Theses and Dissertations from UMD
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Item THE RELATIONSHIP OF PERCEIVED WORKLOAD AND PSYCHOMOTOR PERFORMANCE TO BRAIN DYNAMICS DURING VARYING DEGREES OF TASK DEMAND AND CONTROLLABILITY IN A FLIGHT-RELATED COMPENSATORY TRACKING TASK(2024) Pietro, Kyle; Hatfield, Bradley D.; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The assessment and prediction of cognitive-motor performance holds great importance for any discipline connected to human operators in the context of safety-critical behavior. A study of mental workload is essential to understanding the intrinsic limitations of the human information processing system, and the resultant cognitive-motor behavior. Mental workload and the quality of cognitive-motor performance are generally known to be impacted by task demand. However, one feature of task demand far less understood is the controllability of a system (e.g. the responsiveness of a flight platform and its handling qualities). In the realm of Human-Machine Interface, the assessment of system controllability has typically been conducted through subjective measurements, such as the Cooper-Harper Rating Scale, a widely used metric in aircraft design to measure perceived operator workload and handling qualities, first proposed in 1969. A fundamental element of the decision making process for handling qualities associated with operator workload includes the reporting of the control compensation required to overcome deficiencies and errors that could impact and inhibit the successful completion of a task. Yet, the Cooper-Harper Rating Scale, and all other subjective rating scales are limited by a lack of objectivity, reliability, reduced sensitivity to dynamic changes in operator workload, and, are solely dependent on subjective estimates of effort to control compensation within a system, despite such wide usage in the field. To overcome such limitations, the contribution of this dissertation is the estimation of perceived operator workload, based on objective brain dynamics captured during varying levels of task demand and controllability. Therefore, the objective of this dissertation was to ascertain how objective brain dynamics and subjective ratings would respond to flight-related compensatory tracking tasks when handling qualities and task demand are manipulated. More specifically, this dissertation assessed the relationship between objective brain dynamics and subjective rating scales explicitly related to mental workload, as reported during compensatory tracking tasks of varying complexity, while also challenged with progressively increasing levels of controllability (i.e., levels of handling qualities). Thus, Aim 1 was to assess the effects of varying levels of handling qualities (i.e., HQR1, HQR2, HQR3) on mental workload and psychomotor performance. Aim 2 was to investigate the effects of increased task demand (i.e., Single-axis vs. Multi-axis) on mental workload and psychomotor performance. Finally, Aim 3 was to examine the empirical relationship between objective brain dynamics and subjective ratings of workload. Accordingly, this dissertation employed a 2 Condition (Single-axis vs. Multi-axis) x 3 Level of Handling Qualities (HQR1, HQR2, HQR3) design. Perceived workload, psychomotor performance, and brain dynamics, derived from EEG power spectra and spectro-temporal analyses, were assessed in twenty-two volunteer participants in the Naval Reserve Officers’ Training Corps. Overall, the findings of this dissertation support a characterization of the human information processing system as a finite resource with a limited capacity. When challenged with increasing levels of handling qualities, parietal alpha power decreased, behavioral performance was significantly attenuated, and subjective ratings of workload were higher, as was expected. Accordingly, there was a significant relationship between objective brain dynamics and subjective ratings of workload. Furthermore, an exploratory wavelet-based analysis revealed some generally high cross-correlations between brain dynamics and psychomotor performance, which may inform future research efforts of more dynamic measurement strategies to capture perceived workload with increased fidelity. Therefore, the results of this dissertation underscore the usage of objective brain dynamics to supplement subjective rating scales, which can provide additional insights to enhance our understanding of brain and motor coordination under varying levels of task demand and system handling qualities.Item INTERACTIONS OF SOCIAL EXPERIENCE, ALCOHOL SENSITIVITY, AND THE SEROTONERGIC