Saudi Cultural Missions Theses & Dissertations
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Item Restricted Neural Mechanisms of Treatment for Mental Disorder(2023-06) Shalabi, Abdulrhman; Liddle, Peter; Liddle, Elizabeth“Cognitive control” refers to the ability to regulate thoughts and actions in the service of goals or plans (Braver, 2012). Coordination between the central and peripheral autonomic nervous systems (ANS) maintains arousal and attention levels, which are essential for effective cognitive control. Diamond (2013) proposed a cognitive control model that builds on three core cognitive functions: cognitive flexibility, inhibitory control, and working memory. Abnormality in active inhibitory cognitive control is implicated in a broad range of psychiatric and personality disorders, including schizophrenia, attention deficit hyperactivity disorder (ADHD), impulsivity, and substance abuse, among many others. Transcranial direct current stimulation (tDCS) and cognitive training are two neuromodulation techniques which have the potential to modulate cortical functions to introduce long-lasting neuronal plasticity. The antisaccade task is a visual inhibitory control task frequently used to assess cognitive control. It requires the participant to suppress an automatic stimulus-driven saccadic eye movement and instead make a goal-driven saccade in the opposite direction. In this thesis, by conducting two separate studies, we used the antisaccade task to examine the effect of tDCS and computerised cognitive training on inducing neuroplastic changes for the oculomotor control network (OCN). Chapter 1¢introduces relevant concepts to the subject of this thesis with a technical account of the methods used. The details of the first study are discussed in Chapter 2 - Chapter 4, where we used eye-tracking during antisaccade performance with the continuous assessment of cortical activity using Magnetoencephalography (MEG). Chapter 2 will discuss the short-term neuroplastic changes introduced by the tDCS on the functional connectivity within the resting state networks assessed using MEG. We found evidence of increased connectivity following the engagement in the antisaccade task for both active tDCS and sham conditions, but with different spatial patterns. Following tDCS delivered over the frontal cortex, there was increased connectivity with the frontal cortex. In contrast, in the sham condition there was increased connectivity with the posterior cortex. The effects of tDCS stimulation on the ANS activity during the task performance were further assessed via pupillometry as a measure of Locus Coeruleus (LC) activity in Chapter 3. Our results showed that faster pupil dilation, reflecting increased arousal and sympathetic activity, was associated with faster saccade reaction times. In Chapter 4, we investigated the immediate effects of tDCS stimulation on the cerebral cortex during active cognitive inhibition followed by a correct saccadic response. The tDCS introduced neuromodulatory changes in the putative Alpha and low-Beta band during the anticipatory and post-stimulus periods, reflecting enhanced cortical engagement in a task-beneficial pattern. Chapter 5 reports on the second study in which we used functional magnetic resonance imaging (fMRI) to evaluate the neuromodulatory effects of prolonged computerised cognitive training games (RECOGNeyes) on the resting state functional connectivity of the OCN and pupil dilation. Following gaze-control training, the connectivity within the left hemisphere was strengthened, while the intra-right hemisphere and the interhemispheric connectivity were diminished. Chapter 6 provides a summary of the findings and concluding remarks. Our result furthers our knowledge of the processes involved in the performance of the antisaccade task, the mechanisms of action and the neuroplastic effects of two neuromodulation techniques. However, the exact mechanisms underlying these methods' beneficial effects demand further exploration.37 0Item Restricted EXPLORING THE USE OF TRANSCRANIAL DIRECT CURRENT STIMULATION IN UPPER-LIMB REHABILITATION(2022) Alabdulaali, Luluh Abdulaziz; Jenkinson, Ned; Punt, T. DavidUpper limb motor function is an important factor in many activities of daily living. Stroke patients and older people suffer from limitation in upper limb function that reduces their independence and quality of life. Transcranial direct current stimulation (tDCS) is a promising intervention to enhance upper limb motor function. Its safety, tolerability and cost-effectiveness make it an easily applicable instrument to be employed in clinical and research settings. This thesis, therefore, sought to investigate the motor behaviour of the upper limb and in what way the tDCS could enhance it. We shed light on the difference in the recovery between distal and proximal segments of the upper limb by testing our hypothesis that stimulating the Primary Motor Cortex (PMC) using tDCS could improve the movement of the distal segment more than proximal segment. Three studies were undertaken: secondary research, systematic review and meta-analysis and behavioural experimental study. The finding of the secondary research demonstrated the possibility of the superior effect of anodal tDCS stimulating the PMC on improving the tasks that require primarily fine hand movement more than tasks that require primarily arm movement in chronic stroke patients. The systematic review and meta-analysis indicated a moderate quality of evidence that tDCS stimulating the PMC enhances fine dexterity and has no significant effect on gross dexterity. The fine dexterity improved in chronic stroke patients more than in subacute and acute stroke patients. Furthermore, the bilateral tDCS montage showed the highest beneficial effect of tDCS. Finally, the findings of the behavioural study highlighted the significant deterioration in fine and gross dexterity in healthy active lifestyle older people compared to healthy young participants. The older participants showed strong pinch grip which was similar to that of young participants. We suggested that the age-related cortical changes are the underlying cause of dexterity deterioration, also, the hand strength is not indicator for hand function because loss of dexterity in older people could be present with or without muscle weakness. Overall, tDCS is a promising intervention has an additional value to motor rehabilitation for improving upper limb motor function. The targeted stimulation is the key to getting the highest benefit of tDCS. tDCS stimulating the primary motor cortex showed beneficial effect on fine dexterity. The targeted area for improving gross dexterity needs to be explored. We hope this thesis will add to the enhancement of the application of the tDCS.22 0