What happens in the brain during a seizure?

The short answer is that complex chemical changes happen in nerve cells in your brain and lead to a sudden surge of unusual electrical activity.

To understand this, you need to know that brain cells can either excite (start) or inhibit (stop) other brain cells from sending messages. Usually there is a balance in your brain of cells that start and stop the messages. But when a seizure happens, there may be too much or too little activity, which causes an imbalance between the starting and stopping messages. These chemical changes can lead to the surges of electrical activity that cause seizures.

A single seizure is not a disease . Recurring seizures that are considered epilepsy can be thought of as a disease or disorder. The terms disease and disorder essentially mean the same thing.  Merriam-Webster online medical dictionary defines these terms as:

  • A disorder is “an abnormal physical or mental condition”
  • A disease is “ an illness that affects a person” or "a condition that prevents the body or mind from working normally”

Seizures are symptoms of many different disorders or diseases that affect the brain. Some seizures are so mild that you hardly notice them, while others are very severe.

"There are many types of seizures, because different parts of the brain control different behaviors, movements and experiences."

If I have just one or two seizures, how likely is it that I will get epilepsy?

  • If you have one seizure without a clear cause, there’s about a 1 in 2 chance you’ll have another one, usually within 6 months.
  • If you have one seizure with a known cause (like a brain injury or other known brain condition), then you are twice as likely to have another seizure.
  • If you have two seizures, there's about a 4 in 5 chance that you'll have more.
  • If your first seizure happened at the time of an injury or infection in the brain, you are more likely to develop epilepsy. Often, more seizures don’t happen until weeks or months after the injury or infection.

Are there tests to see if I might have more seizures?

Yes. Tests can be done to see how your nervous system is working. If certain results are found on these tests, it’s likely that you will have more seizures. But people can still have seizures and epilepsy with normal results on most tests.

One of these tests is an EEG test, or electroencephalogram (“e-LEK-tro_en_SEF-uh_LOG-ram”). An EEG can look at electrical activity in the brain. It may help predict whether you will have more seizures. Certain patterns on the EEG are typical of epilepsy. If your brain waves show patterns of that type, you are about twice as likely to develop epilepsy.

Examples of Electroencephalogram Results

Normal Adult EEG  (no signs of epilepsy)


Primary Generalized Epilepsy EEG

Authored By: 
Patty Obsorne Shafer RN, MN
Authored Date: