Melbourne School of Psychological Sciences - Theses
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ItemLongitudinal prospective study of self-esteem and psycho-social function after childhood traumatic brain injury: delineating the contribution of injury, environmental, and individual factors( 2023-07)Background: Traumatic brain injury (TBI) is a significant public health burden that is a key contributor to lifelong disability. Such injuries can disrupt brain networks undergoing maturation during childhood and derail their ongoing development, contributing to profound changes in functioning. Sustaining a childhood TBI may also influence how individuals perceive themselves i.e., their self-esteem; however, current evidence base is weakened by retrospective, cross-sectional designs, and recruitment of heterogeneous samples. The overall aim of this prospective, longitudinal investigation was to examine the impact of paediatric TBI on self-esteem across childhood/adolescence and into young adulthood, and identify factors that contribute to individual variation in self-esteem. Method: The original study comprised 112 children and adolescents with mild-severe TBI (Anderson et al., 2013). For comparison, 43 typically developing controls matched on age, sex, and socioeconomic status were included. Participating families, both children and their parents, completed assessments at an outpatient clinic or at home at 6- and 12-months post-injury. At the 13-year follow-up time point, 29 young adults with childhood TBI and 10 typically developing controls were recruited from the existing cohort. Consenting participants completed questionnaires online. Results: As documented in three published and one submitted manuscript (chapters 6-9), findings revealed that some aspects of self-esteem may be especially vulnerable to deterioration following TBI. Specifically, perceived competence in both academic and behavioural domains was found to be significantly lower amongst children and adolescents with TBI, relative to typically developing controls. Individual variance in longitudinal self-esteem outcomes was documented in relation to injury factors (TBI severity, injury age, presence of frontal lobe pathology), environmental variables (parent mental health, family function, peer relations), and individual characteristics (social isolation, emotional wellbeing). For young adult survivors of childhood TBI, low self-esteem was endorsed by a sizeable proportion (approximately 20% or 1 in 5 TBI participants). Conclusions: Evidence for links between self-esteem and a multitude of injury, environmental, and individual factors accord with both developmental and brain-injury specific theoretical frameworks, and caution against exclusive reliance on injury-related variables when determining consequences of childhood TBI, especially in the context of self-esteem. While injury severity had some influence, environmental, and individual factors consistently made the largest and most significant contribution to global and domain-specific self-esteem. Collectively, results from the present investigation underscore the importance of routine and ongoing screening of non-injury, potentially modifiable risk factors, which likely represent useful targets for clinical interventions and rehabilitation programs seeking to optimise self-esteem in the short- and long-term following childhood TBI.
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ItemPersistent post concussive symptoms in children: a neuroimaging approach( 2021)Persisting post-concussion symptoms (PPCS) refer to a collection of concussion symptoms (such as headache, dizziness, mood changes) that persist after the normal recovery period. In children, almost 30% of cases of concussion still have symptoms three months after injury, leading to poorer emotional wellbeing, school absences and a lower overall quality of life. It remains unclear as to what causes PPCS in children and how clinicians should diagnose the condition, however early intervention is known to be beneficial. This thesis sought to utilise novel neuroimaging techniques to gain a better understanding of the aetiology of PPCS in children and to provide clinical recommendations as to the use of neuroimaging for its diagnosis. Firstly, a systematic review and methodological critique conducted on existing neuroimaging research into concussion and mild traumatic brain injury was conducted to identify novel neuroimaging modalities which required further study. The literature was found to suffer from methodological heterogeneity, small sample sizes, and wide neuroimaging acquisition timeframes, however three novel neuroimaging modalities were highlighted as possible targets for investigation: diffusion weighted imaging (DWI), susceptibility weighted imaging (SWI), and resting state functional magnetic resonance imaging (rs-fMRI). Following on from the systematic review, the thesis investigated the aetiology of PPCS across two studies. As part of a larger study into concussion recovery, 45 children underwent neuroimaging at a two-week timepoint to assess whether there was an observable difference between children who recover normally and those who were predicted to have delayed recovery as per the Post-Concussion Symptom Inventory. No evidence of a difference was found between the groups for DWI, SWI, and rs-fMRI, with Bayesian analysis showing that there was no difference between the two groups on DWI. It was concluded neuroimaging is unlikely to successfully differentiate between normally recovering children and those who are likely to develop PPCS, given current technological constraints. In addition, it is likely that the aetiological factors of PPCS are more psychological in nature rather than arising from purely biological processes post-concussion.
