EEG responses to mood induction
Measurements were performed at the EEG-laboratory of the University of Akureyri between end of July and beginning of October 2019. After completion of informed consent, participants answered all questionnaires mentioned in section 2.3 and the EEG-cap was mounted. The first two conditions recorded were at rest for 3 min with eyes open and 3min with eyes closed, with the screen of the stimulus computer turned off and dimmed light. Subsequently participants performed an emotional pictures memory task, which was not used for the present study. The next condition was a Stroop task. In the final condition participants received a printed three part form containing questions about current mood. All instructions were given verbally through headphones or on the screen of the stimulus computer. Firstly, participants answered one question on their current mood. Next, a 5 min musical piece, thought to evoke temporary sadness or dysphoria, was played and participants were asked to freely experience any emotions they might feel. We used a musical excerpt from Prokofiev’s “Russia Under the Mongolian Yoke”, remastered at half speed. This has been used and found to be effective in inducing a transient dysphoric mood in previous research on cognitive vulnerability to depression (Jarrett et al., 2012; Lau et al., 2004; Olafsson et al., 2020). Immediately after the music had finished, participants answered again the question on their current mood. They were then instructed to wait for 5 minutes for a challenging cognitive task. Finally, participants answered once again the question regarding their current mood. After this, participants were informed that no difficult task would follow and that the study was completed. EEG recording EEG data was gathered using BrainVision BrainAmp Recorder and Amplifier (Brain Products GmbH, Gilching, Germany) and digitized at a sampling rate of 256 Hz. Recording was conducted using 32 electrodes (Fp1, Fp2, F3, F4, C3, C4, P3, P4, O1, O2, F7, F8, T7, T8, P7, P8, Fz, Cz, Pz, FC1, FC2, CP1, CP2, FC5, FC6, CP5, CP6, FT9, FT10, TP9, TP10) referenced to FCz and grounded at AFz. One additional electrode served as lower vertical electrooculogram. Electrode positioning was in accordance with the standardized international 10-20 system by using an EasyCap. Electrodes were filled with electrolyte containing a mild abrasive (OneStep Abrasive Plus) in order to achieve low impedance of <10kOhm in all channels. We present here EEG-data from 3min rest with eyes open condition and the first 3min of the free-thinking period after listening to the sad music.
Steps to reproduce
We analyzed EEG-data from 3min rest with eyes open condition and the first 3min of the free-thinking period after listening to the sad music. EEG-data was pre-processed using BrainVision Analyzer (Brain Products GmbH, Gilching, Germany). Data was filtered from 0.5-30 Hz with zero-phase shift Butterworth filters. Then, re-referencing was performed by averaging the activity of all electrodes and subtracting this mean from all other channels. Next, an independent component analysis (ICA, infomax restricted) was performed in order to automatically remove eye-blink artefacts. The vertical lower oculogram was used as a vertical activity channel. As a last pre-processing step, a raw data inspection was done in order to automatically identify and exclude artefacts by applying the standard thresholds as implemented in Brain Vision Analyzer.The two 3min recordings were divided into 2sec segments. For each segment, we calculated the Fast Fourier Transform (FFT). The FFT of all segments that were not marked as containing artefacts were averaged for each participant, separately for the two conditions rest and sad mood induction. From the average FFT we extracted average band power in the delta (1-4 Hz), theta (5-7 Hz), alpha (8-13 Hz), and beta (14-30 Hz) range for statistical analysis. EEG channels were grouped for lobes and hemisphere for the purpose of conducting an analysis of variance with factors lobe and hemisphere, but used individually for post-hoc illustrations of results. When more than one electrode was recorded for one such region, averaging was performed. These regions were frontal-left (Fp1, F3, F7), frontal right (Fp2, F4, F8), central left (C3), central right (C4), parietal left (P3, P7), parietal right (P4, P8), temporal left (T7), temporal right (T8), occipital left (O1), and occipital right (O2).