Melbourne School of Psychological Sciences - Theses
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Bugs and Brains: The Gut and Mental Health Study Characterising the gut microbiota in anxiety, depression, irritable bowel syndrome, and their comorbidity
Background: The community of microorganisms inhabiting the gastrointestinal tract, collectively known as the gut microbiota, is intimately involved in the maintenance of host health. Comprehensive characterisation of the gut microbiota may enable us to better understand conditions whose pathophysiologies remain poorly understood, including internalising mental health disorders (anxiety and depressive disorders) and irritable bowel syndrome (IBS). While existing research has sought to characterise the gut microbiota in these conditions, the two systematic reviews included within this thesis reveal that studies have failed to consider essential confounders, including age, dietary intake, medication use, biological sex, and body mass index. The inadequate consideration of IBS and internalising disorder co-occurrence was also highlighted. Accordingly, this thesis aimed to investigate the gut microbiota in medication-free females with either IBS or an internalising disorder, as well as females with comorbid IBS and anxiety/depression, whilst controlling for key covariates (age, dietary intake, body mass index). Study 1 aimed to compare the gut microbiota of females with IBS relative to controls, as well as compare microbial composition between the three major IBS subtypes (IBS-diarrhoea, IBS-constipation, IBS-mixed). Study 2 aimed to characterise the gut microbiota of females with an internalising mental health disorder relative to controls. Study 3 aimed to compare and contrast the gut microbiota of females with comorbid IBS and an internalising disorder to controls, as well as to participants with IBS or an internalising disorder separately. Method: This thesis includes 162 females, recruited as part of the Bugs and Brains Study, who belonged to one of four groups: i) 42 controls; ii) 36 participants with an internalising disorder (depressive/anxiety disorder), but no IBS; iii) 42 participants with IBS, but no internalising disorder and iv) 42 participants with both an internalising disorder and IBS. Participants completed comprehensive questionnaires, attended a clinical mental health interview, collected a stool sample, and had their anthropometrics measured within a 1-month period. The gut microbiota was estimated using 16S rRNA gene sequencing on an Illumina MiSeq platform (V4 hypervariable region). Sequences were pre-processed using QIIME2 and following the DADA2 denoising pipeline to produce amplicon sequence variants (ASVs). ASVs were taxonomically assigned against the SILVA database (v.138). Data analysis was performed using R (v.1.3.1073), with the packages phyloseq and picante (alpha diversity), vegan (beta diversity), ANCOM-BC and MaAsLin2 (differential abundance), and randomForest (random forests). Results: Comprehensive multivariate analyses revealed key similarities with regards to the gut microbiota in IBS and anxiety/depression relative to controls. Females with IBS or an internalising disorder tended to be enriched in bacterial species associated with inflammation (e.g., Proteobacteria, Parabacteroides, Alistipes), and participants with either condition harboured a lower relative abundance of immunoregulatory SCFA-producing bacteria relative to controls (e.g., Barnesiella, Bacteroides eggerthii, Lachnospira, Faecalibacterium). Moreover, both the anxiety/depression and IBS groups had higher relative abundances of species known to degrade the essential amino acid tryptophan (i.e., Alistipes). While similar findings were observed in participants with comorbid anxiety/depression and IBS, the gut microbiota composition in this group was heterogeneous, and alterations were not more pronounced than those observed in participants with either disorder separately. Of note, higher abundances of mucin-degrading bacterial taxa were observed in IBS-C and IBS-M relative to controls and the IBS-D group (e.g., Akkermansia muciniphila), suggesting this alteration may be a unique to constipation. Conclusion: This thesis presents a comprehensive characterisation of the gut microbiota in females with IBS, an internalising mental health disorder, and their comorbidity. Similar alterations in the gut microbiota composition relative to controls were identified in these conditions and were not driven by their comorbidity, as participants in the IBS group had no lifetime history of a mental health disorder, and participants in the anxiety/depression group had no lifetime history of IBS. The included studies have great strength in highlighting these findings independent of key confounding factors, including age, dietary intake, BMI, and host sex. Participants in this study were also medication-free and without relevant medical comorbidities. While these studies are well placed to examine the cross-sectional associations between gut bacteria with IBS and internalising disorders, future research should seek to integrate functional analyses and examine other microbial members of the gut microbiota. Longitudinal research designs that combine taxonomic and functional investigations will elucidate the true complexity of gut microbe interactions with host mental health and gastrointestinal functioning.
