After attending Casimirianum, where he gained his abitur in 1892, Berger enrolled as a mathematics student at the Friedrich Schiller University of Jena with the intention of becoming an astronomer.

The incident made such an impression on Berger that, years later in 1940, he wrote: "It was a case of spontaneous telepathy in which at a time of mortal danger, and as I contemplated certain death, I transmitted my thoughts, while my sister, who was particularly close to me, acted as the receiver.

"[5] On completion of his military service, and obsessed by the idea of how his mind could have carried a signal to his sister, Berger returned to Jena to study medicine with the goal of discovering the physiological basis of "psychic energy.

Berger married his technical assistant, Baroness Ursula von Bülow, in 1911 and later served as an army psychiatrist on the Western front during World War I.

[10] Filled with doubt, he took five years to publish his first paper in 1929, which demonstrated the technique for "recording the electrical activity of the human brain from the surface of the head.

[12] Having visited the EEG laboratory at Jena in 1935, American roboticist William Grey Walter noted that Berger:... was not regarded by his associates as in the front rank of German psychiatrists, having rather the reputation of being a crank.

[13] After British electrophysiologists Edgar Douglas Adrian and B. H. C. Matthews confirmed Berger's basic observations in 1934, the importance of his discoveries in electroencephalography (EEG) was finally recognized at an international forum in 1937.

[14] By 1938, electroencephalography had gained widespread recognition by eminent researchers in the field, leading to its practical use in diagnosis in the United States, England, and France.

[15] Numerous sources report that, given their hostile relationship, the Nazis forced Berger into retirement that same year with a complete ban of any further work on EEG.

[17] In 2005, Dr. Susanne Zimmermann, medical historian at the University of Jena, found evidence that Berger had not been forced into retirement but had "served on the selection committee for his successor"[18] Berthold Kihn, who was sacked as a Nazi after the war.

Moreover, official records at the University of Jena dating from the 1930s proved that Berger had served on the Erbgesundheitsgericht (Court for Genetic Health) that imposed sterilizations, while his diaries contained anti-Semitic comments.

[19] Dr Zimmermann's findings corroborated research published in Germany in 2003, documenting Berger's invitation by the SS racial hygienist Karl Astel to work for the EGOG (Erbgesundheitsobergericht, Higher Genetic Health Court) in 1941.

[23] British physician, Richard Caton (1842-1926), had previously described electrical potentials recorded from the exposed cortices of dogs and nonhuman apes.