Saudi Cultural Missions Theses & Dissertations
Permanent URI for this communityhttps://drepo.sdl.edu.sa/handle/20.500.14154/10
Browse
4 results
Search Results
Item Restricted Neural correlates of hallucination proneness in the general population: Behavioural and multimodal MRI-based approaches(Saudi Digital Library, 2025) Althuwaini, Haya; Meyer, GeorgHallucinations in healthy people are more common than previously assumed and may occur without the distress or impairment typically associated with clinical psychosis. Studying hallucination proneness (HP) in non-clinical populations provides opportunities to explore underlying mechanisms of hallucinatory experiences while minimising confounding factors such as medication, chronic illness, and comorbidity. This thesis explores the cognitive and neural correlates of HP in healthy individuals. The psychosis continuum model provides a theoretical framework, proposing that healthy hallucinators occupy an intermediate position between clinical hallucinators and healthy controls in terms of anomalous experiences, while remaining below the threshold for clinical intervention. Therefore, a central focus of this research is to evaluate whether the findings support this continuum model of psychosis. The thesis adopts multimodal, multi-cohort cross-sectional design studies, integrating findings from a systematic review, a large-scale population survey, and two empirical studies combining behavioural and magnetic resonance imaging (MRI) methods. First, the systematic review (Chapter 2) synthesised results from 22 MRI studies examining auditory and visual hallucinations in non-clinical populations. Although there was considerable methodological heterogeneity, involvement of the superior temporal gyrus (STG), insula, and anterior cingulate cortex (ACC) was observed. The neural correlates of hallucinations in healthy hallucinators showed both overlapping and distinct features compared to clinical groups, suggesting that similar brain networks may be engaged, but through different mechanisms. Current evidence remains inconclusive as to whether clinical and non-clinical hallucinations share the same underlying pathophysiology or arise from distinct processes. Chapter 3 reports the first psychometric validation of the Arabic version of the Launay-Slade Hallucination Scale-Extended (LSHS-E) in a general population sample from Saudi Arabia (n = 428). The Arabic version demonstrated strong reliability and validity, with a four-factor structure consistent with previous cross-cultural studies. This chapter also introduced the Arabic version of the positive dimension - Community Assessment of Psychic Experiences (PCAPE), supporting future research on HP in Arabic-speaking populations. Chapters 4 and 5 report two empirical MRI studies conducted on a university-based cohort initially comprising 491 participants. From this larger sample, individuals in the highest (n =31) and lowest (n = 35) tertiles of LSHS-E scores were selected for MRI and associated behavioural experiments. Chapter 4 combined two attention-based signal detection tasks with functional MRI (fMRI). Behaviourally, the high HP group showed significantly lower perceptual sensitivity and faster reaction times under conditions of cross-modal distraction, but no consistent group differences in response bias, suggesting altered sensory discrimination and inhibitory control. fMRI revealed robust task-related activations across auditory, visual and attentional networks with only subtle, non-significant group differences. A trend-level increase in activation in the right Rolandic operculum in the high HP group was observed but did not provide support for the continuum hypothesis. Chapter 5 employed diffusion tensor imaging (DTI) to investigate white matter microstructure. Contrary to previous findings in schizophrenia, the high HP group showed significantly lower mean diffusivity (MD) in the right superior longitudinal fasciculus (SLF) and corticospinal tract (CST). Hallucination scores were negatively correlated with diffusivity measures in these tracts. These results challenge the assumption that HP reflects a milder form of clinical pathology and instead raise the possibility that lower diffusivity may reflect more efficient or protective white matter organisation in non-clinical individuals prone to hallucinations. The findings do not support a simple dimensional model of psychosis. Rather, they suggest that HP in healthy individuals is characterised by distinct cognitive and neural features. The thesis offers novel contributions to the understanding of HP and provides important cross-cultural insights by including the first neuroimaging investigation of HP in a healthy, Arabic-speaking population.19 0Item Restricted Neuroplasticity and Systematic Audiovisual Training in Virtual Reality: A Multimodal MRI Investigation(University of Liverpool, 2024-03) Alwashmi, Kholoud; Meyer, GeorgThe integration of information from different sensory modalities is a fundamental process that enhances perception and performance. This study explores the audio-visual (AV) integration and its impact on behavioural performance using virtual reality (VR). The research involved twenty healthy participants who underwent daily VR training for four weeks, focusing on an AV adaptation of a scanning training paradigm used in hemianopia rehabilitation. The investigation aimed to understand how functional brain changes contribute to improvements in behavioural performance during AV learning tasks, and how microstructural changes in white matter (WM) tracts, measured through diffusion tensor and kurtosis imaging (DTI, DKI), are linked to functional connectivity changes in relevant brain areas. The results revealed a significant reduction in the response time (RT) after training for the voluntary eye movement task (the trained task). Behavioural performance was improved in both visual and AV conditions, with the latter exhibiting faster RT facilitated by audio cues. This learning effect transferred to two untrained tasks, a visual search task and an involuntary visual task. Functional magnetic resonance imaging (fMRI) demonstrated increased activation in multisensory brain regions involved in early-stage AV processing, the thalamus, inferior parietal lobe, and cerebellum, which was correlated with behavioural enhancements. DTI analysis indicated a decrease in mean diffusivity (MD) in the superior longitudinal fasciculus II (SLF II), connecting frontal and parietal regions, correlating significantly with observed behavioural gains. Additionally, fractional anisotropy (FA) increased in optic radiations post-training, connecting the thalamus with visual areas. Functional connectivity analysis revealed a significant increase in functional connectivity between primary visual and auditory cortices post-training, supported by DKI microstructural changes