Human Physiology Theses and Dissertations

Permanent URI for this collection

https://hdl.handle.net/1794/3528

Browse

Browsing Human Physiology Theses and Dissertations by Author "Christie, Anita"

Now showing 1 - 2 of 2
  • Thumbnail Image
    ItemOpen Access
    Physiological Consequences of Mild Traumatic Brain Injury in Individuals with Acute and Chronic Symptoms
    (University of Oregon, 2019-04-30) Yasen, Alia; Christie, Anita
    Mild traumatic brain injury (mTBI) is the subject of increasing public health concern. Symptoms following mTBI, as well as risk factors for prolonged recovery, have been well-described. The physiological mechanisms behind these physical symptoms, and time course of recovery after injury, however, remain largely unknown. The purpose of this dissertation, therefore, was to assess the acute and chronic impact of mTBI on motor cortex function and associated neurotransmitter concentrations. A secondary goal of this dissertation was to establish the relationship between motor cortex function and the risk factors of female sex and APOE genotype in acute and chronic mTBI patients. Motor cortex function and neurotransmitter concentrations were assessed using transcranial magnetic stimulation and magnetic resonance spectroscopy, respectively. It was found that excitability, as assessed by the amplitude of the motor evoked potential (MEP), was lower in the Chronic group (participants with chronic symptoms from mTBI, lasting at least 3 months post-injury) compared to the control groups (p=0.02), but no differences in glutamate, the primary excitatory neurotransmitter, were found in the motor cortex between any group (p=0.93) or over time acutely following mTBI (p=0.70). Intracortical inhibition, as assessed by the duration of the cortical silent period (CSP), was higher in individuals acutely following mTBI (within 72 hours of mTBI diagnosis) and throughout two months of recovery (p=0.02), but no differences in GABA, the primary inhibitory neurotransmitter, were found in the motor cortex between any group (p=0.06) or over time following acute mTBI (p=0.57). There were no differences in MEP amplitude, CSP duration, glutamate concentration, or GABA concentration between males and females, or carriers of the apoε4 allele at any time point following mTBI (p≥0.10). This dissertation represents a compilation of studies which are among the first to document motor cortex excitability, intracortical inhibition, glutamate, and GABA concentrations in individuals with acute and chronic symptoms from mTBI. The data suggest a possible functional change longitudinally following mTBI, despite an expected neurochemical profile. Results from these studies suggest that humans may not follow the same neurometabolic timeline as the rodent model following mTBI. This dissertation contains previously published and unpublished co-authored material.
  • Thumbnail Image
    ItemOpen Access
    The Interaction of Mental and Neuromuscular Fatigue and the Impact of Mental Fatigue on Function Across Different Age Groups
    (University of Oregon, 2019-09-18) Morris, Amanda; Christie, Anita
    Fatigue is a multidimensional concept with physical and psychological components. While neuromuscular fatigue has been studied extensively, its effects on cognitive function have been studied, few studies have focused on its impact on cognitive function. Further, the effect of mental fatigue on neuromuscular measures or physiological outcomes is not fully understood. Three studies were conducted to determine the interactions between mental and neuromuscular fatigue and the impact of mental fatigue on function and, to determine age related differences in these interactions. Study one investigated neuromuscular function in the tibialis anterior of young and older adults (transcranial magnetic stimulation, electrical stimulation, and force measurements) before and after a 20-minute mental fatigue task. Results suggested that mental fatigue may cause increased cortical inhibition in both age groups and that 20 minutes of a mentally fatiguing task may cause a decrease in the ability to produce maximal force in young adults, providing evidence of an interaction between mental fatigue and physical function. Study two examined the effect of neuromuscular fatigue on cognitive function in young and older adults. Measures of cognitive function (reaction time and errors during a 3-minute cognitive task) were taken before and after 16-minutes of intermittent isometric contraction of the ankle dorsiflexor muscles. Neuromuscular fatigue negatively affected cognitive function (slowed reaction time) in young adults only. Results suggested that a neuromuscular fatigue task may negatively affect cognitive function in young but not older adults. Study three examined the postural response to force platform perturbations in young and older women in response to mental fatigue. Only young women experienced mental fatigue (slower reaction times) and this was accompanied by significantly faster center of pressure velocity during the mental fatigue condition compared with the control condition. Performance of the mental fatigue task, not necessarily development of mental fatigue, affects neuromuscular activation in young women only, but does not affect the magnitude of postural response to perturbation. Taken together, these studies demonstrate that there is a complex and age-specific relationship between mental fatigue and physical function and physical fatigue and cognitive function. This dissertation includes unpublished co-authored material.