Abstract
This article examines the epistemological conditions under which the brain's electrophysiological trace was first constituted as a mathematical object of analysis. Rather than treating information as a cultural metaphor externally projected onto the brain, the paper reconstructs how specific tools of signal analysis made the trace into an object that the informational lineage would come to require. Hans Berger's research of 1929-1931 secured the trace as an effect of nervous processes in the brain, but read it as the signal of a single source. The case study is Günther Dietsch's 1932 paper, the first application of Fourier analysis to the EEG signal. The article shows that spectral decomposition did not merely describe the signal but constituted it as a decomposable causal object, resolving a single continuous curve into a discrete set of components, each varying independently of the rest. No improvement of the recording apparatus could achieve this; only the mathematical intervention could. The case is read through the causal-deflationary theory of information in López and Lombardi (2019), according to which a source informs a destination only when a variable of the destination can be manipulated by the source. What 1932 builds is the object of a theory of information needs, not yet the measure that such a theory would later compute on it. That is what avant la lettre means here: mathematics made the trace informational before the theory existed.