An electroencephalogram (EEG), also called a brain wave test, is a diagnostic test which measures the electrical activity of the brain (brain waves) using highly sensitive recording equipment attached to the scalp by fine electrodes.
EEG is performed to detect abnormalities in the electrical activity of the brain which may help diagnose the presence and type of various brain disorders, to look for causes of confusion, and to evaluate head injuries, tumors, infections, degenerative diseases, and other disturbances that affect the brain. The test is also used to investigate periods of unconsciousness. EEG may also confirm brain death in someone who is in a coma. EEG cannot be used to measure intelligence or diagnose mental illness. Specifically, EEG is used to diagnose the following:
seizure disorders (such as epilepsy or convulsions)
structural brain abnormality (such as a brain tumor or brain abscess)
Brain cells communicate by producing tiny electrical impulses, also called brain waves. These electrical signals have certain rhythms and shapes, and EEG is a technique that measures, records, and analyzes these signals to help make a diagnosis. Electrodes are used to detect the electrical signals. They come in the shape of small discs that are applied to the head and connected to a recording device. The recording machine then converts the electrical signals into a series of wavy lines that are drawn onto a moving piece of graph paper. An EEG test causes no discomfort. Although having electrodes pasted on the skin may feel strange, they only record activity and do not produce any sensation. The patient needs to lie still with eyes closed because any movement can affect results. The patient may also be asked to do certain things during the EEG recording, such as breathing deeply and rapidly for several minutes or looking at a bright flickering light.
An EEG is performed by an EEG technician in a specially designed room that may be in the doctor's office or at a hospital. The patient is asked to lie on a bed or in a comfortable chair so that a relaxed EEG recording can be done. The technician either measures the scalp and marks the spots where small discs (electrodes) will be placed or fits the head with a special cap containing between 16 and 25 of these discs. The scalp is then rubbed with a mild, scratchy cleanser that may cause mild discomfort for a short while. The discs are attached to the body with a cream or gel. Alternatively, the technician may secure the discs to the skin with an adhesive. The heart may also be monitored during the procedure.