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. 2021 Feb 18;11:4128. doi: 10.1038/s41598-021-83337-3

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© The Author(s) 2021

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Examples of scalp EEG waveforms associated with intracranial IEDs. (a) Scalp IEDs are less clear than their intracranial counterparts which results in inferior SNR. (b) Representative examples of incomplete discharge propagation (FCD + HS subject) in simultaneous scalp EEG and iEEG recordings. For clarity, only the right lateral temporal chain of scalp electrodes is illustrated. Automatically detected intracranial IEDs are marked by red dots under the intracranial portion of the signals (light blue background). Associated scalp waveforms are below (b1,b3) or near the limit of visual identifiability (b2,b4) but all were robustly detectable as a scalp zero-crossing pattern. (b2) shows trial-to-trial variability. (b3,b4) show how scalp EEG artifact or background rhythms interfere with visual detection. The first column (avg.) shows a small waveform resulting from signal averaging (c.f. Fig. 3a of Koessler et al.¹⁸). (c) Transformation of a multi-channel scalp EEG signal to a zero-crossing (z.c.) pattern (c3) through the steps of prefiltering (c1) and zero-crossing detection (c2).