Electroencephalograph (EEG)

A device used to record the electrical activity of the brain.

Electroencephalography is used for a variety of research and diagnostic purposes. It is usually conducted using electrodes, metal discs attached to the scalp or to wires connected to the skull or even to the brain itself. The signals obtained through the electrodes must then be amplified in order to be interpreted. EEG patterns typically take the form of waves, which may be measured according to both their frequency and size (also referred to as amplitude). The electrical activity of animals' brains had been recorded as early as 1875, but it was not until 1929 that the first human EEG was reported by Austrian psychiatrist Anton Berger. Since then, it has been used to study the effects of drugs on the brain, as well as the localization of certain behavioral functions in specific areas of the brain. EEGs have also been widely used in sleep research. While the deeper stages of sleep are characterized by large, slow, irregular brain waves, and, in some cases, bursts of high-amplitude waves called "sleep spindles," REM (rapid eye movement) sleep, during which most vivid dreaming occurs, resembles the faster brain-wave pattern of the waking state.

As a diagnostic tool, EEGs have been used to diagnose epilepsy, strokes, infections, hemorrhages, inadequate blood supply to the brain, and certain tumors. They are especially useful because they can pinpoint the location of tumors and injuries to the brain. EEGs are also used to monitor patients in a coma and, during surgery, to indicate the effectiveness of anesthetics.