Wireless cEEGrid Electrode Recording Procedure

The cEEGrid recording procedure was identical for both original studies. For better electrode to skin conductance, the skin around the ears was prepared with abrasive gel (Abralyt HiCl, Easycap GmbH, Hersching, Germany) and cleaned with 70% alcohol. Thereafter, a small amount of abrasive gel was placed on the cEEGrid electrodes (TMSI, Oldenzaal, Netherlands; Debener et al., 2015 (link)) before it was attached with double-sided adhesive around the ear. Impedances were kept below 20 kΩ. Each participant was equipped with two cEEGrids, one around the left and one around the right ear. Electrodes R4a and R4b of the right cEEGrid served as ground and reference, respectively (Figure 1B). The two cEEGrids were connected to a 24-channel mobile amplifier (SMARTING, mBrainTrain, Belgrade, Serbia) which transmitted the data via Bluetooth to a recording computer. The cEEGrid data were acquired with a sampling rate of 500 Hz. The transmitted cEEGrid data as well as the onset markers of the 10-min blocks were integrated using the Lab Recorder software based on the Lab Streaming Layer¹ to time synchronize these data streams (Mullen et al., 2015 (link)).