A medical test that records the electrical activity of the heart, used in seeking to diagnose heart disorders. Electrodes are attached painlessly to the chest, wrists, and ankles; these transmit information about the electrical changes in the heart as it undergoes each rest-contraction cycle, generally recorded as a graph on a sheet of paper (sometimes also on a screen), which physicians analyze for information about normalities and abnormalities in the heart’s functioning. An ECG can be done in a doctor’s office, clinic, or hospital; in some cases, as in an intensive care unit, the ECG machine may remain attached for hours or days, until the need for such monitoring has passed.
A medical test that records the electrical activity of the brain, as an aid in the diagnosis of such disorders as epilepsy, brain tumors, mental retardation, and mental disorders. Electrodes are painlessly attached to the patient’s scalp and, as an extremely weak current is passed between them, the electroencephalograph records the brain’s electrical activity during a variety of activities, including responses to bright lights, drugs, visual exercises, or sleep.
Device for receiving and recording the electrical activity of the brain. In most cases electrodes are attached to various areas of the head and the patient is asked to remain quiet while the brain-wave activity is recorded; during neurosurgery electrodes may be placed directly on the surface of or within the brain.
Amplification, recording, and analysis of the electrical activity of the brain. The record obtained is called an electroencephalogram (EEG).