SYSTEM(2024) Ho, Ta-wen; Herberholz, Jens; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Social isolation has been shown to correlate with increased alcohol consumption in various animal species. In humans, a decreased sensitivity to acute alcohol is correlated with future alcohol dependence and addiction. A plausible explanation for this correlation is that alcohol sensitivity decreases after isolation; however, our understanding of the mechanistic interaction between social isolation and sensitivity to acute alcohol is still in its infancy. The serotonergic system is one promising candidate that could be involved in this interaction because of its wide range of behavioral and physiological effects, especially those related to social experiences. In my dissertation, I investigated the roles of the serotonergic (5-HT) system with three separate aims: In the first aim, I measured the effects of several 5-HT agents (neurotoxin, reuptake blocker, and receptor agonist/antagonists) in freely-behaving crayfish that were communally housed (COMs) or individually isolated (ISOs) prior to ethanol (EtOH) exposure. I found that 5-HT is important in regulating the social differences in EtOH sensitivity, and 5-HT2βPRO receptors emerged as candidates to produce this interaction between 5-HT and EtOH. My results from this aim suggest that these receptors are downregulated in isolated crayfish, leading to reduced behavioral EtOH sensitivity. The second aim employed single-cell neurophysiology and pharmacology in the lateral giant (LG) circuit of reduced ex vivo crayfish preparations to investigate the cellular-molecular mechanisms that underlie the interaction between 5-HT and specific EtOH receptor targets. I found that the LG neurons are stimulated by EtOH, and social differences in EtOH sensitivity between COMs and ISOs are paralleled at the level of these single neurons. Specifically, my results suggest that social isolation causes downregulation of 5-HT2βPRO receptors and 5-HT1αPRO receptors on the LG neurons and upregulation of these receptors subtypes in GABAergic neurons that send feed-forward inhibition onto the LG neurons. In my third aim, I developed a wearable, miniature, cyclic voltammetry device that is capable of detecting (injected) monoamine neurotransmitters (including 5-HT) in freely-behaving crayfish. With improved sensor sensitivity in the future, this will allow measurements of 5-HT release patterns in crayfish with different social histories, including during EtOH exposure. Together, the results from my dissertation will inform work in other model systems and improve our understanding of the interactions between social experience, the 5-HT system, and alcohol use.Item Sculpting Sounds: INTRINSIC PHYSIOLOGY AND INHIBITORY ANATOMY OF THE AVIAN AUDITORY BRAINSTEM(2024) Baldassano, James; MacLeod, Katrina; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Soundwaves are rapidly modulated, multi-dimensional stimuli. The cochlea decomposes these signals into frequency and intensity information which is conveyed via the auditory nerve into the brain. How does the brain manage to extract these multidimensional signals from auditory nerve activity? How does it sculpt this input so that both the microsecond precision of “where?” and the spectrotemporal modulations of “what?” are encoded with high fidelity? Birds are powerful models for studying early auditory processing because they interact with sounds similarly to mammals but have a simpler neuronal architecture. We describe the intrinsic physiology and anatomy and auditory brainstem neurons involved in spectrotemporal processing. In birds, the auditory nerve synapses onto two anatomically distinct cochlear nuclei, cochlear nucleus magnocellularis (NM) which encodes frequency/timing information, and the more heterogeneous cochlear nucleus angularis (NA) which encodes intensity information. NA has been shown to encode the acoustic envelope, likely through a subset of neurons that respond preferentially to modulations in their inputs via an adaptive spike threshold. We first examined the intrinsic basis of this adaptive threshold and found that a dendrotoxin-sensitive low threshold potassium conductance is responsible for it. In addition to the intrinsic properties of neurons, inhibition sculpts a number of auditory processes. The majority of inhibition in the avian auditory brainstem originates in the superior olivary nucleus (SON), which has multiple response types & projects either to multiple lower order ipsilateral nuclei, including NA & NM, or to the contralateral SON. Retrograde labeling experiments have demonstrated that these projections originate from distinct populations of SON neurons, however it