In
1929, a German psychiatrist named Hans Berger, who worked in the
city of Jena, announced to the world that:
These were revolutionary discoveries, and, in fact, Berger founded an entirely new and very important branch of medical science, named clinical neurophysiology.
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 1957.
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.
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From: EEG Brain Mapping Author: Renato M.E. Sabbatini, PhD In: Brain & Mind Magazine, August/September 1997. |
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