Understanding process dynamics and individual differences in moral judgement updating
Moral judgements play an important role in society - they shape interpersonal relationships, group dynamics, and form the basis for our legal and political systems. Yet, moral judgements are not made in isolation, but in a complex informational context. Further, moral judgements often need to be updated as we learn new information. However, the moral judgement process in such dynamic environments, and individual differences in moral judgement across informational contexts, are poorly understood. In this thesis a new paradigm was developed for studying moral judgements of fairness-related actions, which was used across three studies to derive novel insights into these issues. In Study 1 we characterised moral judgement updating, showing that people flexibly switch between relying on context-independent to relying on context-dependent moral norms, as they learn contextual information. While doing so, participants remained stable with respect to broader moral virtues of generosity, balance and (condemning) selfishness. In Study 2, we showed that individual differences in importance people assign to norms when making their decisions differed according to their personality, for both context-independent and context-dependent norms. The importance people placed on selfishness- and generosity-based norms in their judgements correlated with Agreeableness, Extraversion, Conscientiousness and Openness to Experience, stably across two judgements with and without contextual information. In Study 3, we showed that people slow their moral judgements when expecting contextual updates and when judging negatively valenced actions. Using the Diffusion Decision Modelling (DDM) framework, we show that these slowing effects can be understood as changes in distinct aspects of the unfolding decision process – shifts in the boundary settings (for context expectancy) and shifts in the bias parameter and the drift rate parameter (for valence). Across these studies, the thesis presents a new understanding of moral judgement as a highly context-sensitive and dynamic decision process, and suggests that this context-sensitivity may be supported by decision-making processes related to caution (and confidence). Moreover, I discuss the potential usefulness of DDM framework to aid further investigations of moral judgement processes and inform our understanding of neural underpinnings of moral judgements in information-dynamic settings.
From the top-down and the bottom-up: A complementary reasoned action and social practice framework for low carbon behaviour
Climate change is one of the biggest challenges our planet faces, and understanding human behaviour is key to changing its course. This research aimed to combine the strengths of two approaches to predict carbon-relevant household infrastructure behaviour: a top-down, reasoned action approach, and a bottom-up, social practice theory perspective. Four studies were conducted. Study 1 elicited beliefs about six carbon-relevant household infrastructure behaviours from both theoretical perspectives. It demonstrated that the two perspectives were indeed commensurable at the belief level, with each perspective eliciting different, complementary sets of beliefs underlying behaviour. Study 2 demonstrated that both of these sets of beliefs predicted behavioural intentions. However, of the contextual beliefs elicited by the social practice perspective, it was one type in particular that appeared to influence intentions – beliefs about the more concrete components of behavioural context. Studies 3 and 4 piloted and refined a practical behaviour change intervention, informed by the processes people appeared to follow in order to account for concrete contextual beliefs. This intervention influenced both intentions (indirectly) and hypothetical behaviour (directly). It was concluded that social practice and reasoned action approach perspectives are indeed commensurable, with each demonstrating unique value for predicting carbon-relevant household infrastructure behaviour, without compromising either. It was also concluded that the current standard social psychological, top-down behaviour paradigms currently dominating research and policy stand to benefit from a stronger focus on concrete behavioural context, such as that provided by a social practice theory perspective.
How personality psychology and cognitive neuroscience can enrich one another: Insights from information seeking to machine learning
Personality psychology investigates individual differences in emotion, behaviour, cognition, and motivation, whereas cognitive neuroscience investigates the neurobiological bases of these phenomena. This substantial content overlap suggests that these areas are well placed to integrate knowledge. Accordingly, I present results from two empirical research programs that demonstrate how combining theories and methods from personality psychology and cognitive neuroscience can provide a new perspective on outstanding research questions and spur novel research programs. Part 1 (Studies 1-5) assessed how theory from personality psychology can address a current question in cognitive neuroscience: why people seek information that provides no extrinsic reward. One explanation is that uncertainty is aversive, and information reduces this uncertainty. This would suggest that the personality trait uncertainty intolerance would relate to information seeking. However, this conflicts with a theory from personality psychology whereby openness/intellect (describing tendencies toward imagination and intellect; thought to relate to greater tolerance for uncertainty) is grounded in increased information seeking. Because no explicit confirmatory study has assessed the putative negative relation between uncertainty intolerance and openness/intellect, Study 1 (N = 308) investigated—and confirmed—these relations. Next, Studies 2 (N = 151) and 3 (N = 301) assessed personality trait correlates of information seeking to gauge relative evidence for either conflicting theory. Openness/intellect did not predict information seeking; however, joyous exploration (a facet of curiosity positively related to openness/intellect) predicted information seeking across both studies, and uncertainty intolerance predicted information seeking in Study 3. These results informed a conceptual model featuring two motivations to seek information—either to explore (related to joyous exploration and openness/intellect) or to feel safe (related to uncertainty intolerance and neuroticism)—each differentially elicited depending on how the situation is perceived. To evaluate this model, Study 4 (N = 436) assessed personality and situation perception predictors of information seeking across four stimulus sets. Study 5 (N = 316) provided a partial replication and extension. Results provided consistent evidence for the exploration pathway, but more tentative evidence for the safety pathway. These findings suggest that an incorporation of person and situation factors can assist theory-development for information seeking. Part 2 provided a complementary approach to interdisciplinary dialogue by investigating how methods from cognitive neuroscience could be applied to explore possible neural bases of personality. Specifically, the machine learning technique multivariate pattern analysis was used to explore, then confirm, relations between personality and spectral power derived from electroencephalography. Study 6 (N = 174) found that agreeableness and neuroticism could be consistently decoded in particular frequencies across four testing conditions. Study 7 (N = 197) failed to replicate Study 6 in the full testing sample, but when subsequent analyses were stratified by country, agreeableness could be decoded in participants from Australia and neuroticism from participants from Germany. Caution is warranted for these latter findings given their unexpected nature and the smaller sample size of individual groups. The advantages of employing new methods are counterbalanced by a need to accept some measure of uncertainty in our inferences. However, open documentation of this complexity can spur new investigations to gain future insight into the neural bases of personality. Together, these studies emphasise the challenges, but also substantial benefits, from combining knowledge and methods from personality psychology and cognitive neuroscience to constrain existing theory, form links between research domains, and propose new avenues for research.
Persistent post concussive symptoms in children: a neuroimaging approach
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.
Pro-attitudinal advocacy, depolarization, and communicative intentions: The role of self-persuasion
In the currently fractured attitudinal landscape, many people hold extreme attitudes on important socio-political issues and frequently advocate for their attitudes. As a result of advocating for one’s own attitudes, i.e., engaging in pro-attitudinal advocacy, people may unconsciously persuade themselves (i.e. self-persuade) to polarize further. Moreover, pro- attitudinal advocacy may lead to an unwillingness to engage with those on the opposite side of the attitude spectrum. Such processes may explain polarization in our electorates over time. Given that polarization leads to disrupted social cohesion, a critical question is how we might depolarize attitudes, and encourage open communication. In this thesis, I sought to examine a candidate mechanism of depolarization: self-persuasion. More specifically, this thesis explored self-persuasion occurring during pro-attitudinal advocacy as a way of a) depolarizing attitudes and b) opening up communicative practices in ways that encourage advocates to display open communicative intentions (e.g. willingness to engage with dissimilar others). Across seven studies, participants (N = 1946) were asked to engage in online advocacy to justify their attitudes towards contemporary socio-political and moral issues, such as migration and climate-change. I explored specific factors relevant to pro- attitudinal advocacy, including meta-cognitive confidence (confidence in one’s thoughts and arguments), advocacy framing (moral versus practical framing), and style of advocacy (defending one’s position versus attacking the opposing position). Results indicate that a) low meta-cognitive confidence in one’s advocacy attempt predicts attitude depolarization and greater receptiveness to opposing views, especially if one enjoys effortful cognitive activity (Studies 1 and 2), b) compared to moral justifications, using practical justifications to support one’s attitude predicts attitude depolarization and lower intentions to proselytize, via lower expression of moral language (Studies 3-5), and c) compared to defending one’s position, attacking the opposing position predicts more open communicative practices, such as seeking attitude-inconsistent information, via heightened motivation to hold accurate worldviews (i.e. accuracy motivation; Studies 6 and 7). Interestingly, our findings suggest that although attitudes sometimes depolarize, depolarization is not a necessary pre-requisite for open communicative intentions, such as seeking attitude-inconsistent information. This suggests that pro-attitudinal advocacy may influence behavior, even if attitudes remain unchanged. Further, in addition to self-persuasion, we find other mechanisms, such as, message content and accuracy motivation, which may predict depolarization and increase open communicative practices. We find evidence to suggest that re-framing advocacy attempts, such as encouraging practical as opposed to moral justifications, may depolarize attitudes and encourage more civil discourse between dissimilar others. Overall, our findings have implications for bridging gaps between opposing groups, particularly in online communication environments.
