Understanding the development and structure of bipolar disorders

Bipolar disorders are characterised by recurrent periods of depressive (feeling intensely low) and manic (feeling extremely happy) symptoms with disturbances in cognitive and motor activity of varying severity, duration, and frequency. The chronicity associated with bipolar disorders often leads to poor psychological outcomes with an elevated risk of suicide and psychiatric comorbidity. Bipolar disorders are highly heritable, and a positive family history remains the strongest predictor for the development of a bipolar disorder. Clinically, bipolar disorders have proven difficult to identify which is partly due to a lack of consensus around diagnostic definitions and difficulties differentiating bipolar subtypes from one another. Current categorical approaches are limited in their ability to capture the heterogenous nature of bipolar disorders or their relationships with other symptoms of psychopathology. To contribute to our understanding of bipolar disorders, this project examined the structure of bipolar disorders and processes that may lead to affective disorders. The first section of this thesis reviews the literature concerned with Akiskal's model of affective temperament and its relationship to mood disorders. Temperament is defined as an individual's predisposition towards patterns of emotional reactivity, which remain stable over time and are inheritable. Akiskal's theory describes five affective temperaments (depressive, hyperthymic, irritable, cyclothymic and anxious) that are thought to constitute the behavioural phenotypes in the pre-morbid course of affective disorders. The review provides partial support for a continuum model of temperament in which individuals with a bipolar disorder generally yielded higher scores on a measure of temperament than genetically at-risk first-degree relatives across depressive, irritable, cyclothymic and anxious subtypes. Although mixed, the findings have implications for identifying those at risk or within prodromal phases of bipolar disorder and could provide important insights into the clinical evolution of mood disorders. However, this review was based on a limited number of studies, of varying quality, and should therefore be interpreted with caution. To investigate the structure and development of bipolar disorders the second section of the thesis includes a network analysis of bipolar disorder symptoms and common psychiatric diagnoses to explore comorbidity and pathways from psychopathological states. According to network models, mental disorders (clusters of symptoms) occur, not because the symptoms have common underlying causes, but because symptoms are connected in a network of causal relationships. Networks were constructed using symptoms scores of 7076 participants from a general population sample. Results revealed symptoms of energy and activity as core features of bipolar disorders given their centrality and connectivity within the bipolar network. In addition, community analyses revealed four communities including a 'pure mania' community and a 'mixed' community consisting of irritability, distractibility and racing thoughts amongst depression and anxiety disorders. Analyses highlighted 'racing thoughts' as a possible bridge between communities, suggesting the presence of racing thoughts as a risk factor for convergence or comorbidity. The findings have clinical implications such as the development of interventions that target key connections to decouple strongly connected symptoms and 'deactivate' networks. However, as symptoms were assessed cross-sectionally they provide limited insight into how networks may change over time.