Epilepsy is a brain disorder in which clusters of nerve cells, or neurons, in the brain sometimes signal abnormally. In epilepsy, the normal pattern of neuronal activity becomes disturbed, causing strange sensations, emotions, and behavior. Sometimes it causes convulsions, muscle spasms, and loss of consciousness. Epilepsy is a disorder with many possible causes. Some of these causes vary anywhere from illness to brain damage to abnormal brain development and can lead to having a seizure. Anything that disturbs the normal pattern of neuron activity can lead to having a seizure. Epilepsy may develop because of an abnormality in brain wiring, an imbalance of nerve signaling chemicals called neurotransmitters, or some combination of these factors. Having a seizure does not necessarily mean that a person has epilepsy. Only when a person has had two or more seizures is he or she considered to have epilepsy. EEGs and brain scans are common diagnostic test for epilepsy.