Effects of behavioural activation on emotional cognition and mood

Depression is one of the leading causes of disability worldwide and its prevalence has increased further during the COVID-19 pandemic. There is a need for effective treatments that can be easily and cheaply disseminated worldwide. Behavioural activation is known to be an effective intervention for depression which can be disseminated by non-specialist practitioners. However, its exact mechanism of action is currently unknown, which impedes our understanding for how to deliver it most effectively. The aim of this thesis is to examine the efficacy of a 4-week course of non-specialist behavioural activation and to investigate its possible mechanisms of effect. To this end, two experiments were carried out with participants suffering from low mood. The first study examined the intervention in an online video format during the COVID-19 pandemic and compared it with a passive control group. We examined its effects on self-reported measures of mood and found significant improvements on measures of depression, activation, state anxiety and anhedonia. We also found that the intervention led to a more positive affective bias on accuracy and misclassification measures of the Facial Emotion Recognition Task. Moreover, early changes on emotional cognition correlated with later improvements in depressive symptoms. The results of this study indicate that this format of behavioural activation can not only be effective during a global pandemic, but its effects may be carried out through early changes in emotional cognitive processing, which could help us predict who it will be most suitable for. The second study compared the intervention to both an active control group, which only carried out activity monitoring, as well as a passive control group. We again found that behavioural activation had significant beneficial effects on self-reported measures of mood and activation in comparison to both of the groups. Activity monitoring on its own also led to significant decreases in depression symptoms, albeit to a lesser extent than behavioural activation. We did not replicate the emotionally cognitive effects from the first study, possibly due to reduced power as a result of technical and COVID-19 related disruptions to the data collection. We found that early increases in environmental reward predicted future decreases in depression symptoms, indicating another mechanistic factor that may be important for the success of behavioural activation. We found no significant effects of the two behavioural interventions on actigraphy parameters indicating participants' physical activity and circadian rhythm. Early changes on these parameters did not predict future depressive symptoms, suggesting that they may not be mechanistically involved. In conclusion, both of the experiments clearly showed that a 4-week format of non-specialist behavioural activation can provide significant benefits on self-reported mood measures. Moreover, activity monitoring on its own may be a useful intervention for depression. These findings can inform policy related to mental health provision during societal crisis periods and other times of unusual strain on mental health services. Reward processing and actigraphy factors did not appear to play a mechanistic role in behavioural activation. Further replication is needed to clarify the effects of the intervention on emotional cognition and environmental reinforcement, which may be promising mechanistic factors allowing for prediction of treatment success.