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ItemInvestigating the influence of food product health warnings on dietary decisions using survey, behavioural and neural evidence( 2018)The sharp increase in obesity rates seen globally over the past five decades has necessitated the introduction of new health intervention approaches for promoting healthier dietary behaviour. The application of health warning messages to product packaging is now a successful component of tobacco control policy in over 300 countries, and recent proposals have argued that a similar approach might assist in reducing the impact of obesity and diet-related disease. However, there is currently limited empirical support for the use of health warnings in this context. The primary aim of the present thesis was to investigate whether health warnings are effective in promoting healthier dietary behaviour. A combination of survey, behavioural and electroencephalography (EEG) data are presented here to study this question and supplementary questions concerning the psychological and neural mechanisms through which health warnings influence intentional and automatic behaviours, and the design characteristics of health warnings that optimise their efficacy. In Study 1, two survey-based experiments sought to validate health warning stimuli for use throughout the thesis, and to examine how health warning design characteristics (positive or negative message framing, text-only versus text-and- graphic warnings) influence perceived efficacy and behaviourally relevant cognitive and affective responses to these stimuli. Health warning message topics that were perceived to be effective for influencing dietary behaviour were selected for use in subsequent experiments. The results indicated that health warnings featuring negatively framed messages accompanied by graphic imagery were perceived as most effective and evoked the strongest negative emotional responses. This pattern of results is consistent with prominent theories of behaviour change contending that health communication messages promote behaviour change intentions by increasing the perceived threat associated with unhealthy behaviours. Study 2 was conducted to identify appropriate snack food stimuli for use in subsequent behavioural and EEG experiments measuring the influence of health warnings on dietary self-control. Participants rated images of snack food stimuli on scales measuring food attributes that have been shown to motivate dietary choices. A set of snack food stimuli that spanned the full range of perceived health and taste attributes was selected. This was necessary, as health-related dietary self-control involves trading off the short-term hedonic rewards associated with eating tasty food against the expected long-term health consequences associated with eating unhealthy foods. Studies 3 and 4 aimed to test whether health warnings were capable of improving dietary self-control by priming healthy eating goals as food choices were made. Study 3 employed a behavioural paradigm in which fasted participants first provided subjective health and taste ratings for the food items selected in Study 2 and then, in two decision stages, indicated whether they would like to eat these foods at the end of the experiment. Between the two decision stages, participants were randomly assigned to one of four health warning conditions (one for each of the health warning design characteristics) and exposed to health warning stimuli, or to non-message stimuli in a control group. A measure of dietary self-control captured the propensity for participants to select healthy but not tasty items or to reject unhealthy but tasty items. Health warning group participants displayed improved dietary self- control following exposure to the intervention, with the negatively framed graphic warning group improving the most, while control groups participants displayed no change. Study 4 analysed EEG data measured while viewing food stimuli during the decision stages of the paradigm used in Study 3, in order to investigate the influence of health warnings on neural measures of food cue reactivity that have been related to dietary choice behaviour. Analysis of event-related potential (ERP) data revealed that early sensory attention, indexed by the N1, was modulated in accordance with the perceived health qualities of food stimuli but that this modulation was not influenced by health warning exposure. However, health warning exposure attenuated the amplitudes of the P3 and late positive potential in response to palatable food stimuli. These components of the ERP are thought to index the deployment of motivated attention in accordance with current decision goals. The results of Studies 3 and 4 supported the hypothesis that health warnings are capable of priming health goals, reducing automatic appetitive responses to food stimuli, and promoting healthier dietary behaviour. Overall, these findings indicate that food product health warnings, particularly those featuring graphic imagery and presented using a negative message frame, have the potential to promote healthier dietary behaviour by increasing intentions to eat healthily, and by priming these intentions at the crucial moment of dietary decision making, counteracting the appetitive influence of environmental food cues.
