Forgotten rhythms? Revisiting the first evidence for rhythms in cognition

Abstract

Practically every neuroscientist knows that human brain rhythms were first recorded in the 1920s by Hans Berger, who coined the term 'alpha waves' for the regular activity of around 10 cycles per second that was clearly visible in many of his recordings. Almost 100 years later, alpha rhythms are still the subject of active investigation and continue to intrigue researchers. What we have perhaps forgotten though, is the clever experimentation that was carried out during the first decades of electroencephalogram (EEG) research, often using sophisticated, custom-made analysis and stimulation devices. Here, I review selected findings from the early EEG literature regarding the character, origin, and meaning of human brain rhythms, beginning with Berger's publications and then focusing on the use of regular visual stimulation as a tool to understand intrinsic brain rhythms. It is clear that many of these findings are still relevant to open questions about the role of rhythmic brain activity. In addition, they also contain some general lessons for contemporary neuroscientists, meaning that there is great value in looking back at these forgotten publications.

Keywords: Hans Berger; alpha rhythms; good scientific practice; history of neuroscience; photic driving.

FIGURE 1

Sample recordings by Hans Berger from a family member and a patient. (a) Figure 3 in Berger (1935a): ‘J.B., 14 years old’. Typical of his earlier work, the electrocardiogram is depicted in the top trace, and a time trace showing 1/10 s is shown below. The centre trace is the EEG, here recorded using silver chloride needle electrodes in a bipolar montage on forehead and occiput. (b) Figure 4 in Berger (1935a): ‘M.M., 33 year old man. Large gap in the skull from the left forehead to the parietal region.’ Here, the EEG was recorded epidurally using silver chloride needle electrodes placed 4.5 cm apart inside the gap in the skull. At the time marked with the arrow and S, a needle was briefly inserted into the patient's left index finger. R indicates the subsequent extinction of alpha. [Reprinted by permission from Springer Nature Customer Service Centre GmbH: Springer Nature, Naturwissenschaften (Das Elektrenkephalogramm des Menschen, Hans Berger), Copyright © 1969, Verlag von Julius Springer (1935)]

FIGURE 2

Examples of the exquisite illustrations that can be found in older literature. (a) Figure 10 from Berger (1938): ‘Location of silver foil electrodes a and b above forehead and occiput.’ These were Berger's favoured locations for his bipolar electrode montage, as they led to alpha rhythms of greatest amplitude. [Reprinted by permission from Springer Nature Customer Service Centre GmbH: Springer Nature, Archiv für Psychiatrie und Nervenkrankheiten (Über das elektrenkephalogramm des menschen. XIV Mitteilung, Hans Berger), Copyright © 1938, Verlag von Julius Springer (1938)]. (b) Figure 4 from Berger (1937a) illustrating the separation of cortex into superficial (äußere Hauptzone) and deep (innere Hauptzone) layers. Berger theorized about laminar differences in alpha and his beta waves in a detailed table in the same publication. [Reprinted by permission from Springer Nature Customer Service Centre GmbH: Springer Nature, Naturwissenschaften (Das Elektrenkephalogramm des Menschen und seine Deutung, Hans Berger), Copyright © 1969, Verlag von Julius Springer (1937)]