EEG and HF data under stress

The study included 40 healthy students: 21 males and 19 females. Participants were free from cardiovascular and neurological issues and not on medications affecting the autonomic nervous system. Written consent was obtained. Underlying stress levels were measured using the Thai Perceived Stress Scale (T-PSS-10) [59], and only those with low to moderate stress were included. Experiments were conducted between 2 p.m. and 4 p.m. to control the effect of circadian rhythms on physiological activity.
A mental arithmetic task (MAT) was employed to induce stress, with participants performing tasks under both control and stress conditions in a within-subject design to reduce individual variability. The experiment involved six stages: Habituation (no recordings), baseline (Eyes Open, EEG and ECG recorded for 5 minutes), low-stress Arithmetic Stress Task 1 (5 minutes with 50% accuracy), a 2-minute Break, high-stress Arithmetic Stress Task 2 (with auditory distraction to simulate real-world stress and increase cognitive load), and a 5-minute Recovery period.

EEG data from 29 subjects (13 males and 16 females) were included for PAC analyses, each having between 5 and 200 epochs of artifact-free 2-second data per condition.
Baseline ECG signals from the 29 subjects were further digitally high-pass filtered at 1 Hz and carefully examined to exclude any cardiac arrhythmias, such as bradycardia (heart rate < 60 bpm), tachycardia (heart rate > 100 bpm), or premature contractions. HF Norm values were then extracted using LabChart Software (ADInstruments). Subjects with low HRV were identified as those with HF Norm values below the median (14 subjects), while the other 14 subjects were classified as high HRV.