Editing Seizure (section)

===Focal seizures===
[[Focal seizure]]s originate within a network limited to one [[Cerebral hemisphere|hemisphere]] of the brain.<ref name="Berg2010">{{Cite journal |last=Berg |first=Anne T. |last2=Berkovic |first2=Samuel F. |last3=Brodie |first3=Martin J. |last4=Buchhalter |first4=Jeffrey |last5=Cross |first5=J. Helen |last6=Van Emde Boas |first6=Walter |last7=Engel |first7=Jerome |last8=French |first8=Jacqueline |last9=Glauser |first9=Tracy A. |last10=Mathern |first10=Gary W. |last11=Moshé |first11=Solomon L. |last12=Nordli |first12=Douglas |last13=Plouin |first13=Perrine |last14=Scheffer |first14=Ingrid E. |date=2010 |title=Revised terminology and concepts for organization of seizures and epilepsies: Report of the ILAE Commission on Classification and Terminology, 2005–2009 |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1528-1167.2010.02522.x |journal=Epilepsia |language=en |volume=51 |issue=4 |pages=676–685 |doi=10.1111/j.1528-1167.2010.02522.x |issn=1528-1167}}</ref> They may arise from the cerebral cortex or subcortical structures. For a given seizure type, the site of onset tends to be consistent across episodes. Once initiated, the seizure may remain localized or spread to adjacent areas, and in some cases, may propagate to the opposite hemisphere (contralateral spread). Despite this potential for spread, the initial focus remains consistent.

They are subdivided based on whether consciousness is preserved or impaired, a classifier defined by awareness and responsiveness during the event:<ref name="Beniczky2025" />

* Focal preserved consciousness seizure: the person remains aware and responsive.
* Focal impaired consciousness seizure: awareness and/or responsiveness are affected.

They can manifest with motor, sensory, autonomic, cognitive, or emotional symptoms, depending on the regions involved. Some focal seizures can evolve into focal-to-bilateral [[Generalized tonic–clonic seizure|tonic-clonic seizures]], where abnormal brain activity spreads to both hemispheres.