is not clear if there is a relationship between response types and postsynaptic target. We used in vitro electrophysiology and neuronal reconstruction to establish a relationship between response types and targets. While the function of inhibition is well documented in timing circuits, its role in intensity processing is less clear. We used dynamic clamp to model inhibitory conductances while recording from NA neurons in vitro to determine how inhibition impacts the range of inputs that a NA neuron can encode before its firing rate saturates.Item OVARIAN STROMAL CELLS IMPROVE SURVIVAL, BUT NOT GROWTH, IN PRE- AND EARLY ANTRAL FELINE FOLLICLES(2024) Marks, Batsheva Naomi; Keefer, Carol; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Ovarian stromal cells act as crucial support and regulators for in vivo folliculogenesis; however, less is known about their effect on in vitro grown follicles. The objective of this study was to investigate the impact of ovarian stromal cell co-culture or conditioned medium (CM) on survival and development of cat pre-, early, and antral follicles in vitro. Ovaries were obtained from cats older than six months (n = 3), then enzymatically digested to release stromal cells. The ovarian stromal cells were allowed to grow to confluency in a T75 flask, before being cryopreserved for long term storage in liquid nitrogen. Cells were thawed one week prior to follicular culture onset, and passaged once before CM collection. CM was subsequently removed 24 - 48 hours after feeding, and stored at -80C until used. Ovarian follicles were mechanically isolated from cats older than six months (n = 23 cats, 155 follicles), encapsulated in 0.5% alginate hydrogel. The isolated follicles were then divided into five treatment groups (control, ovarian stromal cell co-culture, 20% CM, 50% CM, and 100% CM in Endothelial Cell Growth Medium), and classified based on initial diameter as preantral (224.4 + 4.7 m), early antral (394.8 + 7.4 m), or antral (592.2 + 18.8 m). Culture subsequently lasted for 13 days, and survival and growth of the follicles were evaluated on Days 0, 4, 6, 8, 11 and 13. At the end of culture, follicles were assessed via qRT-PCR for expression of CYP19A, FSHR, and GDP9 to further quantify development. Statistical analysis was done in R software. Follicles in 100% CM had higher survival up to Day 11 of culture as compared to other treatment groups (Cox proportional hazards model, p < 0.01). Initial stage also influenced survival, with antral follicle survival significantly lower than that of pre- and early antral follicles (p < 0.0001). However, no differences in growth were detected across the treatment groups, nor across initial size classifications (Kruskal-Wallis test, p > 0.05). Post culture qRT-PCR analysis of the three selected genes showed upregulation of CYP19A in 50% CM follicles compared to the control (ANOVA, p < 0.05). However, there were no differences in CYP19A expression between the control and other treatment groups, or in GDF9 and FSHR expression among culture groups (p > 0.05). In summary, the findings demonstrated that conditioned medium collected from primary culture of ovarian stromal cells improves in vitro survival and modulates CYP19A expression of isolated cat follicles. Further research to identify paracrine factors present in conditioned medium will elucidate the roles of ovarian stromal cells pertaining to follicle survival during in vitro folliculogenesis.Item HIPPOCAMPAL GLUCOSE TRANSPORT AND OXIDATION IN RESPONSE TO DISRUPTED BLOOD FLOW IN AN AGING RAT MODEL OF HEART FAILURE(2023) Pena, Gabriel Santiago; Smith, J. Carson; Kuzmiak-Glancy, Sarah; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The primary objective of this dissertation was to investigate, in a rodent model of cardiovascular disease promoted by transverse aortic constriction (TAC), whether cerebral hypoperfusion stemming from chronic high pulsatile blood flow, and cerebral hypoperfusion stemming from low cerebral blood flow differentially affected hippocampal glucose transport and hippocampal mitochondrial function. We first, characterized the changes in right and left carotid hemodynamics and diameter in response to TAC and in a SHAM control group at three different time points (20-, 30-, and 40 weeks) post-surgery. Then, right, and left hippocampal mitochondrial content and substrate oxidation were investigated, and protein expression of glucose transporters and mitochondrial quality control markers were quantified. In this study, both the SHAM and TAC conditions included male and female rats to address possible sex differences. We report that all time points within TAC, right carotid blood