Electroencephalogram (EEG)

Video Thumbnail 0010 What is an EEG

An EEG (Electroencephalogram) is a test used to evaluate the electrical activity in the brain and detect problems associated with that activity.

Your brain cells communicate via electrical impulses and are active all the time, even when you're asleep. An EEG amplifies and records this activity to detect problems with the brain’s communication.

Why do I need this test?

Measuring electrical activity within the brain is an important tool in evaluating issues in the brain.

An EEG can help diagnose:

  • Several types of brain disorders, most notably epilepsy
  • Lesions of the brain, which can result from tumors or stroke
  • Disorders that influence brain activity, such as Alzheimer’s disease, certain psychoses, and memory problems
  • Drug intoxication
  • Trauma, or the extent of brain damage in comatose patients
  • Sleep disorders and narcolepsy
  • Encephalitis and encephalopathy

It may also be used during surgical procedures, for example, to monitor blood flow in the brain.

A continuous EEG is used to help find the right level of anesthesia for someone in a medically induced coma. It might also be used to confirm brain death in someone in a persistent coma.

There are various other reasons for your healthcare provider to recommend an EEG because they are extremely helpful in making an accurate diagnosis and creating an effective treatment plan.

Are there any risks?

The EEG has been used for many years and is considered a safe procedure. The test causes no discomfort.

The electrodes simply record activity. They do not produce any sensation. In addition, there is no risk of getting an electric shock.

In rare instances, an EEG can cause seizures in a person with a seizure disorder due to the flashing lights or the deep breathing that may be involved during the test. If you do get a seizure, your healthcare provider will treat it immediately.

Please alert your physician if you have a seizure disorder. Other risks may be present, depending on your specific medical condition. Be sure to talk about any concerns with your healthcare provider before the procedure.

What should I do to prepare?

Several simple preparations are important to a successful test:

  • Tell your healthcare team about all medications (prescription and over-the-counter as well as herbal supplements) that you are taking. They will let you know if you should take your usual medications before your test or not.
  • Do not drink alcohol on the day of your test.
  • Do not eat or drink anything that contains caffeine on the day of the test, because caffeine can affect the test results.
  • You may wash your hair the night or day before the test but do not use hair products (conditioner, cream, spray, gel or oil). Hair products can prevent the obtaining of a good and useful recording.
  • Hair should also be free of weaves, extensions, and braids.
  • If you are instructed to be sleep-deprived, follow your physician’s instructions regarding when and how long to sleep in the 24 hours or more before the test.

You may want to wear loose clothing. You may be asked to remove jewelry during your test, so it's also a good idea to leave any valuables at home.

Young children may need some special preparation. Your doctor can provide tips to help alleviate any fears or issues for your child.

The physicians at Semmes Murphey Clinic have a world-renown reputation in pediatric surgery and treatment based on their many years’ experience treating patients at both LeBonheur Children’s Hospital and St. Jude Children’s Research Hospital. Your doctor will help you prepare your child for this test and any phase of their treatment.

What should I 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. Anesthesia or sedatives are not necessary for an EEG.

The EEG will be administered by a trained technologist who will be in the room throughout the test.

Here are some things you can expect to happen during an EEG:

  • A technician measures your head and marks your scalp with a special pencil to indicate where to attach the 16 to 25 electrodes. Those spots on your scalp might be scrubbed with a gritty cream to improve the connection and 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 to an instrument that amplifies and records the brain waves.
  • Once the electrodes are in place, an EEG typically takes 30 to 60 minutes. The test can be longer if you need to sleep during the test.
  • If you need to be monitored for a longer period, you may also be admitted to the hospital for prolonged EEG (24-hour EEG) monitoring.
  • In cases where prolonged inpatient monitoring is not possible, your doctor may consider doing an ambulatory EEG.
  • You should be relaxed and 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.
  • Video is routinely recorded during the EEG. Your body motions are captured by a video camera while the EEG records your brain waves. This combined recording can help your doctor diagnose and treat your condition.

Once the test is completed, the electrodes will be removed, and the electrode paste will be washed off with warm water, acetone, or witch hazel. In some cases, you may need to wash your hair again at home.

There are no post-test side effects. The skin where the electrodes were placed may be red or irritated afterward, but this will wear off in a few hours.

If you used a sedative, it will take time for the medication to begin to wear off. Arrange to have someone drive you home.

Once home, rest and don't drive for the rest of the day.

Your healthcare provider will inform you when you may resume any medicines you stopped taking before the test.

When will I receive my results?

A doctor trained to analyze EEGs will interpret your recording. He or she will pay special attention to the basic waveform, but also examine brief bursts of energy and responses to stimuli, such as flashing lights.

The results will be sent to your doctor who will discuss the results at your next appointment.

This information was provided by the specialists at Semmes Murphey Clinic. Readers are encouraged to research trustworthy organizations for information. Please talk with your physician for websites and sources that will enhance your knowledge and understanding of this issue and its treatments.

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