Checking Brain Waves

EEG is the name commonly used for electroencephalography (e-LEK-tro-en-SEF-uh-LOG-rah-fee). EEG is an important test for diagnosing epilepsy because it records the electrical activity of the brain. It is safe and painless. Electrodes (small, metal, cup-shaped disks) 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 were once only recorded on paper, but computerized, paperless EEGs are now used more often.

What can the EEG show?

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, or seizures. 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 specific area of the brain, such as the left temporal lobe, indicate that partial seizures might possibly come from that area. Primary generalized epilepsy, on the other hand, is suggested by spike-and-wave discharges that are widely spread over both hemispheres of the brain, especially if they begin in both hemispheres at the same time.

Topic Editor: Steven C. Schachter, M.D.
Last Reviewed: 12/15/06