AN INVESTIGATIVE STUDY OF THE NEUROPSYCHOLOGICAL AND NEUROPHYSIOLOGICAL FEATURES OF SUBJECTIVE SLEEP QUALITY

Background: Disordered sleep is a national health issue affecting an estimated 50-70 million US adults. The documented consequences of disordered sleep include impaired daily function, increased risk for chronic health conditions, and greater morbidity. To abate the deleterious consequences and to better understand the development and maintenance of disordered sleep, researchers have attempted to study the influence of emotional, cognitive, and behavioral features of sleep and sleep-related behaviors. Purpose: The purpose of the present study was to explore the neurophysiological and neuropsychological features of subjective sleep quality to conceptualize disordered sleep within various existing theoretical models. Methods: Participants were 75 University undergraduate students enrolled in introductory psychology and neuroscience classes across several semesters (Age: 18-39, M = 20.15, SD = 3.01; 67% Female). Participants were asked to complete a series of self-report inventories assessing personality, mood, affect, and sleep behavior. Next, participants underwent neurophysiological investigation (via encephalographic recordings) with the purpose of establishing a measurement of baseline cortical asymmetry and recording of event-related potentials during a modified oddball task. Finally, participants completed the Psychomotor Vigilance Task (PVT) as a measure of neuropsychological functioning. Results: Correlational analyses and regression models highlighted the significant contribution of personality, affect, and mood, to subjective sleep quality. Specifically, poorer sleepers reported higher levels of self-reported negative personality traits (e.g., neuroticism and behavioral inhibition), affect and mood in addition to being more likely to endorse more dysfunctional beliefs and attitudes about sleep. When considering neuropsychological performance on a psychomotor vigilance task, poorer sleepers had slower reaction times and made more errors. However, there were no significant neurophysiological findings relating to subjective sleep quality. Discussion: Findings were reviewed within the context of various theoretical models including the reinforcement sensitivity, stimulus control, cognitive, and neurocognitive models of disordered sleep. Implications for future research and clinical practice are discussed

Stereoscopic depth increases intersubject correlations of brain networks

Three-dimensionalmovies presented via stereoscopic displays have becomemore popular in recent years aiming at a more engaging viewing experience. However, neurocognitive processes associated with the perception of stereoscopic depth in complex and dynamic visual stimuli remain understudied. Here, we investigate the influence of stereoscopic depth on both neurophysiology and subjective experience. Using multivariate statistical learning methods, we compare the brain activity of subjects when freely watching the same movies in 2D and in 3D. Subjective reports indicate that 3D movies are more strongly experienced than 2D movies. On the neural level, we observe significantly higher intersubject correlations of cortical networks when subjects are watching 3D movies relative to the same movies in 2D. We demonstrate that increases in intersubject correlations of brain networks can serve as neurophysiologicalmarker for stereoscopic depth and for the strength of the viewing experience

Investigating the neural correlates of ongoing experience

Spontaneous thoughts are heterogeneous and inherently dynamic. Despite their time-variant properties, studies exploring spontaneous thoughts have identified thematic patterns that exhibit trait-like characteristics and are stable across time. Concurrently, structural and functional neuroimaging studies have shown unique and stable whole-brain network configurations linked to behaviour either through the static and dynamic intrinsic communication and activity of their core regions or through informational exchange with each other. This thesis aimed to explore how these within and between network interactions at different temporal scales might relate to variations in ongoing experience. We utilised different neuroimaging modalities (diffusion weighted and functional magnetic resonance imaging) and applied both static and dynamic analyses techniques. We found evidence of inter-individual variation in all cases associated with different patterns of spontaneous thoughts. Experiment 1 found that variation in white matter architecture projecting to the hippocampus, as well as the stable functional interaction of the hippocampus with the medial prefrontal cortex were linked to the tendency of experiencing thoughts related to the future or the past. Experiment 2 found that static functional connectivity of the precuneus and a lateral fronto-temporal network was related to visual imagery. Furthermore, we found that coupling of a lateral visual network with regions of the brainstem and cerebellum was associated with ruminative thinking, self-consciousness and attentional problems. Importantly, our results highlighted an interaction among these associations, where the brainstem visual network coupling moderated the relationship between parietal-frontal regions and reports of visual imagery. Finally, Experiment 3 used hidden Markov modelling to identify dynamic neural states linked to thoughts related to problem-solving and less intrusive thinking, as well as better physical and mental health. Collectively, these studies highlight the utility of using both static and dynamic measures of neural function to understand patterns of ongoing experience

