Abstract
Modeling and experimental parameters influence the Electro‐ (EEG) and Magnetoencephalography (MEG) source analysis of the somatosensory P20/N20 component. In a sensitivity group study, we compare P20/N20 source analysis due to different stimulation type (Electric‐Wrist [EW], Braille‐Tactile [BT], or Pneumato‐Tactile [PT]), measurement modality (combined EEG/MEG – EMEG, EEG, or MEG) and head model (standard or individually skull‐conductivity calibrated including brain anisotropic conductivity). Considerable differences between pairs of stimulation types occurred (EW‐BT: 8.7 ± 3.3 mm/27.1° ± 16.4°, BT‐PT: 9 ± 5 mm/29.9° ± 17.3°, and EW‐PT: 9.8 ± 7.4 mm/15.9° ± 16.5° and 75% strength reduction of BT or PT when compared to EW) regardless of the head model used. EMEG has nearly no localization differences to MEG, but large ones to EEG (16.1 ± 4.9 mm), while source orientation differences are non‐negligible to both EEG (14° ± 3.7°) and MEG (12.5° ± 10.9°). Our calibration results show a considerable inter‐subject variability (3.1–14 mS/m) for skull conductivity. The comparison due to different head model show localization differences smaller for EMEG (EW: 3.4 ± 2.4 mm, BT: 3.7 ± 3.4 mm, and PT: 5.9 ± 6.8 mm) than for EEG (EW: 8.6 ± 8.3 mm, BT: 11.8 ± 6.2 mm, and PT: 10.5 ± 5.3 mm), while source orientation differences for EMEG (EW: 15.4° ± 6.3°, BT: 25.7° ± 15.2° and PT: 14° ± 11.5°) and EEG (EW: 14.6° ± 9.5°, BT: 16.3° ± 11.1° and PT: 12.9° ± 8.9°) are in the same range. Our results show that stimulation type, modality and head modeling all have a non‐negligible influence on the source reconstruction of the P20/N20 component. The complementary information of both modalities in EMEG can be exploited on the basis of detailed and individualized head models.
Highlights
Electro- (EEG) and magnetoencephalography (MEG) source analysis of evoked response components is influenced by a variety of modeling and experimental parameters, some of them are well-known, while others are often considered to be less important or even negligible (Brette & Destexhe, 2012; Hämäläinen, Hari, Ilmoniemi, Knuutila, & Lounasmaa, 1993)
In this sensitivity group study of five healthy participants, we showed that different stimulation types, measurement modalities, and head modeling procedures all have a similar and non-negligible influence on source analysis of the somatosensory P20/N20 component
Our study makes it possible to record the effect sizes of modality and head modeling in comparison to the more understandable effect size of stimulation type
Summary
Electro- (EEG) and magnetoencephalography (MEG) source analysis of evoked response components is influenced by a variety of modeling and experimental parameters, some of them are well-known, while others are often considered to be less important or even negligible (Brette & Destexhe, 2012; Hämäläinen, Hari, Ilmoniemi, Knuutila, & Lounasmaa, 1993). We will put all influences side-by-side with regard to changes in source location, orientation, and strength within the reconstruction process and thereby answer the following four main questions: How is the source reconstruction of the P20/N20 component affected when changing (a) the modality (EEG, MEG, and EMEG), (b) the detailedness of the head model (3CI or 6CA) for standard and individually calibrated skull conductivity, (c) the stimulation type (EW, BT, or PT) for the most integrated modality (EMEG) and three different head models, and (d) are all parameters influential or can they be ordered by their degree of influence/sensitivity?
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