## 2 Materials and Methods  
### Brain Mediators of Pain Database  
The Brain Mediators of Pain dataset comprises EEG recordings from 51 healthy participants subjected to standardized painful laser stimulation [38; 39]. Laser stimuli were applied to the dorsum of the left hand using a Thulium-YAG laser stimulator (Model: StarMedTech (Starnberg, Germany)), emitting at a wavelength of 1960 nm. Each stimulus delivered an energy of approximately 0.4 J over a pulse duration of 1 ms. The spot size of the laser was approximately 7 mm in diameter. Stimuli were applied in a pseudo-randomized sequence at three intensity levels (low, medium, high), with 20 trials per level, totaling 60 trials per subject. The interstimulus interval was randomized between 8 and 12 s to prevent habituation and expectancy effects. The stimuli levels were carefully calibrated on an individual basis to ensure perceptual relevance and consistency. Namely, stimulus intensities were individually adjusted using psychophysical calibration. Pain thresholds were first determined using the method of limits. Then, 20 supra-threshold stimuli were applied and rated by the participant on an NRS from 0 (no pain) to 100 (worst tolerable pain). A regression line was fitted to each subject's ratings, and energies matching NRS values of 30, 50, and 70 were used for low, medium, and high intensity, respectively. Then, this procedure ensures personalized calibration: Low intensity (NRS \(\simeq\) 30), Medium intensity (NRS \(\simeq\) 50), High intensity (NRS\(\simeq\) 70). Moreover, mean stimulus energies were as follows: Low: 480 \(\pm\) 40 mJ, Medium: 530 \(\pm\) 40 mJ, High: 580 \(\pm\) 50 mJ. This psychophysical calibration method ensures that the differences between the stimulus levels are both perceptually meaningful and physiologically validated (for details see [[https://osf.io/bsv86/-accessed](https://osf.io/bsv86/-accessed)]([https://osf.io/bsv86/-accessed](https://osf.io/bsv86/-accessed)) on 1 December 2024). EEG data were collected using 65 electrodes, covering all positions from the international 10-20 system, with 2 additional electrodes placed below the outer canthus of each eye. Figure 1 shows the EEG montage used. During acquisition, the EEG signals were referenced to the FCz electrode and grounded at AFz, with a sampling rate of 1000 Hz. The signals were filtered with a high-pass of 0.015 Hz and a low-pass of 250 Hz. The data were downsampled to 500 Hz. For artifact detection, a 1 Hz high-pass filter and a 50 Hz notch filter were applied to remove line noise. Finally, for the purpose of this study, the EEG data were downsampled again to 256 Hz and band-pass filtered between 4 and 60 Hz to preserve the theta (4-8 Hz), alpha (8-13 Hz), beta (13-30 Hz), and gamma (30-60 Hz) frequency bands. For simplicity, EEG channels and conventional 10-20 electrodes are preserved. Then, the LE, RE, Na, Ext, and ECG records were removed. The demographic summary in Table 1 presents the key characteristics of the study participants. The sample is composed of 26 men and 25 women, resulting in a nearly balanced distribution between genders. The participants' ages range from a minimum of 20 to a maximum of 37 years, indicating a relatively young cohort. The mean age is 26.74 years with a standard deviation of 3.86, reflecting moderate age variability within the group. Figure 1: Brain Mediators of Pain EEG Montage. The topoplot illustrates the sensor positions in a 10–20 placement EEG electrode system, containing 65 channels. In addition, it highlights, in color, the main parts of the brain (\(\|\) Frontal left, \(\|\) Frontal right, \(\|\) Frontal right, \(\|\) Central right, \(\|\) Posterior right, \(\|\) Posterior left, \(\|\) Central left). Regarding the pain classification paradigms--see Figure 2--the motor paradigm required participants to release a button as quickly as possible after receiving the pain stimulus, and reaction times served as an indicator of intensity.