Background: We report on a biological artifact that is unknown in the EEG-literature, presumably due to its invisibility in the unfiltered raw EEG. On account of its probable electrogenesis, we discuss Arterial Pulse Impedance Artifact (APIA). One may also call it a virtual artifact because it only becomes manifest as the averaged mean value of power spectra from consecutive 2s epochs across a total length of 5 min (150 epochs). Presentation of the hypothesis: APIA has a cardiac origin, mediated by the superficial head arteries. The arterial pulse induces rhythmic changes in the electrical impedance between the cortical generator inside the skull and the recording electrode that is outside.

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