Psychiatry - Theses
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ItemAdjunctive Natural Low Dose Docosahexanoic Acid (DHA) Omega-3 in Residual Symptoms in Depressed Patients( 2021)The stated goal of psychiatric treatment is the remission of all presenting symptoms and a return of the patient to full pre-morbid functional status. Increasingly, the presence of residual symptoms of disorder have been linked to an early relapse of the underlying psychiatric syndrome. While pharmacological treatments of moderate to severe psychiatric disorders are the main therapeutic approach, remission is achieved in around 30% of patients with the first treatment. Adjunctive treatment regimens based on medications, so-called ‘nutraceuticals’ or psychotherapy, have been investigated for their ability to alleviate these persistent residual symptoms. Among adjunctive treatments omega-3 polyunsaturated fatty acids (PUFAs) have been investigated for their effects on symptoms of depression and anxiety. While many questions remain, one PUFA, docosahexaenoic acid (DHA), has shown promise as an adjunct to the treatment for the presenting complaints in Major Depressive Disorder but has not been investigated for residual symptoms. This exploratory study utilised a double-blind, placebo-controlled, cross-over methodology to investigate the efficacy of DHA in patients with residual symptoms of depression and anxiety meeting DSM-V criteria for a Major Depressive Disorder. Depression and anxiety symptoms were assessed at the end of 12-weeks of either placebo or DHA (and then the crossed-over situation) with clinician and patient rated scales and compared using a repeated measures analysis of variance. Neither the last observation carried forward nor the observed cases sets of data showed any statistically significant changes in depression or anxiety symptoms during treatment with placebo or DHA. Changes in patient rated scales, assessed using the same statistical methodology, were concordant with the findings from the clinician rated scales. It is concluded that DHA, in the doses used in this study, does not offer significant clinical benefits to patients with persistent residual mood symptoms. Several factors specific to the patient population studied are discussed which may explain the apparent lack of clinical effect. Further studies are suggested which could overcome some of the barriers to efficacy encountered in this trial.
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ItemThe Brain-Behavioural Basis of Human Safety Learning: An investigation of Pavlovian conditioned inhibition( 2022)Safety learning allows individuals to associate stimuli with the absence of threat, thus conferring the ability to suppress fear and anxiety in safe situations, and by consequence, maintain psychological and physiological well-being. Disrupted safety learning is thought to be a key component of anxiety-related disorders, but as yet, the basic mechanisms of safety learning remain incompletely understood and lack a formal theoretical definition. Across two studies of healthy adults, this thesis sought to examine the behavioural (Study 1) and neural (Study 2) basis of safety learning in humans. Based on long-standing principles of associative learning theory, a novel iteration of the Pavlovian conditioned inhibition paradigm was developed and implemented in lab-based and 7-Tesla functional magnetic resonance imaging (fMRI) settings. Study 1 (N = 73) was an investigation of the behavioural aspects of safety learning, and moreover, sought to validate the utility of the Pavlovian conditioned inhibition paradigm as an experimental model for safety learning, as well as examining individual differences in trait measures of anxiety. This paradigm trained a robust safety signal (the conditioned inhibitor, X) which was conditioned by delivering threat (loud noise) to a conditioned stimulus on its own (A+), but omitting threat when that stimulus was presented in conjunction with the inhibitor (AX-). As a control cue, two stimuli were similarly unreinforced in compound, but neither was presented alone on other trials (BC-). The paradigm also controlled for several possible confounds, including the use of a safety signal as a control cue, rather than using a novel or neutral cue, among other factors. Both the control safety signal and the conditioned inhibitor were shown to inhibit physiological and cognitive threat responses at test, when paired with aversive conditioned stimuli. However, the inhibitor conferred a significantly greater degree of inhibition for cognitive threat responses, as measured by threat-expectancy ratings during a summation test. Further, trait anxiety was positively correlated with threat expectancy towards the inhibitor during learning, indicative of threat responses to safety signals, which are thought be a feature of maladaptive anxiety. Study 2 (N = 49) investigated the functional neural correlates of safety learning via conditioned inhibition. The same paradigm from Study 1 was adapted for use in neuroimaging, using ultra-high field fMRI. Activations were compared between the safety signals directly (AX vs BC), and learning-specific activation was assessed via contrasts between early and late conditioning trials, and conditioning phase activity versus test phase, under the hypothesis that this should identify regions recruited to form stimulus-safety associations when these contingencies are new and unfamiliar. It was found that conditioned inhibition involved activity across a distinct set of cortico-striatal regions, which aligned with known subcortical circuits of the basal ganglia. Further, though showing similar behavioural responses to the inhibitor, the standard safety signal evoked no subcortical engagement, and instead was associated with an expanse of cortical activity, consistent with regions observed in differential fear-safety processing. In total, these studies indicate that the framework of Pavlovian conditioned inhibition can serve as an experimental model for characterising safety learning in humans, with implications for clinical translational work. It suggests that robust safety learning occurs by way of expectancy violation, or in other words, that a stimulus acquires safety value by predicting the unexpected omission of threat, in line with the principles of formal learning theory. Further, though current human studies often emphasise the safety-learning roles of various higher prefrontal regions, Study 2 demonstrates that safety learn- ing engages several subcortical brain regions that are well-known for their involvement in other domains of reinforcement learning. I discuss the theoretical implications that this research has for defining safety through the lens of associative learning, the neurobiology of safety acquisition, and a basis for separating processes of safety acquisition and safety expression between associative subcortical systems and higher cortical brain regions respectively. Several future directions are proposed for the ongoing study of safety learning, including characterisation of safety prediction errors and testing hypotheses of deficient safety learning in psychiatric disorders.
