Electroencephalograph

Electroencephalograph, instrument for recording the brain's electrical activity using several small electrodes on the scalp. Its results are produced in the form of an electroencephalogram (EEG). The EEG is a convenient method for the investigation of brain disturbances and disease (benign and malignant tumors, disturbances in blood vessels, epilepsy, inflammation, metabolic changes). The German psychiatrist Hans Berger began to record electrical activity in human brains in 1929. There are certain normal patterns for “brain waves” in the alert and the sleeping individual. In a normal person, several varieties of rhythmic activity appear in different circumstances. The most prominent rhythm, noticeable when a healthy subject closes his or her eyes, shows a period of 8–13 cycles per sec that is chiefly present at the occipital pole of the cerebral hemispheres. This is the alpha rhythm. Sleep removes this rhythm and may substitute others in its place. Theta rhythm, with a frequency of 4–7 cycles per sec, occurs typically in the parietal and temporal regions of the brain and is associated with childhood and with emotional stress in some adults. Beta rhythm, with frequencies higher than 15 cycles per sec, is generally associated with activation and tension.

See also: Brain.