What is an electroencephalogram (EEG)?

An electroencephalogram, commonly referred to as an EEG, is a procedure that measures your brain activity. It is ordered for the diagnosis of all conditions that affect your brain. The EEG test measures the natural electrical activity arising from your brain.

For an EEG, a technician places small metal disks called electrodes on your scalp. These electrodes connect to a monitoring machine that follows the electrical impulses your brain cells - or neurons - are firing off to communicate with each other. Monitoring that communication demonstrates how well the various parts of your brain are functioning.

Why is an EEG prescribed?

Generally, doctors recommend an EEG for monitoring seizures or in cases where the presence of epilepsy is suspected. An EEG may be performed on a patient presenting signs consistent with unrecognized epilepsy, such as:

• Disorientation.
• Loss of Consciousness.
• Amnesia.
• Alteration in Mood.

An EEG may also be performed to look for the presence of epilepsy in other conditions associated with:

• Conditions like Alzheimer’s disease and other dementias.
• Unconsciousness.
• Inflammatory diseases such as infections of the brain including encephalitis.
• Injury to the head.
• Neoplasms

What are the types of EEG tests?

Depending on the medical problem, doctors will request various EEG tests. There are different EEG tests, which include:

• Routine EEG: Routine EEG scanning may require looking into flashing lights or taking breaths at times during the procedure. A routine EEG test of this type may last between 20 and 30 minutes.
• Prolonged EEG: Prolonged EEG provides an additional level of information compared to a routine EEG. Sometimes a provider will call for a prolonged EEG test to find out, for example, if a memory blank is caused by a seizure. Prolonged EEGs usually last approximately one hour or even more.
• Ambulatory EEG: This test allows you to continue with your daily activities while a machine keeps track of your brain activity through an EEG. Ambulatory EEGs involve the person putting on a small portable EEG appliance for a day or two.
• Video EEG: If the reason for the EEG is to capture seizures as requested by your provider, they may further request that you undergo a video EEG where they record what you are doing and can also hear what you are saying. This test is sometimes referred to as EEG monitoring, EEG telemetry or video EEG monitoring.
• Sleep EEG: Your doctor may suggest a sleep EEG with a sleep study, known as a polysomnogram because this will give more data than a sleep study alone. They may order this test for you when there is a sleep disorder probably due to epilepsy.

How does EEG work?

An electroencephalogram (EEG) measures the electrical impulses within the brain emanating from the brain cells. The electrodes that are placed on the scalp to measure the electrical activity in the brain are connected to wires that are extensible and measure the electrical activity of the brain. The electrodes:

• Transmit signal information to the EEG unit.
• The EEG device records the brain waves and produces a visual output in the form of waveforms (traces) on a computer screen, which reconstructs the pattern of brain activity caught.
• Patterns of your brain waves frequency differ when; you are awake, sleeping, or when external stimuli alter your brain cells.
• The image displayed on the computer is referred to as an EEG.
• Your practitioner will note an abnormality in the patterns seen on the EEG.

How do I prepare for an EEG?

There are different types of EEGs. Your health care practitioner will elaborate on what specific test you will be undergoing, including what specific test they are carrying out, the procedures followed during the test, duration of the test, and whether you should bring someone to escort you home after the test. Regardless of what type of EEG, you should do the following:

• Inform your doctor about medications that you are taking.
• Wash your hair the night before your test, but do not use conditioner or any other hair products that might interfere with the transmission of the brain activity information from the electrodes.
• If you are instructed not to, do not sleep the night before the test.

What happens during a routine EEG?                            

During a routine EEG:

• You sit in a chair or lie on a bed.
• A technician presses about 23 electrodes to your scalp using a gooey paste similar to glue. The electrodes cause no sensation and are pain-free. They are just there to record your brain activity.
• You will be instructed to relax with your eyes open or closed.
• Your technician may ask you to look at a bright light to test the activity in the visual part of your brain.
• They'll ask you to breathe deeply several times.

A routine EEG can take about 20 to 30 minutes to perform.

What occurs after a routine EEG?

Your technician will remove the electrodes and clean the area of your scalp to which they applied them. Unless your provider has told you otherwise, you can go home and resume your activities as usual. You may feel the glue or paste holding the electrodes in place feeling sticky on your hair and skin; you may even want to wash your hair when you get home.

What are the dangers or side effects of an EEG?

EEGs rarely cause adverse effects. A few individuals may experience dizziness by taking deep breaths during the test. In some types of epilepsy, deep breathing (hyperventilation) or light (photic) stimulation during the EEG can induce an epileptic seizure. This rarely happens, and if it does happen, your technologist will know what to do to help you in the event that a seizure occurs. You might lose some hair or have irritation on your skin where the electrodes were on the head.

When will I receive my test result?

You will have another appointment with your health care provider who will examine the brain wave patterns that the test demonstrates.

What do the results of an EEG test reveal?

For more details regarding your results, your physician is the best person to approach. They will examine for abnormal brain waves and rhythms that may be caused by dysfunction of the brain or active epilepsy.

What are the next steps if I have an abnormal EEG test result?

That would depend on your condition. Your doctor may refer you to a specialist, such as a neurologist, for the diagnosis and treatment or management of your condition.

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