Depression is characterized by low reward sensitivity, which is a potential maintaining factor of depressive symptoms. This is why treatment for depression should include evidence-based interventions that target reward insensitivity. Up until now, there is a lack of research that studies reward sensitivity as main outcome measure or focus of interventions, especially in the online format. However, it is crucial to identify psychological interventions that are most effective in treating low reward sensitivity. Previous studies showed that behavioral activation can be a powerful intervention to increase the availability of rewards in everyday life. In addition, mindfulness-based interventions offer effective interventions with regards to low reward sensitivity since mindfulness refocusses attention on the present moment.

This study aims to evaluate the effectiveness of different online interventions compared to a waitlist control condition in a randomized controlled trial. The sample will include participants with mild to moderate depressive symptoms, who have been preselected for their low trait reward responsiveness. Inclusion and exclusion criteria will be confirmed via a preliminary online survey and a telephone screening, which will be administered by a trained psychologist. Suicidal participants or participants who suffer from severe depression will be excluded. Those will be informed about possibilities to get intensive professional help. Further exclusion criteria will be an ongoing psychotherapy, an antidepressant medication which has been taken for a shorter time period than four weeks, persons with a lifetime diagnosis of bipolar disorder (I and II), psychotic disorders or a substance use disorder.

Participants will be randomly assigned into four groups. The randomization will be stratified according to their depression score (mild or moderate). The investigators aim to include 50 participants per group (N = 200 in total). The first group ("Behavioral Activation") will be instructed to include daily positive activities and fill out a mood protocol, which covers the time period shortly before, during and after the activity. The second group ("Mindfulness and Gratitude") will fill out a mindfulness diary and reflect upon daily pleasant situation via revisiting the impressions of their five senses during this situation. In addition, participants will specify how long they have dealt with the situation and will name something they are grateful for. The third group will do a combination of the two interventions. The fourth group will be the waitlist control condition and receive the intervention material of the third group after two weeks.

Participants will receive a pre-intervention online survey with questionnaires as a baseline measurement. This survey includes a psychoeducation video and an instruction video explaining the intervention rationale and the daily excercises. Participants will receive working sheets to protocol their daily exercises over a course of two weeks. In addition, participants are encouraged to report their results and possible problems with the implementation of the excercises in a short online survey. In addition, every day a different case study will be presented which deals with obstacles and shows strategies to solve problems. Furthermore, participants are able to contact the principal contact person of the study (Laura Potsch) via telephone to help with problems. After two weeks of daily interventions, participants will receive a post-questionnaire to measure treatment effects and will receive a follow up questionnaire after 4 months.