Novel bifunctional cap for simultaneous electroencephalography and transcranial electrical stimulation

Abstract

Neuromodulation induced by transcranial electric stimulation (TES) exhibited promising potential for clinical practice. However, the underlying mechanisms remain subject of research. The combination of TES and electroencephalography (EEG) offers great potential for investigating these mechanisms and brain function in general, especially when performed simultaneously. In conventional applications, the combination of EEG and TES suffers from limitations on the electrode level (gel for electrode-skin interface) and the usability level (preparation time, reproducibility of positioning). To overcome these limitations, we designed a bifunctional cap for simultaneous TES–EEG applications. We used novel electrode materials, namely textile stimulation electrodes and dry EEG electrodes integrated in a flexible textile cap. We verified the functionality of this cap by analysing the effect of TES on visual evoked potentials (VEPs). In accordance with previous reports using standard TES, the amplitude of the N75 component was significantly decreased post-stimulation, indicating the feasibility of using this novel flexible cap for simultaneous TES and EEG. Further, we found a significant reduction of the P100 component only during TES, indicating a different brain modulation effect during and after TES. In conclusion, the novel bifunctional cap offers a novel tool for simultaneous TES–EEG applications in clinical research, therapy monitoring and closed-loop stimulation.

Novel flexible cap for application of transcranial electric stimulation: a usability study

“…The flexible cap also allows for the integration of recording electrodes, as introduced by Wunder et al [19]. In this study, the low preparation effort and high reproducibility were highlighted by the operators, and the participants reported a good and comfortable fit of the cap.…”

“…The flexibility of the knitted fabrics allowed a very good fit to individual head shapes with an elongation of about 320 % [19]. This, and the diffusion barrier infiltrated into the textile surrounding the electrode defined the desired effective electrode area, which contributes to stimulation.…”

“…However, even the value of 10 kΩ is fully acceptable for a typical electric stimulation (with 2 mA), translating to a voltage of 20 V, which is within the safety limit [26]. True impedance measurements during active stimulation with the textile stimulation electrodes were introduced by Wunder et al, [19].…”

Dry Electrodes for Surface Electromyography Based on Architectured Titanium Thin Films

“…The raw signal was processed using an adapted and custom MATLAB code [31,32]. For the signal processing, only 5 s of both the resting state and contraction were used.…”

“…So, PSD is a useful tool to compare the signal quality of the different dry electrodes in the frequency domain, and also to understand how they behave when compared to conventional ones. Moreover, although the analysis of the PSD spectra is useful to evaluate the performance of the electrodes in the frequency domain, a well-known approach for a direct signal quality assessment is the calculation of the signal to noise ratio (SNR), e.g., using the sEMG amplitude during contraction The raw signal was processed using an adapted and custom MATLAB code [31,32]. For the signal processing, only 5 s of both the resting state and contraction were used.…”