Focal seizure

Focal seizure
Other names	Partial seizures, localized seizures
Specialty	Neurology

Focal seizures are seizures that originate within brain networks limited to one hemisphere of the brain. In most cases, each seizure type has a consistent site of onset and characteristic patterns of spread, although some individuals experience more than one type of focal seizure arising from distinct networks. Seizure activity may remain localized or propagate to the opposite hemisphere.^[1] Symptoms will vary according to where the seizure occurs. When seizures occur in the frontal lobe, the patient may experience a wave-like sensation in the head. When seizures occur in the temporal lobe, a feeling of déjà vu may be experienced. When seizures are localized to the parietal lobe, a numbness or tingling may occur. With seizures occurring in the occipital lobe, visual disturbances or hallucinations have been reported.^[2] Some focal seizures begin with an aura — a subjective experience that precedes or constitutes the seizure itself, particularly in focal preserved consciousness seizures.

Under the 2025 classification of the International League Against Epilepsy (ILAE), focal seizures are divided into three types: those with preserved consciousness, those with impaired consciousness, and those that evolve to bilateral tonic–clonic activity.^[3] Historically known as "partial seizures," focal seizures were previously subdivided into "simple partial" (preserved consciousness) and "complex partial" (impaired consciousness). These terms have been deprecated in favor of biologically grounded terminology aligned with advances in neurophysiology and imaging.

Focal seizures are defined by their origin within a brain network confined to one cerebral hemisphere. Although clinical features such as the location of the epileptogenic zone or the context of occurrence are important in diagnosis and treatment, they are not part of the formal seizure classification.

Under the 2025 classification of the ILAE, focal seizures are divided into three types based on the level of consciousness and seizure evolution: focal preserved consciousness seizures (FPC), focal impaired consciousness seizures (FIC), and focal to bilateral tonic-clonic seizures (FBTC).^[1] These biologically grounded categories replace older terms such as "simple partial" and "complex partial", which relied on descriptive criteria that did not always reflect underlying mechanisms.

Focal preserved consciousness seizures formerly known as simple partial seizures) occur when seizure activity is confined to one region of the brain without impairing the individual's awareness or responsiveness.^[4] These seizures are often brief, lasting only seconds to a couple of minutes, and the person remains fully aware of their surroundings during the event. They may report unusual sensations or experiences, such as tingling, auditory or visual hallucinations, or a sense of déjà vu. The symptoms are localized to the part of the brain where the seizure originates, and the person typically retains full memory of the event afterward.^[1]

Focal impaired consciousness seizures (formerly known as complex partial seizures) are characterized by a reduction or complete loss of awareness and responsiveness during the seizure. The onset of these seizures can lead to a variety of symptoms, including motor automatisms (such as lip-smacking or hand movements), cognitive disruptions (such as disorientation or memory loss), and emotional experiences (such as fear or anxiety). Unlike FPC seizures, individuals experiencing FIC may not remember the event afterward and may appear confused, dazed, or unresponsive.^[1] These seizures usually last from 30 seconds to 2 minutes, and may progress to focal to bilateral tonic-clonic seizures if the seizure activity spreads to both hemispheres. Common causes include temporal lobe epilepsy, though extratemporal origins have been observed in about 10-30% of patients.^[5]

Focal to bilateral tonic-clonic seizures begin as focal seizures but spread to involve both hemispheres, resulting in a tonic-clonic seizure. These seizures are typically associated with complete loss of consciousness and the typical tonic-clonic activity, which involves muscle stiffening (tonic phase) followed by rhythmic jerking (clonic phase).^[1]

The symptoms of focal seizures depend on which brain regions are affected and how seizure activity propagates through neural networks. While focal seizures are classified by consciousness and evolution (preserved, impaired, or focal to bilateral tonic–clonic), their clinical presentation is captured using semiological descriptors, as outlined in the ILAE 2025 classification.