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ItemCharacterising changes in brain structure and neuropsychological function in the psychoses of epilepsy( 2018)Psychosis of epilepsy (POE) is a poorly understood condition which can have a devastating impact on people with epilepsy. Despite over a century of investigation into the relationship between epilepsy and psychosis, the structural neurobiological basis and neuropsychological deficits of POE remain unclear. Research in schizophrenia, the paradigmatic psychotic disorder, strongly suggests that psychosis is underpinned by abnormal neurodevelopmental processes which lead to altered brain structure and psychotic symptoms in later life. Moreover, both epilepsy and psychosis are increasingly understood as disorders of large-scale brain networks such as the default mode network (DMN) and the cognitive control network (CCN). The neurodevelopmental model of psychosis on the one hand, and the contemporary understanding of epilepsy and psychosis as network disorders on the other, underpin the primary aim of this thesis, which was to investigate changes in brain structure and neuropsychological function in POE. Understanding the structural neurobiological and neuropsychological deficits of POE is critical as it may provide insights into its neurobiological and developmental mechanisms. Following the introductory chapters (1-3), a systematic review of the neuroimaging literature in POE was undertaken. The results of this review informed the 3 structural neuroimaging studies and 1 neuropsychological study that followed. Study 1 comprised the first examination of volumetric changes in hippocampal subregions in POE, undertaken in the largest POE sample to date (n = 50). It addresses the methodological limitations of past studies of the hippocampus in POE, which were identified via the systematic review. The results of Study 1 showed hippocampal volume loss on a postero-anterior gradient, with severe decreases in the tail, and moderate volume decreases in the body, but no difference in the hippocampal head in POE relative to matched epilepsy controls (EC). These findings suggest that posterior hippocampal atrophy may be a structural biomarker of POE. The hippocampus can be further subdivided into distinct subfields which, along with the hippocampal fissure, were not captured by the assessment of hippocampal subregions undertaken in Study 1. Specific subfields, and the hippocampal fissure, have been shown to be affected in other non-epilepsy related psychotic disorders, and have not previously been examined in POE. Therefore, Study 2 comprised the first assessment of hippocampal subfields and the hippocampal fissure in POE. The results revealed an enlarged right hippocampal fissure in POE, with no difference in subfield volumes relative to EC. Moreover, because the volume of the right hippocampal fissure was not related to duration of epilepsy or age of habitual seizure onset, hippocampal fissure enlargement is likely underpinned by abnormal neurodevelopment. Together, Studies 1 and 2 provide strong evidence for structural hippocampal abnormalities in POE. Study 3 examined changes in cortical thickness, area, and volume in POE relative to EC, comparing patients with postictal psychosis (PIP) and interictal psychosis (IP) - the two main POE subtypes. This study was also motivated by the findings of the systematic review, which highlighted that only two studies have examined cortical changes in POE, one showing cortical thickening in PIP and the other showing cortical thinning in IP. Study 3 directly investigated this distinction, revealing cortical thickening in nodes of the CCN and DMN in POE overall, with more extensive thickening in visual processing regions in IP. Study 4 comprised an examination of the neuropsychological performance of POE patients and was informed by the structural changes identified in Studies 1-3. The results revealed that patients with POE displayed significantly poorer performance on tasks supported by nodes of the DMN (verbal memory and visual memory) relative to EC and healthy controls (HC), and on tasks supported by the CCN (working memory and verbal fluency), relative to HC. Considered together, the results of this thesis advance our knowledge of the structural neurobiological basis and neuropsychological deficits of POE. Specifically, they suggest that hippocampal abnormalities and cortical thickening in nodes of key brain networks are involved in its neuropathogenesis, and underpin altered neuropsychological function. The findings of this thesis also provide initial evidence that these structural changes may reflect the impact of epilepsy on neurodevelopmental processes, and provide some new insights into the neurobiological mechanisms underpinning POE. A neurodevelopmental model of POE is proposed, wherein altered hippocampal development and interruption of normal synaptic pruning leads to cortical thickening within specific large-scale brain networks. These structural changes may underpin the cognitive deficits and psychiatric symptoms of POE.