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ItemKnowledge of and Attitudes towards Dementia among Older Chinese Adults: A cross-national comparative study between Melbourne and Beijing( 2021)Dementia is a public health priority globally. In the absence of effective treatments to reverse or cure dementia to date, targeted information on dementia risk reduction strategies and the importance of a timely diagnosis of cognitive impairment is crucial for ageing people to manage their brain health. However, previous studies indicate that insufficient knowledge of dementia and negative attitudes towards dementia are barriers to engage with available information and help-seeking behaviours. In particular, culturally and linguistically diverse (CALD) populations in Australia, such as Chinese immigrants, often face specific barriers which need more investigation. Therefore, the aim of this thesis is to investigate and compare the knowledge of and attitudes towards dementia between older Chinese adults living in Melbourne, Australia and those in Beijing, China. Based on the socioecological framework, this thesis explored older Chinese adults' knowledge of and attitudes towards dementia on four levels: intrapersonal, interpersonal, community, and sociocultural level. This framework was used in study design, result integration and interpretation. A mixed-method approach was employed and consisted of three sub-studies, including one quantitative study (Study One) and two qualitative studies (Study Two and Study Three). Study One assessed and compared dementia knowledge and its associated factors between older Chinese adults in Melbourne and those in Beijing. A convenience sample of 379 older Chinese adults aged 50 or above were included, 226 from Beijing and 153 from Melbourne. Their level of dementia knowledge was assessed cross-sectionally using the Alzheimer's Disease Knowledge Scale (ADKS). This study found that older Chinese adults in both groups had similar levels of dementia knowledge and knowledge subdomains. Of the seven subdomains, older Chinese adults were most knowledgeable about the life impact of dementia as well as treatment and management, and least knowledgeable about caregiving and risk factors. Younger age and self-reported concerns about dementia were significantly associated with higher levels of dementia knowledge in the Melbourne group. In the Beijing group, a positive family history of dementia was significantly associated with a higher level of dementia knowledge. Study Two explored and compared older Chinese adults' attitudes towards dementia between Melbourne and Beijing. Based on the tripartite model of attitude, semistructured interviews were conducted with 46 Chinese adults aged 50 and over, including 21 from Melbourne and 25 from Beijing. The study found that older Chinese adults in both groups reported stigma and stereotypes associated with dementia. Most of them reported being afraid of developing dementia and thought it was a tragedy for families, particularly for adult children. However, they believed there was nearly no impact on patients themselves and the community in general. Most participants preferred home care, but acknowledged that formal care might be an alternative needed in the future. In the Beijing group, older adults perceived dementia as a common chronic disease in later life and called for more support in response to dementia from the community, government and society as a whole. Most of them expressed concerns about developing dementia in the future and considered the financial situation as a key determinant for the type of dementia care they would select. In terms of risk factors, they highlighted the important role of physical health conditions in the development of dementia. Older Chinese immigrants in the Melbourne group perceived dementia as an unpleasant topic, but not of many concerns to them specifically. Most of them expressed less concern about developing dementia in the future. Not many of them expressed interest in learning more about dementia. The majority stated they would consider their children's advice about participating in dementia education programmes. Meanwhile, they would be worried about language barriers and transportation limitations when considering participation in such programmes. Study Three explored and compared attitudes towards dementia from older Chinese adults' significant others' perspectives, including adult children, health professionals and community service providers. In total, 25 adult children (13 from Melbourne and 12 from Beijing), 13 health professionals (five from Melbourne and eight from Beijing) and ten community services providers (five from Melbourne and five from Beijing) were interviewed. Results indicated that across Melbourne and Beijing, all three groups of significant others reported that older Chinese adults usually avoided the topic of dementia or people living with dementia (PwD). They preferred home care if they developed dementia in the future. Adult