Focal seizures (also called partial seizures and localized seizures) are seizures which affect initially only one hemisphere of the brain. The brain is divided into two hemispheres, each consisting of four lobes – the frontal, temporal, parietal and occipital lobes. A focal seizure is generated in and affects just one part of the brain – a whole hemisphere or part of a lobe. 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. Types As of 2017, focal seizures are split into two main categories, focal onset aware, and focal onset impaired awareness. What was previously termed a secondary generalised seizure is now termed a focal to bilateral seizure. In focal onset aware seizures, a small part of one of the lobes may be affected and the person remains conscious. This can often be a precursor to a larger focal onset impaired awareness seizure. When this is the case, the focal aware seizure is usually called an aura. A focal impaired awareness seizure affects a larger part of the hemisphere and the person may lose consciousness. If a focal seizure spreads from one hemisphere to the other side of the brain, this will give rise to a focal to bilateral seizure. The person will become unconscious and may experience a tonic clonic seizure. When people have multiple focal seizures they generally have a condition known as temporal lobe epilepsy. (A generalized seizure is one that involves both sides of the brain from the onset.) Simple partial seizures Simple partial seizures are seizures which affect only a small region of the brain, often the temporal lobes or structures found there, such as the hippocampi. People who have focal aware seizures remain conscious. Focal aware seizures often precede larger focal impaired awareness seizures, where the abnormal electrical activity spreads to a larger area of the brain. This can result in a tonic-clonic seizure. Presentation Simple partial seizures are a very subjective experience, and the symptoms vary greatly between people. Since symptoms can be subtle, diagnosis can be delayed by months or years. The