What Is an EEG (Electroencephalogram)

An EEG, or electroencephalogram, is a test that records the electrical signals of the brain by using small metal discs (called electrodes) that are attached to your scalp. Your brain cells communicate with each other using electrical impulses. They’re always working, even if you’re asleep. That brain activity will show up on an EEG recording as wavy lines. It’s a snapshot in time of the electrical activity in your brain. 

EEG Uses

EEGs are used to diagnose conditions like:

  • Brain tumors
  • Brain damage from a head injury
  • Brain dysfunction from various causes (encephalopathy)
  • Inflammation of the brain (encephalitis)
  • Seizure disorders including epilepsy
  • Sleep disorders
  • Stroke

An EEG may also be used to determine if someone in a coma has died or to find the right level of anesthesia for someone in a coma.

EEG Risks

EEGs are safe. If you have a medical condition, talk with the doctor about it before your test.

If you have a seizure disorder, there’s a slight risk that the flashing lights and deep breathing of the EEG could bring on a seizure. This is rare. A medical team will be on hand to treat you immediately if this happens.

In other cases, a doctor may trigger a seizure during the test to get a reading. Medical staff will be on hand so the situation is closely monitored.

Preparing for an EEG

There are some things you should do to prepare for EEG:

  • Don’t eat or drink anything with caffeine for 8 hours before the test.
  • Your doctor may give you instructions on how much to sleep if you’re expected to sleep during the EEG.
  • Eat normally the night before and day of the procedure. Low blood sugar could mean abnormal results.
  • Let your doctor know about any medications — both prescription and over-the-counter — and supplements you’re taking.
  • Wash your hair the night before the test. Don’t use any leave-in conditioning or styling products afterward. If you are wearing extensions that use glue, they should be removed.

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