UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
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Item Early emotional caregiving environment and associations with memory performance and hippocampal volume in adolescents with prenatal drug exposure(2023) Kohn, Brooke Hannah; Riggins, Tracy; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Early adversities, including prenatal drug exposure (PDE) and a negative postnatal emotional caregiving environment, impact children’s long-term development. The protracted developmental course of memory and its underlying neural systems offer a valuable framework for understanding the longitudinal associations of pre- and postnatal factors on children with PDE. This study longitudinally examines memory and hippocampal development in 69 parent-child dyads with PDE histories to investigate how the early emotional caregiving environment affects children with PDE’s neural and cognitive systems. Measures of physical health, drug exposure, and the emotional caregiving environment were collected between 0-24 months. At age 14 years, adolescents (N=69, 52.17% Female) completed multiple measures of episodic memory. at ages 14 (n=27) and 18 (n=17) years, a subset of adolescents underwent magnetic resonance imaging (MRI) scans. Latent constructs of episodic memory and the caregiving environment were created using Confirmatory Factor Analysis. Multiple regressions revealed a negative emotional caregiving environment during infancy was associated with poor memory performance and smaller left hippocampal volumes at 14 years. Better memory performance at 14 years predicted larger right hippocampal volume at 18 years. At 18 years, the association between the emotional caregiving environment and hippocampal volume was moderated by sex, such that a negative emotional caregiving environment was associated with larger left hippocampal volumes in males but not females. Findings suggest that the postnatal caregiving environment may modulate the effects of PDE across development, influencing neurocognitive development.Item ACUTE EXERCISE INDUCED MICROSTRUCTURAL AND FUNCTIONAL CHANGES IN THE HIPPOCAMPUS OF OLDER ADULTS(2023) Callow, Daniel; Carson, Jerome J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Declining memory function is a common complaint of aging adults and a primary symptom of mild cognitive impairment (MCI) and Alzheimer’s disease (AD). The hippocampus is often the first brain area to exhibit noticeable deficits in age and pathologically-related cognitive decline and is a necessary structure for proper memory function. More specifically, the dentate gyrus (DG) and the third cornu ammonis area (CA3) of the hippocampus directly support mnemonic discrimination (MD), which is the process of reducing interference among new representations and distinctly encoding them as independent memories. Poor MD is associated with age and is a presymptomatic biomarker of cognitive decline and is believed to result from reduced neurogenesis, angiogenesis, and synaptogenesis within the DG/CA3 subregion of the hippocampus. While causes and treatments for memory decline remain elusive, lifestyle interventions, especially physical activity, have received attention as cost-effective and safe means of ameliorating and potentially preventing cognitive decline in a growing aging population. Animal and human studies suggest exercise benefits the hippocampal structure, preserving neurogenesis and angiogenesis in aging rodents and macrostructure and memory in older adults. However, the mechanisms by which exercise affects the human hippocampus remains a significant knowledge gap in the field and is a critical aspect in understanding the long-term impact exercise has on the aging hippocampus. To better address this gap, researchers have begun implementing acute exercise studies, which allow for greater control of non-exercise-related factors, are cheaper and more time efficient to conduct than training studies, and can predict and inform training-related adaptations. Unfortunately, limitations in the study designs, population tested, specificity of cognitive tasks, and spatial resolution of human imaging techniques have posed significant barriers to our understanding of how acute exercise relates to healthy brain aging at the functional and microstructural levels. Therefore, the objective of this dissertation was to expand our understanding of how acute aerobic exercise alters the function and microstructure of the aging hippocampus. Three within-subject studies were conducted comparing the relationship between a 30-minute bout of moderate to vigorous intensity aerobic exercise vs seated rest on MD performance, hippocampal microstructure, and high-resolution hippocampal-subfield microstructure and functional activity in healthy older adults. In study one, acute exercise preserved MD performance compared to decrements exhibited after seated rest in a pre and post-condition study design. In study two, a post-condition-only study design, acute exercise elevated microstructural diffusion within the hippocampus, indicative of a hippocampal neuroinflammatory response and upregulation of neurotrophic factors. Finally, in study three, a post-condition-only study design, we found that acute exercise resulted in lower MD, suppressed MD-related DG/CA3 network hyperactivity (indicative of healthier network function), and led to higher DG/CA3 extracellular diffusion. However, these neuroimaging-based correlates of hippocampal neuroplasticity and network function were not associated with differences in MD performance. These findings suggest that higher-intensity acute exercise can alter memory performance and stimulate neuroplasticity and neurotrophic cascades within the hippocampus and the DG/CA3 subfield, potentially via different mechanisms. Furthermore these results give insight into the immediate neurotrophic and behavioral effects of acute moderate to vigorous intensity aerobic exercise in older adults and provide new methods and tools for better understanding if and how exercise promotes healthy brain aging. Finally, these initial findings lay a foundation for optimizing exercise prescription and identifying future effective exercise treatments.Item Assessing the Impact of Typical Variations in Stressful Life Events on Hippocampal Development in Childhood(2021) Botdorf, Morgan; Riggins, Tracy; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The negative impact of extreme stress on early