in these regions and the sagittal stratum, encompassing WM tracts connecting these lobes. These findings highlight learning-induced functional and microstructural changes in extended brain networks contributing to AV integration and attention. It also demonstrates the complementary nature of the DTI and DKI, providing insights into task-relevant brain networks. Overall, the complex relationship between functional and microstructural brain adaptations, alongside functional connectivity changes, underscores how immersive VR training promotes multisensory integration and neuroplasticity. Understanding these dynamics could inform tailored interventions and optimize training paradigms for enhanced sensory processing and rehabilitation outcomes.22 0Item Restricted Assessment of advanced MRI techniques within the spinal cord as applied to Multiple sclerosis patients(University of Exeter, 2024-06-26) Al-shaari, Hussein; Fulford, JonathanRationale: Multiple sclerosis (MS) is a complex inflammatory autoimmune disease of the central nervous system (CNS) characterized by inflammation, demyelination, and axonal damage. Magnetic resonance imaging (MRI) is a non-invasive technique that has become integral to the clinical management of MS over the past 20 years. While conventional MRI has played an important role in MS diagnosis and disease progression, its relationship with clinical signs remains limited, because of a lack of specificity. Recognizing this limitation, new advances in MRI technology present exciting opportunities for more accurate insights into MS pathophysiology. Techniques like diffusion tensor imaging (DTI) and magnetization transfer imaging (MTI) have emerged as effective tools. Unlike conventional MRI, these advanced methods have a better association with the subtle pathology alterations associated with MS. DTI allows for the visualization of microstructural abnormalities in white matter tracts, providing more detailed information of demyelination and axonal integrity. On the other hand, MTI offers novel insights into the dynamics of bound and free water, offering information on the underlying pathophysiology. Research on techniques such as DTI and MTI, typically focuses on imaging of the brain and its findings frequently do not have a direct application to the spinal cord. Thus, there is currently a lack of knowledge regarding spinal cord changes in patients with MS using these techniques. Aims: The aim of this thesis was to evaluate the potential of DTI and MTI for determining cervical spinal cord (CSC) changes when using automated data processing software such as spinal cord toolbox (SCT) in assessing changes in the CSC in patients with relapsing remitting multiple sclerosis (RRMS). Method: The assessment of the cervical spinal cord (CSC) using these MRI techniques was investigated for each inter-vertebral level, spanning four vertebral segments between the upper limit of the vertebral body of C2 and lower limit of the vertebral body of C5 over the regions of interest within the whole cord white matter (WM), ventral column (VC), lateral column (LC), and dorsal column (DC). This thesis was developed to explore two parts. The first part focused on the assessment of the reliability of DTI and MTI in the CSC. A total of 20 healthy participants were recruited and scanned on two separate visits. The second part focused on the potential of DTI and MTI to evaluate changes in tissue structure in relapsing-remitting multiple sclerosis (RRMS) patients in comparison to the same healthy participants recruited for the reliability study. For this, 13 patients with RRMS were recruited through the MS clinic. Expanded disability status scale (EDSS) was used as a clinical measure to examine the correlation with DTI and MTI parameters. Results: The reliability assessment of both DTI and MTI in the CSC found that the relative within-participants reliability varied depending on location of the ROIs. There was difference in the mean values of the DTI measures magnetic transfer ratio (MTR) value between the RRMS group and controls, however the significance of these differences differed depending on the ROI location. The correlation between DTI and MTI metrics and EDSS did not reach significant levels. Conclusion: This thesis has demonstrated the potential of DTI and MTI to identify alterations in RRMS patients. The results will be helpful in guiding diagnosis as well as future research into MS disease therapies and patient monitoring.21 0Item Restricted Neural changes during short-term novel spoken and sign language learning: fMRI and DTI studies(2023-01-31) Alotaibi, Sahal; Meyer, GeorgIt is conventionally thought that language processing is supported by two different brain areas: Broca's area for language production, and Wernicke's area for comprehension. Recent neuroimaging data, however, has shown that the brain networks underlying language processing are more complex than initially thought and closely integrated for spoken language and sign language. In this thesis, we conducted two longitudinal studies at three different approaches, behavioural, functional and structural imaging, which investigate the neural processing underlying spoken and sign language learning. In the first study, Magnetic Resonance Imaging (MRI) brain scans were taken from 20 English-speaking healthy volunteers before and after attending a novel spoken language-training course, learning phonetically minimal distinctions in Arabic that are allophones in the participant’s first language, of one hour for three consecutive days. The same paradigm was applied in the second study for 26 Englishspeaking healthy volunteers who were taught British sign language. Again, minimal contrasts between sign language gestures were learnt. Behavioural results for both studies show performance improvement in all variables including a phonetic discrimination task, and a pronunciation task for spoken language, and a gesture discrimination task and a signing task for the sign language group. Functional MRI results illustrate significant brain activity increasing in multiple language regions including left inferior frontal gyrus (IFG), bilateral middle temporal gyrus, left angular gyrus and the right cerebellum. Moreover, functional connectivity increased significantly after training between these areas. These areas also show significant DTI changes represented by increasing fractional anisotropy (FA) and decreasing in mean diffusivity (MD) and radial diffusivity (RD). The fMRI and DTI changes are correlated with the participant’s behavioural improvement. These findings reveal a high degree of similarity in the neural activity underlying signed and spoken languages. Furthermore, the rapid neural changes noted as an impact of short-term learning oppose the conventional belief that brain changes associated with language learning require long training periods.36 0