Melbourne School of Psychological Sciences - Theses
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ItemNeighbourhood disadvantage and internalising symptoms in adolescents: the mediating role of stressful life events, temperament, and maternal aggression( 2013)Purpose of the study: Disadvantaged neighbourhoods are associated with increased risk for anxiety and depression in adolescents. However the mechanisms for this relationship are not fully understood. Using a longitudinal design, I investigated whether several potential mediators, including stressful life events, maternal aggressive, dysphoric and positive behaviour, and adolescent temperament (Surgency, Negative affectivity, Effortful Control, Affiliation), could help explain the relationship between neighbourhood disadvantage and symptoms of anxiety and depression in early- to mid-adolescence. Method: A community sample of 245 adolescents and their parents participated in a range of assessments at baseline (age approximately 12-13 years old), including an observational assessment of parent-adolescent interactions, and a battery of adolescent-rated questionnaires. Neighbourhood disadvantage was assessed by combining Postal Area data collected during this first wave of assessment with a measure of disadvantage called the Socio-Economic Indexes For Areas (SEIFA) developed by the Australian Bureau of Statistics Adolescents were followed-up approximately 4 years later and completed questionnaires assessing depressive and anxious symptoms. Results: Analyses revealed that adolescents from disadvantaged neighbourhoods were more likely to report a greater number of stressful life events, and depressive and anxious symptoms. They were also more likely to score higher on temperament measures of Negative Affectivity, and lower on measures of Surgency and Effortful control. Mothers from disadvantaged neighbourhoods were more likely to display aggressive and dysphoric behaviour for longer periods, and positive behaviour for shorter periods, however no differences were detected in regard to the frequency of these behaviours. Mediational analyses using a bootsrapping approach determined that stressful life events and three temperament dimensions (low Surgency, low Effortful Control, high Negative Affectivity) significantly mediated the relationship between neighbourhood disadvantage and symptoms of anxiety and depression at baseline. Stressful life events and maternal aggression significantly mediated the relationship between neighbourhood disadvantage and change in depressive and anxious symptoms from baseline to follow-up. Conclusion: The research reported in this thesis provides evidence that disadvantaged neighbourhoods differ from less disadvantaged neighbourhoods in several different ways. In addition, various factors were found to partially mediate the relationship between neighbourhood disadvantage and anxiety and depression at different periods during adolescence. Temperament appears to be important earlier in adolescence, maternal affective behaviour seems to be important during mid- to later-adolescence, while stressful life events appear to act throughout adolescence. These findings suggest that the neighbourhood environment is likely to influence adolescents both directly, and indirectly through its effects on more proximal and individual risk factors. It was concluded that prevention and intervention programs targeting a range of risk factors in adolescents from disadvantaged neigbourhoods could be particularly effective at reducing the prevalence of internalising disorders in adolescents.
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ItemGetting to the heart of teen depression: the relationship between depression and cardiovascular risk in adolescents during wakefulness and sleep( 2013)Depression has been identified as an independent cardiovascular risk factor in adults, where its presence results in higher rates of mortality and adverse cardiac events in patients with and without known cardiovascular disease (CVD). Recent literature suggests preclinical signs of cardiovascular risk are also present in adolescents experiencing depressive symptoms, however little is known about the effects of adolescent clinical depression on cardiovascular health. Moreover, no study has investigated the cardiovascular functioning of clinically depressed individuals during sleep, a state which involves cardiovascular changes including the characteristic decrease or ‘dip’ in blood pressure (BP). The aim of this study was to determine whether clinical depression is associated with an increased risk of cardiovascular disease in otherwise healthy adolescents. Experiment One sought to examine cardiovascular functioning during quiet wakefulness. Participants (n = 889, 352 male) aged 12-18 years were recruited from Victorian secondary schools in the general community. Subsequent to completing mood questionnaires and clinical interviews, 50 eligible participants (25 [6 male] clinically depressed, 25 [6 male] control) took part in a morning cardiovascular assessment at the University of Melbourne. Variables assessed included automatic clinical and continuous beat-to-beat finger arterial BP, heart rate (HR), endothelial functioning, pulse transit time (PTT), as well as cholesterol, glucose and glycohaemoglobin levels. In addition, the cumulative risk of present modifiable risk factors such as smoking was calculated according to the Pathobiological Determinants of Atherosclerosis in Youth (PDAY) risk score, which has been shown to predict coronary calcification in young populations. It was predicted that, compared to controls, depressed adolescents would show evidence of a number of early pathophysiological processes. As hypothesised, between-group analyses