How we evaluate and overrule our perceptual decisions
To navigate the world safely, it is critical that we are able to rapidly evaluate and overrule about our perceptual judgements. This thesis investigated the cognitive processes which underlie two forms of decision evaluation: discrete ‘changes of mind’ (i.e. decision reversals) and continuous confidence judgements. Three specific research questions were posed and addressed. Firstly, what sources of sensory information influence the likelihood and speed with which we change our minds about a perceptual decision? Secondly, what are the moment-to-moment information processing dynamics that underlie decision reversals? And finally, can information which is seemingly extraneous to a perceptual decision, specifically the amount of physical effort invested into reporting a decision outcome, affect retrospective judgements of decision confidence? These research questions formed the basis of three studies, which make up the core empirical chapters of this thesis. Study 1 investigated whether ‘absolute’ sensory information affects change-of-mind behaviour, across two experiments. In both experiments, participants indicated which of two flickering grey squares was the brightest with a button press. Following each initial decision, the stimuli remained on screen for a brief period and participants were free to change their response. To manipulate absolute sensory evidence the overall brightness of the two squares was varied, while either their luminance difference (Experiment 1) or luminance ratio (Experiment 2) was held constant. In both experiments increases in absolute evidence led to faster, less accurate initial responses and slower changes of mind. Change-of-mind accuracy decreased when the luminance difference was held constant, but remained unchanged when the luminance ratio was fixed. To account for these findings, we examined the predictions of six models: three existing change-of-mind models and three alternative models which have previously been used to account for the effects of absolute evidence on one-off decisions. Overall, a leaky competing accumulator model best accounted for participants’ behaviour. This suggests that the biologically relevant features of leak and partial inhibition within a decision process may be important in accounting for change-of-mind behaviour. Study 2 investigated the information processing dynamics underlying initial decisions and changes of mind. In particular, this study addressed the outstanding question of whether information processed prior to a decision being made (‘pre-decisional information’) has any influence on the likelihood and speed with which that decision is later reversed. As in Study 1, participants indicated which of two flickering grey squares was the brightest. Following each decision, the stimulus briefly remained on screen and participants were free to change their response. Critically, with each screen refresh a random luminance value was added to the mean luminance value of each square. Using psychophysical reverse correlation, we then retrospectively examined the impact that this luminance noise had on participants’ decisions on a frame-by-frame basis. Strikingly, we found that even the very first frame of sensory evidence participants saw influenced the likelihood and speed of later decision reversals. This indicates that pre-decisional information can influence later change-of-mind behaviour, and challenges the most prominent model of perceptual changes of mind, the extended Diffusion Decision Model (extended DDM), which predicts a complete insensitivity to pre-decisional information. To account for our findings within the DDM framework, we developed a novel variant of the extended DDM in which initial sensory information exerts a long-lasting bias over ongoing evidence accumulation. When fit to just the behavioural response data alone, this model was able to recreate the information usage patterns we observed. This suggests that an initial 'snapshot' of sensory information may exert a long-lasting bias over later sensory evidence accumulation, thus influencing later self-corrective behavior. Finally, Study 3 investigated the effect of foregone physical effort expenditure on decision confidence judgements. In this study, a dynamic luminance discrimination task was again employed. However, participants reported their decisions by squeezing one of two hand-held dynamometers until a pre-specified force threshold was reached. To manipulate the amount of effort required to report a choice, we varied how hard participants needed to squeeze on each trial across three individually calibrated levels (low, medium, high). After each decision, participants gave a confidence rating on a continuous scale ranging from 0 (‘certainly incorrect’) to 100 (‘certainly correct’). It was found that when more effort had been invested into reporting a decision, participants were more confident that the decision was correct. Broadly put, this suggests that people are sensitive to a ‘motoric sunk cost effect’ whereby greater foregone effort expenditure leads to an inflated sense of decision confidence. Overall, these findings suggest that: a) change-of-mind decisions are sensitive to absolute as well as relative sources of sensory information, b) that initial, pre-decisional, sensory information can influence the speed and likelihood with which a decision is later reversed, and c) that additional sources of information beyond sensory evidence, specifically action dynamics, can feed into and/or modulate the processes which underlie self-evaluative behaviour. These findings are consistent with post-decisional evaluative behaviours arising out of a continued unfolding of the initial decision process, with time-varying dynamics, which receives top-down modulation from additional self-monitoring process(es).
