An electroencephalogram (EEG) is a test that detects electrical activity in your brain using small, flat metal discs (electrodes) attached to your scalp. Your brain cells communicate via electrical impulses and are active all the time, even when you’re asleep. This activity shows up as wavy lines on an EEG recording.

An EEG is one of the main diagnostic tests for epilepsy. An EEG may also play a role in diagnosing other brain disorders.

An EEG can determine changes in brain activity that may be useful in diagnosing brain disorders, especially epilepsy. An EEG can’t measure intelligence or detect mental illness. An EEG may be helpful for diagnosing or treating the following disorders:

• Epilepsy or other seizure disorder
• Brain tumor
• Head injury
• Brain dysfunction that may have a variety of causes (encephalopathy)
• Inflammation of the brain (encephalitis)
• Stroke
• Sleep disorders
• Dementia

An EEG may also be used to confirm brain death in someone in a persistent coma. A continuous EEG is used to help find the right level of anesthesia for someone in a medically induced coma.