Neurodiagnostics

What is an EEG?

An electroencephalogram (EEG) is a test that detects electrical activity in your brain using small, 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 can also play a role in diagnosing other brain disorders.

Why it’s done

An EEG can determine changes in brain activity that might be useful in diagnosing brain disorders, especially epilepsy or another seizure disorder. An EEG might also be helpful for diagnosing or treating the following disorders:

  • Brain tumor

  • Brain damage from head injury

  • Brain dysfunction that can have a variety of causes (encephalopathy)

  • Inflammation of the brain (encephalitis)

  • Stroke

  • Sleep disorders

How you prepare

Food and medications

  • Avoid anything with caffeine on the day of the test because it can affect the test results.

  • Take your usual medications unless instructed otherwise.

Other precautions

  • Wash your hair the night before or the day of the test, but don't use 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.

  • If you're supposed to sleep during your EEG test, your doctor might ask you to sleep less or avoid sleep the night before your test.

What you can expect

During the test

  • You'll feel little or no discomfort during an EEG. The electrodes don't transmit any sensations. They just record your brain waves.

  • A technician measures your head and marks your scalp with a special pencil to indicate where to attach the electrodes. Those spots on your scalp might be scrubbed with a gritty cream to improve the quality of the recording.

  • A technician attaches 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. Testing for certain conditions require you to sleep during the test. In that case, the test can be longer.

  • You relax in a comfortable position with your eyes closed during the test. At various times, the technician might ask you to open and close your eyes, perform a few simple calculations, read a paragraph, look at a picture, breathe deeply for a few minutes, or look at a flashing light. Source: Mayo Clinic