The Effects of Television and Internet News on Stigmatisation of Schizophrenia
Numerous content analyses have found that the news media commonly depict schizophrenia in the context of crime and violence perpetration. However, there is a dearth of experimental literature examining how such news stories, especially those of television and internet media, affect the public’s perceptions of persons with the disorder. Moreover, there is a lack of research examining how specific elements included in news reports may differentially affect stigma. Such features of concern include the presence or absence of labelling and symptoms, the victim being a family member or member of the public, and the magnitude of crime committed. The present thesis aimed to address these gaps in the literature by comprehensively examining how modern news media reporting of schizophrenia in the context of crime and violence, stigmatises persons with the disorder. The specific types of stigmatic responses examined were stereotypes, emotions, personal distancing behaviours, structural discrimination, psychiatric treatment attitudes and criminal justice system attitudes. A brief analysis of how Australian television news media depict schizophrenia in the context of crime and violence was first conducted in order to create evidence-based stimuli for the three experimental studies of this thesis. Study 1 (N = 741) examined the effects of including or omitting the label and symptoms of schizophrenia in violent crime news stories as well as the effects of news medium viewed. The study found that a news story about an individual who committed murder caused similar increases in stigmatic responding towards schizophrenia compared to a mundane news story whether or not it included the label and symptoms of schizophrenia. However, for a limited number of measures, only the story with the labelling and symptoms increased stigma compared to the mundane control. Viewing news stories in television or internet formats led to markedly similar patterns of stigmatic responding towards schizophrenia. Study 2 (N = 838) examined the comparative stigmatising effects of viewing a news story about a person with schizophrenia murdering a member of the public versus murdering family members, as well as the type of news medium viewed. The study found viewing violent crime news stories including murder of a partner, parent and member of the public, all led to similar patterns of stigmatic responding towards schizophrenia compared to viewing a mundane control news story. Replicating study 1, viewing news stories via internet or television resulted in markedly similar stigmatic responses. Study 3 (N = 800) investigated whether mentioning versus not mentioning schizophrenia’s labelling/symptoms in news stories about crime perpetration influenced the stigmatisation of schizophrenia in a way that depended on the crime’s severity. The study found that when schizophrenia’s labelling/symptoms were omitted, the majority of participants presumed mass murderers and single murderers had a mental illness, but generally did not assume non-violent criminals had a mental illness. Consequently, the presence or absence of schizophrenia’s labelling/symptoms had little effect on fear of schizophrenia for those who saw murder news stories but affected fear of schizophrenia for those who viewed a non-violent crime news story.
The development of overt aggression across adolescence: The role of temperamental and environmental risk factors and the contribution of overt aggression to the emergence of antisocial psychopathology
Purpose of the study: The research reported in this study aimed to model the stability and change in overt aggression in a community sample of Australian adolescents over six years, and to contribute to the development of a comprehensive etiological model of antisocial psychopathology. It examined the impact of sex, effortful control (a temperamental risk factor), callous and unemotional traits (a hypothesized primary factor associated with youth psychopathy) and conditional aversive parenting (an environmental risk factor) and their interactions, on latent trajectories of overt aggression. It was hypothesized that combinations of these risk factors will predict much of the variation in overt aggression across adolescence and that variation in overt aggression would predict features of Conduct Disorder and Antisocial Personality Disorder in early adulthood. Method: A risk-enriched community sample of 245 adolescents and their parents participated. Repeated measurement of overt aggression occurred at four time points using the Child Behaviour Checklist/6-18 and Youth Self Report, from early adolescence (mean age=12.4 years) to early adulthood (mean age= 18.9 years). At Time 1 self-report questionnaires were used to assess the individual difference factors, and an observational measure of parent-adolescent interactions were recorded. At Time 4, both semi structured interviews and questionnaires were used to assess antisocial psychopathology and the other dimensions examined. Latent growth curve modeling was used to examine the patterns of stability and change in overt aggression over time. Growth mixture modeling was then used to examine the relationships between the latent trajectories, the predictor covariates and the distal outcomes. Results: In the sample as whole, self-reported overt aggression remained stable across adolescence, while parent-reported overt aggression decreased slightly. Two trajectories (almost equal in size) of self-reported overt aggression were evident in the sample: a low and slightly increasing trajectory and a moderate to high, stable trajectory. Low effortful control was associated with the moderate-high trajectory, and while there was some evidence of an association between callous and unemotional trait and the moderate-high trajectory, this association was not significant in the final model. Neither sex nor conditional aversive parenting was found to predict trajectories of overt aggression. Moderate-high stable overt aggression across adolescence was found to be prospectively associated with higher levels of antisocial psychopathology in early adulthood. Conclusions: The findings reported in this study contribute to the understanding of the etiological factors involved in the persistence of overt aggression across adolescence. The findings suggest that low effortful control may be the most important individual difference factor contributing to the persistence of overt aggression in adolescence, and suggests that research examining the role of callous and unemotional traits should incorporate measures of normal temperament or personality. The absence of any sex differences in the current study suggests that persistent overt aggression in both male and female Australian children and adolescents is worthy of attention and treatment. The findings also have implications for the prevention, early intervention and treatment of overt aggression and antisocial psychopathology, in particular, the potential for adapting interventions based on temperamental differences, and targeting effortful control and its components in future prevention efforts.
