seizure
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What is a seizure?
A seizure is a sudden, uncontrolled burst of electrical activity in the brain that can manifest in a variety of symptoms, such as changes in behavior, shaking, and altered consciousness. Seizures are categorized as either focal (partial) or generalized, and both types may be preceded by a prodrome, which is an early warning symptom.
Seizures can be triggered by underlying conditions such as fever, stroke, or flashing lights. Other causes include genetic disorders, congenital abnormalities, brain injuries, and infections. If a person experiences recurrent seizures, they may be diagnosed with epilepsy, a chronic neurological condition.
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What happens in the brain during a seizure?
During a seizure, there is a sudden, uncontrolled burst of electrical activity in the brain, which can manifest differently depending on whether it is a focal or generalized seizure. Focal seizures start in one area of the brain, while generalized seizures affect both hemispheres. This abnormal electrical signaling can cause a range of symptoms, from changes in behavior and movement to altered consciousness. Studies of temporal lobe epilepsy suggest that seizures may be linked to defects in neurons or abnormal swelling of astrocytes, which are neuronal support cells that regulate neuron activity.
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What are some common causes of seizures?
Seizures can stem from various factors, including genetic disorders or congenital abnormalities affecting brain blood vessels. Acquired conditions such as stroke, severe concussion, traumatic brain injury, and degenerative brain diseases like Alzheimer's can also trigger seizures. Infections, brain tumors, and even lack of sleep are potential causes. External triggers such as flashing lights and certain medications can induce seizures in susceptible individuals. Additionally, drug use, including alcohol intoxication or withdrawal, and high fever, especially in young children, can lead to seizures. Some epileptic seizures have unknown causes and are called idiopathic.
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How are seizures classified or grouped?
Seizures fall into two main categories: focal and generalized. Both seizure types can be preceded by a prodrome, which is an early warning symptom where someone experiences an altered emotion or sensation.
Focal Seizures
Focal seizures start in one hemisphere of the brain, staying in that area, and symptoms appear in one part of the body. They can be simple, where electrical discharges don't spread and only an aura is experienced, or complex, where discharges spread, causing altered consciousness and repetitive movements. Afterward, the affected person may not remember the seizure.Generalized Seizures
These seizures result from abnormal electrical activity in most or all of the brain, causing convulsions, brief loss of consciousness, muscle jerks, and loss of muscle tone. Types of generalized seizures include absence (or petit mal), atonic, clonic, myoclonic, tonic, and tonic-clonic (or grand mal). Generalized seizures may occur when the electrical discharges of a focal seizure spread to both hemispheres of the brain, or they may have a generalized onset, meaning they begin on both sides of the brain simultaneously.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
What are some signs and symptoms of different types of seizures?
Seizures fall into two primary categories: focal and generalized. Both types can be preceded by a prodrome, which is an early warning symptom that includes altered emotion or sensation.
Focal seizures originate in one hemisphere of the brain, causing symptoms on one side of the body. Simple partial seizures manifest as an aura, while complex partial seizures involve loss of consciousness, staring, and repetitive movements.
Generalized seizures involve the entire brain and include several types:
* Absence seizures: Brief loss of consciousness, often with minor movements like blinking.
* Atonic seizures: Loss of muscle control, leading to collapse.
* Clonic seizures: Repetitive jerking movements, especially in the neck, face, and arms.
* Myoclonic seizures: Sudden, brief jerks or twitches.
* Tonic seizures: Muscle stiffening, potentially causing loss of consciousness and falling.
* Tonic-clonic seizures: Involve a tonic phase of stiffening and loss of consciousness, followed by a clonic phase of convulsions. These can also cause screaming, tongue biting, and incontinence.3 Britannica SourcesCreated from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles. -
How are seizures diagnosed and treated?
Seizures are diagnosed through medical history, symptoms, and tests like electroencephalograms (EEGs), which detect brain electrical activity abnormalities. Additional testing includes computed tomography (CT) and magnetic resonance imaging (MRI).
Treatment varies based on the cause; if the cause is untreatable, antiepileptic drugs may be prescribed. Other strategies include vagus nerve stimulation, behavioral therapy, surgery, and a ketogenic diet (high-fat, low-carbohydrate). During a seizure, clothing should be loosened, the head cushioned, and the person turned to their side after the seizure has ended.
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seizure, sudden, uncontrolled electrical activity in the brain. Seizures produce a wide range of symptoms, including changes in behaviour, shaking or sudden movements, and changes in consciousness. Often the cause of a seizure is unknown.