flow velocities and pulsatility were greater than the left, but did not worsen over time. No differences in mitochondrial content were found within TAC nor between TAC and SHAM, but within TAC animals there were impairments in right hippocampal coupled and uncoupled respiration when compared to the left. When compared to the SHAM controls, right and left hippocampi of TAC animals had higher protein expression of mitochondrial quality control markers, but no differences in glucose transporter expression were found. Thus, while both high blood flow and/or pulsatility as well as low cerebral blood flow may lead to brain hypoperfusion, the metabolic consequences of the two may not be the same. The results from this dissertation contribute to the expanding literature characterizing the intersection between cardiovascular disease and neurodegeneration.Item ALLOSTATIC LOAD INFLUENCES VASCULAR FUNCTION AND SYMPATHOLYSIS IN YOUNG BLACK ADULTS(2024) Eagan, Lauren Elizabeth; Ranadive, Sushant M; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the U.S., Black individuals tend to face a disproportionately higher risk for hypertension. This is largely attributed to chronic sympathetic activation induced by heightened exposure to psychosocial stressors. Allostatic load (AL), an index of cumulative physiological dysfunction from chronic stress, is associated with hypertensive risk and is also heightened in Black adults compared to those of other racial groups. Indeed, increased sympathetic activity is a hallmark characteristic of both hypertension and AL. The inability to blunt sympathetic-induced vasoconstriction during exercise (impaired functional sympatholysis) is also associated with hypertension. This dissertation aimed to investigate whether AL was associated with measures of vascular health in young Black adults, both at rest and during a sympathetic stressor. In our first study, we examined associations between AL and indices of vascular function and structure among young Black adults at rest, finding that higher AL was associated with greater macrovascular dysfunction and amplified wave-reflections. Additionally, we identified significant correlations among greater self-perceived stress with smaller brachial artery diameters and greater wave-reflections. The second aim of this dissertation focused on the associations between AL and the magnitude of functional sympatholysis among this population. Results indicated a positive association between AL and functional sympatholysis, with amplified sympatholytic responses among young Black females, as compared to their male counterparts, when forearm volume was controlled for. Overall, our findings suggest that elevated AL might predict macrovascular dysfunction at rest, with larger arterial diameters potentially compensating for chronic stress. These adaptive mechanisms, commonly observed in aging and diseased states, may also explain the positive correlations between AL and the functional sympatholytic response in young Black adults. Our consistent observations of the redundant vascular mechanisms among young Black adults allowing for adaptation to chronic stress strengthen our findings and further highlight the complex interplay between stress and cardiovascular health in Black adults.Item Sex and the Evolution of a Double Hermaphrodite(2023) Ficklin, John Alexander; Haag, Eric S; Biology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The Kryptolebias marmoratus species complex contains the only known self-fertile hermaphroditic vertebrates. There are three species in this clade and all three live in the mangrove forests across the tropical Americas. All three have individuals with both testis and ovarian tissue in their gonads with two using self-fertility as their main mode of reproduction, and all three have apparent different sex determination and sexual modes. In this dissertation, I explore aspects of sex in these species. K. marmoratus is the androdiecious and self-fertile member of the species complex with sequential hermaphroditism. In this species, the control of sex change from hermaphrodite to male is poorly understood. Individuals that were believed to be genetically identical could be raised in the same environment and change sex at drastically different times or not at all. Small fluctuations and variance in the hormonal profiles of individuals was thought to be a potential cause and while androgen dosing can lead to masculinization of both the gonad and the soma, it was not enough to maintain a permanent transition like what is seen in nature. In K. ocellatus, the obligate outcrosser of the K. marmoratus species complex, it was believed that they were