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.
To continue reading this article, you must login
Subscribe to Harvard Health Online for immediate access to health news and information from Harvard Medical School.