International 10 20 system

Subjects were seated in a comfortable chair in a silent and temperature‐controlled room. They wore protective goggles and were asked to focus their attention on the stimuli and relax their muscles. EEG data were recorded using 64 Ag–AgCl scalp electrodes placed according to the International 10‐20 system (Brain Products GmbH; Munich, Germany; band pass: 0.01–100 Hz; sampling rate: 1,000 Hz), using the nose as reference. Electrode impedances were kept below 10 kΩ. Electro‐oculographic (EOG) signals were simultaneously recorded using surface electrodes to monitor ocular movements and eye blinks.

EEG data were collected from 96 healthy participants (51 females) aged 21.6 ± 1.7 years (mean ± SD). All participants gave their written informed consent and the experimental procedures were approved by the local ethics committee. Details of experimental design and recordings have been published previously (Hu et al., 2014 (link)).
In brief, nociceptive-specific radiant-heat stimuli were generated by laser and a total of 40 pulses, 10 for each of the four stimulus energies (E1: 2.5 J; E2: 3.0 J; E3, 3.5 J; E4, 4.0 J), were delivered in a pseudorandom order. The inter-stimulus interval varied between 10 and 15 s. After each stimulus, subjects were instructed to rate the intensity of the painful sensation elicited by the laser pulse, using a visual analog scale (VAS) ranging from 0 to 10 (0 corresponds to “no pain,” “<5” corresponds to “heat pain,” “≥5” corresponds to “acute pain,” and “10” corresponds to “pain as bad as it could be”; Jensen and Karoly, 1992 ). EEG data were continuously recorded using 64 Ag-AgCl scalp electrodes placed according to the International 10–20 system (Brain Products GmbH; Munich, Germany; pass-band: 0.01–100 Hz; sampling rate: 1000 Hz), using the nose as reference. Electrode impedances were kept below 10 kΩ. Electro-oculographic (EOG) signals were simultaneously recorded using surface electrodes to monitor ocular movements and eye blinks.

The EEG measurement took place in a soundproof booth with absence of phones or other technology aside from the study equipment. Participants were seated in a comfortable chair at a viewing distance of approximately 150 cm to the screen, with a visual angle of about 15 degrees, and had a keyboard in front of them to advance between trials during the break via a mouse click. Measurement of the rest state task lasted 4 min total, plus an open-ended break between eyes-open and eyes-closed trials. A black fixation cross was presented in the middle of a gray screen (visual angle: 43° in Germany and 67° in UK). The EEG systems at both sites had 64 electrodes which followed the international 10–20 system (Brain Products GmbH) with a ground electrode at FpCz and Reference at FCz. The impedance of the electrodes was monitored closely as to not exceed 15 kΩ.

Electroencephalography (EEG) was recorded using a 64-channel BrainVision system with active Ag-AgCl electrodes mounted on an actiCAP, according to the International 10–20 system (Brain Products, Gilching, Germany). Electrodes were nose-referenced, and the ground was set at FPz. Signals were sampled at 1,000 Hz and filtered using a 0.01–100 Hz band-pass filter. Eye movements and blinks were recorded using right eye EOG with electrodes placed at the suborbital ridge and just lateral to the external ocular canthus. Electrode impedance was kept below 20 kΩ.