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
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item BRAIN BASIS OF HUMAN SOCIAL INTERACTION: NEUROCOGNITIVE FUNCTIONS AND META-ANALYSIS(2023) Merchant, Junaid Salim; Redcay, Elizabeth; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Social interactions, or the reciprocal exchange between socially engaged individuals, plays a central role in shaping human life. Social interactions are fundamental for neurocognitive development, and a key factor contributing to mental and physical health. Despite their importance, research investigating the neurocognitive systems associated with human social interaction is relatively new. Human neuroimaging research has traditionally used approaches that separate the individual from social contexts, thereby limiting the ability to examine brain systems underlying interactive social behavior. More recent work has begun incorporating real-time social contexts, and have implicated an extended network of brain regions associated with social interaction. However, open questions remain about the neurocognitive processes that are critical for social interactions and the brain systems that are commonly engaged. The current dissertation aims to address these gaps in our understanding through a set of studies using computational and data-driven approaches. Study 1 examined the relationship between social interaction and mentalizing, which is the ability to infer the mental states of others that is considered to be critically important for social interactions. Prior work has demonstrated that mentalizing and social interaction elicit brain activity spatially overlapping areas, but spatial overlap is not necessarily indicative of a common underlying process. Thus, Study 1 utilized multivariate approaches to examine the similarity of brain activity patterns associated with mentalizing outside of social contexts and when interacting with a peer (regardless of mentalizing) as a means for inferring a functional relationship between the two. Study 2 investigated brain regions commonly engaged across social interactive contexts using coordinate-based meta-analysis, which is an approach for aggregating findings across neuroimaging literature. This involved an exhaustive search strategy to find fMRI and PET studies that utilize social interactive approaches, and calculated spatial convergence across studies as a means to uncover brain regions that are reliably implicated during social interaction. The results from Studies 1 and 2 offer major advancements for a neuroscientific understanding of social interaction by demonstrating a functional link with mentalizing and through elucidating brain systems that are commonly reported in studies using social interactive approaches.Item Developing New Experimental Techniques to Understand Neuronal Networks(2021) Aghayee, Samira Sadat; Losert, Wolfgang; Biophysics (BIPH); Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Studying the propagation of action potentials across neuronal networks and how information is stored and accessed in their dynamic firing patterns has always been the essence of neuroscience. Emerging evidence shows that information in the brain is encoded in the simultaneous or avalanche-like firing of multiple, spatially separated groups of neurons. Thus, understanding the collective behavior of neurons is essential for understanding how the brain processes information and encodes memory. Since its discovery, the advent of optogenetics has brought upon a revolution in neuroscience, where individual neuronal circuits are able to be selectively probed and their connections decoded. This ability has been used by many groups to great effect, with some groups even using optogenetic stimulation to create phantom sensations, which are typically encoded in the functional activity of distinct neuronal populations. However, in-vivo optogenetic excitation relies inherently on the quality and accuracy of the stimulation method, with many problems arising due to biological effects such as animal motion, the scattering nature of brain tissue, and cell health. Typically, groups either use digital micromirror arrays or spatial light modulators, with the former lacking transmission efficiency and the latter having a high technical skill barrier due to its propensity to induce artifacts into intended patterns of light. This dissertation attempts to reduce the barrier towards the use of spatial light modulators in optogenetics by improving targeting accuracy, reducing the effects of unmodulated light and related artifacts, and developing new methods of stimulation which reduce the power density directed at neurons. To accomplish the first step, improving targeting accuracy, I created and demonstrated a real-time capable particle-based motion tracking algorithm to correct for animal motion. To reduce the effects of optical artifacts, I developed and patented a method of using Fresnel lenses convolved with intended light patterns to project higher orders of diffraction and un-diffracted light axially away from the object plane. To improve cell health during stimulation, I researched the use of optical vortices to stimulate neurons, allowing for ion channel activation with reduced power per unit area. Finally, I set the stage for new science by creating neuroimaging platforms integrating these techniques and capable of imaging activity across multiple scales. Other avenues for improvement are outlined as well in this dissertation, as well as new scientific questions that can be asked, leveraging these developments contained within.Item Understanding the Relevance of Extended Amygdala Reactivity to Dispositional Negativity(2021) Grogans, Shannon Elizabeth; Shackman, Alexander J; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Elevated dispositional negativity (DN; i.e., neuroticism/negative emotionality) is associated with a range of deleterious outcomes, including mental illness. Yet, DN’s neurobiology remains incompletely understood. Prior work suggests that DN reflects heightened threat-elicited reactivity in the extended amygdala (EAc), a circuit encompassing the central nucleus (Ce) and the bed nucleus of the stria terminalis (BST), and that this association may be intensified for uncertain threat. We utilized a multi-trait, multi-occasion DN composite and neuroimaging assays of threat anticipation and perception