revealed depressed adolescents had significantly poorer endothelial functioning, which resulted in decreased vasodilation, and shorter PTT suggesting deterioration in vascular integrity and structure. Depressed adolescents also presented with higher fasting glucose and higher triglyceride levels compared with controls. Furthermore, risk score calculations revealed significantly higher PDAY risk scores in the depressed group indicative of increased engagement in unhealthy behaviours and a higher probability of having advanced atherosclerotic lesions. Contrary to predictions however, no significant differences were found in BP or HR measurements. In order to have a more complete understanding of the cardiovascular health of depressed adolescents, Experiment Two was designed to asses BP and HR during sleep. The BP profile at sleep onset was of particular interest as a blunted decline in BP is associated with target organ damage and increased cardiovascular risk. A subgroup of female participants (8 clinically depressed, 10 control) who completed Experiment One also participated in an overnight cardiovascular assessment. Whole-night polysomnography was conducted with continuous beat-to-beat finger arterial BP and HR monitored via Portapres and ECG, respectively. Data were analysed as an average of the first 6 hours of sleep as well as 2-minute epochs of stable sleep averaged within sleep stages. Further analyses of 30-second epochs were averaged across the pre-sleep wakefulness and the first ≥5 minutes of continuous stable Stage 2 in the sleep onset period. Analyses revealed that although no significant group differences in BP or HR were found during morning wakefulness, depressed adolescents presented with higher systolic, diastolic and mean arterial BP across the whole night and across sleep stages. The difference between groups (~11 mmHg) was found to not only be statistically but also clinically significant. Depressed adolescents also displayed a blunted systolic BP decline at sleep onset compared with controls. This heightened nocturnal BP and blunted decline represent early changes in BP regulation and could be a preclinical marker for depressed adolescents at high risk of cardiovascular disease. A number of plausible mechanisms may explain the heightened BP including a failure to shift to parasympathetic dominance during sleep, increased cortisol levels as a result of a dysregulated hypothalamic-pituitary-adrenocortical axis, and limited vasodilation at night due to endothelial dysfunction as found in Experiment One. Although the mechanisms are still unclear, the results suggest that depression has a significant adverse effect on the cardiovascular system in the early stages of life. Given that risk factors are known to continue to adulthood, the heightened nocturnal BP, increased triglyceride and vascular changes may increase risk for future cardiovascular problems such as hypertension. Identification of those at high-risk and intervention should therefore be actioned as early as adolescence as a way to decrease the prevalence and global burden of CVD.
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ItemBrain network correlates of adolescent self-control( 2013)The ability to engage self-control by overcoming automatic habits and impulses is critical to the progression from adolescence to adulthood, and can predict long-term health outcomes. Research into self-control has involved a number of techniques, with the psychology of individual differences and cognitive neuroscience featuring prominently. Despite their diverse perspectives, these two fields have converged recently to suggest that variations in both cognitive and personality-based measures of self-control rely on a common set of functional interactions within and between two canonical large-scale brain systems: The so-called cognitive control (CCN) and default-mode networks (DMN). However, very little is known about how individual differences in self-control during the teenage years relate to the functional activity and connectivity of these networks. This thesis aimed to fill this gap using a series of functional magnetic resonance imaging (fMRI) experiments designed to assess, in detail, the large-scale functional brain networks that support adolescent self-control as defined using both cognitive and questionnaire-based measures. To achieve this, data from the same sample of participants was used in a series of five experiments that progressed in the focus on large-scale brain networks from simple brain mapping, through individual differences analyses of activity and functional connectivity, and then ending with modularity analyses. During each experiment, a specific interest was also to determine the similarities and differences between the task-related versus the resting-state CCN and DMN to determine how self-control networks are engaged during task performance. The main hypothesis was that the task-related activity and functional connectivity of core regions that comprise the CCN and DMN would be most related to individual differences in cognitive and effortful control. Methods: The participants comprised a healthy sample of adolescents (N=73; mean age (SD) =16.5(0.5); 51% female) from a longitudinal study who completed questionnaire measures of effortful control, a temperamental index of self-control capacity in daily life; an fMRI interference control paradigm (the Multi-Source Interference Task; MSIT); and a resting-state fMRI sequence. Using these data, five experiments were then devised to investigate how the task-related activity, task-related functional connectivity, and resting-state functional connectivity of the CCN and DMN support self-control behaviours as measured by self-reported effortful control (ECc), parent-reported