brain development is well-documented. An emerging body of work suggests that less extreme and more typical variations in stressful experiences (e.g., parental divorce, changing schools) may also exert an impact on the brain, especially in early childhood; however, more systematic research is needed. Across, three studies, this dissertation addressed this gap by exploring effects of typical variations in stressful life events on development of the hippocampus, a brain region highly susceptible to stress. Study 1a assessed the impact of stressful life events on the development of hippocampal subfield volumes (i.e., CA1, CA2-4/dentate gyrus (DG), subiculum) in an accelerated longitudinal sample of 102 4- or 6-year-old children who were each followed for 3 years. Analyses revealed that experiencing more stressful life events was related to smaller CA1 and CA2-4/DG volumes in the 6- (but not 4-) year-old cohort. Study 1b used the same sample described in Study 1a to investigate the impact of stressful life events on functional connectivity between the hippocampus and stress-related cortical regions. Analyses revealed a significant association in the 4- (but not 6-) year-old cohort, such that experiencing more stressful life events was related to greater connectivity between the hippocampus and the insula, a region important for emotional processing. Study 2 assessed moderating effects of sex and socioeconomic status (SES) on the association between stressful events and hippocampal subfield volumes using a large (n = 4,348), diverse subsample of 9-10-year-old adolescents from the Adolescent Brain and Cognitive Development Study. Analyses revealed that stressful life events were related to smaller subiculum volumes, but these associations did not vary by sex or SES. Overall, these findings provide evidence of the impact of typical variations in stressful life events on both hippocampal structure and functional connectivity. Findings also highlight the complexity of stress effects on the brain as these experiences may impact the hippocampus in an age-dependent manner. These results advance our current understanding of how stress influences hippocampal development and pave the way for studies to assess the implications of findings both for cognitive processes and the development of stress-related disorders.Item Is nap status related to memory, sleep physiology, and the hippocampus in early childhood?(2020) Allard, Tamara L; Riggins, Tracy; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Research suggests there may be links between developmental changes in sleep (e.g., transition out of a nap), memory, and brain (specifically, hippocampus). The purpose of this investigation was to explore differences in sleep physiology, visuospatial memory, and hippocampal volume based on nap status. Participants were 3 to 5-year-old children (n=51) who were habitual nappers (napping >5 days/week), semi-habitual nappers (3–4 days/week), or non-nappers (<2 days/week). Participants completed a memory task before and after a wake and nap session. Polysomnography (PSG) and hippocampal volumes were also assessed. Findings demonstrated that, regardless of nap status, children performed better on a memory task following a nap. PSG revealed that habitual nappers spent marginally more time in nREM2 sleep and less time in SWS compared to semi-habitual nappers. Finally, non-nappers demonstrated a larger hippocampus than the other groups. These findings support the suggestion that developmental differences in these domains are related during childhood.Item Effects of early and concurrent parenting and child cortisol reactivity on hippocampal structure and functional connectivity during childhood: A prospective, longitudinal study(2017) Blankenship, Sarah Louise; Dougherty, Lea R; Riggins, Tracy; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Offspring of depressed mothers are at increased risk for emotional and behavioral disorders and social impairment. One proposed mechanism of risk transmission is through exposure to maladaptive parenting styles, as depressed mothers display higher levels of hostility and lower levels of support than non-depressed mothers. Rodent models indicate that the early parenting environment programs the endogenous stress response system, the hypothalamic-pituitary-adrenal (HPA) axis, through a cascade of epigenetic processes, ultimately elevating levels of glucocorticoid stress hormones (i.e., cortisol in humans). Elevated cortisol levels have been linked to both structural and functional changes in the hippocampus, a medial temporal lobe structure implicated in regulation of the HPA axis and the pathophysiology of depressive disorders. Despite elucidation of the pathways through which parenting influences neurobiological development in rodents, research examining these associations in humans is only emerging. The present study aimed to translate the rodent literature by examining the effects of early and concurrent parenting on hippocampal structure and functional connectivity during childhood, with a specific emphasis on exploring the mediating role of cortisol reactivity, in a longitudinal sample of offspring of depressed mothers and a community comparison group. At 3-6 and 5-10 years, observational measures of parenting and children’s salivary cortisol responses to a laboratory stressor were assessed. At 5-10 years, children completed structural and resting-state functional MRI scans. Findings revealed timing- and region-dependent associations. Early positive parenting predicted larger hippocampal head volumes whereas concurrent positive parenting predicted smaller body volumes. Early cortisol reactivity predicted larger body volumes whereas concurrent cortisol reactivity predicted smaller tail volumes. Concurrent parenting (positive and negative) predicted hippocampus subregion connectivity with regions of the cerebellum. Early cortisol reactivity predicted increased hippocampal connectivity with the cuneus and regions of the cingulate gyrus. There was a significant indirect effect of greater T1 Negative Parenting on smaller left hippocampal tail volume through increased concurrent cortisol reactivity. Significant interactions with maternal depression were also observed. This research provides a necessary translation of the rodent literature and elucidates possible timing-dependent neurobiological pathways through which early experience may confer increased risk for poor outcomes in human offspring.