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. 2021 Oct 14;21(20):6827.
doi: 10.3390/s21206827.

Validation of Soft Multipin Dry EEG Electrodes

Janne J A Heijs  1 , Ruben Jan Havelaar  2 , Patrique Fiedler  3 , Richard J A van Wezel  1   2 , Tjitske Heida  1
Affiliations

Validation of Soft Multipin Dry EEG Electrodes

Janne J A Heijs et al. Sensors (Basel). .

Abstract

Current developments towards multipin, dry electrodes in electroencephalography (EEG) are promising for applications in non-laboratory environments. Dry electrodes do not require the application of conductive gel, which mostly confines the use of gel EEG systems to the laboratory environment. The aim of this study is to validate soft, multipin, dry EEG electrodes by comparing their performance to conventional gel EEG electrodes. Fifteen healthy volunteers performed three tasks, with a 32-channel gel EEG system and a 32-channel dry EEG system: the 40 Hz Auditory Steady-State Response (ASSR), the checkerboard paradigm, and an eyes open/closed task. Within-subject analyses were performed to compare the signal quality in the time, frequency, and spatial domains. The results showed strong similarities between the two systems in the time and frequency domains, with strong correlations of the visual (ρ = 0.89) and auditory evoked potential (ρ = 0.81), and moderate to strong correlations for the alpha band during eye closure (ρ = 0.81-0.86) and the 40 Hz-ASSR power (ρ = 0.66-0.72), respectively. However, delta and theta band power was significantly increased, and the signal-to-noise ratio was significantly decreased for the dry EEG system. Topographical distributions were comparable for both systems. Moreover, the application time of the dry EEG system was significantly shorter (8 min). It can be concluded that the soft, multipin dry EEG system can be used in brain activity research with similar accuracy as conventional gel electrodes.

Keywords: brain imaging; dry electrodes; electroencephalography (EEG); gel electrodes; validation study.

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Conflict of interest statement

The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. P.F. was employed at ANT Neuro b.v. (Hengelo, The Netherlands) during the design of the study, and not during the period of data analysis and the writing of the manuscript. Moreover, P.F. was not involved in the data collection and data analysis.

Figures

Figure 1
Figure 1
The 32-channel layout of the soft, multipin, dry EEG system, indicating the location and shore hardness of short pins (green), medium pins (blue), and long pins (orange).
Figure 2
Figure 2
Pattern-reversal visual evoked potential (VEP) evoked by the checkerboard paradigm, for the gel EEG system (blue; left) and dry EEG system (red; right). (a) The average VEP (μV) per channel over subjects. (b) The global field power over time (GFPt; μV) averaged over subjects. Shaded areas indicate the confidence interval (mean ± 2x standard deviation). (c) The standardized topographic distribution (Z-score) of the two main components of the VEP. Black lines encircle the pixels that were significantly different between the two systems.
Figure 3
Figure 3
Auditory evoked potential (VEP) evoked by the auditory steady-state response task for the gel EEG system (blue; left) and dry EEG system (red; right). (a) The average AEP (μV) per channel over subjects. (b) The global field power over time (GFPt; μV) averaged over subjects. Shaded areas indicate the confidence interval (mean ± 2x standard deviation). (c) The standardized topographic distribution (Z-score) of the two main components of the AEP. Black lines encircle the pixels that were significantly different between the two systems.
Figure 4
Figure 4
Power spectral density (PSD) of the 40 Hz Auditory steady-state response (ASSR) for the gel EEG system (blue; left) and dry EEG system (red; right). (a) Absolute PSD of the 40 Hz-ASSR (μV2/Hz), averaged over channels per subject. (b) Standardized PSD of the 40 Hz-ASSR (Z-score), averaged over channels per subject. Black lines indicate average PSD over all subjects and channels; shaded areas indicate the confidence interval (mean ± 2xSD).
Figure 5
Figure 5
Power spectral density (PSD) of the eyes open/eyes closed task for the gel EEG system (blue) and the dry EEG system (red). (a) Absolute PSD (μV2/Hz) during the period of open eyes (left) and a period of closed eyes (right). (b) Standardized PSD (Z-score) during the period of open eyes (left) and a period of closed eyes (right). Lines indicate the average power over all channels and subjects. Shaded areas indicate the confidence interval (mean ± 2xSD). (c) The standardized topographic distribution (Z-score) of the alpha band during eyes open (left) and eyes closed (right) for the gel EEG system and the dry EEG system. Black lines in the topographic distribution encircle the pixels that were significantly different between systems.
Figure 6
Figure 6
General performance. (a) Application time (min) for the gel EEG system (blue) and the dry EEG system (red). (b) Percentage of data rejection (%) per channel averaged over subjects for the gel EEG system (left) and the dry EEG system (right). 0% = no data rejected; 100% = all data rejected. Color bar from 0–50%. (c) Experienced comfort for the gel EEG system (blue) and the dry EEG system (red), rated by the subject before (open) and after the experiment (shaded). 1 = extremely comfortable; 10 = maximum imaginable pain. * p < 0.05.
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