effortful control (ECp), MSIT interference effect, and MSIT accuracy. The experiments were designed to build upon each other to comprehensively address the thesis aim. Chapter 6 established the main measures used throughout the thesis related to the sample, and to the behavioural and brain measures related to self-control. The second experimental chapter (Chapter 7) examined how MSIT-related activation and within each region comprising the CCN and DMN correlated with EC and MSIT performance. Chapter 8 then established the functional connectivity parameters for each participant and employed the graph theoretic measure of node strength to investigate correlations between behaviour and the resting-state and task-related functional connectivity of each region. More specific pair-wise functional connectivity relationships between brain regions were then investigated in Chapter 9 in order to identify functional connectivity sub-networks related to each behavioural variable. Finally, Chapter 10 then integrated the results into a broader functional connectivity picture using a data-driven technique to identify how the putative network nodes aggregated into functionally specialized modules. Results: Contrary to the main hypothesis of this thesis, the results indicated that each behavioural measure was related to a different large-scale brain network, which appeared to be specific to the condition under investigation (i.e., task or rest). For example, the MSIT interference effect was associated with a putative visual attention network during task performance but not at rest; MSIT accuracy was mainly associated with the connectivity of default-mode regions; and effortful control was correlated with complex subnetworks where interactions between the CCN and DMN appeared to be most important. The importance of interactions between networks was then emphasised in the modularity analysis, which showed subtle, but behaviourally important, differences in network modular organization between the task and resting-state conditions. Conclusion: Overall, the results of the thesis supported the idea that competitive and cooperative relationships between the cognitive control and default mode networks support adolescent self-control. However, the experiments highlighted the importance of the engagement of different subnetworks for different measurements of self-control, and functional connectivity differences between rest and task conditions that may predict behaviour. Together, these findings emphasise the importance of considering the flexibility of large-scale networks when considering the neural basis of adolescent self-control, rather than a single canonical brain region or circuit.
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ItemSpeaking for themselves: how do adolescents define their quality of life after a traumatic brain injury?( 2013)Traumatic brain injury (TBI) is a leading cause of morbidity and mortality in young people (Yeates et al., 2002). The status of quality of life (QoL) in paediatric TBI is mixed. Our recent meta-analysis of paediatric QoL (Di Battista et al., 2012) found that good QoL outcomes are contingent on milder injuries, proxy reporting and early assessment whereas poor outcomes reflect more severe injuries and later assessment. Available paediatric QoL data is largely based on the health-related quality of life (HRQoL) paradigm; where a good outcome is contingent on what one can accomplish or achieve, as assessed by proxies. Information on the subjective well-being (SWB) component of QoL is limited. When estimating the HRQOL in adolescents, the presence of anxiety and depression and the quality of social relationships are important considerations, because adolescents are entrenched in social development during this phase of maturation. The influence of anxiety, depression and loneliness on HRQOL in adolescent survivors of TBI has not been documented. The goal of this study was to explore the adolescent experience of quality of life, anxiety, depression and loneliness after a traumatic brain injury. This study is a mixed-methods assessment of the impact of mood states and loneliness on quality of life (QoL) in adolescents who have survived a traumatic brain injury (TBI). METHOD: mixed method/cohort pilot study (11 adolescents, mild to severe TBI; 9 parents), using self-report (anxiety, depression, HRQoL, loneliness) and proxy-report measures (anxiety, depression and HRQoL) and clinical psychiatric interviews (adolescent only). The adolescent experience of these states is not accurately reflected by parental proxy. Self-reported depression and age at injury were associated with health-related quality of life outcomes, while anxiety was not. Severity of injury was not related to secondary outcomes. Adolescent narratives revealed that having experienced a TBI does not a priori impact upon perceived QoL. The impact of a TBI on QoL could be positive or negative. Post-injury changes in ability were not always attributed to the injury, but rather to a sense of normal age-related changes as identified by the adolescent. Changes as a result of the injury were not always considered important to the adolescent’s view on QoL. Adolescents identified social and inter-personal discrepancies and the emotional consequences of these discrepancies. Ultimately, the individual’s appraisal of their identity from pre to post injury life related to their current sense of well-being. Friendships were very important considerations for post-injury well-being. Processes of post-traumatic growth were identified in the adolescent narrative. The findings of this study are novel and have important implications for both research study design and clinical care settings involving adolescent survivors of a TBI.