children participants from Melbourne reported more proactive and positive attitudes towards dementia among older Chinese adults as compared to adult children from Beijing. Specific findings were reported regarding the impact of the migration experience in the Melbourne group, including language barriers, transportation limitations, limited social networks and the more independent parent-child relationship than the traditional Chinese parent-child relationship. These barriers influenced help-seeking behaviours not only in relation to cognitive concerns and dementia but also for other health concerns. With the specific comparison between immigrants and non-immigrants in older Chinese people, this thesis contributes new knowledge on the impact of the migration experience and the sociocultural environment on participants' knowledge of and attitudes towards dementia. With this, the results of this thesis have the potential to inform the development of targeted strategies to enable and maintain dementia health promotion for older Chinese adults living with or without migration experience.
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ItemAssociations between early adversity, brain development, and mental health during adolescence( 2022)Early adverse experiences, like childhood maltreatment and socioeconomic disadvantage, are associated with lifelong consequences for mental health. However, the underlying neurobiological mechanisms of these associations are yet to be characterized. It has been suggested that adverse experiences may shape mental health via alterations in neurodevelopment. The aim of this thesis was to investigate how childhood maltreatment and socioeconomic disadvantage (which are both highly prevalent in the general community and are strong predictors of poor mental health outcomes), influence brain development during childhood and adolescence, and how those changes, in turn, contribute to mental health outcomes. An additional aim of the thesis was to examine environmental and psychological factors that may buffer the effects of adversity on brain development and mental health. This thesis used structural magnetic resonance imaging and resting state functional magnetic resonance imaging data from two studies, the Orygen Adolescent Development Study, and the Adolescent Brain Cognitive Development Study, in order to comprehensively characterize associations between childhood maltreatment, socioeconomic status (SES), and brain structure and functional connectivity as well as mental health. In the first and second study we investigated associations between childhood maltreatment (as well as specific dimensions of maltreatment) and longitudinal development of functional connectivity during adolescence, and showed that total maltreatment, abuse, and neglect, are associated with deviations in typical patterns of functional connectivity development. We also showed that these alterations in functional connectivity development are associated with mental health outcomes. Next, in the third study, we systematically synthesized the association between SES and brain structure, function, and connectivity, and showed that while there were some consistencies in findings, results were often mixed (especially at the level of individual SES indices). In the fourth and fifth study, we focused specifically on neighborhood disadvantage given that our review (third study) identified this to be a relatively unexplored SES indicator. In the fourth study, we showed that neighborhood disadvantage is associated with longitudinal alterations in brain-predicted-age trajectory, which was found to be moderated by temperamental effortful control. In the sixth study, we demonstrated cross-sectional alterations in functional connectivity as a function of disadvantage. We also showed that some of these alterations were associated with poor mental health. However, some associations between neighborhood disadvantage and functional connectivity were found to be moderated by positive parenting and favorable school environments. Finally, in studies six and seven, we demonstrate the independent and interactive effects of different SES indicators on brain structure and connectivity. We show that household income moderated the association between neighborhood disadvantage/low parent educational attainment and connectivity/brain structure. Overall, the findings of this thesis build knowledge around the impact of early adverse experiences on brain structure and functional connectivity, as well as mental health, during childhood and adolescence. Using whole-brain approaches, longitudinal data, and large samples, we were able to demonstrate that both childhood maltreatment and low SES are associated with widespread alterations in brain structure and function. These findings bring us one step closer to understanding the neurobiological pathways through which adversity ‘gets under the skin’ and impacts children’s mental health and wellbeing, and opens up exciting avenues for future research.
