An electroencephalogram (EEG) evaluates electrical activity produced by the brain, which can signify or rule out certain conditions, most commonly seizure disorders. The EEG takes about an hour to complete, and the results are automatically sketched on paper, while a video monitor records the movement of the patient, which can disrupt the test.

It is easier to read an EEG of an adult, since there is less variance in brain activity. This is not true of an EEG test used on a child. There is often so much variance in brain activity that an EEG in children may be consistent with epilepsy where none exists. Generally, seizure disorder in children, without the presence of identifiable seizures requires testing other than an EEG to have confirmed results.

As a test progresses, if it is used to examine seizure disorder, a person may be directed to look at flashing lights, which might trigger a seizure. The lights are stopped if evidence from the EEG shows that a person is in pre-seizure mode. Thus the person generally doesn’t have a seizure, but shows electrical activity consistent with what would become a seizure.

An EEG may also be used to evaluate other conditions. For example, people who come to a hospital in an altered state of consciousness, perhaps after a head injury, would probably have an EEG performed. Migraines have been shown to have a similar EEG pattern, and people who suffer from them may have an EEG to confirm diagnosis. Some psychiatric disorders that are organic in nature can also show a distinct pattern of electrical activity.

People with tumors, or with brain abscesses may also show lack of electrical activity in some aspects of the test. As well, an EEG can measure total lack of brain activity, confirming the death of a patient.

Generally an EEG is most helpful in measuring a patient who can be compliant. A screaming child, for example, or a patient with extreme mental disturbance, who cannot remain calm, will have a corrupted EEG test. For children, an EEG is usually scheduled during a child’s naptime.

Not all brain functions can be measured by an EEG. X-rays or more complex scans would probably follow an EEG that suggests a tumor or cranial swelling in order to confirm the diagnosis. The electrical patterns of the brain are measured against “normal scans.” Thus the EEG can be an excellent tool for suggesting variance. However, physicians may have to look further to confirm the actual meanings of variance.