using genetic sex determination to differentiate between males and the females that had hermaphroditic gonads. While we found strong evidence against heteromorphic sex chromosomes, all tests for homomorphic sex chromosomes came back inconclusive due to apparent K. hermaphroditus DNA contaminating the dataset. K. hermaphroditus, the self-fertile hermaphrodite species with exceptionally rare males, appears to be extending its range further and further south and/or hybridizing with K. ocellatus at rates previously underappreciated. The hermaphrodites of the Kryptolebias genus still hold many evolutionary and physiological secrets but can potentially be revolutionary to the understanding of vertebrate sexual development and evolution.Item CORTICAL REPRESENTATIONS OF INTELLIGIBLE AND UNINTELLIGIBLE SPEECH: EFFECTS OF AGING AND LINGUISTIC CONTENT(2023) Karunathilake , I.M Dushyanthi; Simon, Jonathan Z.; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Speech communication requires real-time processing of rapidly varying acoustic sounds across various speech landmarks while recruiting complex cognitive processes to derive the intended meaning. Behavioral studies have highlighted that speech comprehension is altered by factors like aging, linguistic content, and intelligibility, yet the systematic neural mechanisms underlying these changes are not well understood. This thesis aims to explore how the neural bases are modulated by each of these factors using three different experiments, by comparing speech representation in the cortical responses, measured by Magnetoencephalography (MEG). We use neural encoding (Temporal Response Functions (TRFs)) and decoding (reconstruction accuracy) models which describe the mapping between stimulus features and the cortical responses, which are instrumental in understanding cortical temporal processing mechanisms in the brain.Firstly, we investigate age-related changes in timing and fidelity of the cortical representation of speech-in-noise. Understanding speech in a noisy environment becomes more challenging with age, even for healthy aging. Our findings demonstrate that some of the age-related difficulties in understanding speech in noise experienced by older adults are accompanied by age-related temporal processing differences in the auditory cortex. This is an important step towards incorporating neural measures to both diagnostic evaluation and treatments aimed at speech comprehension problems in older adults. Next, we investigate how the cortical representation of speech is influenced by the linguistic content by comparing neural responses to four types of continuous speech-like passages: non-speech, non-words, scrambled words, and narrative. We find neural evidence for emergent features of speech processing from acoustics to linguistic processes at the sentential level as incremental steps in the processing of speech input occur. We also show the gradual computation of hierarchical speech features over time, encompassing both bottom-up and top-down mechanisms. Top-down driven mechanisms at linguistic level demonstrates N400-like response, suggesting involvement of predictive coding mechanisms. Finally, we find potential neural markers of speech intelligibility using a priming paradigm, where intelligibility is varied while keeping the acoustic structure constant. Our findings suggest that segmentation of sounds into words emerges with better speech intelligibility and most strongly at ~400 ms in prefrontal cortex (PFC), in line with engagement of top-down mechanisms associated with priming. Taken together, this thesis furthers our understanding on neural mechanisms underlying speech comprehension and potential objective neural markers to evaluate the level of speech comprehension.Item UNDERSTANDING HONEY BEE COLONY MORBIDITY AND MORTALITY THROUGH PHYSIOLOGY AND LIFESPAN(2022) Nearman, Anthony James; vanEngelsdorp, Dennis; Entomology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Managed honey bee colonies (Apis mellifera) are a critical component of our agroecosystem. As such, we need to understand and address risk factors that contribute to colony loss. Fundamental to this understanding is a need to detail the connection between individual bee’s physiology, life histories, and colony fitness. In this dissertation I first present an in-depth review of honey bee physiologies important for colony success (Chapter 1); I then examine standard methods for rearing honey bees in a laboratory setting and the importance of individual bee lifespan on colony loss (Chapter 2); followed by identification of honey bee physiologies that relate to chronological age as a means of measuring