to demonstrate that individuals with elevated DN show heightened BST activation during threat anticipation. Analyses revealed that DN is uniquely predicted by BST reactivity to uncertain threat. DN was unrelated to Ce activation during threat anticipation or EAc activation during ‘threatening’-face presentation. Follow-up analyses revealed that the threat paradigms are not interchangeable probes of EAc function. These observations lay the foundation for future studies necessary to determine causation and improve interventions.Item AN INVESTIGATION OF NEURAL MECHANISMS UNDERLYING VERB MORPHOLOGY DEFICITS IN APHASIA(2019) Pifer, Madeline R; Faroqi-Shah, Yasmeen; Hearing and Speech Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Agrammatic aphasia is an acquired language disorder characterized by slow, non-fluent speech that include primarily content words. It is well-documented that people with agrammatism (PWA) have difficulty with production of verbs and verb morphology, but it is unknown whether these deficits occur at the single word-level, or are the result of a sentence-level impairment. The first aim of this paper is to determine the linguistic level that verb morphology impairments exist at by using magnetoencephalography (MEG) scanning to analyze neural response to two language tasks (one word-level, and one sentence-level). It has also been demonstrated that PWA benefit from a morphosemantic intervention for verb morphology deficits, but it is unknown if this therapy induces neuroplastic changes in the brain. The second aim of this paper is to determine whether or not neuroplastic changes occur after treatment, and explore the neural mechanisms by which this improvement occurs.Item TARGETING MAGNETIC NANOCARRIERS IN THE HEAD FOR DRUG DELIVERY AND BIOSENSING APPLICATIONS(2016) Ramaswamy, Bharath; Shapiro, Benjamin; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Magnetic nanocarriers have proven to be effective vehicles for transporting therapeutic and diagnostic agents in the body. Their main advantage is their ability to be manipulated by external magnets to direct them to specific targets in the body. In this dissertation, I study the transport, safety and efficacy of moving drug coated magnetic nanocarriers in different types of tissue. Movement of magnetic nanocarriers of sizes ranging from 100 nm to 1µm with different biocompatible coatings (Starch, PEG, Lipid and Chitosan) was quantified in different tissue types using an automated cryostat system. The safety of moving magnetic nanocarriers in live rodent brain tissue was assessed using electrophysiology, calcium imaging and immunohistochemistry. Moving magnetic nanocarriers in brain tissue did not significantly affect the firing ability of single neurons, synaptic connectivity and the overall functioning of the neuron network. As part of efficacy studies, steroid-eluting magnetic nanoparticles were targeted using external magnets to the inner ear of mice to counter hearing loss caused by cisplatin chemotherapeutics. This targeted steroid delivery to the cochlea significantly reduced the change in hearing threshold at 32 KHz caused by cisplatin injections and protected the hair cells from significant damage. Finally, I explore the potential of spin-transfer torque nano-oscillators, which are multi-layered ferromagnetic nanocarriers, as high-resolution in vivo wireless biosensors. These nanocarriers have been shown to detect action potentials from crayfish lateral giant neurons and that the microwave magnetic signals from these devices can be detected wirelessly by near field induction.Item Examination of the Brain Processes Underlying Emotion Regulation within a Stress Resilient Population(2011) Costanzo, Michelle Elizabeth; Hatfield, Bradley D.; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Emotion robustly affects the quality of cognitive-motor performance under conditions of mental stress. As such, the regulation of emotion is critical to successful execution of motor skills during emotional challenge. Previous investigations of the stress-performance relationship have typically focused on behavioral outcomes, however, few have adopted a cognitive neuroscience approach to examine the involved mechanisms underlying this relationship. Furthermore, it is unclear if individuals who have a history of superior performance under stress (stress resilient population) exhibit brain responses characterized by an efficiency of neural processing and an adaptive emotion regulatory strategy. Using functional magnetic resonance imaging (fMRI), the present study examined activation in critical brain regions during affective challenge (i.e., presentation of International Affective Picture System negative images and Sport-Specific negative images) in 13 elite athletes (intercollegiate football players who have demonstrated successful execution of cognitive-motor skills under mental stress) relative to an age-matched control group (n=12). The present dissertation is organized into three main sections. The first report, entitled Brain Processes during Motor Performance under Psychological Stress, an Independent Component Analysis of EEG, is an examination of brain processes during competitive stress. This study revealed non-essential neuromotor cerebral cortical noise with a quantified increase in complexity during a cognitive-motor task. The second report is entitled Efficiency of Affective Brain Processes in Expert Cognitive-Motor Performers during Emotional Challenge. This fMRI examination of elite athletes revealed processing economy in brain regions critical to self regulation, management of emotional impulses and social cognition. The third report, entitled The Specificity of Neural Regulatory Processes during Emotional Challenge in a Stress Resilient Population, examined with fMRI if elite athletes spontaneously engage in cognitive reappraisal during the presentation of arousing sport-specific images. Results suggest that elite athletes process sports-relevant affective information in an automatic manner, congruent with a cognitive reappraisal strategy, which neutralized the negative impact of the scenes. In conclusion, the results suggest that elite performers are important models of stress resilience and respond not only in an efficient manner to stressful events, but demonstrate an adaptive regulatory response when challenged within their domain of experience.