., 2017, Epilepsy Behav.).
Types of Seizure
Seizures can be generalized, partial or complex partial. Generalized seizures affect a large portion of the brain, but not always the entire brain and are characterized by loss of consciousness. Generalized seizures can present as generalized tonic-clonic seizures, i.e. grand mal seizures, displaying severe motoric exacerbation or as petit-mal seizures with less severe or no motor components. Childhood absence epilepsy is a petit-mal example characterized by 3 Hz spike-wave discharges (SWD) in humans. An example of a related genetic model of generalized absence epilepsy in rats is the WAG/Rij rat model. Similar to what is observed in children, this model shows evidence of SWDs accompanied by a freezing behavior (Nersesyan et al., 2004).
In contrast to generalized seizures, partial (focal) seizures often occur in a single hemisphere or brain region and can be further categorized into simple partial and complex partial seizure. While in simple partial seizures consciousness remains intact, complex partial seizures regularly exhibit an impairment of consciousness The rat pilocarpine (chemical) model of medial (mesial) temporal lobe epilepsy (mTLE) is an important and well-established example of a complex partial limbic epilepsy model in rats. In humans, temporal lobe epilepsy is among the most common as well.
Electrophysiological and motoric seizure Characteristics
Depending on the model or chemical compound used, abnormal activity in the brain may present itself in various ways. Those models include genetic, pharmacological and electrical induced-epilepsy.
According to a review by Dr. D’Ambrosio and Dr. Miller, seizure can vary in duration and may be defined as motor or non-motor because only detected by EEG analysis.
The purpose of a model is to mimic a condition, disease or illness and/or predict efficacy or adverse effect of a treatment for a specific disease, condition or illness. Ideally, animal models should meet the criteria of construct validity (quantitative, degree of similarity of the pathology), face validity (description of the pathology e.g. similar behavior) and predictive validity (manipulation induce similar effects: e.g. pharmacological treatment). A number of models in several species have been characterized and are used to unravel underlying etiology and pathophysiology, to test antiepileptic drugs or the increased susceptibility to seizure (the lowering of a seizure threshold). Seizure/epilepsy models can be genetic or induced in normal animals. Genetic models of seizure are further separated by spontaneous and reflex seizure (seizure caused by a stimulus such as sound). Alternatively, seizure can be induced in normal animals through electrical or chemical means and these induced seizures can be acute, chronic or spontaneous/recurrent (Löscher, 2011). New models are constantly in development to more accurately portray and treat seizures which are at present resistant to existing anti-epileptic drugs. We have created this table to provide you with more information regarding the various species and applications that have been studied in seizure research.
Click here for a list of seizure models and proposed EEG placement.