Window into the Wandering Mind: Investigating the Neural and Pupillometric Correlates of Mind Wandering with a Dual Task Paradigm

Mind wandering (MW) is a heterogeneous and private phenomenon, which is nonetheless omnipresent in people’s lives. Research on this phenomenon has grown considerably during the past decade, thanks also to the development of neuroimaging techniques which have given us a window into the brain’s activity while we are lost in our thoughts. However, there are still two important issues for researchers in this field. The first, is the need to evoke in an experimental setting what is, by definition, a spontaneous phenomenon. This can be solved by developing an experimental task that creates certain conditions in which MW is more or less likely to arise. The second issue is the reliance on individuals’ self-reports, which are inherently subjective, to understand the emergence, and content, of MW. This issue is harder to tackle, but one possibility is to develop a physiological, objective marker of MW. Recently, two candidates have emerged as potential markers of MW: one is the default mode network (DMN), a set of brain areas that show coordinated activity when people drift off to their inner thoughts; the second candidate is baseline pupil size, which has showed sensitivity to changes in external and internal attention, such as during episodes of MW. This thesis describes the development of a novel paradigm for the study of mind wandering, and its use to understand the potential that the DMN and baseline pupil size have as markers of this phenomenon. In three empirical studies, this paradigm successfully modulates individuals’ performance, MW, and on-task focus. Further, evidence from these studies indicates that DMN activity and baseline pupil size don’t provide sufficient precision to be used in isolation as markers of MW: in particular, it is suggested that their predictive power strongly depends on taking into account the content of the MW experience, and the context in which it occurs

The motivational mechanisms driving the antidepressant effect of ketamine

Ketamine is a rapidly-acting antidepressant and has shown to be effective in depressed individuals who have previously failed to benefit from other available treatments. An important question is how ketamine works. Addressing this might help inform more targeted and efficient treatments in the future. The aim of this thesis was to examine the neural, cognitive, and computational mechanisms underpinning the antidepressant response to ketamine in treatment-resistant depression. The work has specifically focused on motivational processing, since ketamine is particularly effective in alleviating symptoms of anhedonia, which are thought to be related to impaired reward-related function. Following a general introduction (Chapter 1), the first experimental chapter (Chapter 2) focuses on identifying suitable reward and punishment tasks for repeated testing in a clinical trial. Test retest properties of various tasks are explored in healthy individuals, assessed by both traditional measures of task performance (e.g., accuracy) and computational parameters. Chapter 3 outlines a pilot simultaneous EEGfMRI study in healthy individuals probing the neural dynamics of the motivation to exert cognitive effort, an important but understudied process in depression. The third study (Chapter 4) uses resting-state fMRI to examine how ketamine modulates fronto-striatal circuitry, which is known to drive motivational behaviour, in depressed and healthy individuals. The final experimental chapter (Chapter 5) examines which cognitive and computational measures of motivational processing (using tasks identified in Chapter 2) change following a single dose of ketamine compared to placebo in depression, using a crossover design. Based on preliminary findings, it is tentatively proposed that ketamine might affect reward processing by enhancing fronto-striatal circuitry functional connectivity, as well as by increasing exploratory behaviours, and possibly punishment learning rates. The general discussion (Chapter 6) discusses these findings in relation to contemporary models of anhedonia and antidepressant action, considering both the limitations of the work presented and possible future directions

