Most people with epilepsy have no warning before a seizure. However some people experience a warning feeling - an odd smell, lights being over-bright, stomach discomfort, or just "not feeling right" - before a seizure. This is called an aura, which is in fact a small seizure itself. Most auras occur seconds before the seizure, but some start earlier.

Auras can take many forms, depending on which part of the brain they happen in. For example, if they're in the part of the brain that controls sight, the person might notice their vision is affected; if they're in the part of the brain that controls mood, the person might (in addition to other seizure symptoms) suddenly feel happier or sadder or angrier.

What form a person's aura takes can tell a doctor where in the brain the person's seizures are starting (called a focal zone). Surgery to cut out or isolate the focal zone may help eliminate the seizures.

If a person experiences two or more different warning sensations (either one after the other, or all at once), this has been thought to indicate that they have more than one focal zone, each causing seizures independently. This sort of epilepsy would not be treatable with surgery, as trying to cut out all these different areas would be too damaging.

Researchers at the Cleveland Clinic Epilepsy Center in Ohio, USA, specifically reviewed the case files of all patients with multiple auras that they had assessed since 1989, to see whether this was true. Thirty-one patients had two types of aura; twelve had three or more. These patients accounted for only 0.4% of all patients with auras they had assessed in 16 years.

All these patients had had extensive video-EEG testing, to find out where in the brain their seizures started. Dr Prakash Kotagal and his colleagues found that over 90% of patients with two or three auras had seizures starting in the non-dominant side of the brain. Seizures here affect consciousness less than seizures in the dominant side of the brain, which means the patient can be aware of them as they spread.

This suggests that multiple auras don't usually indicate multiple focal zones, but instead indicate the spread of the seizure through several areas which produce different symptoms, before spreading throughout the brain in the main seizure. Patients with multiple auras are therefore good candidates for surgery. In total, 19 of the patients in this study had surgery for their epilepsy: ten became seizure-free, showing that surgery can effectively treat these patients.

The significance of multiple auras for surgery has not previously been investigated separately. In their article, published in August in the journal Neurology, the authors call for doctors to be aware of what multiple auras may mean, and to consider treating these patients with surgery.

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