Browsing by Author "Rauch, Laurie"

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    The influence of methylphenidate on heart rate and brain connectivity
    (2018) Van Breda, Keelyn; Rauch, Laurie; Stein, Dan J; King, Michael; Jankiewicz, Marcin
    The central governor model (CGM) proposes that muscle recruitment is regulated by the brain through subconscious homeostatic control of afferent feedback. It has been suggested that the dopaminergic system plays a key role in the CGM, with dopaminergic activation leading to lower fatigue thresholds. Key neural circuits, including the central autonomic network (CAN), may also play a role in altering thresholds by reducing conscious bodily awareness, known as interoception. However, few studies have directly examined the dopaminergic neurotransmitter system and CAN connectivity, during exercise-induced fatigue. Although there is reason to suspect that subjects with high activity (HA) and low activity (LA) levels have different fatigue thresholds, potential differences in dopaminergic function and related circuity have not been compared across these groups. In this thesis, I was therefore interested in examining the impact of a dopaminergic agent, methylphenidate (MPH) on: a) brain connectivity at rest before exercise and during exercise, b) on heart rate (HR) at rest before exercise and during exercise. Furthermore, c) I was interested in whether the effect of MPH administration (MA) on HR and functional connectivity (FC), between CAN regions, pre-exercise impacted HR and FC during exercise and whether this differed between HA and LA subjects. In order to measure the effect of MA on brain connectivity at rest and during exercise I used a functional magnetic resonance imaging (fMRI) scanner. To measure the effect of MA on fatigue thresholds, I used a MRI compatible handgrip device which recorded grip force output during a fatiguing handgrip task. To measure HR before and during handgrip exercise I used a MRI compatible electrocardiogram (ECG) machine. My first study aimed to determine the effect of MA on resting state (R-fMRI) FC between CAN regions and its correlation with HR before exercise. My second study aimed to see the effect of MA on task HR, force output and, FC and EC between CAN regions, during a fatiguing handgrip task. My third study aimed to see the effect of MA on the relationship between HR and FC pre-exercise and HR and FC during exercise and whether this differed between LA and HA subjects. I found that: 1.) MA decreased R-fMRI FC between CAN regions, and that this was associated with an increase in HR during resting state 2.) MA decreased FC between CAN regions with an associated increase in task HR and force output during a fatiguing handgrip task 3.) After MA, R-fMRI FC determines task FC independent of HR 4.) MA significantly increased task HR in LA but not HA subjects 5.) After MA, R-fMRI FC determines task FC independent of HR in LA but not HA subjects. Taken together, the functional uncoupling of CAN regions and increased HR after MA suggests that MA increases the fatigue threshold by diverting attention away from interoceptive cues, such as HR. However, this finding may be more relevant in LA subjects, where MA is also associated with increased HR during exercise.
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    Personality traits and cognitive performance in elite athletes
    (2009) Schoeler, Lieselotte Maria; Rauch, Laurie
    Mental performance consists of cognitive components, such as memory capacity, motor function, or decision making, and psychological components, such as personality traits, psychological well-being, or coping strategies. While certain personality traits have been shown to be associated with specific strengths and weaknesses in an individual’s cognitive abilities only few studies have been done to investigate this relationship in athletes. Our study therefore aims to investigate the correlations between certain personality traits and cognitive performance in a sample of elite hockey players. 25 male athletes completed the ‘WebNeuro Sport’ assessment by the Brain Resource Company.
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    Physiological and psychological measurements during cognitive stress : comparing the effectiveness of two stress intervention techniques.
    (2013) Scribani, Stefano Lewis; Rauch, Laurie
    BACKGROUND: A high level of stress can be detrimental to work performance and general health; in particular cardiovascular health. Work related stress has an effect on the autonomic nervous system and hence also can affect heart rate. By studying heart rate variability we can indirectly observe autonomic regulation in a convenient, non-invasive manner. Greater autonomic control and HRV are beneficial for managing work stress and could be beneficial for improving cardiovascular health particularly in an elderly population. HRV can be modified through changes in respiratory rate, and is enhanced greatly at slow breathing frequencies. OBJECTIVE: To establish meaningful relationships between physiological and psychological measures during a cognitive test; and to determine the effectiveness of short duration use of a beading system. The effects of age on autonomic regulation are also investigated.
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    Stress in the workplace the contrasting effects of 10 minutes of listening to Chopin vs. HRV biofeedback on autonomic reactivity and cognitive performance
    (2012) Smit, Sita; Rauch, Laurie
    Includes abstract. Includes bibliographical references.