Mind-Wandering Experiences in Ageing: Neurocognitive Processes and Other Influencing Factors

The ability to self-generate thoughts in imagination is a central aspect of the human experience. Mind-wandering episodes are multifaceted and are heterogeneous in terms of their content, form (e.g. modality, level of detail), and behavioural outcomes. Older adults’ neurocognitive profile shows impairments in functions highly linked to the generation and management of such episodes, namely episodic memory, attentional control, and abilities associated with the recruitment of the default mode network (DMN). Robust findings have documented a decrease in the frequency of mind-wandering with increasing age. However, age-related changes in thought content, and how this is related to the cerebral organisation of the brain, has largely been neglected. This PhD project aimed to: (i) investigate older adults’ neurocognitive profile alongside the complexities of mind-wandering, and importantly (ii) explore the impact of moderating factors on thought content as we grow older. Converging behavioural and neuroimaging methods were employed to provide a comprehensive account of self-generated thoughts. The first two chapters combined self-reports with electrophysiological and fMRI connectivity data, and demonstrated associations between changes in the recruitment of the DMN and age-related changes in self-generated thoughts. Subsequent experimental chapters considered the influence of key factors believed to impact on the content of thoughts. Examining the influence of culture revealed that native French speakers favoured self-reflection and engaged in more positively oriented thoughts, in comparison to English native speakers. In addition, the manipulation of task difficulty encouraged verbal rehearsal, and meta-awareness mainly targeted the temporal characteristics of thoughts. Finally, after a 4-week meditation intervention, there was a reduction in both negative and past-oriented thoughts. Throughout, behavioural measures demonstrated older adults’ bias toward deliberate on-task thoughts, with evidence of a decrease of negatively oriented thoughts, stable rates of positively oriented thoughts, and an increase of visual thoughts, and task-related interference. Overall, the systematic use of convergent behavioural and neuroimaging methodology has provided a more in-depth understanding of mind-wandering experiences in ageing where previously the frequency of these episodes has only been considered

A behavioural and electrophysiological investigation of cognitive and executive dysfunction in older adults with Williams syndrome

Williams syndrome (WS) is a rare developmental disorder accompanied by mild–moderate learning difficulties. The literature focusing on older adults with WS is limited, thus the thesis examined cognitive and executive dysfunction in adults with WS aged 35+ years, adopting behavioural and electrophysiological methodologies. Claims of premature cognitive ageing, investigated with paired-associates paradigms to measure associative memory ability (Chapter 2), were not supported, rather they highlighted atypicalities capitalising on semantic memory and implementing spontaneous semantic encoding strategies. Further investigation of semantic memory (Levels of Processing paradigm, Chapter 3) showed better recall for ‘deep’ encoded items; however, effect sizes identified atypical access to semantic memory. Importantly, both studies were characterised with greater false alarms and reaction time for rejecting new items, indicative of poor error monitoring, and deficits in executive processes of inhibitory control and attention in WS. Chapter 4 adopted The Sustained Attention to Response Task which is highly sensitive to inhibition and attentional lapse. The WS group showed inhibitory deficits failing to withhold a response, and problems re-engaging attentional control after making an error. Chapters 5 and 6 investigated the neural mechanisms underpinning attentional / inhibitory deficits, employing the Oddball paradigm (ERP), and analysis of the alpha and beta frequency bands during resting states (EEG). The WS group showed a) compromised early monitoring of perceptual input, and inefficient task irrelevant stimulus evaluation, and b) low EEG alpha power indicative of reduced inhibitory control, atypical topographical distributions, and low variability; the latter is associated with poorer behavioural performance. Overall, the thesis has demonstrated how cognitive deficits observed in older adults with WS are grounded in atypicalities in the executive processes of attention and inhibition. It has added to theoretical understanding by advancing our knowledge of both the behavioural and eletrophysiological profiles in older adults with WS, and which sub-serve these atypicalities