An electroencephalogram (EEG) is a test that measures and records the electrical activity of your brain. This is done by placing sensors, that are conected to a computer, onto a patients head. The computer records your brain's electrical activity onto a screen or paper printout as wavy lines. These wavy lines are then observed fro changes in the normal patterns of the brain's electrical activity.
* To identify epilepsy and determine what type of seizures are occurring. EEG is the best test for confirming a diagnosis of epilepsy.
* Encephalopathies: An encephalopathy is any disease that alters brain function, such as Parkinson's disease or cerebral palsy.
* An EEG can identify the location of a suspected brain tumor, inflammation, infection, bleeding, head injury, or disease in the brain, such as Parkinson's disease.
* Evaluated periods of unconsciousness or dementia.
* To Help predict a person's chance of recovery after a change in consciousness.
* An EEG can confirm or rule out brain death in a person who is in a coma.
* An EEG can be used to study sleep disorders such a narcolepsy.
* It is used to study brain activity while a person is receiving anesthesia during surgery.
The patient will lie on their back, or relax in a chair, with their eyes closed. The EEG technologist will attach 16 to 25 metal discs (electrodes) to different places on the patients head. They can use a sticky paste to hold the electrodes in place, or they can use a cap with fixed electrodes onto the patients head instead of individual electrodes. Also they can attach them to the scalp with tiny needles. These electrodes are connected with wires to a machine that amplifies and records the electrical activity inside the brain. The electrical activity is recorded as a series of wavy lines. These lines are either drawn by a row of pens on a moving piece of paper, or as an image on a computer screen.
The procedure is done on a patient when they are usualy resting or asleep. Other procedures are done during the EEG to see how the brain responds to different forms of stimulation.
* The patient will breathe deeply and rapidly (hyperventilate).
* The patient will look at a bright flashing light called a strobe. This is called photic or stroboscopic stimulation.
* To help evaluate a sleeping problem an all-night recording of your brain's electrical activity may be taken.
A normal EEG takes about 1 to 2 hours, and after the test the patient may resume normal activities.
* Excess movement of the head, body, eyes, or tongue.
* The inability to cooperate and remain still throughout the test.
* Medications that treat seizures, sedatives, tranquilizers, and barbitureates. Barbitureates are used to relieve anxiety, control seizures, or produce a sleeplike state.
* Being unconscious as a result of severe drug poisoning or very low body temperature (hypothermia).
* Hair that is dirty, oily, or covered with hairspray or other hair preparations can interfere with the placement of the electrodes.
The frequency range up to 4 Hz. It is found in people who are sleeping and in young children.
The frequency range of 4 to 7 Hz. Only found in children or during sleep.
Frequency of 8 to 12 Hz. Alpha waves are found only in the waking state when your eyes are closed. They disappear with visual activity or mental concentration.
Frequency of 13 to 30 Hz. Normally found when you are alert or have taken high doses of certain medications, such as seizure medications (aniticonvulsants).
Frequency of approximately 30 to 80 Hz. Gamma are involved in higher mental activity, including perception, problem solving, fear, and consciousness.
EEGs used to play a bigger roll in diagnosis of brain injury due to strokes and the diagnosis and identification of brain tumors then they do now. Computer-aided techniques such as CT-scans, or CAT scan, MRIs, and PET scans, have taken over most of the tasks of diagnosing these conditions. They test tend to be more sensitive and specific in the diagnosis of strokes and tumors and are simpler to do and easier to interpret than EEGs.