## 5 Questions for the Future  
Depressive disorder is not one disease: all disease and disorder-related changes in mood, as well as in self-reference and affective processing can, as outlined in this manuscript, theoretically manifest as biases in the processing of self-referential positive and negative information well prior to onset of the disorder. EEG and, specifically, EEG-ERP methodology are currently pursued as means that, if combined with an experimental paradigm, could help unravel the mechanisms of processing preferences and their clinical relevance as traits or state markers of the risk of mental health conditions such as depression. Although preliminary evidence has already been accumulated, future studies should principally replicate and extend the current evidence with a focus on the following guiding questions:  
1. At which stages of stimulus processing does an interaction between self-referential and emotional processing occur? Can the preliminary findings, illustrated in this manuscript, be replicated in larger cohorts of both, cognitively vulnerable and already depressed individuals vs. healthy controls?
2. To what degree can processing preferences for self-related negative and positive stimuli, respectively, be influenced by self-related attentive and cognitively controlled processing, and which of these influences are specific for depression and its risk?
3. Is self-negativity bias the only marker of cognitive vulnerability, or is a self-negativity bias accompanied by a reduced self-positivity bias as well (see Figure 4)?
4. Do the observed electrophysiological ERP correlates of the processing preferences for self-related negative or positive stimuli prove to be temporally stable markers of subjective well-being and cognitive vulnerability?
5. Do the results vary across languages, and do they also apply to a bilingual/multilingual context?  
Importantly, question 5 is receiving increasing attention in a global society in which bilingual and multilingual psychotherapy is becoming more and more prevalent. Recent research, including EEG-ERP studies, has observed a weaker emotional reactivity to negative language content in the second language than in the first, with results being further modulated by mood, proficiency, and language use, e.g., [67, 68]. Future projects and studies that focus on questions (1)-(5), respectively, will fill an important gap between the understanding of processing preferences, their electrophysiological dynamics, and their psychological and clinical significance as depressive vulnerability indicators and markers of subjective well-being. Based on this evidence, experimental tests could then be developed with which depression-associated processing biases as well as indicators of well-being could be detected by means of EEG-ERP measurements and used for depression monitor  
Figure 4: Extended cognitive vulnerability model (EEG cortical processing).  
ing and improvement in well-being in the context of health prevention, intervention, and therapy.  
The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app12157740/s1](https://www.mdpi.com/article/10.3390/app12157740/s1)]([https://www.mdpi.com/article/10.3390/app12157740/s1](https://www.mdpi.com/article/10.3390/app12157740/s1)).  
This research was funded by the German Research Foundation (DFG), HE5880/7-1 granted to C.H.  
Not applicable.  
The author declares no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.