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    Sweating away depression? : the impact of intensive exercise on depression
    (2014) Linde, Jani; Rauch, Laurie; Balchin, Ross
    In periods of prolonged stress and pain from strenuous exercise, the body produces chemicals called endorphins that help it endure pain. These natural analgesics are presumably only released when the level of pain intensity is at least moderately high. The PANIC/separation distress system is built on the same pathways as the physical pain system, and is responsible for the ‘mental pain’ (feelings of panic anxiety, loss and sorrow) that is associated with the loss of an attachment object, or separation from it. Given this overlap, it is reasonable to expect that endorphin release can affect depressive symptoms in a positive way. There is existing evidence that exercise has a beneficial effect on depressive symptoms, yet the underlying physiological mechanism has yet to be properly determined. The purpose of this three-armed prospective randomized control pilot study was therefore to try to establish this mechanism by investigating whether intensive exercise can improve the symptoms of moderate depression as a result of demonstrable increases in plasma β-endorphins. It has previously been established that exercise-induced β-endorphin release correlates positively with the intensity of the exercise. There were two central hypotheses for this study. The first was that the mechanism behind the improvements seen in depressive symptoms due to exercise is the same mechanism that is responsible for the established analgesic effect of exercise, namely endorphin release. The second hypothesis was that only high-intensity exercise (i.e. great that 70 of heart rate reserve) will be sufficient to produce a guaranteed endorphin release, whereas moderate-intensity exercise (just under 50% of the heart rate reserve) and very low intensive exercise would not be sufficient to release endorphins, and would therefore not result in an improvement in depressive symptoms. The main aim was therefore to investigate whether intensive exercise (greater than 70% of heart rate reserve) improves moderate depression, and if so, whether this correlates with a demonstrable increase in β-endorphins. This study therefore wished to determine which of low, moderate or high intensity exercise alleviates the symptoms of depression. It also intended to determine whether an increase in β-endorphins correlates to an improvement in the participants’ depression levels, and whether greater β- endorphin release occurs during high-intensity exercise compared to low- and moderate intensity exercise. Male participants (n = 33) with moderate levels of depression were randomly assigned to one of three experimental groups of varying exercise intensities: High-intensity (160 beats per min (bpm)), Moderate intensity ( 140bpm), and a low-intensity control group (under 120bpm). All participants underwent a six-week exercise program that involved participation for three days per week, for one hour per day (i.e.18 sessions in total). Once weekly, the Hamilton Rating Scale for Depression (HAM-D) and the Montgomery Åsberg Depression Rating Scale (MADRS) were administered to each participant. The participants in the High-and Moderate-intensity exercise groups each had 5ml of blood drawn, once per week, before and after exercise, in order to measure their β-endorphin levels, and to track any changes in these levels over time. The participants in the Control group had blood samples taken twice – once at the start of the study (a baseline measure), before and after exercise, and once on completion of the study, before and after exercise. The results indicate that both Moderate- and High-intensity exercise improved the participants’ depression levels, while the Control group also showed some improvement, but not to the same extent as the other two groups. A significant difference (p = < 0.0001) was found when comparing the initial and final HAM-D scores between all three groups. The participants’ MADRS scores also improved between all three exercising groups. A significant difference (p = 0.0182) was found when comparing the initial scores within each of the three groups to their final MADRS scores. No significant difference was found in the serum β- endorphin levels when comparing the Moderate- with the High-intensity group. The differences between the baseline and post-exercise serum β-endorphin measurements were also not significantly different for both the Moderate- and High-intensity groups (p= 0.953 and p= 0.992 respectively), while the Control’s pre- to post levels decreased significantly (p < 0.017). A significant difference between the Control-, Moderate-, and High-intensity groups (p = <0.022) was found when comparing the three groups’ serum β-endorphin concentrations after they engaged in exercise. Overall, the results of this pilot study go against the hypothesis that only High-intensity exercise would improve symptoms of moderate depression, as both high- and moderate-intensity exercise had a clear positive impact on depression scores. However, consistent with this hypothesis, very-low intensity exercise did not seem to have as beneficial an effect. The mechanism underlying the benefit of exercise on the symptoms of depression cannot be conclusively confirmed given the overall β-endorphin results. A larger sample size and more accurate analysis methods of β-endorphin levels are required in order to test these tentative findings more rigorously.