Motor symptoms are common in focal seizures and can be classified as elementary or complex. Elementary motor features include clonic movements, tonic posturing, dystonia, myoclonus, epileptic spasms, and versive movements, such as forced turning of the eyes or head.^[6][7] Complex motor features involve automatisms — repetitive, seemingly purposeful movements that occur without conscious control. These may include oral automatisms (such as lip-smacking or chewing), gestural movements of the hands or limbs, genital automatisms, or mimic expressions such as smiling or laughing.^[1] Hyperkinetic behavior, involving large and often violent movements of the trunk and limbs, is particularly associated with seizures originating in the frontal lobe.^[8]

In some cases, motor activity progresses in a characteristic pattern known as a Jacksonian march, in which abnormal movements begin in a distal region — typically the fingers or toes — and spread to more proximal areas such as the hand, arm, face, or leg on the same side of the body.^[9] This sequential progression reflects the organization of the motor homunculus and is characteristic of seizures arising from the precentral gyrus. Consciousness is usually preserved during a Jacksonian march, although the seizure may evolve to impaired consciousness or generalize secondarily. The phenomenon is named after English neurologist John Hughlings Jackson, who described the progressive nature of such seizures in the 19th century.

Focal seizures may produce a wide range of sensory symptoms, depending on the region involved. These sensory phenomena often serve as an early warning sign or an aura, which is a brief, subjective sensation that can precede the seizure or constitute the seizure itself in focal preserved consciousness seizures.^[10] Somatosensory features are among the most common, often described as tingling, numbness, or a sense of electric current moving through a limb or across the body. These symptoms typically reflect involvement of the postcentral gyrus or adjacent parietal areas.^[10] Visual phenomena can include simple hallucinations such as flashes of light, geometric patterns, or scotomas, often indicating occipital lobe involvement. More complex visual hallucinations — such as formed images, faces, or scenes — are commonly associated with temporal lobe epilepsy.^[11] Auditory symptoms range from simple sounds (e.g. buzzing, ringing, or tones) to more complex perceptions such as music or voices, which are typically associated with the superior temporal gyrus.^[12] In some cases, complex auditory hallucinations may also be associated with epilepsy.^[13] Olfactory and gustatory auras, often described as unusual smells or tastes, are less common but may arise from the medial temporal lobe or insula.^[14] Vestibular sensations such as dizziness, tilting, or a sense of floating may also occur, particularly in seizures involving the temporoparietal junction or insular cortex. These symptoms may be brief, stereotyped, and difficult for individuals to describe precisely, especially when awareness is impaired.^[14][15]

Autonomic symptoms are common in focal seizures and can occur as either subjective experiences or objective signs. These symptoms can occur with or without impaired awareness. Autonomic seizures may be the only manifestation (referred to as an autonomic aura) or may be followed by other seizure types, such as focal to bilateral tonic-clonic seizures, as the epileptic discharge spreads. Autonomic symptoms result from disruption of the central autonomic network, often due to discharges originating in the mesial temporal lobe.Common autonomic manifestations include cardiovascular changes (e.g., tachycardia, bradycardia, or ictal asystole), respiratory disturbances (e.g., apnea, hyperventilation), and gastrointestinal symptoms (e.g., nausea, hypersalivation). In some cases, ictal asystole can lead to loss of tone, tonic stiffening, or tonic-clonic movements.^[16]

Focal seizures can involve sudden and intense emotional experiences that arise without external stimulus.^[17] Fear is the most frequently reported emotion, often occurring as a brief but overwhelming sensation at seizure onset. Other emotions may include anxiety, sadness, anger, or guilt. These experiences are usually stereotyped across seizures and may be accompanied by autonomic signs such as tachycardia or nausea. Some seizures involve more unusual or striking emotional states. Ecstatic or blissful sensations have been described as profound feelings of peace, clarity, or connectedness. Similarly, mystic experiences, feelings of déjà vécu, or alterations in self-perception may occur in seizures affecting association areas. Gelastic seizures, characterized by inappropriate or involuntary laughter, and dacrystic seizures, involving crying, are less common but can also occur.

Focal seizures can disrupt cognitive functions, including memory, language, attention, and higher-order processing. These manifestations vary according to the cortical regions involved and are particularly common in seizures arising from the temporal or frontal lobes. Language disturbances may include speech arrest, expressive aphasia, or paraphasic errors.^[6]

Individuals may report a vague sense of unease, internal shift, or premonition that something is about to happen.^[6]

Most people with focal seizures due to epilepsy require medications to manage the condition. Not all epileptics find that the medications given are effective at preventing seizures; approximately 30% cannot keep their seizures in remission.^[18] A newer pharmaceutical approach using immunomodulator drugs in addition to standard medication treatments has been suggested and there is some evidence that this approach may reduce the frequency of focal seizures.^[18] It is not clear if this medicine is well tolerated in adults and children.^[18]