Epilepsy. This abstract artwork, based on a patient's description of what an epileptic seizure feels like, shows lightning inside a human brain against a background of nerve cells. The large shaft of lightning runs along the end of a nerve cell and across the gap (synapse) to another cell. The pink spheres spreading across the gap are neurotransmitters, the chemical messengers that carry an impulse from one nerve cell to the next. Epileptic seizures are caused by chaotic electrical activity in the brain. Attacks can be triggered by a variety of factors, such as illness or stress, although the underlying cause is not understood.