Electroencephalogram (EEG)

What is an electroencephalogram?
EEG is the name commonly used for electroencephalography (e-LEK-tro-en-SEF-uh-LOG-rah-fee). EEG is the most important test for diagnosing epilepsy and seizures because it records the electrical activity of the brain. It is safe and painless. Electrodes (they are similar to those used for an electrocardiogram or EKG) are attached to your scalp and connected by wires to an electrical box. (The wires can only record electrical activity; they do not deliver any electrical current to your scalp.) The box in turn is connected to an EEG machine.

The EEG machine records your brain's electrical activity as a series of squiggles called traces. Each trace corresponds to a different region of the brain. EEGs always used to be recorded on paper, but computerized, paperless EEGs are now used more often.

What diseases is an EEG used for?
The EEG shows patterns of normal or abnormal brain electrical activity. Some abnormal patterns may occur with a number of different conditions, not just seizures. For example, certain types of waves may be seen after head trauma, stroke, brain tumor, migraines, syncope or fainting/dizzy episodes, or dementia. A common example of this type is called slowing in which the rhythm of the brain waves is slower than would be expected for the patient's age and level of alertness.

Certain other patterns indicate a tendency toward seizures. Your doctor may refer to these waves as epileptiform abnormalities or epilepsy waves. These include spikes, sharp waves, and spike-and-wave discharges. Spikes and sharp waves in a local area of the brain, such as the left temporal lobe, indicate that the patient may be at risk for developing seizures.

How is an EEG done?
Electrodes (they are similar to those used for an electrocardiogram or EKG) are attached to your scalp and connected by wires to an electrical box. You need not do anything, other than relax. Often the doctor hopes, and you may be encouraged to fall asleep during the test. Generally, the brain waves are only recorded for 20 minutes, though the entire study may take up to 1 hour due to preparation time needed by the technician. In addition to the recording of your brain's electrical activity while you are resting, certain procedures may be done to observe how your brain responds to different forms of stimulation:

• You may be asked to breathe deeply and rapidly (hyperventilate). Usually you will take 20 breaths a minute for 3 minutes.
• You may be asked to look at a bright, flashing light called a strobe. This is called photic or stroboscopic stimulation.
• You may be asked to go to sleep. If you are unable to fall asleep, you may be given a sedative to help you fall asleep. If an EEG is being done to help evaluate a sleep problem, an all-night recording of your brain's electrical activity may be taken.

How do you prepare for an EEG? Since the electrodes are attached to your scalp, it is important that your hair be clean and free of sprays, oils, creams, lotions, braids and other hair preparations. Shampoo your hair and rinse with clear water the evening before or the morning of the test. Do not apply any hair conditioners or oils after shampooing. Also, it is important to avoid foods that contain caffeine (such as coffee, tea, cola, and chocolate) for at least 8 hours before the test. Eat a small meal shortly before the test, because low blood sugar (hypoglycemia) may produce an abnormal test. No alcohol for 24 hours prior to the test.

You should continue to take your medications, including any seizure or anti-epileptic medications you may be prescribed, unless otherwise instructed by your doctor.

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