The electroencephalogram (EEG) is the most common test for the evaluation of seizures and epilepsy. It records the electrical activity of the brain. It is a safe and painless procedure. Routinely the EEG is run for 20 to 30 minutes.

The EEG technologist first measures the patient’s head so that the electrodes can be placed in the correct position. The electrodes are small disks attached to wires. They help record the brain waves. A wax crayon, which is easily washed off, is used to mark the scalp. The technologist scrubs each position on the scalp with a sand-like cream before applying the electrodes. The technologist then applies the electrodes, using a paste that holds them in place for the test.

During the EEG, the technologist will ask patients to open and close their eyes. The technologist may shine flashing lights into the patients eyes (photic stimulation), or may ask them to breathe deeply and rapidly (hyperventilation). These provocative methods may induce certain EEG patterns in special populations and help screen for certain types of epilepsy. The patient may fall asleep briefly during a routine EEG.

In some cases, patients are asked by their doctor to stay up the entire night before the EEG is performed. This sleep deprivation can increase the likelihood that abnormal waves will be recorded. If the patient experiences any possible seizure symptoms during the test, he or she should tell the technologist.

Patients who are pregnant or have a medical problem, such as asthma, heart disease or a recent stroke should tell the EEG technologist at the start of the EEG.

Obtaining an EEG in certain populations or young children can pose significant challenges. For babies, it is helpful to perform the EEG around naptime, preferably after feeding. Electrodes can be applied while the mother holds the child; a bottle may help to calm the baby.

Meriem K. Bensalem-Owen, MD