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ItemDiffusion weighted imaging analysis of children with attention deficit hyperactivity disorder and language problems( 2017)BACKGROUND: Research indicates that children with Attention Deficit Hyperactivity Disorder (ADHD) have three times the risk of co-occurring language problems (LP) compared to typically developing children (Sciberras et al, 2014). The specific types and magnitude of these LP, and neurobiology underlying the co-occurrence remains unclear. OBJECTIVES: a) to establish empirically derived data on the types and effect size of LP seen in children with ADHD compared to controls; and b) to characterise white matter microstructural differences in the dorsal and ventral language networks of children with ADHD (with and without LP), children with LP alone, and non-ADHD controls. METHOD: For Part a) of this study, a systematic review and meta-analyses were conducted according to PRISMA guidelines and rigorously defined inclusion criteria. For Part b) of this study, 163 children (9–11 years) received structural T1 and diffusion magnetic resonance imaging (63: ADHD, 76: Controls met diagnostic criteria). LP were identified using a standardised measure of language ability. High angular resolution diffusion imaging and whole brain tractography were generated using constrained spherical deconvolution. Dorsal and ventral language tracts were defined using include/exclude regions-of-interest on a cohort-specific template. Tract diffusion parameters were compared across groups via linear regression covarying for age, sex, and respective whole brain diffusion parameters. The model was then re-analysed with the addition of an inattention covariate. RESULTS: The review of previous literature for Part a) found evidence of overall, expressive, receptive and pragmatic LP in children with ADHD across the 21 included studies (Hedges g: .98–1.23; ADHD: 1,209; Control: 1,101). While children with ADHD+LP and those with LP alone performed equally poor on a measure of language function, Part b) neuroimaging analysis revealed significant differences in the white matter microstructure of dorsal and ventral language tracts between the groups, and specific aberrations unique to children with LP alone and ADHD+LP respectively. Children with LP alone were right lateralised in their dorsal language stream compared to all other groups. White matter abnormalities in the ventral tracts (the left uncinate fasciculus in particular) were unique to children with ADHD+LP compared to other groups. Finally, dorsal white matter tracts no longer showed a significant association with language ability when inattention was accounted for in the model. DISCUSSION: Part a) of this study provides the first empirical data to demonstrate large and consistent deficits in specific domains of language for children with ADHD. Part b) neuroimaging findings of white matter abnormalities in the language network may account for such language deficits. The results indicate that different neural origins may underlie the development of LP in isolation, compared to co-occurring ADHD and LP. The results further suggest that in some cases, the abnormal white matter tracts are influenced by factors other than language performance, such as inattentive factors. The findings support a need to examine children presenting with ADHD for potentially co-occurring LP so that they do not go undetected and untreated. It is possible that certain LP seen in ADHD are the result of inattention, which has a secondary negative effect on performance on a language measure. To this end, interventions utilising a combination of attention-based and traditional language-based speech-pathology services for these children may be a fruitful area for further investigation.
