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 White Matter Connectivity and Social Cognitive Impairment in a Transdiagnostic Sample(2018) Dwyer, Kristen R; Blanchard, Jack; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Social cognitive deficits are impaired mental operations underlying social interactions and are present across psychotic disorders, including schizophrenia spectrum, bipolar, and depressive disorders. It is unclear what neurobiological factors underlie social cognitive impairment, though one possibility is that impaired white matter connections within social cognitive cerebral networks may give rise to social cognitive impairment in psychosis. This study extended current diffusion tensor imaging (DTI) research to a transdiagnostic sample of individuals with psychotic disorders and controls and employed a Research Domain Criteria (RDoC) multiple units of analysis approach. The current study aimed to (1) assess the relation between social cognition (theory of mind and emotion processing), social functioning, negative symptoms, and general cognitive ability, and (2) examine white matter integrity within the uncinate fasciculus (UF) and inferior longitudinal fasciculus (ILF) through fractional anisotropy (FA) values, and to investigate their relation to social cognition and social functioning. Thirty-three participants, 25 with a history of clinically significant psychotic symptoms and 8 controls, completed the research project. Results indicated that social cognition was positively related to general cognitive ability, but not social functioning. However, better theory of mind was related to improved community functioning. Negative symptoms were differentially related to social cognition as there was only a negative association between theory of mind and expressive negative symptoms. More severe negative symptoms were associated with poorer social functioning and cognitive ability. White matter integrity within either identified tract did not contribute to social cognitive ability. Although FA within the left ILF was related to overall functioning and social functioning and FA within the left UF was related to community functioning, these relationships were in the opposite direction as originally predicted with better functioning contributing to lower FA. This is the first study to investigate white matter microstructure in a transdiagnostic sample using an RDoC approach. Our results indicate that there may be unique challenges involved in implementing RDoC. We encourage future researchers to recruit larger sample sizes, administer several behavioral measures of interest to create latent variables, and consider novel imaging methods to better address the difficulties associated with crossing fiber tracts.Item CORTICAL REPRESENTATION OF SPEECH IN COMPLEX AUDITORY ENVIRONMENTS AND APPLICATIONS(2017) Puvvada, Venkata Naga Krishna Chaitanya; Simon, Jonathan Z; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Being able to attend and recognize speech or a particular sound in complex listening environments is a feat performed by humans effortlessly. The underlying neural mechanisms, however, remain unclear and cannot yet be emulated by artificial systems. Understanding the internal (cortical) representation of external acoustic world is a key step in deciphering the mechanisms of human auditory processing. Further, understanding neural representation of sound finds numerous applications in clinical research for psychiatric disorders with auditory processing deficits such as schizophrenia. In the first part of this dissertation, cortical activity from normal hearing human subjects is recorded, non-invasively, using magnetoencephalography in two different real-life listening scenarios. First, when natural speech is distorted by reverberation as well as stationary additive noise. Second, when the attended speech is degraded by the presence of multiple additional talkers in the background, simulating a cocktail party. Using natural speech affected by reverberation and noise, it was demonstrated that the auditory cortex maintains both distorted as well as distortion-free representations of speech. Additionally, we show that, while the neural representation of speech remained robust to additive noise in absence of reverberation, noise had detrimental effect in presence of reverberation, suggesting differential mechanisms of speech processing for additive and reverberation distortions. In the cocktail party paradigm, we demonstrated that primary like areas represent the external auditory world in terms of acoustics, whereas higher-order areas maintained an object based representation. Further, it was demonstrated that background speech streams were represented as an unsegregated auditory object. The results suggest that object based representation of auditory scene emerge in higher-order auditory cortices. In the second part of this dissertation, using electroencephalographic recordings from normal human subjects and patients suffering from schizophrenia, it was demonstrated, for the first time, that delta band steady state responses are more affected in schizophrenia patients