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Depression is a highly debilitating illness for which there is currently sub-optimal treatment outcomes. Anhedonia (a loss of interest and pleasure) is a core symptom of depression that predicts poorer illness course and is currently not well repaired in psychological treatments. Acute and relapse prevention outcomes may be improved by clarifying which psychological mechanisms cause and maintain anhedonia, so that mechanisms can be systematically targeted in therapy. Mind wandering (a shift in contents of thoughts away from an ongoing task and/or events in the external environment to self-generated thoughts and feelings) has previously been linked to lower levels of happiness in the general population (e.g., Killingsworth & Gilbert, 2010). However, it has yet to be established if mind wandering relates to reduced positive affect in the context of depression. Therefore, the purpose of this thesis was to further explore the role of mind wandering in driving anhedonic symptoms. This thesis employed different research designs in order to establish if mind wandering is a causal mechanism driving anhedonia. Studies used a triangulation of measures to first establish correlational support (e.g. using self-report questionnaire measures, laboratory and real life positive mood inductions). Following this, studies aimed to examine if a causal relationship between mind wandering and positive affect exists by manipulating levels of mind wandering in the laboratory, real-world settings and using an empirically tested clinical intervention (Mindfulness Based Cognitive Therapy; MBCT). Using self-report measures of mindfulness and anhedonic symptoms, studies 1a and 1b found that the acting with awareness facet of mindfulness (a measure of trait mind wandering) was uniquely related to anhedonic depression symptoms in both a large community (n=440) and treatment-seeking previously depressed sample (n=409). These unique relationships remained significant when controlling for other facets of mindfulness and general depression symptoms. Study 2 (n=70) examined the relationship between mind wandering and reduced positive affect in both controlled laboratory and real world environments. Levels of mind wandering were found to be unrelated to emotional reactivity to positive laboratory mood induction tasks, but greater levels of mind wandering were significantly correlated with reduced happiness and increased sadness change to real world positive events. Next, two experimental studies were conducted on unselected samples which attempted to manipulate levels of mind wandering to observe the effect on emotional reactivity. In study 3 (n=90), a brief mindfulness manipulation of mind wandering proved unsuccessful, so it was not possible to determine how altering mind wandering impacted on positive reactivity. Analysis during the pre-manipulation mood induction revealed a significant correlation between greater spontaneous levels of mind wandering and lower self-reported happiness reactivity. In study 4 (n=95), participants followed audio prompts delivered via a smartphone application to manipulate mind wandering whilst completing everyday positive activities. This manipulation was successful but results revealed no significant condition differences in positive or negative emotional reactivity. Analysis during the pre-manipulation positive activity revealed greater mind wandering was trend correlated with reduced change in positive affect. A final empirical study (study 5; n=102) was designed to investigate the mediating role of mind wandering on the effect of MBCT on change in positive emotional experience. Recovered depressed participants undertaking MBCT were compared to recovered depressed participants in a no-intervention control group. Correlational analysis pre-intervention revealed no support for an association between mind wandering and positive reactivity to the mood induction tasks but mind wandering measured during everyday life (using experience sampling methodology; ESM) did relate to lower positive affect and higher negative affect. Participants in the MBCT group demonstrated a reduction in trait and ESM mind wandering, relative to participants in the control group. Furthermore, participants in the MBCT group demonstrated a significant decrease in anhedonic symptoms and increase in daily levels of positive affect. Change in trait mind wandering was found to mediate changes in self-reported anhedonic symptoms when controlling for change in other mindfulness facets, however change in ESM mind wandering did not mediate change in daily positive affect. MBCT also had no impact on emotional reactivity to positive mood induction tasks. Overall the findings from this thesis provide correlational support for the link between mind wandering and reduced positive affect in different testing environments. However, evidence of a causal relationship is currently limited. Consequently, a key recommendation from this thesis is to redirect attention to other driving mechanisms as targeting mind wandering in the treatment of anhedonic clients is unlikely to lead to large improvements. The theoretical, methodological and clinical implications of these findings are discussed along with suggestions for future research. |