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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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ItemThe role of positive affect and depressive illness in the structural development of the neural reward system during adolescence( 2012)Disturbances in positive affect are a primary feature of depressive disorders. The relationship between positive affect and depression has long been described in the personality and temperament literature, and, consistent with the definition of temperament, a biological basis for this relationship has been proposed. Over the past two decades a growing body of evidence suggests an association between neurological systems hypothesised to support the experience of positive affect, particularly the dopaminergic reward system, and depression. Interestingly, neurodevelopmental research has shown that the development of the dopaminergic system undergoes significant remodelling during adolescence, a period of life that, relative to childhood, is associated with a marked increase in risk for developing a depressive illness. These coincident effects have led researchers to postulate that brain development during this period of life may be related to both normal and abnormal changes in positive affectivity observed in adolescence; however there have been very few clear expositions of the particular mechanisms involved in determining healthy or pathological outcomes. To date there have been very few empirical investigations of the relationships between positive affect, brain development and depression. This study aimed to address this shortcoming by prospectively describing structural brain development in key subcortical regions of the dopaminergic reward system (i.e., nucleus accumbens, hippocampus, pallidum, caudate, putamen) in a group of adolescents at high and low risk (determined by childhood temperament) of developing depression. Volumetric change was the chosen variable of interest firstly because it can be meaningful described longitudinally, and secondly, because there is a gap in current knowledge about how the aforementioned structures change volumetrically during this period of life. After a review of the literature, a model was proposed that described how dysregulated positive affect might contribute to abnormal brain development in the dopaminergic reward system during adolescence. Subsequently, three key aims for this investigation were described. The first aim was to further clarify normal structural development, and it was hypothesised that all regions of interest would undergo significant volumetric change consistent with previous descriptions (Study 1). Secondly, it was hypothesised that temperamental positive affect measured prior to adolescence would predict differences in brain development in reward related regions (Study 2). Finally, it was hypothesised that the experience of depression during early to middle adolescence would be associated with deviant brain development relative to healthy controls during this period of life (Study 3), and that this pattern of development would be similar to that described for individuals with low positive affect (i.e., patterns described in Study 2). The current study longitudinally investigated a community sample from metropolitan Melbourne, Australia, of 89 adolescents at ages 12 and 16 years that were selected based on high/low risk for depressive illness. Children with a prior history of depressive illness were excluded, allowing for a prospective investigation into the onset of depression during adolescence. Structural MRI data, cognitive ability, depressive symptoms and lifetime clinical diagnoses were obtained at both assessments. Temperamental measures of positive affect were obtained at the baseline assessment. MRI imaging analysis was conducted using Freesurfer (v 4.5; longitudinal stream) to obtain subcortical brain volumes from both time points. In Study 1, the overarching hypothesis that each of the ROIs would undergo significant change was generally supported, and some novel findings regarding sex differences and hemisphere effects were observed. In Study 2, lower levels of positive affect were associated with smaller left hippocampal volumes. Developmentally, positive affect moderated development of the right hippocampus and right caudate, whereby lower levels of positive affect were associated with smaller changes in volume over time (i.e., less plasticity) relative to higher levels of positive affect. In Study 3, the experience of depressive illness in early adolescence was associated with deviant brain development, relative to healthy adolescents, in the left (both sexes) and right (females only) caudate and the left (both sexes) and right (females only) putamen. Furthermore, independent of time, depressed males had smaller left hippocampal volumes. There was some support for the hypothesis that the deviant development associated with depression was similar to that associated with temperamentally low positive affect, although the effects associated with depression were more widely distributed across the subcortical regions and moderated by sex. These findings were contextualised within the current literature and possible explanations for these findings were reviewed. It was concluded that brain development during adolescence is influenced by the experience of positive affect, and it was suggested that this might be a biological mechanism that further explains the prospective relationship between temperament and depressive illness during adolescence. Furthermore, the alterations to brain development trajectories associated with the experience of depression may act like a biological scar, which could contribute to the high risk of recurrence associated with adolescent onset depression. The finding of developmental effects, as well as the difficulty of integrating some of the findings with the existing adult and child literature from cross-sectional investigations, strongly emphasised the importance of taking a developmental perspective when studying the relationships between brain structure and depression. Finally, conceptual challenges regarding an evolving definition of positive affect (i.e., one that draws upon psychological and neurobiological perspectives), as well as clinical implications arising from this study, particularly relating to early intervention strategies targeting low positive affectivity, were discussed. Throughout the final chapter several suggestions for future research are discussed.