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ItemEffective connectivity in major depressive disorder and its association with treatment response: a functional magnetic resonance imaging investigation( 2021)Despite effective first-line treatments for major depressive disorder (MDD), prognostic outcomes for many young people remain poor. Recent investigations into the interactions between brain regions, both at rest and during specific tasks, appear to suggest that abnormalities in these connections may contribute to the manifestation of depressive symptoms. An improved characterisation of brain associated dysfunction in MDD may elucidate contributing factors to this heterogeneity in treatment response. This thesis used functional magnetic resonance imaging and dynamic causal modelling across three studies to characterise abnormalities in the directional interactions between brain regions. Due to the lack of research examining how different emotional expressions modulate these directional interactions, Study 1 aimed to explore changes to effective connectivity present during the implicit processing of negatively valenced emotional expressions in a sample of healthy adolescents and young adults (N = 92, Mean age = 20.1 +/- 2.9 years). Processing sad and fearful facial expressions were associated with greater positive connectivity from the amygdala to dorsolateral prefrontal cortex (dlPFC). Compared with processing sad faces, processing fearful faces was associated with significantly greater connectivity from the amygdala to dlPFC. Study 2 aimed to examine whether there were differences in effective connectivity between MDD patients and healthy controls during the processing of facial expressions. The healthy controls from Study 1 were compared with a sample of MDD patients (N = 88, Mean age = 19.8 +/- 2.7 years). Following their scan, these patients were randomised to receive cognitive behavioural therapy for 12 weeks, plus either fluoxetine or placebo. Depressed patients demonstrated reduced inhibition from the dlPFC to ventromedial prefrontal cortex (vmPFC) and reduced excitation from the dlPFC to amygdala during sad expression processing. During fearful expression processing patients showed reduced inhibition from the vmPFC to amygdala and reduced excitation from the amygdala to dlPFC. Treatment responders demonstrated greater excitation from the amygdala to dlPFC during sad expression processing and reduced excitation from the amygdala to vmPFC connectivity during fearful expression processing. Finally, Study 3 aimed to examine differences in the effective connectivity at rest between regions commonly implicated in the neurobiology of depression, using the healthy controls (N = 90; Mean age = 20.1 +/- 2.7) and MDD patients (N = 94; Mean age = 19.7 +/- 2.8) from Study 2. Depressed patients demonstrated greater inhibitory connectivity from the rostral anterior cingulate (rACC) to the dlPFC, anterior insular cortex, dorsal anterior cingulate (dACC) and left amygdala. Moreover, treatment responders illustrated greater inhibitory connectivity from the rACC to dACC, greater excitatory connectivity from the dACC to subgenual anterior cingulate (sgACC) and reduced inhibitory connectivity from the sgACC to amygdalae at baseline. Together the findings from these studies detail widespread but distinct alterations associated with MDD which occur at rest and during the implicit processing of sad and fearful facial expressions. These results commonly suggest that MDD is marked by abnormal interactions between regions of the salience, central executive and default mode networks. Across both of our tasks, treatment responders did not demonstrate connectivity which was more similar to healthy controls, but rather illustrated unique alterations that may have predicated their enhanced treatment response. Moreover, while these parameters were shown to be overall predictive of treatment response, in both tasks this was particularly strong for those treated with CBT and placebo. We suggest that this effect may be due to treatment with selective serotonin reuptake inhibitors altering connectivity variability in such a way that this baseline configuration is less informative of future response.
