Melbourne School of Psychological Sciences - Theses
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ItemBrain connectivity networks and longitudinal trajectories of depression symptoms in adolescence( 2014)Adolescence is a period of increased risk for the onset of depression, and evidence suggests that depressive episodes in adolescence increase the risk for further episodes later in life. It follows that adolescence is a developmental window during which lifelong risk for depression may be shaped in the brain. The aims of this thesis were: 1) to identify longitudinal trajectories of depressive symptoms in a sample of adolescents, using growth mixture modelling; 2) to relate these trajectory groups to psychosocial risk factors and outcomes, and to neurobiological outcomes in young adulthood. A connectomic approach was used to examine brain structural connectivity and relate individual variation to depression trajectories. This research was conducted as part of the Orygen Adolescent Development Study (ADS), a prospective longitudinal study of Melbourne children. The analysis was based on a sample of 243 neurologically healthy adolescents (121 males and 122 females), who were recruited from a random selection of Melbourne schools. Participants were comprehensively assessed using a battery of measures of brain structure, temperament, family processes, and psychopathology. Data were obtained from four phases of data collection over eight years. Depression scores from each of the four time points were used to model latent class growth trajectories, and a four-group solution was selected as the best-fitting model: a normative group with ongoing stable low levels of depression, two groups with declining depressive symptoms, and one group with increasing symptoms across adolescence. Trajectory class was shown to be predictive of a range of psychosocial variables including temperament, childhood maltreatment, and young adult quality of life. Diffusion-weighted MRI brain images were acquired at the final time point, and used to perform white matter tractography and brain network analysis. Key topological properties of the resulting connectivity networks were identified. The four depression trajectory groups were tested for mean differences in brain connectivity variables at global and local levels of analysis. This analysis revealed no differences between the groups at the whole-brain level, but differences in several specific regions and connections, primarily in the corticolimbic network. The groups that had experienced elevated depression symptoms in early adolescence differed from the normative group in a greater number of areas than the group who had experienced depression later. The implications of these results are that earlier onset of mood disorder is associated with reduced efficiency in a greater number of brain regions. Early onset of depression has a lasting effect on brain structure, and affected tracts correspond to areas of white matter that are still maturing during this period, particularly frontolimbic and parietal regions.