Is the neurophysiologic measurement of the electrical activity of the brain by recording from electrodes placed on the scalp, or in the special cases on the cortex. The resulting traces are known as an electroencephalogram (EEG) and represent so-called brain waves. This device is used to assess brain damage, epilepsy and other problems. In some jurisdictions it is used to assess brain death. EEG can also be used in conjunction with other types of neuroimaging.


Historically four major types of continuous rhythmic sinusoidal EEG waves are recognized alpha, beta, delta and theta.

beta (>13 Hz), - alpha (8-13 Hz), - theta (4-8 Hz), - delta (0.5-4 Hz).


An EEG is also used to determine brain death. It may be used to prove that someone on life-support equipment has no chance of recovery.


Scientists first captured and recorded brain waves in dogs in 1912. By the 1950s the EEG was used commonly throughout the United States.


The greatest advantage of EEG is speed. Complex patterns of neural activity can be recorded occurring within fractions of a second after a stimulus has been administered. EEG provides less spatial resolution compared to MRI and PET. Thus for better allocation within the brain, EEG images are often combined with MRI scans. EEG can determine the relative strengths and positions of electrical activity in different brain regions.


Research and clinical applications of the EEG in humans and animals are used to

(1) monitor alertness, coma and brain death;

(2) locate areas of damage following head injury, stroke, tumour, etc.;

(3) test afferent pathways (by evoked potentials);

(4) monitor cognitive engagement (alpha rhythm);

(5) produce biofeedback situations, alpha, etc.;

(6) control anaesthesia depth (“servo anaesthesia”);

(7) investigate epilepsy and locate seizure origin;

(8) test epilepsy drug effects;

(9) assist in experimental cortical excision of epileptic focus;

(10) monitor human and animal brain development;

(11) test drugs for convulsive effects;

(12) investigate sleep disorder and physiology.

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