• Median scores on the daily Mood Zoom questionnaire [ Time Frame: 5 weeks ]
  Scoring six emotions (Anxious, Elated, Sad, Angry, Irritable and Energetic) on a Likert scale (scale range 1-7). Higher values represent higher levels of the emotion. The six subscales will be combined into 'Positive affect' (Elated, Energetic), 'Negative affect' (Sad, Anxious) and 'Irritability' (Angry, Irritable) scores by averaging.
• Motor activity [ Time Frame: 5 weeks ]
  Motor activity (in Hz) as measured by the GeneActive actigraphy watch
• Change in speed during recognition of positive and negative facial expressions [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Reaction times for correctly recognised positive versus negative faces in facial expression recognition task (FERT)
• Change in emotional categorisation (ECAT) [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Reaction times for correctly classifying positive versus negative personality characteristic words
• Change in recall in the Emotional memory task (EREC) [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Number of positive and negative words correctly (and incorrectly) recalled in the EREC task
• Change in reward sensitivity [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Sensitivity to reward as measured by the Probabilistic Instrumental Learning Task
• Change in performance on Auditory Verbal Learning Task (AVLT) [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Accuracy on AVLT (number of items recalled across blocks)
• Change in levels of behavioural activation [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Score on the Behavioural Activation for Depression Scale (total score range 0-150). Higher scores indicate higher levels of activation.
• Change in mood [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Score on the Beck Depression Inventory (total score range 0-63). Higher scores indicate higher levels of depression.
• FERT as a possible predictor of mood change [ Time Frame: Will be assessed at week 3 and week 5 of the intervention ]
  Correlation between Hit rate on the FERT at week 3 and the change in BDI at week 5
• Change in environmental reward [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Score on the Environmental reward observation scale (total score range 10-40). Higher scores indicate higher levels of environmental reward.
• Change in subjective experience of social support [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Score on the Multidimensional Scale of Perceived Social Support (total score range 12-84). Higher scores indicate higher levels of support.
• Change in anxiety [ Time Frame: Will be assessed at week 0, week 3 and week 5 of the intervention ]
  Score on the State-trait anxiety inventory (both State anxiety and Trait anxiety subscales scores range from 20-80). Higher scores indicate higher levels of anxiety.
• EREC as a possible predictor of mood change [ Time Frame: Will be assessed at week 3 and week 5 of the intervention ]
  Correlation between number of correctly recalled positive versus negative personality characteristic words at week 3 and and the change in BDI score at week 5
• ECAT as a possible predictor of mood change [ Time Frame: Will be assessed at week 3 and week 5 of the intervention ]
  Correlation between reaction times for correctly classifying positive versus negative personality characteristic words at week 3 and the change in BDI score at week 5
• FERT as a possible predictor of mood change [ Time Frame: Will be assessed at week 3 and week 5 of the intervention ]
  Correlation between Reaction times on the FERT at week 3 and the change in BDI at week 5

• Depression
• Depressive Disorder
• Mood Disorders
• Cognition

• Behavioral: Behavioural activation
  4-week programme based on the behavioural activation treatment provided in the NHS IAPT services. The programme includes psychoeducation on the relationship between activity and depression, examining the depressed person's level of activity, helping them identify activities they would like to increase and supporting them in the planning and conduct of those activities.
• Behavioral: Activity monitoring
  4-week programme where participants simply monitor their general daily activities in a diary.

• Experimental: Behavioural activation group
  Intervention: Behavioral: Behavioural activation
• Active Comparator: Activity monitoring group
  Intervention: Behavioral: Activity monitoring
• No Intervention: Waiting list control group

Inclusion Criteria:

• Female or male
• Age: 18 to 65 years
• Competency to give informed consent
• Scores above 14 on BDI-2 (bottom criterion for mild depression)

Exclusion Criteria:

• Previous participation in a study that used the emotional test battery (ETB)
• Currently undergoing any form of psychotherapy or counselling
• Taking antidepressant medication for less than 3 months, or changing existing psychiatric medication within the past month
• Current or past a diagnosis of psychosis or a bipolar disorder
• Current diagnosis of an eating disorder, a borderline personality disorder, or a substance abuse disorder
• Any other factor that would indicate the participant isn't able to comply with the requirements of the study according to the opinion of the chief investigator (severe insomnia, chronic fatigue syndrome, neurological conditions impairing cognitive function etc.)
• Symptoms of depression are too severe (score 20 and above on the PHQ-9 questionnaire or according to the evaluation of study psychiatrist)