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ItemThe neural basis of threat and safety reversal learning in healthy subjects and patients with Social Anxiety Disorder( 2021)Responding flexibly to changing sources of threat and safety is critical to the adaptive regulation of emotions, including fear. Anxiety disorders, including social anxiety disorder (SAD), have been linked to maladaptive forms of fear regulation. At a neural systems level, such flexibility is thought to rely on an extended neural circuitry involving the dorsal anterior cingulate cortex (dACC) and ventromedial prefrontal cortices (vmPFC), although precisely how this occurs remains unclear. Furthermore, few studies have examined this in young, unmedicated SAD patients. To address this, this thesis used functional magnetic resonance imaging (fMRI), and autonomic and subjective measures during a threat and safety reversal learning task, in three studies. Study 1 examined the neural correlates of threat and safety reversal learning and their associations with individual differences in anxious responding in a large sample of healthy adolescents and young adults (N=94; 21.31 years). Overall, participants demonstrated successful threat and safety reversal learning. At a whole-brain level, threat reversal was associated with significant activation of the bilateral anterior insular cortex and dACC, in particular its rostral subregion. Conversely, safety reversal led to significant activation of the anterior vmPFC, together with posterior mid-line regions. Study 2 aimed to characterise the neural, subjective, and autonomic correlates of reversal learning in patients with SAD (N=41; 19.85 years), and compare them to matched patients with major depressive disorder (N=19; 19.42 years) and to healthy controls (N=60; 20.3 years). No significant differences were observed between groups at either a neural, subjective, or autonomic level. Threat learning elicits robust changes across multiple affective domains. It has been argued that the underlying causes of such changes may be dissociable at a neural level, but there is currently limited evidence to support this notion. To address this, Study 3 examined the neural mediators of trial-by-trial skin conductance responses (SCR), and subjective reports of anxious arousal and valence in participants performing the threat and safety reversal learning task during ultra-high field fMRI (N=27; 21.93 years). Our results suggest the broad neurocircuitry of threat learning, including the dACC, anterior insula and vmPFC, mediated the experience of subjective arousal, while only a subset of these regions mediated threat-related SCR and valence. Furthermore, our data suggest dual vmPFC mechanisms modulate SCR during threat learning. Conversely during safety reversal, positive mediators were located in the vmPFC for all domains. We therefore conclude that appropriate responding during safety reversal learning is facilitated by participants engaging self- and valence-based processes. Taken together, our findings complement existing neurocircuitry models of human fear regulation and provide further insights into regional contributions to flexible threat-safety signal processing. We add novel evidence to support distinct underlying neural processes within these regions facilitating autonomic and subjective responding during threat learning and safety reversal. I discuss the implications of these findings for our understanding of brain function and affective processing more broadly. We showed that patients with SAD did not show impairments in threat and safety reversal learning. I discuss how we may otherwise approach studying hypothesised maladaptive fear regulation in future studies.
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ItemThe role of lifestyle, cardiovascular factors and biomarkers on health status in older adults at risk of cognitive deterioration( 2021)Recent developments in neuroscience have heightened the possibilities to tackle the prodromal stage of dementia. The purpose of this thesis is to identify the relationships between physical health, cognitive function, vascular risk burden and peripheral biomarker candidates in 108 older adults at risk of cognitive decline. The AIBL Active trial participants, aged 60 years and older (32 cases of MCI, 76 cases of SMC) with at least one cardiovascular risk factor present, completed a neuropsychological test battery and provided cross-sectional health data and physical activity information using a validated questionnaire and pedometer recordings. Cardiovascular parameters and blood tests determined if the participants met the clinical definition of metabolic syndrome that referred to a cluster of vascular and metabolic disturbances due to obesity and insulin resistance. This thesis utilised a preferred statistical standardisation of metabolic syndrome factors and obtained continuous variable (z-scores) to indicate the composite cardiovascular risk burden that addressed the progressive nature of the syndrome. Regression models adjusted for covariates examined the associations between the parameters and cognitive function. Almost two-thirds of participants met the national physical activity guidelines for older Australians with MCI or SMC (moderate-to-vigorous physical activity (MVPA) over 150 minutes per week), according to self-report (average 317 minutes/week). The pedometer estimated a mean of 6,926 steps/day for all participants. Participants with lower body mass index (BMI) and higher self-efficacy were 18% and 24% respectively more likely to meet the guideline recommendations. The risk severity of metabolic syndrome was inversely associated with pedometer tracked physical activity and the six-minute walk test, independent of global cognitive performance. The six-minute walk test has a stronger association with metabolic syndrome and may be a preferable assessment tool to evaluate exercise capacity compared to the timed-up-and-go test in participants at risk of cognitive decline. The metabolic syndrome components are traditional vascular and metabolic risk factors, but few cognitive studies have examined the combined risk severity. While cognitive tests scores were similar between the two groups with or without a clinical diagnosis of a metabolic syndrome, the continuous standardised z-scores for metabolic syndrome were associated with lower cognitive performance for global cognition and executive functions. Therefore, the combined risk burden (z-score) was more sensitive to cognitive associations than the presence or absence of the clinical syndrome. Multivariate regression analyses showed separate linear associations between vascular risk factors (fasting homocysteine, glucose and Framingham scores) and lower cognitive functions. The importance and originality of this thesis are that several peripheral biomarkers showed significant associations with cognition, including between increasing plasma tumour necrosis factor (TNF-alpha) and executive dysfunction and between increasing brain-derived neurotrophic factor (BDNF) and better global cognition. A model hypothesising the relationship between physical health, cognition, vascular risk factors and biomarkers is proposed. A higher cardiometabolic risk burden may point to opportunities for cognitive testing and lifestyle modification recommendation in older adults as individuals may experience cognitive changes. The findings in the peripheral biomarker analyses add to the evidence of associations between TNF-alpha, BDNF and cognitive deficits. Future longitudinal research will be needed to establish a direct link between health factors, biomarkers and cognitive decline in older adults at risk of cognitive deterioration.
