A seizure is a sudden disruption of brain activity caused by excessive, synchronized neuronal firing that results in changes in behavior. This neurological condition is common, affecting approximately 50 million individuals around the world. Depending on the regions of the brain involved, seizures can lead to changes in movement, sensation, behavior, awareness, or consciousness. Symptoms vary widely. Some seizures involve subtle changes, such as brief lapses in attention or awareness (as seen in absence seizures), while others cause generalized convulsions with loss of consciousness (tonic–clonic seizures). Most seizures last less than two minutes and are followed by a postictal period of confusion, fatigue, or other symptoms. Status epilepticus is a medical emergency consisting of a seizure that lasts longer than five minutes, or multiple seizures without full recovery between episodes. Seizures are classified as provoked when they are triggered by a known cause such as fever, acute head trauma, or metabolic imbalance. Unprovoked seizures occur when no immediate trigger is identified. Recurrent unprovoked seizures define the neurological condition epilepsy.
Signs and symptoms The clinical signs and symptoms associated with a seizure are also referred to as seizure semiology. Seizure semiology varies depending on the brain regions involved and the type of seizure. This may affect movement, sensation, autonomic functions, or cognitive and emotional processing. Motor symptoms can include muscle stiffening (tonic activity), rhythmic jerking (clonic activity), sudden muscle jerks (myoclonus), sudden loss of muscle tone (atonia), eye deviation, or other repetitive involuntary movements (automatisms). Sensory disturbances may involve tingling, visual phenomena, vertigo, hallucinated sounds, among others, while autonomic features can include changes in heart rate, respiration and epigastric sensations. Cognitive or emotional symptoms may manifest as confusion, fear, altered perception, memory phenomena such as feelings of familiarity (déjà vu) and other alterations in cognitive function. Some individuals experience an aura associated with their focal seizures, characterized by subjective sensations such as unusual smells, a sudden emotional shift, or feelings of déjà vu. Most seizures last less than two minutes and may be followed by a recovery phase known as the postictal state, which may include confusion, fatigue, or other neurologic symptoms. Seizures lasting more than five minutes or occurring in rapid succession without recovery are classified as status epilepticus, a medical emergency that can result in long-term brain injury or death.
Classification
Seizures are classified according to their site of onset in the brain, clinical features, and level of consciousness during the episode. In 2025, the International League Against Epilepsy (ILAE) released an updated classification of seizures that distinguishes four major types: focal, generalized, unknown whether focal or generalized, and unclassified seizures. Seizures are further characterized based on whether consciousness is preserved or impaired, as determined by responsiveness during the event.
Focal seizures Focal seizures (previously known as partial seizures) originate within a network limited to one hemisphere of the brain. They may arise from the cerebral cortex or subcortical structures. For a given seizure type, seizure usually starts in the same part of the brain each time. Once initiated, the seizure may remain localized or spread to adjacent areas, and in some cases, may travel to the opposite hemisphere (contralateral spread). Despite this potential for spread, the initial focus remains consistent. Focal seizures are subdivided based on whether consciousness is preserved or impaired, a classifier defined by awareness and responsiveness during the event. They are also differentiated by the localization or spread of epileptiform activity. The three major classifications of focal seizures are described below:
Focal preserved consciousness seizure: the person remains aware and responsive. Focal impaired consciousness seizure: awareness and/or responsiveness are affected. Focal-to-bilateral tonic-clonic seizures: abnormal brain activity spreads from one area to both brain hemispheres; awareness and/or responsiveness are affected. Focal seizures can manifest with motor, sensory, autonomic, cognitive, or emotional symptoms, depending on the regions involved. They often present with unilateral symptoms, but bilateral symptoms may also be seen, even when a seizure is not classified as focal-to-bilateral. This is because several structures in the brain have bilateral effects in the body (e.g. primary visual cortex). Focal impaired consciousness seizures are the most common type of seizure in individuals older than one year of age, affecting 36% of epilepsy patients overall.
Generalized seizures
Generalized seizures originate at a specific point within, and quickly spread across both hemispheres through interconnected brain networks. They can be divided into three broad categories:
Absence seizures: involve brief lapses in awareness Generalized tonic–clonic seizures: involve stiffening (tonic phase) followed by rhythmic jerking (clonic phase) Other generalized seizures: encompass various motor and non-motor types These categories include several subtypes of seizures, each with their own distinctive symptoms and diagnostic criteria. Like focal seizures, generalized seizures can present with asymmetric or bilateral symptoms, so thorough evaluation and history-gathering is necessary for diagnosis. One key difference between generalized and focal seizures is the age at onset, which is significantly lower in patients with generalized seizures. Generalized tonic–clonic seizures, previously known as grand mal seizures, are associated with the highest morbidity and mortality. They are the primary risk factor for sudden unexpected death in epilepsy (SUDEP).
Unknown (whether focal or generalized) seizures When available information is insufficient to determine whether a seizure is focal or generalized, it is classified as unknown. These seizures can be classified by level of consciousness and observable symptoms when possible.
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