The EEG pen-on-paper sound: History and recent advances.

The electroencephalogram (EEG) is one of the most useful technologies for brain research and clinical neurology, characterized by non-invasiveness and high time resolution. The acquired traces are visibly displayed, but various studies investigate the translation of brain waves in sound (i.e., a process called sonification). Several articles have been published since 1934 about the sonification of EEG traces, in the attempt to identify the "brain-sound." However, for a long time this sonification technique was not used for clinical purposes. The analog EEG was in fact already equipped with an auditory output, although rarely mentioned in scientific papers: the pen-on-paper noise made by the writer unit. EEG technologists often relied on the sound that pens made on paper to facilitate the diagnosis. This article provides a sample of analog video-EEG recordings with audio support representing the strengths of a combined visual-and-auditory detection of different types of seizures. The purpose of the present article is to illustrate how the analog EEG "sounded," as well as to highlight the advantages of this pen-writing noise. It was considered so useful that early digital EEG devices could be equipped with special software to duplicate it digitally. Even in the present days, the sonification can be considered as an attempt to modify the EEG practice using auditory neurofeedback with applications in therapeutic interventions, cognitive improvement, and basic research.