1 What is an EEG (Electroencephalogram)?

An electroencephalogram (EEG) is a test that is used to detect electrical activity in your brain by using small, flat metallic discs (electrodes) attached to your scalp. 

Your brain cells communicate via impulses and are always active, even when you are 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 may also play a role in diagnosing other brain disorders.

2 Reasons for Procedure

The main reason for an EEG is determining changes in brain activity that may be useful in making a diagnosis of brain disorders, especially epilepsy.

An EEG cannot be used to measure intelligence or to detect mental illness.

However, it may be useful in diagnosing or treating the following disorders:

  • Epilepsy or other seizure disorders
  • Brain tumor
  • Head injury
  • Brain dysfunction that may have a variety of causes (encephalopathy)
  • Inflammation of the brain (encephalitis)
  • Stroke
  • Sleep disorders
  • Dementia

An EEG can also be helpful to make a confirmation of brain death in someone who is in a persistent coma. A continuous EEG id used to help find the right level of anesthesia for an individual in a medically induced coma.

3 Potential Risks

EEGs are safe and painless tests. But in some cases, there is a risk of seizures.

Seizures are unintentionally triggered in individuals with epilepsy during the test, but appropriate medical care is provided if needed.

4 Preparing for your Procedure

You need to do the following to prepare for an EEG:

  • Wash your hair the night before the day of the test.
  • Do not use any conditions, hair creams, sprays or styling gels. Hair products can make it difficult for the sticky patches that hold the electrodes to adhere to your scalp.
  • Avoid caffeine, as it is known to affect the test results.
  • Take your usual medications, unless instructed otherwise.
  • If you are supposed to sleep during your EEG test, your doctor may ask you to sleep less or even avoid sleep entirely the night before your EEG.

5 What to Expect

Here’s what you can expect during and after your EEG (Electroencephalogram) test.

During the test

You will be quite comfortable during an EEG, experiencing little to no discomfort. The electrodes do not transmit any sensations. They merely record your brain waves.

You can expect the following to happen during an EEG:

  • 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 may be scrubbed with a gritty cream to improve the quality of the recording.
  • A technician 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, makes bigger, the brainwaves and records them on computer equipment. Once the electrodes are in place, an EEG typically takes up to 60 minutes. If you need to sleep for the test, it may take up to three hours.
  • 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 look at a flashing light.
  • The video is frequently recorded during the EEG. Your body motions are captured by a video camera while the EEG simultaneously records your brain waves. This combined recording may help your doctor diagnose and treat your condition.

After the test

After the test, the technician removes the electrodes or cap. If no sedative was given, you should feel no side effects after the procedure, and you can return to your normal routine.

If you used a sedative, it will take a little while for the medication to begin to wear off. Arrange to have someone drive you home. Once home, rest and don't drive for the remainder of the day.

6 Procedure Results

The test is conducted by technicians. Doctors trained to analyze the EEG interpret the recording, and the results are sent to the doctor who ordered the EEG.

Your doctor may schedule an appointment to discuss the results of the test. It’s advisable to bring along a family member of friend.

It can be difficult to absorb all of the information provided during an appointment. The individual who accompanies you may remember something you forgot or missed.

Write down the questions that you want to ask your doctor. Do not be afraid to ask questions or speak up if you do not understand something your doctor says.

You might want to include the following questions:

  • Based on the results, what are my next steps?
  • What kind of follow-up, if any, do I need?
  • Are there any factors that might have affected the results of this testing some way?
  • Will I need to repeat the test at some point in the future?

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