Research
Among his many research interests in neurology, Berger studied brain circulation, psychophysiology and brain temperature. However his main contribution to medicine and neurology was the systematic study of the electrical activity of human brain and the development of electroencephalography (EEG), following the pioneering work done by Richard Caton (1842–1926) in England with animals. In 1924, Berger made the first EEG recording in man and called it Elektrenkephalogramm.
Using the EEG he was also the first to describe the different waves or rhythms which were present in the normal and abnormal brain, such as the alpha wave rhythm (7.812–13.28 Hz), also known as "Berger's wave"; and its suppression (substitution by the faster beta waves) when the subject opens the eyes (the so-called alpha blockade). He also studied and described for the first time the nature of EEG alterations in brain diseases such as epilepsy.
His method involved inserting silver wires under the patients scalp, one at the front of the head and one at the back. Later he used silver foil electrodes attached to the head by a rubber bandage. As a recording device he first used the Lippmann's capillary electrometer, but results were disappointing. He then switched to the string galvanometer and later to a double-coil Siemens recording galvanometer, which allowed him to record electrical voltages as small as one ten thousandth of a volt. The resulting output, up to three seconds in duration, was then photographed by an assistant.
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