An electroencephalogram (EEG) is a test used to evaluate the electrical activity in the brain. Brain cells communicate with each other through electrical impulses, and an EEG can be used to help detect problems associated with this activity. The test tracks and records brain wave patterns. Small metal discs with thin wires (electrodes) are placed on the scalp, and then send signals to a computer to record the results.

Common uses for an EEG include diagnosing epilepsy and other seizure disorders, diagnosing head injuries, brain tumors, brain dysfunction that might have a variety of causes (encephalopathy), inflammation of the brain (encephalitis), stroke, and dementia. It can also be used to determine the level of consciousness in a person who is in a coma, and it may be used in research for brain-computer interface systems.

During the test, you may be asked to breathe deeply and rapidly (hyperventilate), or you may be exposed to a bright flashing light. These actions can help reveal brain wave patterns not seen during the resting state. The EEG is painless and generally considered safe. There is no risk of electric shock, as the electrodes do not transmit any sensations. They just record your brain waves.