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ItemNeural correlates of memory dysfunction across stages of schizophrenia-spectrum disorder( 2020)Schizophrenia-spectrum disorders are severe mental illnesses characterised by hallucinations, delusions, blunted affect and disorganised thought patterns. A core feature of these disorders is cognitive deficits, which are associated with functional disability. Episodic memory, in particular, is one of the most severely impacted areas of cognitive functioning in schizophrenia-spectrum disorder, and memory deficits predict poorer clinical prognosis and increased functional disability. However, the longitudinal course of episodic memory deficits in schizophrenia-spectrum disorders is currently poorly defined, with the focus to date being on areas of functioning that are already impaired in early illness stages, such as verbal memory. In order to better understand trajectories, it may be important to examine areas of functioning that are preserved early in the illness, such as visual associative memory. Furthermore, there is currently a poor understanding of the neural underpinnings of memory impairment in schizophrenia-spectrum disorders, making it difficult to develop targeted interventions aimed at ameliorating these deficits. It is plausible that episodic memory impairments in these disorders is related to underlying dysfunction in the brain regions and networks that underlie this ability – namely, the hippocampus and its connections to the prefrontal cortex. This thesis utilised longitudinal cognitive assessment and cross-sectional multi modal neuroimaging to address three primary research aims: 1. To investigate the longitudinal course of episodic memory ability over a 5-11-year follow-up period in individuals with first-episode psychosis. 2. To investigate relationships between visual associative memory performance and hippocampal subfield volumes in FEP individuals and individuals with chronic schizophrenia-spectrum disorders. 3. to investigate whether visuospatial associative memory ability is related to white matter microstructure in the hippocampal-prefrontal pathway in FEP individuals and individuals with chronic schizophrenia-spectrum disorders. Results showed that visual associative memory ability was preserved in in individuals who had recently experienced a first psychotic episode, but deteriorated over a 5-11 year follow-up period. Conversely, verbal associative memory ability improved over the follow-up period to the same degree in FEP individuals and healthy controls. In a subsequent cross-sectional study, we found that, while hippocampal subfield volume reductions were present only in individuals with chronic schizophrenia-spectrum disorder, poorer episodic memory performance was associated with reduced subfield volumes in the CA4/dentate gyrus (DG) and in the stratum layers in both FEP individuals and those with chronic schizophrenia-spectrum disorder. Finally, we found that abnormal white matter microstructure in a number of memory-related ROIs and hippocampal-prefrontal pathways was present only in individuals with chronic schizophrenia-spectrum disorder. Furthermore, microstructural abnormalities in the fornix and the hippocampal-thalamic pathway were associated with poorer memory performance in individuals with chronic schizophrenia-spectrum disorder, but not FEP individuals. These findings provide new insights into the neural underpinnings of episodic memory impairment across stages of schizophrenia-spectrum disorder, and suggest that hippocampal structure may be more relevant to memory impairment in FEP individuals, with memory-related white matter abnormalities emerging in later illness stages.
