A seizure is best thought of as an uncontrolled, abnormal burst of electrical and chemical activity that spreads rapidly between nerve cells (millions upon millions of them) in the brain. A seizure may start in one region of the brain (the "focus") and spread to other parts. The first symptoms of a seizure, referred to as the "aura" (often a strange sensation or smell) reflect the function of that part of the brain first affected by the epileptic activity. A seizure that initially causes only twitching of one hand and then goes on to convulsions with loss of consciousness, for example, reflects seizure activity that starts in the front part of one hemisphere and then spreads to involve wides
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pread areas on both sides of the brain.
Seizures are a feature of a variety of states of ill-health, and have many differing causes. Seizures may be the only manifestation of disease, may be caused by a specific brain disorder, or are seen as part of a more generalised bodily illness.
Primary epilepsy refers to seizures, often seen in children and teenagers, where the brain is abnormally prone to seizure activity, probably due to an inherited tendency. Secondary seizures, on the other hand, are typically due to spread from a seizure focus (a scar). Finally, isolated seizures may be related to an underlying transient medical condition, and will stop as soon as the underlying condition is effectively treated; examples would include organ failure (liver or kidney failure), infections such as meningitis, head injury, brain surgery, drug and alcohol abuse.
In all forms of epilepsy, stress, sleep deprivation, a change in diet or medication, alcohol, certain specific activities, and menstruation and pregnancy in women may precipitate individual seizures.
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