What Is Epilepsy?

Epilepsy—also called seizure disorder—is a disease of the brain that causes recurrent, unprovoked seizures. When someone has epilepsy, the brain’s electrical functions are disrupted by abnormal bursts of electrical energy that are more intense than usual.

These disruptions in electrical activity may cause abnormal sensations such as numbness, strange taste or smell, a loss of consciousness or uncontrolled bodily movements. Often, the person is only partially aware of the seizure.

There are two main types of epilepsy:

Generalized epilepsy: Abnormal electrical discharges that involve all areas of the brain at the beginning of the seizure are called generalized seizures. In many generalized epilepsies, the brain looks completely normal and has no structural abnormality to explain the seizure. This type of epilepsy is thought to be caused by a genetic (inherited) predisposition.

In some cases, generalized epilepsies are associated with brain abnormalities, which are sometimes caused by:

  • Brain infections
  • Head injuries
  • Lack of oxygen

Focal epilepsy: Abnormal electrical activity that starts in a small area in the brain and spreads to the rest of the brain is called focal seizure. Focal epilepsies are often caused by a lesion (or scar) detectable on an MRI scan. Typical lesions that cause focal epilepsy are:

  • Hippocampal sclerosis (hardening of the hippocampus)
  • Scarring after stroke or trauma
  • Small area of disorganized brain tissue
  • Benign brain tumor
  • Malformed blood vessel

When seizures are triggered by something other than abnormal electrical activity in the brain, they are not caused by epilepsy. Non-epileptic seizures may be caused by:

  • Low blood sugar
  • Infections
  • Drug overdose or withdrawal
  • Emotional stress

Related Resources


  • Video-EEG Monitoring: EEG portion of the test looks at electrical activity of the brain and the video recording shows how the body responds during a seizure.
  • Wada Testing: Learn more about this test, which examines each side of your brain.
  • Specialized Treatment for Epilepsy: The Northwestern Medicine Comprehensive Epilepsy Center maintains the highest designation by the National Association of Epilepsy Centers.


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