Browsing by Author "Gourgouvelis, Joanne"
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Item Mechanisms by which exercise promotes cognitive function in both depressed and non-depressed individuals(2017-12-01) Gourgouvelis, Joanne; Murphy, Bernadette; Yielder, PaulMajor depressive disorder (MDD) is a debilitating disease characterized by low mood, memory deficits, poor sleep quality and alterations in biochemical markers associated with neuroplasticity. Less than half of MDD patients receive an efficacious treatment, warranting the need for novel treatment strategies. Exercise as an add-on therapy is a promising approach shown to improve mood, however, its mechanism of action remains unknown. To advance our understanding of the mechanisms by which exercise affects brain function this thesis studied both healthy and MDD individuals. Study One used a functional magnetic resonance imaging (fMRI) subsequent memory paradigm to investigate the effects of an eight-week exercise intervention on neural function in healthy and MDD groups. FMRI results showed significant deactivation in the hippocampus and across several memory-associated regions in both groups suggesting a potential increase in neural efficiency. Study Two evaluated exercise as an add-on to antidepressant medication (ADM) and cognitive behavioural group therapy (CBGT) for MDD. Exercise led to a robust decrease in depression scores (p=0.007, d=2.06), with 75% of the patients achieving either response or remission compared to 25% of those who received ADM and CBGT only. Exercise also led to greater improvements in sleep quality (p=0.046, d=1.28), cognitive function (p=0.046, d=1.08) and plasma brain-derived neurotrophic factor (BDNF), p=0.003, d=6.46. Furthermore, BDNF was positively correlated with improvements in depression (p=0.002, R2 = 0.50) and sleep quality (p=0.011, R2 = 0.38). Study Three found that exercise for healthy, young adults did not improve cognitive performance or biomarkers, despite the neural changes seen in the fMRI study. Overall, this thesis demonstrates that exercise promotes neuroplasticity in both healthy and MDD patients, substantially improving mood and cognitive performance in MDD. Plasma BDNF levels and sleep quality appear to be good indicators of treatment response and potential biomarkers associated with the clinical recovery of MDD.Item Mechanisms by which exercise promotes hippocampal function in both depressed and non-depressed individuals: A feasibility study(2012-08-01) Gourgouvelis, Joanne; Yielder, Paul; Murphy, BernadetteDepression is one of the top ten health problems in the world, affecting millions of Canadians. Research indicates that exercise is an effective treatment for depression but it is not clear on exactly how and why it works. Animal studies show that exercise improves the ability of the brain to function. It can even lead to new cell formation in a part of the brain called the hippocampus, which is important for memory processing. This study is investigating whether exercise may also improve hippocampal function in depressed humans. One way exercise may improve brain function is by normalizing levels of the hormone cortisol, and its toxic effects on the hippocampus. Exercise may also normalize levels of biochemical markers called cytokines involved in inflammation, while improving levels of growth factors important to brain cell function. This feasibility study aimed to develop protocols to investigate changes in hippocampal activity while participants are performing memory tests involving association of images and words in a functional magnetic resonance scanner before and after a 12 week exercise program. It also aimed to develop and validate protocols to measure changes in cortisol, cytokines and growth factors which are likely to be affected by exercise. Our preliminary imaging results revealed hippocampal dysregulation in the depressed brain, and biomarker analysis revealed abnormal concentrations of interleukin-6, vascular endothelial growth factor and salivary cortisol when compared to normal healthy controls. However, following the 12-week exercise program a more normalized pattern of hippocampal activation associated with successful memory encoding was observed. Additionally, biomarker concentrations either resembled or were closer to normal healthy values. Over the long term, the project arising from this feasibility study has the potential to provide a tool to improve exercise prescription, to predict exercise responders and to guide development of combined treatment approaches related to biochemical markers in order to optimize depression outcomes for Canadians.