compared with healthy individuals, contrary to the prevailing dominance of gamma band studies in literature. Further, the results from this study suggest that the inadequate ability to sustain neural responses in this low frequency range may play a vital role in auditory perceptual and cognitive deficit mechanisms in schizophrenia. Overall this dissertation furthers current understanding of cortical representation of speech in complex listening environments and how auditory representation of sounds is affected in psychiatric disorders involving aberrant auditory processing.Item Feasibility of in vivo SAXS imaging for detection of Alzheimer's disease(2017) Choi, Mina; Chen, Yu; Badano, Aldo; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Small-angle x-ray scattering (SAXS) imaging has been proposed as a technique to characterize and selectively image structures based on electron density structure which allows for discriminating materials based on their scatter cross sections. This dissertation explores the feasibility of SAXS imaging for the detection of Alzheimer's disease (AD) amyloid plaques. The inherent scatter cross sections of amyloid plaque serve as biomarkers in vivo without the need of injected molecular tags. SAXS imaging can also assist in a better understanding of how these biomarkers play a role in Alzheimer’s disease which in turn can lead to the development of more effective disease-modifying therapies. I implement simulations of x-ray transport using Monte Carlo methods for SAXS imaging enabling accurate calculation of radiation dose and image quality in SAXS-computed tomography (CT). I describe SAXS imaging phantoms with tissue-mimicking material and embedded scatter targets as a way of demonstrating the characteristics of SAXS imaging. I also performed a comprehensive study of scattering cross sections of brain tissue from measurements of ex-vivo sections of a wild-type mouse brain and reported generalized cross sections of gray matter, white matter, and corpus callosum obtained and registered by planar SAXS imaging. Finally, I demonstrate the ability of SAXS imaging to locate an amyloid fibril pellet within a brain section. This work contributes to novel application of SAXS imaging for Alzheimer's disease detection and studies its feasibility as an imaging tool for AD biomarkers.Item Reward modulation of inhibitory control during adolescence: An age related comparison of behavior and neural function(2010) Hardin, Michael George; Fox, Nathan A; Human Development; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The developmental period of adolescence is distinguished by a transition from the dependent, family-oriented state of childhood to the autonomous, peer-oriented state of adulthood. Related to this transition is a distinct behavioral profile that includes high rates of exploration, novelty-seeking, and sensation-seeking. While this adolescent behavioral profile generally aids in the transition to autonomy, it comes at a cost and is often related to excessive risk-taking behavior. Current models attribute the adolescent behavioral profile to a developmental discordance between highly sensitive reward-related processes and immature inhibitory control processes. Specifically, reward-related processes appear to develop in a curvilinear manner characterized by a heightened sensitivity to reward that peaks during adolescence. On the other hand, inhibitory processes show a protracted linear developmental trajectory that begins in childhood and continues gradually throughout adolescence. Thus, the unique developmental trajectories of these two sets of processes leave the adolescent with highly sensitive, reward-driven processes that can only be moderately regulated by gradually developing inhibitory processes. Despite the usefulness of these models of adolescent behavior, they remain incompletely supported by data, as few studies specifically examine the interaction between reward-related and inhibitory processing. The current study addresses this particular gap in the adolescent neural development literature by administering a reward-modified inhibitory control task to children, adolescents, and young adults during functional neuroimaging. Three key findings emerged from the current study. First, adolescents showed greater inhibition-related neural responses than both adults and children when potential monetary reward was available. Second, adolescents reliably showed greater striatal recruitment with reward than both adults and children. These differences in striatal response occurred as all three age groups showed significant reward-related behavioral improvements. Third, when reward was not present, adolescents and children showed deficient inhibitory behavior relative to adults. Findings from this study support models proposing interactive relationships between heightened adolescent sensitivity to reward and protracted development of inhibitory control. Additionally, the current findings expand these models by suggesting heightened adolescent sensitivity to reward may facilitate developmentally inefficient inhibitory control processes in a bottom-up manner.