The electroencephalogram (EEG), the graphic recording of the electric activity of the human brain, kindled far-reaching speculations about the imminent deciphering of mind and brain in the 1930s. Regardless of the thousands of neurons in the human cortex, recording from a person at rest produced a surprisingly regular line oscillating at 10 per second that disappeared at the moment of mental activity. With ever more groups specializing in electroencephalography, however, the deciphering of mind and brain did not materialize but moved further away in the information produced. In the various approaches employed in EEG research, such as the analysis of the graphic code, the search for pathognomic patterns or the imaging of cognitive processing, visualization guided research as well as theorizing, its productivity continued to keep the epistemological question open.