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. 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. 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. 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.