The acute and habitual effects of alcohol consumption on sleep in late adolescents
Adolescence is a critical time period for human development. It is associated with major interrelated changes to the brain and sleep regulatory systems. These changes continue into young adulthood, and often coincide with the onset and acceleration of alcohol use. This is concerning as research suggests alcohol consumption may harm the developing brain and sleep systems. Indeed, sleep is an essential neurophysiological process that is necessary for optimal health, functioning, and development. Disturbances to sleep are associated with adverse physiological and psychological consequences. Alcohol is well-known for its sleep disturbing properties. Research has reliably shown that pre-sleep alcohol ingestion in light-drinking late adolescents leads to characteristic objective sleep disruption. These effects are bi-phasic, manifesting as sedation in the first half of the sleep period, followed by major sleep disruption in the second half. However, there is growing evidence that young people may be less sensitive to the initial sedative effects of alcohol. Critically, the effects of acute alcohol consumption on sleep have not yet been investigated in young people who habitually engage in heavy alcohol use. It is well-established that chronic heavy alcohol use leads to enduring sleep disturbances, such as degradations in slow wave sleep (SWS), that persist into periods of long-term abstinence. This has been investigated exclusively in adults with long-term alcohol use disorders. It is currently unknown whether heavy-drinking young people also suffer disturbances to normal sleep. Due to their ongoing development, it is possible that young people experience unique alcohol-related sleep disturbances. These disturbances could negatively impact physical and mental health. The current study aimed to investigate the effects of acute and habitual alcohol use on sleep quality, architecture, and electroencephalography (EEG) spectral power, in male and female late adolescents, aged 18 to 21 years. Forty-six late adolescents were recruited (mean +/- standard deviation): 9 light-drinking males (20.0 +/- 0.9 years; 13.5 +/- 10.3 standard drinks [10g of ethanol] in the previous 30 days), 13 light-drinking females (19.4 +/- 1.2 years; 12.3 +/- 8.0 standard drinks), 11 heavy-drinking males (20.1 +/- 0.7 years; 133.4 +/- 78.8 standard drinks), and 13 heavy-drinking females (19.2 +/- 0.9 years; 81.9 +/- 25.6 standard drinks). Following an initial adaptation night, participants completed in-laboratory polysomnography under two conditions: pre-bedtime alcohol (peak breath alcohol concentration [BrAC] .10%) and placebo (BrAC .00%) consumption. Experimental nights were non-consecutive and counterbalanced over participants. Participants abstained from alcohol for 48 hours prior to testing. This single-blind, mixed-model study design included two repeated- (acute alcohol vs. placebo consumption, first vs. second half of the sleep period) and two between- (male vs. female, habitual heavy vs. light drinking) measures factors. Sleep quality (sleep onset latency, arousals, wake after sleep onset, sleep efficiency) and architecture (stage N1 sleep, stage N2 sleep, SWS, rapid eye movement [REM] sleep) variables were independently scored using standard American Academy of Sleep Medicine (2007) criteria by two experienced sleep researchers. Discrepancies between scorers were resolved by an independent adjudicator. All scorers were blinded to participant group and experimental condition. Power spectral analysis was conducted for five EEG frequency bands: beta (16 – 30 hertz; Hz), sigma (12 – <16 Hz), alpha (8 – <12 Hz), theta (4 – <8 Hz), and delta (0.5 – <4 Hz) for each sleep stage. Data were analysed using mixed-model analysis of variance and post-hoc t-tests. Correlations between habitual alcohol consumption, and sleep quality and architecture variables, were also performed. Mean BrAC at lights out was .08 +/- .01 percent following pre-sleep alcohol, and .00 +/- .00 percent following placebo consumption. Following acute alcohol consumption, in the first half of the sleep period, both heavy- and light-drinking late adolescents demonstrated fewer arousals (p< .001), less stage N1 sleep (p< .001), more SWS (p= .007), longer REM sleep onset latencies (p< .001), and less REM sleep (p< .001), compared to placebo. There were no differences observed in sleep onset latency (p= .720), wake after sleep onset (p= .850), or sleep efficiency (p= .811). In the first half of the sleep period, alpha EEG spectral power was higher following alcohol consumption in stage N2 sleep (p< .001), SWS (p< .001), and REM sleep (p= .005). Although delta spectral power was higher in SWS (p= .008) and REM sleep (p< .001) in the first half of the sleep period, delta power was lower in stage N2 sleep (p= .006). In the second half of the sleep period, there were more arousals (p< .001), more wake after sleep onset (p< .001), lower sleep efficiency (p< .001), more stage N1 sleep (p< .001), and less SWS (p= .004), following acute alcohol consumption compared to placebo, in both heavy- and light-drinking late adolescents. No differences in EEG spectral power were observed in the second half of the sleep period. By