Electroencephalogram (EEG)

What Is It?

An electroencephalogram (EEG) is a recording of the brain's electrical activity. Metal electrodes attached to the skin on the outside of the head transform electrical activity into patterns, commonly called brain waves. A polygraph machine records the brain waves. In some cases, the waves are transmitted to a computer screen. A basic EEG takes about 45 minutes, with a range of 30 minutes to 90 minutes.

Lightweight EEG devices allow people to walk around and perform normal daily activities while the devices detect and record brain waves over longer periods of time.

What It's Used For

Doctors most often order an EEG to help diagnose a seizure disorder or monitor effectiveness of anti-seizure medicine in people with epilepsy. It also may be used to evaluate someone with confusion, head injuries or other conditions that may be caused by an abnormality in the brain. An EEG can help to diagnose certain types of brain illnesses that cause worsening mental impairment and brain dysfunction, such as encephalopathy caused by severe liver or kidney disease. Occasionally, an EEG may be used to confirm brain death, for example, in someone on life support who is in a deep coma.

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