## 3 Results
### RQ1: Which Electrophysiological Signals May Index Emotional Processing?
#### 3.1.1. Eeg  
Different methods were identified to analyze EEG activity. The first one focused on five typical frequency bands: delta (0-3 Hz), theta (4-7 Hz), alpha (8-12 Hz), beta (13-20 Hz) and gamma (>20 Hz). Most studies concluded that lower frequencies were effectively associated with emotional processing and regulation. For instance, the lowest frequency range, delta, was observed to be prominent in schizophrenic patients during ER tasks [60]. Theta frequency showed an increase in activity in frontal and parietal regions with fearful pictures during the induction of emotional responses [50]. Besides, this trend was also found in ER processes, and it was used as a marker to characterize Social Anxiety Disorder patients [40]. Moreover, this increase in activity was visible in reappraisal (ER strategy) conditions to differentiate between gender, in which women tended to show higher activity than men [51]. However, this trend was not only visualized in theta frequency. Beta and theta frequencies also showed higher relative power spectra during ER tasks on fathers of autistic children [39]. Furthermore, it was proposed that beta frequency range could be an indicator of emotional, attentional, and cognitive involvement in the stimulus, and was associated with response inhibition in ER therapies [37]. On the other hand, it was identified that a weaker low beta event-related desynchronization occurred with lower psychosocial functioning in patients with schizophrenia [28]. Finally, a great alpha band power determined a quick recovery from discomfort status during ER [56]. The other type of analysis was the neural response time-locked to the event of interest, also known as Event-Related Potentials (ERP) [38]. [PERSON] et al. [57] determined that there was no correlation between frequency dynamics (theta) and ERP components [57]. Many of the reviewed works only studied ERP components that are sensitive to emotions. Figure 4 summarizes the ERP associated with emotion processing and regulation observed in the reviewed studies. Most of the studies that analyzed early potentials were associated with emotional response or recognition. For instance, the P1 component showed a large amplitude in response to positive stimuli compared to neutral stimuli in children with ADHD [38]. On the other hand, P2 and N2 presented higher amplitudes for high arousal and negative valence stimuli in healthy participants [47]. Usually, the Late Positive Potential (LPP) was employed to assess emotional processing during ER. For instance, [PERSON] et al. concluded that LPP can be modulated by reappraisal strategy and observed a drastic reduction of LPP during the distancing versus attend condition [52]. Furthermore, [PERSON] et al. determined that the LPP amplitude decreased after reappraisal training, indicating that cognitive reappraisal was an effective strategy to reduce the neural response to negative stimuli [45]. This trend was also observable in participants with depression. However, there was an important difference: the employed strategy. Those participants tended to suppress their emotions to avoid negative