The History of EEG

In an electroencephalogram, or EEG, brain waves (oscillating electric currents) from the scalp are recorded. In 1874, brain waves were first recorded by the Englishman Richard Caton, who connected primitive equipment directly to the cerebral cortex of a rabbit. In 1929 the German psychiatrist Hans Berger published the first information about scalp-recorded brain waves of humans. The invention of the differential input amplifier by B. H. C. Matthews in 1934 revolutionized the high- gain amplification of biologic electrical signals, including brain waves. Frederic Gibbs, Hallowell Davis, and William Lennox, of the Harvard Medical School, published (1935) the first paper in English on the EEG in epilepsy in humans. The EEG is extensively used in diagnosing epilepsy and in the study of how the brain functions in animals and humans.

An EEG is painless and harmless. The data gained from it is interpreted and correlated with other medical data by physicians as an aid to diagnosis. The different types and causes of epileptic seizures are correlated with certain recognizable focal or diffuse brain wave abnormalities, such as spikes. Treatment with anticonvulsant drugs or, in rare instances, neurosurgical removal of brain scars often depends on the data furnished by an EEG. Minute brain wave currents in the scalp, measured in microvolts, are amplified as changes in potential, which are then written out in a series of wavy lines or channels, one above the other, each channel corresponding to recording electrodes over different brain areas. Scalp-recorded activity originates primarily in the underlying cerebral cortex. During brain operations designed to ameliorate some forms of epilepsy, brain waves are recorded directly from the cerebral cortex and from depth electrodes in subcortical nuclei.

Brain waves are classified according to frequency bands in cycles per second (Hz), the most common of which are alpha activity (8 to 14 Hz), beta activity (above 14 Hz), delta activity (below 4 Hz), and theta activity (4 to less than 8 Hz), activity defined as a series of waves. Characteristic EEG patterns correspond to the level and type of behavioral activity. For example, alpha activity is usually produced during periods of relaxation. In most people alpha activity is abolished by attention. Beta activity occurs in bursts in the anterior part of the brain and is associated with mental activity.