Melbourne School of Psychological Sciences - Theses
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ItemAdolescent-onset depression: the interplay between family relationships, brain development and inflammation( 2014)Adolescence is an important life phase in which to explore psychological functioning. The emergence of depression during adolescence has been linked to aspects of both the family environment and brain developmental processes, although few studies have explored these two key variables together to prospectively determine adolescent vulnerability to depression. Consequently, the aim of the present thesis was to determine whether volume change in the pre-frontal cortex (PFC), amygdala and hippocampus partially, but significantly, mediate the effects of maternal behaviours on the onset of depression during adolescence. A secondary aim of this study was to explore a specific mechanism through which these changes in the brain may occur; specifically, systemic inflammation as marked via the production of CReactive Protein (CRP). Overall, it was expected that family interactions charaterised by higher rates and longer durations of Aggressive and Dysphoric maternal behaviours would predict the onset of clinical depression. Moreover, it was hypothesized that such maternal behaviours would predict changes in brain volume previously reported in depressed samples, as well as increased levels of CRP. Lastly, it was anticipated that elevated levels of CRP associated with more hostile maternal behaviours would partially, but significantly, mediate the relationship between parenting and structural brain development. Data from the larger Adolescent Development Study (ADS) were used to explore these aims and hypotheses. The ADS is a prospective longitudinal research study that consists of four waves of data collection, with data for this research project drawing on each of these four data collection time points in the following areas; magnetic resonance imaging (MRI) (T1, T3 and T4), family interaction tasks (T1), diagnostic assessment of mental health (T1 -T4) and saliva samples to measure inflammation (T2). As such, participants in this research comprised a smaller sub-sample of the total ADS sample population. This sub-sample consisted of N = 160 adolescents (females = 80), of which N = 32 (females = 22) received a diagnosis of clinical MDD. Path analysis techniques were used to analyse the data. The findings from the present study confirmed that maternal behaviours and changes in brain volume over time both increase vulnerability to MDD onset during adolescence. However, no evidence was found that changes in brain volume across the ages of 12 to 19 years in the PFC, amygdala or hippocampus mediated the effects of these maternal behaviours on mental health outcomes. Moreover, maternal behaviours were also found to result in detectable changes in brain volume over time, highlighting how even subtle variations in parenting behaviour influences biological development. However, when the immune system was included in these analyses, results suggested that CRP did not mediate the influence of maternal behaviours on these structural changes in the brain. The complexities of these interactions and their implications for our understanding of etiological models of depression during adolescence are considered.
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ItemDevelopment of the prefrontal cortex and its relationship to self-regulatory abilities during adolescence( 2014)Adolescence is a period of significant brain maturational changes in regions associated with self-regulation. While normative patterns of cortical thinning are postulated to underlie adaptive functioning, aberrations of this process are thought to result in poor self-regulatory abilities. This study characterises the development of three regions known to underlie regulatory processes, the anterior cingulate cortex (ACC), dorsolateral prefrontal cortex (dlPFC) and ventrolateral prefrontal cortex (vlPFC), during adolescence. The study also examines the relationship between development of these cortical regions with three aspects of self-regulation: i. temperamental effortful control, ii. proactive and reactive forms of cognitive control, and iii. cognitive reappraisal, an adaptive emotion regulation strategy. Ninety-two adolescents (47 females) were examined longitudinally during early (mean age = 12.67), mid- (mean age = 16.42) and late adolescence (mean age = 18.78). Structural MRI scans were obtained at early and mid-adolescence, and cortical thickness of the regions of interest was measured using a semi-automated software (FreeSurfer). Effortful control (measured using the Early Adolescent Temperament Questionnaire-Revised), and proactive and reactive cognitive control (measured using a modified Stroop task), were also examined at early and mid-adolescence. Finally, cognitive reappraisal was measured at late adolescence using the Emotional Regulation Questionnaire. Linear mixed models were employed to analyse brain development between early and mid-adolescence, including sex and hemisphere effects. Subsequently, general linear and linear mixed models were employed to investigate the relationship between change in cortical thickness and change in effortful control/cognitive control over time. Finally, general linear models were employed to investigate the relationship between change in cortical thickness and use cognitive reappraisal strategies during late adolescence. Sex effects were included in all models. Findings revealed that the ACC, dlPFC and vlPFC exhibited significant reductions in cortical thickness between early and mid-adolescence across both hemispheres and sexes. Greater effortful control across time (i.e., averaged across early and mid-adolescence) was related to greater thinning of the left ACC, dlPFC and vlPFC over time, while greater proactive cognitive control across time was related to greater thinning of the right ACC. In addition, greater thinning of the left dlPFC and vlPFC was related to greater engagement in cognitive reappraisal during late adolescence in females. In relation to the development of self-regulation, greater relative increase in effortful control was related to greater thinning of the left dlPFC at trend level. However, greater relative increase in proactive control was related to less thinning of the right vlPFC, and greater relative increase in reactive control was related to less thinning of the left ACC (the latter in males alone). These findings highlight a complicated and dynamic relationship between cortical and self-regulatory development during adolescence, with different patterns of cortical maturation being advantageous for different forms of self-regulation. The importance of investigating sexual dimorphism in brain-behaviour relationships is also emphasised, as different associations were identified between cortical maturation and self-regulation in males and females. These findings suggest that early to mid-adolescence is a developmentally sensitive period for self-regulation, and provide a foundation for understanding abnormal patterns of brain development, and associated behavioural difficulties and psychopathology.