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In 1929 a psychiatrist in the German university town of Jena reported that the human brain gives off a faint, rhythmic electrical signal that can be picked up through the scalp. That recording, the electroencephalogram or EEG, is still used in hospitals today. This post tells Hans Berger's story from his paper and peer-reviewed histories, and works through the physics of reading a brain-wave trace.
Who was Hans Berger?
According to an appraisal published for his 150th birthday in Arquivos de Neuro-Psiquiatria, Berger was born on 21 May 1873 in Coburg, Germany. At 18 he enrolled at the University of Berlin to study mathematics and astronomy, left after half a year and joined the army. In 1892 he fell from a horse and was nearly killed. A family story holds that his sister, far away, sensed at that moment that he was in danger, and the authors write that this left him determined to understand what he called telepathy.
He then studied medicine, qualified in 1897 and joined the psychiatric clinic at the University of Jena. He stayed there for his whole career, directing the clinic from 1919 to 1938 and serving as rector of the university from 1927.
What was he actually trying to measure?
Berger's real question was about energy. Following ideas popular in his time, he believed mental work must draw on the brain's energy budget, and he tried to measure that budget piece by piece. First he recorded changes in blood volume through skull defects in patients. Then he measured brain temperature, publishing a monograph in 1910. In 1902 and 1907 he tried to record electrical currents from the brains of dogs, copying the British physiologist Richard Caton, and mostly failed: in his first attempt, four of five recordings showed nothing.
How did he record the first human EEG?
He came back to the problem in 1924. His first subject was a 17-year-old boy with a gap in his skull left by surgery. On 6 July 1924, with electrodes placed around the scar, he saw a feeble current on a string galvanometer, an instrument then used for heart recordings. He spent years improving his electrodes and instruments, moving to a more sensitive Siemens galvanometer in 1926.
The appraisal describes how he worked: in the evenings, roughly from 5 to 8 pm, largely alone, for five years before he published anything. He made 73 recordings of his son Klaus and 56 of himself. Every trace carried a time scale marked in tenths of a second, and he recorded the heartbeat alongside, so he could show the rhythm came from the brain and not from the heart or muscles.
His first report, Über das Elektrenkephalogramm des Menschen ("On the electroencephalogram of man"), appeared in Archiv für Psychiatrie und Nervenkrankheiten in December 1929 and ran from page 527 to page 570. By 1931 he had collected 1,133 records from 76 people. He described two main rhythms, which he called alpha and beta waves, and noticed that the alpha rhythm was blocked when a person opened their eyes.
Why did scientists doubt him at first?
Many physiologists doubted that an orderly rhythm could come from a multitude of brain cells firing in all directions, and Berger published mainly in German psychiatry journals. In 1934 Edgar Adrian, who had shared the 1932 Nobel Prize for discoveries about neurons, and Bryan Matthews repeated the recordings in Cambridge. They titled their paper in Brain The Berger rhythm: potential changes from the occipital lobes in man. The appraisal notes that they set out expecting to show his traces were artefacts and ended up confirming them, including the blocking of the rhythm when the eyes open.
Recognition came late. Berger was forced to stop his EEG research in 1935, was not reappointed as clinic director in 1938, and died in 1941.
Worked example: how do you read a brain-wave trace?
Berger's later records ran at an average paper speed of 3 cm per second, according to the same appraisal. Here is how you would read a trace like his. The wave counts below are sample numbers for practice, not data from his records.
Suppose you count 8 complete waves spread over 24 mm of paper.
Paper speed: 3 cm/s = 30 mm/s.
Time covered: 24 mm ÷ 30 mm/s = 0.8 s.
Frequency: 8 waves ÷ 0.8 s = 10 waves per second, or 10 Hz.
Period: 1 ÷ 10 Hz = 0.1 s. Check: 0.1 s × 30 mm/s = 3 mm between peaks, and 8 × 3 mm = 24 mm. It fits.
What mistakes do students make with traces like this?
Counting peaks instead of waves. Nine peaks have eight gaps between them, so they span eight waves, not nine. Measure from the first peak to the last and divide by the number of gaps.
Mixing units. Paper speed is often given in cm/s and spacing in mm. Convert before you divide.
Confusing frequency and period. Frequency is waves per second; period is seconds per wave. Multiply them and you should get 1.
If frequency and period still feel abstract, the Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read. For the biology of how neurons carry electrical signals in the first place, our guide to neural control and coordination follows the NCERT Class 11 chapter.
What can a student take from how Berger worked?
Build in your own checks. Berger put a time scale and a heartbeat trace on every record so nobody could dismiss his rhythm as noise. Label every graph you draw and ask what else could explain it.
Treat failure as information. His 1902 attempt mostly failed. He returned to the problem twice before it worked.
Separate the tool from the theory. His theory of psychic energy did not survive. His measuring method did.
Next step: read the section on how a nerve impulse is generated in the NCERT Class 11 chapter on neural control, the tiny signals that Berger's galvanometer was adding up.
