In 1875, Richard Caton (Fig. 1-1), a physiologist from the Royal Infirmary School of Medicine, Liverpool, England, successfully recorded electrical activity from an animal brain.¹ He reported his experiments in the British Medical Journal.² His paper stated that “…the galvanometer has indicated the existence of electrical currents. The external surface of the gray matter is usually positive in relationship to the surface of section through it….” This was the first description of electrical activity from animal brains. After Caton’s discoveries, electroencephalogram (EEG) work shifted to Eastern Europe. Caton’s work remained unrecognized for the next 25 years because at that time, communication in the scientific world was extremely slow. In 1890, Adolf Beck, from the Jagiellonian University in Krakow, Poland, found oscillatory potentials when recording between two electrodes placed on the occipital cortex of a rabbit. Unaware of Caton’s earlier work, he claimed to be the first to discover animal brain electrical activity. Interestingly, there was another twist to the EEG history. There was another physiologist, Fleischl von Marxow, from the University of Vienna, who also described similar brain electrical activity in animals and deposited his findings in a sealed envelope at the Imperial Academy of Science of Vienna in 1883. Depositing a sealed envelope containing scientific discoveries pending confirmation was a common custom in the European scientific community at that time. Obviously, he was also unaware of Caton’s work.

When Beck’s article appeared in the German journal, Centralblatt, in 1890,³ it caught von Marxow’s eye and allowed him to open the sealed envelope deposited in 1883. Beck and von Marxow then started to argue, each claiming to be the first to discover brain electrical activity. Noticing the argument of these two esteemed physiologists, Caton settled the argument with a letter that stated: “In the year 1875, I gave a presentation before the Physiological Section of the British Medical Association in which electrical currents of the brain in warmblooded animals were demonstrated and.…. May I be permitted to draw your attention to the following publication (Br Med J. 1875; 2:278).… I have published this, so I think it must be conceded that I am already an earlier discoverer.” This letter settled the argument, and Caton was accepted as the first to discover brain electrical activity in animals.

After this discovery, more than 50 years had passed when Hans Berger (Fig. 1-2) first described electrical activity from electrodes placed on the human scalp. Berger was a psychiatrist from Jena, Germany, and was interested in objective measures of human brain function and the mind.¹ He postulated that there would be localized increase of blood flow and increased heat by chemical breakdown in the cortex in response to movement or sensory stimulation of extremities. Using crude techniques, such as plethysmography and thermometry, he attempted to demonstrate these changes. His hypothesis turned out to be amazingly correct and can be now demonstrated by positron emission tomography (PET), single photon emission computerized tomography (SPECT), and functional magnetic resonance imaging (fMRI). When he began to use electrical recordings, he was able to successfully record oscillatory potentials of around 10 hertz (Hz), which he called “alpha rhythm” (Fig. 1-3). He also found that alpha rhythm was best seen in an awake subject with closed eyes and it attenuated when the subject’s eyes opened or the subject performed a mental task. His first paper appeared in 1929 and was titled “Electroenkephalogram
des Menschen.”⁴ His “Electroenkephalogram” is now referred to as electroencephalogram in English. He subsequently found that the frequency of EEG activity slowed down during sleep or in disturbed consciousness. He postulated that electrical activity travels from one area to another through the process of mental activity, predicting the activity of the corticocortical network system during various brain functions. Berger’s pioneering discoveries were at first received with skepticism, primarily because such a slow oscillation like alpha rhythm [having a duration of about 100 milliseconds (ms)] could not be explained by known electrical activity of the nervous system (i.e., action potentials, which have a duration of 1 to 2 ms). In 1935, however, prominent physiologists Adrian and Mathews, from England, finally approved Berger’s work and apologized for their long disbelief, and called the EEG waves as “Berger rhythm.”⁵ Subsequently, the interest in EEG research quickly spread all over the world. In 1936, there were six EEG laboratories in the United States. They were Brown University (H. Jasper), University of Iowa (J. Knott), Tuxedo Park in New York (A. Loomis), Boston University (W. Lennox), Harvard University (H. Davis), and Mayo Clinic (L. Yeager and D. Klass). As early as 1935, Gibbs et al.⁶ discovered 3-Hz spikewave discharges in association with absence seizures. In 1936, Jasper⁷ found focal spikes in focal seizure. In the same year, Walter⁸ found focal slowing corresponding to the site of a brain tumor. Since then, research and clinical application of EEG in various neurological diseases has made rapid progress and EEG has become an essential diagnostic tool in the field of clinical neurology, neurosurgery, and psychiatry.