The routine EEG is the most common test for epilepsy. The EEG technologist first measures the patient’s head so that the electrodes, which are small, metal, cup-shaped disks attached to wires, can be placed in the correct position. A wax crayon, which can be easily washed off later, is used to mark the points on the scalp. Next, the technologist applies the electrodes, usually using a paste that holds them in place for up to several hours. The technologist often scrubs each position on the scalp with a mildly abrasive cream before applying the electrodes. This will help improve the quality of the recording.
The electrodes only record the brain waves. They do not stimulate the head with electricity, and pose no danger to the patient. The EEG machine then records the brain waves as a series of waveforms called traces. Recordings on paper are now mostly replaced by computerized, paperless EEG.
The patient may fall asleep briefly during a routine EEG, because the room is quiet and often dimly lit, which is ideal, because an EEG obtained during both wakefulness and sleep may provide extra information. During the EEG, the technologist will ask patients to open and close their eyes several times, may shine flashing lights into their eyes (photic stimulation), or may ask them to breathe rapidly or deeply (hyperventilation). Patients who have a medical problem, such as asthma or heart disease, which makes it unsafe to hyperventilate should tell the EEG technologist at the start of the EEG. Similarly, a pregnant woman usually should not undergo hyperventilation or photic stimulation and should make sure to tell the technologist that she is pregnant at the start of the test.
In some cases, the doctor may ask the patient to stay up the entire night before the EEG is performed. This sleep deprivation can increase the likelihood that epilepsy waves will be recorded. If the patient experiences any possible seizure symptoms during the test, he or she should tell the technologist.
Obtaining an EEG in children is usually easy, but it can pose a significant challenge. For babies, it is helpful to perform the EEG around naptime. Electrodes can be applied while the mother holds the child; a bottle may help to calm the baby. Then the baby is allowed to sleep naturally. Sedation is required for some babies and young children to allow the technologist to apply the electrodes and to record sleep activity. Children have difficulty lying still during EEG recordings, and the doctors who interpret these studies must separate the waves caused by movement and muscle activity from the brain waves.
At the NYU CEC, we have experienced technologists running three routine EEG rooms simultaneously to accommodate our patients. Often, if a patient comes in for an initial evaluation, he or she will undergo EEG testing at the time of the visit, so that the doctor can get information immediately. Also, if a patient has had normal EEGs and normal video EEG studies without experiencing a typical event, he or she may call on the day of experiencing symptoms, or just after having had a seizure to arrange an EEG immediately. This may be very helpful as otherwise normal EEGs may show abnormalities around the time of a patient’s seizure.
The actual recording usually lasts only 20 to 40 minutes, and the same amount of time is generally needed to prepare for it. Thus, the routine EEG procedure usually takes 1 to 1_ hours. The test is performed by an EEG technologist. The patient can help by washing his or her hair the night or morning before the test, but should avoid using conditioners, hair creams, sprays, or styling gels.
After the EEG recording is done, the technologist will remove the electrodes from the patient’s scalp, and the patient is free to go home and wash the paste out of his or her hair. The paste is lanolin- or water-based and is easily washed off. The doctor usually reads the EEG after the patient has left.