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ItemThe Australian Imaging, Biomarkers and Lifestyle study of ageing (AIBL) Veterans study - Post traumatic stress disorder and risk of Alzheimer's disease( 2020)Background Epidemiological studies have suggested an association between posttraumatic stress disorder (PTSD) and Alzheimer’s dementia in Vietnam veterans. These studies, however, did not use biomarkers of Alzheimer’s disease (AD) to either confirm the diagnosis or assess the relative prevalence of AD pathology when investigating the risk of dementia in PTSD. Aim This study aimed at testing the hypothesis that Vietnam veterans with combat PTSD have an increased risk for Alzheimer’s disease in comparison with veteran controls as measured by biomarkers such as amyloid-beta and tau retention in the brain and regional hypometabolism and atrophy. Method Vietnam veterans with a history of PTSD as defined by the Clinicians-Administered PTSD scale (CAPS) score of 40 or above and veteran control subjects as defined by CAPS score of 30 or below and with no current clinical evidence of dementia participated in the study. Outcome measurements were amyloid-beta and tau deposition and regional brain metabolism and volumetry. Amyloid-beta and tau burden was estimated by the Specific Uptake Value Ratio (SUVR) of 18F-florbetaben, and 18F-AV-1451 respectively. 18F-fluorodeoxyglucose positron emission tomographic (PET) scan measured regional brain metabolism, and 3-Tesla T1 MP-RAGE Magnetic Resonance Imaging (MRI) estimated regional volumetry. Comprehensive neuropsychological battery measured cognitive function. Results Between March 2014 and June 2017, 83 male Vietnam Veterans (controls, n=30, CAPS=4; lifetime PTSD, n=53, CAPS=73.95; lifetime and current PTSD, n=30, CPAS=52.50) completed the assessments. There was no significant difference between the two groups in the uptake of 18F-florbetaben, 18F-AV-1451 or 18F-fluorodeoxyglucose, or regional brain volumetry. The rate of apolipoprotein E e4 allele was not significantly different between the groups. Compared with control veterans, the PTSD participants had a significantly lower level of education, predicted premorbid Intelligent Quotient (IQ), and total intracranial volume and higher depression rating score. The Montreal Cognitive Assessment score was significantly lower in the PTSD group than in controls. The group differences in Montreal Cognitive Assessment did not remain, however, when adjusted for premorbid IQ or depression in a multilinear regression model analysis. Conclusions Posttraumatic stress disorder is not associated with an increased prevalence of biomarkers of Alzheimer’s disease. The proxy measures of cognitive reserve, a factor that may delay the onset of Alzheimer’s dementia, were relatively low in subjects with PTSD, and this may explain the previously reported higher incidence of dementia in subjects with PTSD compared to age-matched controls.
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ItemTopographic organization of the human insular cortex and subcortex in health and neuropsychiatric illness( 2020)The structure, function and connectivity of the human brain are topographically organized. This topographic organization provides profound insight into cortical information processing, representation of mental states, and accounts for individual variation in behavioral traits and cognition. Whereas classical models of brain topography focus on distinct cortical patches defined by discrete boundaries, contemporary evidence from neuroimaging suggests that topographic variation may be better conceptualized in terms of a set of continuous gradients of gradual change that overlap in space. My work aims to reconcile these two conceptualizations of brain topography, particularly with respect to the insular cortex, a topographically complex and functionally heterogeneous cortical lobe whose organization has remained disputed for centuries. Using modern functional neuroimaging techniques, I showed that the insula’s topography is best conceptualized as a continuum of gradual change oriented along an anterior-posterior axis. I found that individual variation in the insula’s functional topography associates with human cognitive and emotional traits as well as somatosensory functions. Having characterized the functional architecture of the insular cortex in healthy adults, my next aim was to investigate whether neuropsychiatric illness is associated with alterations in the insula’s functional organization. To this end, I compared the insula’s functional connectivity gradients between individuals with schizophrenia and healthy controls. I found evidence suggesting subtle reorganization of the insula’s functional topography in schizophrenia. In particular, the connectivity profile along the anterior-posterior topographic axis of the insular cortex was altered and less differentiated in individuals with schizophrenia. I showed that the extent of reorganization of the insula’s functional topography significantly associates with the severity of clinical symptoms, particularly negative symptoms of psychosis and intellectual impairment. Finally, I applied the new methodology that I developed to map the insula’s topography to study other brain regions, including the entire human subcortex. This unveiled four hierarchical scales of subcortical organization, recapitulating well-known anatomical nuclei at the coarsest scale and delineating 27 new bilateral regions at the finest. Based on this work, I developed a new MRI subcortical atlas to enable holistic connectome mapping and characterization of cortico-subcortical circuits. The new subcortex atlas was personalized to account for connectivity differences across individuals and utilized to uncover a reproducible association between subcortical functional connectivity and tobacco use. Overall, this thesis provides fundamental insight into the functional organization of the human insular cortex and subcortex in health and neuropsychiatric illness, particularly focusing on the distinction between classical models of topographic variation based on discrete regions and contemporary representations involving continuous gradients. The new methodology that I developed is not limited to the insular cortex and the subcortex and can be applied to other cortical and subcortical regions in humans as well as other species.