Theses and Dissertations from UMD
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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
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Item Is a new waist circumference and BMI needed for African Americans for the diagnosis of metabolic syndrome?(2012) Udahogora, Margaret; Jackson, Robert T.; Nutrition; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)African Americans are noted as having a low prevalence metabolic syndrome (MetS), which is partly attributed to a reported use of MetS criteria, such as waist circumference that is not appropriate for this population group. The purpose of this study was: 1) to investigate the gender specific optimal waist cut off points, which best identify individuals with metabolic abnormalities consistent with MetS, and are independent of body mass index (BMI) cutoff values; 2) to determine the gender specific cutoff values of BMI in relation to multiple metabolic risk factors; and 3) to assess the prevalence of metabolic syndrome. In this cross-sectional study, NHANES data from 1999-2006 was analyzed. 1445 participants had complete variables for metabolic syndrome criteria. The waist circumference of 95 cm for males and 98 cm for females were found as appropriate cut-off values to identify central obesity. Body mass index at which metabolic syndrome was observed was 28 kg/m² for males and 32 kg/m² for females. Using our newly estimated waist circumference thresholds, the age-adjusted prevalence of MetS was 30.9% in males and 30.3% in females. The results indicate that for the early detection of metabolic syndrome in African American adult males, a lower cutoff value of 95 cm, rather than the 102 cm currently used is needed. The metabolic syndrome abnormalities appear at higher body mass index and waist circumference among women. Based on our findings, the prevalence of metabolic syndrome is currently underestimated among African American adult males.Item The neural substrates of graphomotor sequence learning.(2007-01-25) Swett, Bruce; Contreras-Vidal, Jose L; Braun, Allen R; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Performing sequences of movements easily and automatically is an integral part of our everyday lives. This dissertation examines how a set of individual movements are assembled into a movement sequence, focusing on the neural regions involved, and the timing of their participation. A second, related question is whether the order of encoding of the individual movements can be detected with kinematic and neuroimaging methods. Understanding how sequences are learned is important for expanding our knowledge of how the brain performs neural computations within healthy persons, and of the alterations of these processes in persons with neurological disorders. To examine these questions, we combined behavioral, kinematic and neuroimaging methods to examine motor sequence learning in healthy adults. The behavioral task involved subjects learning to copy a novel sequence of line-pairs (a graphomotor trajectory sequence learning paradigm) while blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) data were simultaneously acquired. Sequence learning, measured by normalized jerk, was best characterized by a curve with a double exponential fit, implying that an early, fast learning process (time-bins 1-2) merged with a slower learning process (bins 3-5). The early portion of the sequence learning process was characterized by dorsal and ventral visual stream activation; dorsal lateral premotor cortical activity; and deactivation of the anterior putamen, head of the caudate nucleus and posterior vermis. The deactivation of portions of the basal ganglia and cerebellum during the early phase of sequence learning may indicate that these regions were being reset, due to the high number of errors being produced. The pattern of neural activity in the the second, slower phase of sequence learning suggests that emphasis in the sequence learning process had shifted from visuomotor mapping to improving the kinematic and dynamic motor plans for the new sequences (sequence encoding). Taken together, a model of graphomotor sequence learning emerges, including patterns of neural activation and functional connectivity that correspond to changes in subject performance. This model adds to our current understanding of the neural substrates of graphomotor sequence learning, and may be important in explaining the alterations to these networks in persons with neurodegenerative disorders.