design, heavy-drinking participants had consumed more alcohol in the previous 30 days, and across their lifetimes, than light drinkers (p< .001). There were no differences in objective sleep quality between heavy- and light-drinking late adolescents. However, a correlational analysis showed that, in the placebo condition, higher alcohol consumption in the previous 30 days was associated with higher wake after sleep onset (Spearman's Rho= .312, p= .035), and lower sleep efficiency (Spearman's Rho= -.327, p= .027). Heavy drinkers had less all-night visually scored SWS (p= .026), and more stage N2 sleep (p= .008), than same-aged light drinkers, in the placebo condition. Furthermore, higher previous 30-day alcohol consumption was related to lower SWS (Spearman's Rho= -.261, p= .040) and higher stage N2 sleep (Spearman's Rho= .250, p= .027) percentage, in the placebo condition. Irrespective of experimental condition, heavy drinkers had shorter REM sleep onset latencies, compared to same-aged light drinkers (p= .038). Although there were no differences in all-night REM sleep percentage, heavy drinkers had less REM sleep in the second half of the sleep period compared to light drinkers, irrespective of condition (p= .016). There were no differences in delta spectral power between heavy- and light-drinking late adolescents in any sleep stage. However, heavy-drinking late adolescents had higher sigma spectral power in SWS (p= .029), and stage N2 sleep (p= .021), than same-aged light drinkers, regardless of experimental condition. There was an interaction between sex, acute alcohol use, and habitual alcohol use, for all-night SWS percentage (p= .003). This interaction suggested that heavy-drinking males had higher all-night SWS percentage following alcohol consumption compared to placebo, however, heavy-drinking females had lower all-night SWS. In light-drinking males and females, there were no differences in all-night SWS percentage following alcohol or placebo consumption. The current study demonstrated that both heavy- and light-drinking late adolescents experience substantial sleep disruption following a high dose of alcohol prior to sleep. In contrast to the adult literature, the current investigation reported no differences in sleep onset latency, wake after sleep onset, or sleep efficiency, in the first half of the sleep period. This supports growing evidence that young people may experience less initial physiological sedation following alcohol consumption. However, a direct adult comparison is needed to verify this. This unique physiological response could potentially contribute to higher levels of alcohol use in young people, as it permits them to consume higher doses of alcohol before experiencing sedation. The current study replicated previous findings of higher alpha and delta spectral power following pre-sleep alcohol in young people. This may represent alpha-delta sleep – a potential electrophysiological indicator of sleep disruption. It is possible that these objective sleep disturbances may compromise the restorative properties of sleep and contribute to the alcohol hangover. The current study reported more wake after sleep onset, and less sleep efficiency, following acute alcohol consumption, which may contribute to sleep restriction in young people. Critically, this investigation provided novel evidence that pre-sleep alcohol consumption disrupts sleep in heavy-drinking late adolescents. This indicates that this population may be repeatedly experiencing sleep disruption during the final stages of neural development. Furthermore, these effects may be amplified in heavy-drinking young women, however further research is needed to replicate these novel findings. Finally, the present study uniquely demonstrated that heavy habitual alcohol use in young people is associated with disturbances to normal sleep, irrespective of pre-sleep alcohol consumption. Despite their relatively short drinking histories, the pattern of deficits was similar to those reported in adults with long-term alcohol use disorders, including lower all-night SWS percentage. Furthermore, some sleep abnormalities may be unique to this developing age group, such as elevated sigma spectral power during SWS and stage N2 sleep. Evidence suggests SWS plays a functional role in neurophysiological growth and repair, and learning and memory. Enduring degradations in SWS may be particularly detrimental in young people, as neural development is still ongoing, and academic pressure is high, during this time period. Although longitudinal research is required, the sleep deficits observed in the current investigation may represent alcohol-related changes to the brain and sleep systems, and/or a predisposition to heavy alcohol use. In summary, the current study provided key objective evidence that both acute and habitual alcohol use in late adolescence disrupts sleep. This could have deleterious effects on the health, functioning, and development of young people. It is imperative that action is taken to prevent or reduce alcohol-related sleep disturbances during the final stages of human development. Interventions should aim to delay and reduce alcohol consumption, enhance cognitive function, and improve sleep quality to protect the health and wellbeing of young people.