colony demographics and health (Chapter 3); and then apply potential age- and disease-related physiology measures to determine associations with overwinter colony loss and known and unknown risk factor exposure (Chapter 4). Research indicates honey bee colony loss is largely driven by poor nutrition, pesticide exposure, and parasites and the viruses they vector. Management practices and techniques to mitigate the effects of these risk factors decrease loss rates but do not prevent all of them. New knowledge, therefore, is needed to address the gap in knowledge between risk exposure and colony mortality. As a honey bee colony is a complex interaction between multiple groups of individual bees, collective physiological changes among these groups hold promise for understanding why some colonies die while other do not when exposed to the same risk factors. In one experiment (Chapter 2), I demonstrate the importance of access to water on honey bee lifespan. In a literature review informed by the data obtained from these experiments, I discovered that the median lifespan of laboratory specimen has decreased by half over the past 50 years and that this change is predictive of overwinter loss rates reported by beekeepers since 2006. If the age of individual bees can affect the lifespan of a colony, I posited that physiological measures predictive of individual bee age could be useful to ascertain the demographics of a colony’s population, which would in turn be a measure of colony health. To test this hypothesis, I built upon previous physiology studies and examined age-linked cohorts of bees through the fall transition to overwinter. In doing so I derived a set of easily identifiable physiological measures either predictive of individual bee age or a possible unidentified disease state. I then applied these measures to a retrospective cohort study, where I was able to determine that changes in the prevalence among several physiologies were associated with overwinter mortality and known risk factor exposure. These methodologies and results show promise for the use of physiological measures as a potential pragmatic tool to predict colony survivorship, to diagnose past known and unknown risk factor exposures, and to further advance fundamental knowledge of the role demographics play in societal health.Item SIMILAR VASCULAR RESPONSES TO A HIGH-FAT MEAL, REGARDLESS OF RACE AND SOCIAL DETERMINANTS OF HEALTH(2022) Weiner, Cynthia Marie; Ranadive, Sushant M; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Black individuals are at a higher risk for developing cardiovascular disease (CVD), including hypertension, compared to white individuals. Chronic low-grade inflammation contributes to hypertension by causing vascular dysfunction, including increased vascular resistance. Young, healthy, normotensive black individuals exhibit heightened inflammatory biomarkers at rest, a possible factor in the higher prevalence of hypertension seen within this population. Vascular function decreases transiently as a result of an acute inflammatory stimulus, such as with consumption of a high-fat meal (HFM). However, there is limited evidence regarding the racial differences in inflammatory and vascular responses to a HFM in young, healthy black and white individuals. Furthermore, there are limited data regarding the association between social determinants of health (SDH) factors and the physiological components of inflammation and vascular responses. Therefore, the goal of the present study was twofold: to evaluate the racial differences in inflammatory and vascular responses to a HFM and to evaluate the potential impact of SDH factors on these relationships. Five black individuals (5 males, 21.2 ± 1.5 yrs) and 14 white individuals (7 males/7 females, 25 ± 4.1 yrs) completed the study. White individuals were significantly older than black individuals, but were similar in fitness status (VO2peak; 43.4 ± 10.8 ml/kg/min vs. 40.5 ± 5.9 ml/kg/min) and BMI (22.6 ± 2.9 kg/m2 vs. 23.5 ± 3.3 kg/m2). Black and white individuals exhibited similar vascular function, arterial stiffness, wave reflection, and hemodynamic variables (BP, HR) at baseline and following the HFM. Black individuals had a significantly lower total SDH score compared to white individuals, indicating lower SDH across seven domains assessed in the SDH questionnaire. However, SDH was not associated with any of the vascular measurements at baseline or following the HFM. Inflammation was not detected at baseline and following the HFM, as measured by a multiplex immunoassay. Therefore young, healthy black and white individuals maintain vascular function following a HFM, regardless of SDH status.