The neuropsychological relationships between stress and mood

Abstract

Stress is a natural response to challenging situations and plays an important role in mental health. Excessive chronic and acute stress can have detrimental effects on an individual's health. Chronic stress, resulting from prolonged exposure to stressors, and acute stress, arising from sudden or intense events, can both lead to mood disorders such as depression. Mood, which encompasses both positive and negative affective states, can be influenced by stressful events. Effective regulation of these moods is crucial when encountering stressful situations, as it allows an individual to respond appropriately to stressors and recover from negative mood states. On the contrary, ineffective mood regulation hinders an individual's ability to adapt to stressors and ultimately can lead to mood dysregulations and depression. While existing research has established a connection between stress and mood, the implications of large-scale ecological stressors, such as the COVID-19 pandemic, on individuals' moods and depressive symptoms require further investigation. Therefore, in Study 1 I tested the association between COVID-19 and depressive symptoms and explored relevant psychological mechanistic processes such as loneliness, which is considered the pathway via which COVID-19 results in elevated rates of depressive characteristics on the societal scale. The findings confirmed elevated depression prevalence compared to pre-pandemic data. Moreover, such elevation in depressive symptoms was likely to be due to increase in loneliness levels and ruminative behaviours. These results provided support for the close link between chronic stress and depressive symptoms. Stress can be either acute and transient, or chronic and persistent in nature. Limited evidence indicates an association between individuals’ responses to acute stress and their mental outcomes under chronic stress. In Study 2, I investigated the brain functional correlates of individuals’ mood responses to acute stress induced by laboratory tasks. These findings revealed neural functional connections that predicted individuals’ mood changes following acute stress (R2 approaching 0.3), such as the connectivity between the medial prefrontal cortex and the hypothalamus. After identifying the key brain structures associated with individual differences in mood changes to acute stress, I reasoned that intervention techniques targeted at modulating the functions of those brain structures can be potentially effective in improving the individual’s mood after experiencing acute stress, which further leads to better mental health under chronic stress. One antidepressive treatment, namely bright light therapy (BLT), can non-invasively reach subcortical key regions such as the hypothalamus along the visual processing pathway. Therefore, I conducted a meta-analysis in Study 3 which summarised existing literature on the effectiveness of BLT in alleviating depressive symptoms in patients. The results showed BLT significantly reduced depressive symptoms and yielded a higher response rate compared to the control intervention. Overall, I investigated the association between both chronic and acute stress on one hand, and mood and depression on the other hand. Both socioecological and laboratory methods were adopted to respectively capture chronic stress and induce acute stress. The findings revealed neural functional networks that contribute to mood changes under stress, which are viable targets for neuromodulation intervention aimed to reduce depression.