Characterising the long-term psychosocial outcomes of surgery for temporal lobe epilepsy
Surgery is currently the recommended treatment for patients with drug-resistant epilepsy and a well-localised seizure focus. While the focus is on eliminating seizures, it is well-recognised that a good seizure outcome does not automatically equate to improved psychosocial functioning. Our understanding of the psychosocial outcomes of surgery is supported by a wealth of short- (<2 years) to medium-term (<10 years) research. Relatively less is known, however, about patient experiences and psychosocial outcomes over the longer-term. The current thesis conducted a qualitative exploration of the long-term (15-20 years) psychosocial outcomes of surgery for the treatment of temporal lobe epilepsy (TLE), supported by targeted secondary quantitative analyses. Forty adult patients who had undergone anterior temporal lobectomy (ATL) at the Austin Health Comprehensive Epilepsy Program (CEP) between 1994 and 2001 were recruited. Comprehensive one-on-one interviews elicited patient experiences of their surgery and subsequent psychosocial trajectories, supplemented by well-validated questionnaires assessing mood and quality of life, as well as a novel online survey (Living with Epilepsy) examining patient perceptions of their epilepsy and surgery. Finally, reviews were conducted of patient pre- and post-surgical CEP psychosocial records and of detailed long-term follow-up seizure data. Data were analysed using well-established qualitative and quantitative methodology. Study 1 mapped the achievement of key social milestones over the 15- to 20- year post-surgical period and used thematic analysis to explore these experiences from the patient perspective. A common pattern of milestones emerged as patients progressed through achieving return to driving, education and vocational outcomes and finally, family outcomes. This was felt to resemble a process of psychosocial development, providing a broader theoretical framework for understanding post- surgical social trajectories. Building on this, Study 2 used grounded theory analysis to explore how patients reflected on and made sense of their overall post-surgical psychosocial experiences. The resulting model identified surgery as a major life turning point, which could prompt early post-surgical adjustment difficulties and psychological ‘disequilibrium’. Patients then sought to re-establish a sense of normality, drawing on processes of reframing and meaning making. Meaning making refers to the process of integrating experiences and emotional learning into the self-concept. Given psychosocial development and meaning making are both important processes for identity development, Study 3 characterised personal identity and Study 4, social identity, at long-term follow-up. The majority of patients demonstrated a personal identity profile characterised by a higher level of commitment to, rather than exploration of, psychosocial roles and values. The ability to embrace self-identity development and meaning making (as described in Study 2) was associated with higher health-related quality of life (HRQOL), pointing to a process of positive psychological growth as a result of undergoing surgery. Study 4 further highlighted the powerful role of social identity for patient well-being; identifying as someone without epilepsy post- surgery was associated with higher HRQOL, over and above seizure outcome. In conclusion, this thesis represents the longest qualitative follow-up of the psychosocial outcomes of ATL to date. Findings delineated the complex nature of the longer-term post-surgical psychosocial adjustment process and the importance of understanding the patient experience for promoting well-being. It is hoped that this information can be used to guide the development and refinement of comprehensive pre- and post-surgical counselling and rehabilitation programs.
Chromatic contrast sensitivity functions measured using optokinetic nystagmus and psychophysics
Optokinetic nystagmus (OKN) is a sequence of involuntary eye movements comprising slow phases of tracking a moving stimulus followed by fast saccades to reset the eye position. Although previous studies have studied the relationship between human OKN and functional vision via measurement of the contrast-sensitivity function (CSF), it has not been investigated using colour-varying, red-green, equiluminant patterns. In human vision, spatiotemporal changes in luminance convey a stronger sense of motion than do equiluminant patterns; yet, motion can nevertheless be perceived without luminance cues. The present study used spatial-frequency, band-pass luminance and red-green equiluminant noise patterns to measure OKN, and thus characterise the chromatic input to the mechanisms that drive the optokinetic response. The CSFs of 21 observers with normal vision were recorded using OKN and perceptual report. The results of the study demonstrate that an equiluminant red green stimulus can evoke a robust OKN response. There was a high correlation between OKN and perceptual report, for both luminance and colour stimuli, an indication of a common neural mechanism for defining stimulus direction. In all stimulus conditions tested, OKN can deliver a valid alternate technique for measuring the CSF.