Electroencephalogram (EEG)

What Is It?

An electroencephalogram (EEG) is a neurological test which records the electrical activity at the surface of the brain by way of electrodes placed on or in the scalp.

The EEG is performed by placing electrodes on the scalp. Generally, these are superficial stickers which are attached to wires which carry information to the monitor which displays the results. In some cases where a continuous EEG is to be taken for a prolonged period of time, such as in a comatose head trauma victim, the electrodes can be implanted in the scalp as tiny needles.

The electrodes record electrical activity from the surface of the brain which is converted to a trace on the electroencephalogram output, traditionally wiggly lines on a sheet of paper although nowadays they are often simply displayed on a computer screen. The shape, frequency, amplitude and other characteristics of the trace from various regions of the brain are interpreted by a physician, usually a neurologist, and can reveal changes in the electrical activity of the brain.

Evaluation with an EEG varies depending on the clinical situation. In some patients a short EEG will be taken while in others a prolonged EEG overnight or even longer may be required. Patients with epilepsy will often undergo prolonged EEG monitoring in the attempt to catch a seizure on the EEG so that physicians can determine the location it originated from and other characteristics which may help in treatment.

What Is It Used For?

Because the EEG reveals changes in the electrical activity of the neurons in the brain, it can aid in the diagnosis of various pathologies. Traditionally, besides general nervous system research, the EEG has been used to evaluate patients with epilepsy. Seizures, either generalized to the whole brain or focal, can often be seen as a characteristic rhythmic activity on the EEG which is quite different from the normal, seemingly random activity. Therefore, the electroencephalogram is often used to diagnose and work-up patients who present with seizures or activity which is suspicious for epilepsy.

The EEG is also used to evaluate other general changes in the activity of the brain. For example, patients in coma are sometimes followed with EEG both to rule out subclinical seizures but also to evaluate for signs of recovery or brain death. In fact, determination of brain death sometimes utilizes EEG to determine if there is any normal brain activity. While the diagnosis of brain death does not require an EEG, it sometimes helps physicians feel confident that their is no normal brain activity.

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Important Note: This site is not intended to offer medical advice. Every patient is different, and only your personal physician can help to counsel you about what is best for your situation. What we offer is general reference information about various disorders and treatments for your education.

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