Characteristics
About 25 to 30 percent of seizures are provoked seizures (also known as acute symptomatic seizures), being triggered by underlying conditions, such as fever or stroke, or by exposure to flashing lights or moving objects. Unprovoked seizures occur in the absence of any clear cause; in some cases, they happen days after a possible cause, such as a head injury or alcohol withdrawal. Seizures can be a onetime event—some 10 percent of people worldwide experience a single seizure in their lifetime—or a recurring event. Recurrent seizures typically are a sign of epilepsy, a chronic neurological disorder caused by an absence or excess of signaling of neurons in the brain; epilepsy affects more than 50 million people worldwide.
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The duration of a seizure varies, some lasting 30 seconds and others lasting two minutes. A seizure that is more than five minutes in duration or having more than one seizure that occurs over that same amount of time, with no return to consciousness between episodes, is known as status epilepticus. Status epilepticus can result in brain damage or death.
Types of seizures
Seizures are categorized into two broad types: focal (partial) or generalized. Both types of seizures may be preceded by a prodrome, or an early warning symptom, in which the individual experiences an altered emotion or sensation. A prodrome may include an aura, with distortions in vision (e.g., seeing bright lights), hearing strange sounds, changes in taste or smell, feeling strange sensations on the skin, or experiencing a sense of déjà vu or unexplained emotions, such as fear or joy. The person may also sweat, drool, become pale, or experience a change in heart rate. Difficulty speaking or involuntary twitching may also occur.
Focal seizures
Focal seizures—which can be caused by prior injury to the brain, such as from stroke, meningitis, or physical trauma—begin in the left or right hemisphere and remain in that area; thus, symptoms occur in a specific part or on one side of the body. Focal seizures may be characterized as simple partial seizures when the electrical discharges do not spread and the affected person experiences only an aura. This is in contrast to a complex partial seizure, wherein the electrical discharges spread, resulting in a loss of or altered consciousness. Affected individuals may feel like they are dreaming and may stare into space and perform repetitive movements, such as walking in circles or rubbing their hands. Afterward they may not know that the seizure occurred.
Generalized seizures
Generalized seizures occur when electrical discharges of a focal seizure spread to both hemispheres of the brain. Generalized seizures may also have generalized onset, meaning that they begin on both sides of the brain simultaneously. There are several different types of generalized seizures.
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- Absence seizures (or petit mal seizures) are brief, lasting about 5–10 seconds, and may happen dozens or hundreds of times per day; they often occur in children.
- Atonic seizures (also known as drop attacks) last about 15 seconds and involve a loss of muscle control, causing the affected individual to collapse.
- Clonic seizures involve repetitive or rhythmic jerking movements, particularly of the neck, face, and arms, on both sides of the body.
- Myoclonic seizures are characterized by sudden brief jerks or twitching movements and occur especially in the morning.
- Tonic seizures cause muscle stiffening in the arms, legs, and back and sometimes cause the individual to lose consciousness and fall.
- Tonic-clonic seizures (or grand mal seizures) are often seen in epilepsy but can also be caused by other conditions (e.g., brain injury, infection, congenital or development abnormalities, or drug or alcohol withdrawal). Tonic-clonic seizures may be several minutes in duration and involve a tonic phase, which lasts 10–30 seconds and frequently is characterized by screaming and an abrupt loss of consciousness, and a clonic phase, which lasts 30–60 seconds or longer and is characterized by convulsions.
- Tonic-atonic seizures involve a tonic episode followed by an atonic episode.
Causes
Seizures may be caused by genetic disorders or congenital abnormalities, such as abnormalities of blood vessels in the brain. Acquired conditions and injuries associated with seizures include stroke, severe concussion, traumatic brain injury, degenerative brain diseases (e.g., Alzheimer disease or frontotemporal dementia), infection, and lack of sleep. Flashing lights, moving patterns, and certain medications also can trigger a seizure in some persons. Some seizures are related to drug use, including alcohol intoxication and alcohol withdrawal. High fever can cause febrile seizures; this is especially common in children between six months and five years of age.
Diagnosis and treatment
Seizure disorders may be diagnosed based on medical history, symptoms, and various tests, including electroencephalogram (EEG), computed tomography (CT), magnetic resonance imaging (MRI), spinal tap, and blood testing. Treatment varies widely and is based on treating the underlying cause. If the cause cannot be identified or treated, antiepileptic drugs may be prescribed. Some patients also benefit from a ketogenic diet (a low-carbohydrate, high-protein diet). Surgery may be undertaken in cases in which scarred brain tissue is suspected of triggering seizures. Vagus nerve stimulation, in which an implanted device sends mild electrical pulses to the brain via the vagus nerve to stabilize electrical activity in the brain, may be used to prevent or reduce the frequency of seizures.