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    The effect of working memory training on executive function in reduced-obese women: implications for long-term weight loss maintenance (the mind the gap 2 study)
    (2021) Rudner, Trinity; Kroff, Jacolene; Rauch, Laurie
    Background: Weight loss often results in various physiological and behavioural compensatory changes which increase susceptibility to weight regain, resulting in unsuccessful weight-loss maintenance in the long term. Evidence suggests that working memory (WM) plays a key role in self-regulation and executive control, which is vital in overcoming these compensatory responses to weight loss. The current study therefore aimed (1) to identify the compensatory responses that occur with weight loss, (2) to investigate whether WM training (WMT) can improve executive control in reduced-obese women, and (3) compare subjective and objective WM methodologies. Methods: Reduced-obese (n=23) and stable-weight (n=6) women were recruited in this study. All 29 women were characterised at baseline testing for various physiological, behavioural and cognitive outcomes. After baseline testing, a subset of 19 reduced-obese women underwent 6-weeks of WMT, after which they completed post-intervention testing and a 6-month follow up. The series of assessments at baseline and post intervention included: anthropometric measurements; eating and behaviour questionnaires; executive function and working memory tests; metabolic rate; blood profile (HbA1c; glucose; insulin); and appetite measures. Results: Reduced-obese women showed signs of greater eating disordered behaviour and greater post-prandial energy efficiency compared to stable-weight women, although there appeared to be no difference in their executive function. The WMT appeared to result in improved WM capacity in reduced-obese women, which was retained in the long term, and there was some evidence of transfer to behaviour, with an observed reduction in eating-disordered behaviour. When comparing WM methodologies there appeared to be a contradictory relationship between subjective and objective WM measures. Conclusions: The results from this study support the evidence that physiological and behavioural changes occur in those that have lost a significant amount of weight, stressing the importance of finding weight-loss therapies that target these compensatory responses to weight loss. WMT was found to improve WM capacity in reduced-obese women, however, study limitations mean that the effects the training may have had on behaviour and weight maintenance could not be accurately determined. Furthermore, the contradictory relationship found between subjective and objective measures of WM add to the uncertainty that they measure the same underlying construct, which highlights the importance of utilising various types of measures in the analysis of WM and executive function.
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    The influence of low physical activity levels versus extreme physical activity levels on brain structure and working memory
    (2020) Paruk, Tasneem Yusuf; Jankiewicz, Marcin; Rauch, Laurie; King, Michael
    Background: Habitual levels of moderate to vigorous levels of physical activity (MVPA) levels are associated with positive health outcomes and improvement in cognitive function. A challenge facing optimal health outcomes is determining optimal levels of physical activity levels; people can engage in extreme sedentary or high levels of physical activity. For example, levels of low physical activity and participation in ultra-endurance events are increasing. However, the impact of extreme physical activity levels on brain matter volume and working memory is not well understood. This thesis thus investigated the relationship between different levels of MVPA, brain structure, and working memory. The aim of the thesis was to understand the relationship between large volumes of physical activity with global and regional brain matter volumes using brain imaging, and the impact of physical activity on cognitive function using the N-back task. The first part of the thesis examined how habitually high or low levels of MVPA differently impacted brain matter volume in healthy individuals. Whilst, the second part of the thesis investigated the differences in working memory between the low active and high active groups. Methods: Participants aged 20-59 years, were split into a High Activity (HA) group (N = 12, 27.9 ± 26.6 years) that exercised for > 9 hours of per week (MVPA > 540 minutes) and a Low Activity (LA) group (N = 9, 28.33 ± 11.192 years) that exercised < 2 hours (MVPA < 120 minutes). Total and regional brain matter volumes were measured using Magnetic Resonance Imaging (MRI) and analysed using Voxel-Based Morphometry (VBM). Habitual levels of physical activity were measured using the Global Physical Activity Questionnaire (GPAQ). For the second part of this thesis, we tested participants aged 20-59 years. Participants were split into a High Activity (HA) group (N = 6, 24.86 ± 4.67 years) that exercised for > 9 hours of per week (MVPA > 540 minutes) and a Low Activity (LA) group (N = 6, 30.14 ± 15.31 years) that exercised < 2 hours (MVPA < 120 minutes). Working memory was compared between the two groups using a PC-based N-back task. Results: The HA group had greater total brain matter and total white matter volumes vs. the LA group, and brain matter volumes were positively associated with increasing physical activity levels. However, the HA group had reduced regional brain volumes in the postcentral gyrus, middle frontal lobe, and the sub-lobar thalamus. HA and LA groups did not differ in working memory performance on the N-back task. Conclusion: Larger than normal amounts of weekly PA was associated with increased total brain matter and total white matter volumes, however, the volume of three regional brain areas were reduced.
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    Toward a greater understanding of the brain processes underlying handgrip and handgrip fatigue
    (2016) King, Michael T C; Rauch, Laurie; Stein, Dan J; Brooks, Samantha J
    Handgrip is a ubiquitous human movement that determines how we interact with our environment. It is involved in almost every aspect of daily life (e.g. opening a door, handling cutlery, using tools) and like all human movement, its application is limited by muscle fatigue. However, the supraspinal mechanisms of handgrip and handgrip fatigue are not fully understood despite the importance of this fundamental movement, numerous publications, and its presence as a longstanding research topic. This thesis investigates the brain mechanisms of handgrip and handgrip fatigue using fMRI. It begins with a review of the literature in Chapter one, which evaluates the theories and evidence for central control of handgrip and muscle fatigue as well as describing the rationale to perform the experiments in this thesis. The methodology and analyses are also reviewed to provide rationale for their use and to facilitate the interpretation of subsequent experimental results. In order to understand the supraspinal mechanisms of handgrip and handgrip fatigue it is logical to first understand the most fundamental grip type (power vs. precision) and pattern (static vs. dynamic) by which handgrip can be performed.