The type of seizure that originates on one side of the brain is called a focal seizure , also known as a focal onset seizure. These seizures begin in a specific area within one hemisphere of the brain and can cause symptoms corresponding to the brain region affected. Focal seizures may stay localized or sometimes spread to involve both sides of the brain, potentially turning into a bilateral tonic-clonic seizure. They are distinct from generalized seizures, which affect both hemispheres from the onset. Focal seizures can have various manifestations depending on the brain lobe involved—for example, sensory disturbances, motor symptoms, or changes in awareness. These seizures are the most common type and are often associated with conditions like stroke, brain injury, or infections affecting the brain.