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.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Response inhibition and the cortico-striatal circuit(2015) Bryden, Daniel William; Roesch, Matthew R; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The ability to flexibly control or inhibit unwanted actions is critical for everyday behavior. Lack of this capacity is characteristic of numerous psychiatric diseases including attention deficit hyperactivity disorder (ADHD). My project is designed to study the neural underpinnings of response inhibition and to what extent these mechanisms are disrupted in animals with impaired impulse control. I therefore recorded single neurons from dorsal striatum, orbitofrontal cortex, and medial prefrontal cortex from rats performing a novel rodent variant of the classic "stop signal" task used in clinical settings. This task asks motivated rats to repeatedly produce simple actions to obtain rewards while needing to semi-occasionally inhibit an already initiated response. To take this a step further, I compared normal rats to rats prenatally exposed to nicotine in order to better understand the mechanism underlying inhibitory control. Rats exposed to nicotine before birth show abnormal attention, poor inhibitory control, and brain deficits consistent with impairments seen in humans prenatally exposed to nicotine and those with ADHD. I found that dorsal striatum neurons tend to encode the direction of a response and the motor refinement necessary to guide behaviors within the task rather than playing a causal role in response inhibition. However the orbitofrontal cortex, a direct afferent of dorsal striatum, possesses the capacity to inform the striatum of the correct action during response inhibition within the critical time window required to flexibly alter an initiated movement. On the other hand, medial prefrontal cortex functions as a conflict “monitor” to broadly increase preparedness for flexible response inhibition by aggregating current and past conflict history. Lastly, rat pups exposed to nicotine during gestation exhibit faster movement speeds and reduced capacity for inhibitory behavior. Physiologically, prenatal nicotine exposure manifests in a hypoactive prefrontal cortex, diminished encoding of task parameters, and reduced capacity to maintain conflict information.Item Profiles of Social Anxiety Symptoms and Impulsivity in College Students(2014) Lipton, Melanie; De Los Reyes, Andres; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Prior work points to a subtype of Social Anxiety (SA) characterized by disinhibition or high externalizing behaviors (e.g., substance use and Attention Deficit Hyperactivity Disorder (ADHD) symptoms). This study extended prior work by replicating subtypes of SA and impulsivity and examining differences among these subtypes in their expression of externalizing behavior. Three hundred seventy-five undergraduates completed an online study including measures of SA, substance use, ADHD symptoms and impulsivity. Latent class analyses revealed three classes of individuals who were: (a) low SA and low impulsivity, (b) high SA and low impulsivity, and (c) high SA and high impulsivity. Individuals high in both SA and impulsivity exhibited greater likelihoods of exhibiting externalizing behavior concerns, relative to the two other classes, with the largest differences on ADHD symptoms. These findings indicate that identifying differences among SA subtypes in externalizing behavior concerns depends on the externalizing domain.Item Relationship between disinhibition and metabolic control in adolescents with type 1 diabetes(2006-12-05) Sanchez, Lisa; Lejuez, Carl; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Given that adolescence poses a high-risk period for diabetes mismanagement, and consequently, threats to long-term health status, it is important to examine factors that contribute to individual differences in the propensity to exhibit poor management and engage in health incompatible behaviors. Importantly, researchers have identified personality constructs related to disinhibition, including impulsivity, sensation seeking, and risk-taking propensity, to be prospectively linked to engagement in real-world risk behaviors such as use of alcohol, nicotine, illegal drugs, and risky sexual behavior (Lejuez et al., 2002, 2003). However, this relationship has yet to be explored in adolescents with diabetes. Thus, the purpose of the current study was to examine whether disinhibition was related to metabolic control, and the extent to which self-management behavior and drug/alcohol use mediated this potential relationship. The sample consisted of 43 subjects with Type 1 diabetes aged 13-18 years who were recruited from diabetes clinics at Children's National Medical Center. Teens were assessed with self-report and behavioral measures of risk-taking and participated in an interview regarding self-management behaviors. Substance use and diabetes knowledge were measured by self report, and the glycosylated hemoglobin (HbA1c) test was used as a proxy for metabolic control. Results of partial correlational analyses indicated that disinhibition was not directly related to behavioral adherence, engagement in health incompatible behaviors, or glycemic control after controlling for race, gender, and insulin regimen type. Rather, results of regressional analyses suggested that sample characteristics, particularly race and insulin regimen, are the key variables in assessing overall management in adolescence. Results may have important implications for the prevention and treatment of morbidity associated with diabetes.