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                   The History of the Electroencephalogram

                         In 1929, a German psychiatrist named Hans Berger,
                         who worked in the city of Jena, announced to the
world that:

   * it was possible to record the feeble electric currents generated on the
     brain, without opening the skull, and to depict them graphically onto a
     strip of paper. Berger named this new form of recording as the
     electroencephalogram (EEG, for short);
   * that this activity changed according to the functional status of the
     brain, such as in sleep, anesthesia, hypoxia (lack of oxygen) and in
     certain nervous diseases, such as in epilepsy.

                                 First EEG recorded by Hans Berger, circa

These were revolutionary discoveries, and, in fact, Berger founded an
entirely new and very important branch of medical science, named clinical

Berger electrodes were too large to made detailed topographycal studies of
the EEG (in other words, to use electrical activity recorded from the brain
to pinpoint areas of sensory projection, the localization of tumors or of
epileptic foci, etc.).

This was left to W. Gray Walter, a remarkable British
scientist, who, in 1936, proved that, by using a larger
number of electrodes pasted to the scalp, each one having a small size, it
was possible to identify abnormal electrical activity in the brain areas
around a tumor, and diminished activity inside it.

Impressed with the possibilities of building bidimensional maps of the EEG
activity over the brain surface, W. Gray Walter invented the toposcope in

This was a remarkably complex device and showed Grey Walter's inventiveness
(besides being a physician, he was also an engineer). It had 22 cathode ray
tubes (similar to a TV tube), each of them connected to a pair of electrodes
attached to the skull. The electrodes (and their corresponding tubes) were
arranged in a bidimensional geometrical array, such as that each tube was
able to depict the intensity of the several rhythms which compose the EEG in
a particular area of the brain (the frontal , parietal and occipital lobes,
etc.). This array of CRT tubes, were photographed face up, so that a kind of
phosphorescent spiral display showed simultaneously which kind of rhythm was
present in a particular part of the brain.

Gray Walter asked his subjects to perform several mental tasks, with the
result that the EEG rhythms were altered in different ways, times and parts
of the brain. He was the first to prove, for instance, that the so-called
alpha rhythm (present during a resting state) disappears from almost all the
brain during a mental task which demands awareness, being substituted by a
faster rhythm, the beta waves.

It was immediately apparent to neurologists that the toposcope could be a
great help to locate epileptic foci (the points where a convulsion
originates in the brain, due to a local lesion, tumor or functional
alteration). However, it was very complex and expensive and it did not
achieve commercial success or widespread use.

The topographic study of brain electrical activity was born again only when
fast desktop computers became available in the 80s. Thus, EEG brain
topography was developed and is widely in use today. It is also called Color
Brain Mapping.

See also: The Future of EEG Brain Mapping.

 From: EEG Brain Mapping                        
 Author: Renato M.E. Sabbatini, PhD
 In: Brain & Mind Magazine, August/September                  2 of 4 pages