An electroencephalogram (EEG) is a test in which electrodes are placed on a patient’s head to record the brain's electrical activity as a series of brain waves. The information is used to diagnose or monitor a number of conditions including epilepsy, infections, metabolic disorders, head injuries, structural problems in the brain and sleep disorders.

Patients should follow any preparatory recommendations suggested by their physician prior to the test. These may include changes to diet or medication regimen. Patients are usually instructed to wash their hair the night before the test, but to avoid using conditioners or any products that leave residue (e.g., gels, oils).

An EEG typically takes place at a health care provider’s office or a hospital. On the day of the test, up to 25 flat metal discs called electrodes are placed on the patient’s head. As electrical activity occurs in the brain, the electrodes measure what is taking place and send the information to the EEG machine.

Patients may be asked to perform several actions during the test such as breathing deeply or watching a flashing light. These are designed to stimulate brain activity that can be viewed on the EEG.

Following the test, the electrodes are removed, and the patient is allowed to return home. No recovery time is required. A specially trained neurologist known as an electroencephalographer analyzes the results and reports a diagnosis to the patient’s physician. Appropriate treatment follows based on this diagnosis.

A standard EEG is a very safe procedure that poses few risks to patients.