An electroencephalogram (EEG) is a test that evaluates the electrical activity in your brain. This activity shows up as wavy lines on an EEG recording.
An EEG can determine changes in brain activity that may be useful in diagnosing brain disorders, especially epilepsy. 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)
- Sleep disorders
To prepare for an EEG:
Wash and dry your hair the night before or the day of the test, but don’t use any conditioners, hair creams, sprays or styling gels. Hair products can make it harder for the sticky patches that hold the electrodes to adhere to your scalp.
Avoid alcohol and anything with caffeine on the day of the test, because caffeine can affect the test results.
Take your usual medications unless instructed otherwise.
If you’re supposed to sleep during your EEG, your physician may ask you to sleep less or even avoid sleep entirely the night before your EEG.
You’ll feel little or no discomfort during an EEG. The electrodes don’t transmit any sensations. They just record your brain waves.
Here are some things you can expect to happen during an EEG:
A technologist attaches flat metal discs (electrodes) to your scalp using a special adhesive. Sometimes, an elastic cap fitted with electrodes is used instead. The electrodes are connected with wires to an instrument that amplifies the brain waves and records them on computer equipment.
Once the electrodes are in place, an EEG typically takes up to 60 minutes. You relax in a comfortable position with your eyes closed during the test. At various times, the technician may ask you to open and close your eyes, perform a few simple calculations, read a paragraph, look at a picture, breathe deeply (hyperventilate) for a few minutes, or place a flashing light above your face while your eyes are closed.
After the test, the technologist removes the electrodes or cap. You should feel no side effects after the procedure, and you can return to your normal routine.
If you are sleep deprived, arrange to have someone to bring you and drive you home.
Technologists conduct the test. Neurologists trained to analyze EEGs interpret the recording, and the results are sent to the physician who ordered the EEG. Your doctor may schedule an office appointment to discuss the results of the test.