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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2009 - 20102

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    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.
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    CHEMICAL INDUCTION OF SETTLEMENT IN LARVAE OF THE EASTERN OYSTER CRASSOSTREA VIRGINICA (GMELIN)
    (2009) Grant, Melissa; Meritt, Donald W.; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Although numerous studies have been conducted to examine the effects of neuroactive compounds on bivalve larvae, few have identified chemicals capable of inducing settlement behavior in the eastern oyster Crassostrea virginica. In this study, I treated competent C. virginica larvae with select chemicals to identify those which are capable of inducing settlement behavior at an average salinity of 9.6 (±0.1). The compounds γ-aminobutyric acid and acetylcholine chloride, both at 10-4M, did not significantly increase the percentage of larvae exhibiting settlement behavior. As compared with the control, a significant increase in settlement behavior was induced by treatment with 3-isobutyl-1-methylxanthine, 5-hydroxytryptamine, and L-3, 4-dihydroxyphenylalanine all at 10-4M, as well as ammonia as a solution of 7.9mM NH4Cl (pH=8.0). These findings differ somewhat from the results of similar studies involving other species in the Crassostrea genus and may be of value to hatchery personnel or researchers interested in the chemical induction of settlement behavior in the eastern oyster.