Focal (or partial) seizures occur when seizure activity is restricted to brain networks in one hemisphere. There is a site, or a focus, in the brain where the seizure begins. Different areas of the brain have different functions, so a person’s experience during a focal seizure and what other people may witness will depend on which region of the brain the seizure activity is occurring in.
If a seizure begins in a brain region that is responsible for processing visual information, a person could have a temporary disturbance in their vision. If a seizure begins in a brain region that is responsible for movement, a person could have a temporary uncontrollable twitching of one or more body parts. If a seizure begins in a brain region that is responsible for feelings, a person could have a change in their emotions such as a sudden onset of fear.
The most common forms of focal seizures are:
- focal seizure with retained awareness (sometimes referred to as an aura)
- focal seizure with loss of awarness (or focal dyscognitive)
After a focal seizure begins, the seizure activity will either remain in a localized area or the seizure activity may spread to other brain areas either within the same hemisphere or the opposite hemisphere. A focal seizure with retained awareness can evolve into a focal dyscognitive seizure. A focal seizure can also evolve into a generalized tonic-clonic (convulsive) seizure.
Some people with focal epilepsy have a single focus where their seizures always originate. Other people have more than one seizure focus, known as multi-focal epilepsy.