19468 research outputs found
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The Influence of Spike Timing-Dependent Plasticity on a Recurrent Excitatory Neural Network Model
No full textSynaptic plasticity is thought to be the biological foundation of learning and memory, and it may also contribute to other brain computations and functions. Spike timing-dependent plasticity (STDP) modulates long-term synaptic strengths, aligning with Hebbian learning principles such as the asymmetric impact of precise temporal correlations between the spikes of pre- and post-synaptic neurons. In the context of an all-to-all connected excitatory network, we investigated STDP through mathematical analysis and computational simulations, incorporating a pair-based STDP model and the homeostatic phenomenon known as synaptic scaling. Neuron spiking is modeled as a time-inhomogeneous Poisson point process with rate given by a nonlinear activity function, an approach that follows a recently published spiking network model of the brainstem preBötzinger complex (preBötC) that is responsible for inspiratory breathing rhythm. This model formulation is used to examine how different STDP rules (e.g., additive vs. multiplicative update) influence the activity and connectivity of an excitatory neuron population. Numerical simulations revealed that STDP dynamics, combined with synaptic scaling, can induce episodic bursting (i.e., periodic transitions between network states with low and high firing rate). This finding raises the possibility that STDP may play a role in recurrent excitatory networks, for example, the inspiratory rhythm of the preBötC.NeuroscienceBachelors of Science (BS
Stress and Animal Therapy Rewards: The Impacts of Animal Interaction on Neurological Markers of Stress in College Students
No full textStress throughout college is associated with negative outcomes, including poor health, poor academic performance, and depression (Brougham et al., 2009; Hudd et al., 2000). For decades, animal therapy has been used as a treatment option for stress (Johnson, 2008). Although studies have shown that animal therapy can reduce psychological and physical indicators of stress in college students, no study has focused on the benefits of animal therapy on the brain. The current study used electroencephalogram (EEG) to analyze the neurological impacts of animal therapy on college student stress, specifically by measuring theta/alpha frequency ratios which are stress resilience indicators. Participants included 18 first-year college students participating in orientation activities before the start of their freshman year of college (39% Male, 39% Female, 78% White, 11% Hispanic or Latino, 5.5% Multiracial or Biracial, and 5.5% Asian/Pacific Islander). Participants were first asked to answer questions regarding their current mood and stress. An EEG was then used to measure the neurological stress of each participant before, during, and after interacting with a certified animal therapy dog. It was predicted that lower perceived stress and lower theta/alpha ratios, indicating lower stress levels, would be found after participants interacted with the animal therapy dog. Results revealed that there was a significant decrease in perceived stress after animal interaction and that neurological stress was significantly lower after animal therapy than during interaction. While not all hypotheses were supported by the results of this study, it is important to note that EEG technology could have been impacted by mobile, animal interaction. Future research using animal interaction with restricted movement may be important to confirm these results.PsychologyBachelors of Science (BS
Examining the Nutritional Quality of Mixotrophic Dinoflagellates Using Elemental Ratios and Total Lipid Content
No full textMixotrophic phytoplankton use both autotrophy and phagotrophy, but little is known about their role as prey in aquatic ecosystems. It has been hypothesized that mixotrophs provide a stable food source compared to autotrophs under growth-limiting conditions, but further evidence is needed to support this. To that end, we investigated elemental carbon (C), nitrogen (N), and phosphorus (P) ratios and total lipid content in two mixotrophic and one autotrophic algal culture under varying environmental conditions. Heterocapsa steinii, Scrippsiella sp. (mixotrophic dinoflagellates), and Chaetoceros muelleri (autotrophic diatom) were incubated for 7 days under either Redfield (16:1 N:P) or nitrogen-depleted (4:1 N:P) media and under ambient light conditions (66.4 μE/m2/s) or low light conditions (20% of ambient light). Cultures were sampled before and after incubation for cellular particulate organic C, N, P, and total lipid concentrations. While all cultures had positive growth rates under all conditions, the mixotrophs demonstrated higher overall cellular C, N, P, and total lipid concentrations than the autotroph. Under low light, all species showed lower growth rates, C, N, P, and lipid content. Conversely, under ambient light and nitrogen-depleted conditions, the mixotrophs showed more stable C/N, C/P, and N/P ratios relative to the strict autotroph. This suggests that mixotrophs are a more stable food source than autotrophs. This research has implications for nutrient acquisition of higher trophic levels in ecosystems where mixotrophic and autotrophic algae serve as prey.ChemistryBachelors of Science (BS
"Thirsteth for the Blood of America": Propaganda and Violence during the American Revolution
No full textDrawing upon newspapers, political prints, pamphlets, broadsides, and personal correspondence from 1763 to 1783, this study analyzes the American Revolution's explosion of print culture. The sources largely originate from the colonies' three major northern port cities, Boston, Pennsylvania, and New York. Responding to the uptick in print culture, this study analyzes the influence of violence and race in Revolutionary propaganda. How did revolutionary patriot propaganda utilize violence and shape race-making practices? How did patriots revise understandings of race to bolster their cause?HistoryBachelors of Arts (BA
Stream surprises! An investigation into the drivers of stream salamander population dynamics
No full textIn the small streams of riparian forests, salamanders play an integral role in ecosystem functioning. Despite their ecological importance, however, little research has been undertaken to thoroughly understand the factors governing stream salamander population dynamics. Furthermore, salamanders are facing global declines due to intensifying environmental and anthropogenic stressors. To direct effective conservation strategies for stream salamander communities, we must holistically understand their population ecology. In this study, we investigated drivers of stream salamander populations by surveying aquatic salamander diversity, abundance, and larval body size at forested streams in Virginia’s Coastal Plain. We used statistical modeling to relate differences in these response variables to an array of potential drivers across microhabitat and watershed extents. We documented 3 species Eurycea cirrigera (98.5% of individuals), Desmognathus fuscus (1% of individuals), and Eurycea guttolineata (0.5% of individuals). For abundance, we found time of year, stream water volume, and proportion of the watershed composed of evergreen forest to be significant predictors. For larval size, we found temperature, stream water volume, phosphate concentration, and the presence of coarse woody debris to be significant predictors. Our results help inform conservation strategies by highlighting a lack of species diversity, the importance of protecting short stream hydroperiods and deciduous forest patches to maintain abundance, and the potential negative effects of warming water temperatures and increased phosphate concentrations on larval body size.BiologyBachelors of Science (BS
Sex-Dependent Reproductive Outcomes in Adult and Developmentally Lead (Pb) Exposed Zebra Finches
No full textLead (Pb), an environmental heavy metal contaminant, is an ongoing threat to urban songbird populations. While prior studies have found deleterious effects of developmental exposure to Pb on adult fitness in zebra finches (Taeniopygia guttata), there is ambiguity in the direct vs. indirect impact of Pb on developmental mortality. Pb’s impacts on reproductive success across a population have not been investigated in a multigenerational study which would elucidate the true threshold for existential levels of Pb exposure, assuming not all individuals need to receive the highest exposure level for across the board effects. We quantified the reproductive productivity and parenting success of two generations of Pb-exposed and control birds. In the first-generation, birds were exposed to Pb in drinking water once they were sexually mature. The offspring from this first-generation were exposed from conception through to sexual maturity. That second generation of birds were then arranged in breeding rooms with equal ratios of Pb-exposed and Control males and females to allow for mixed treatment pairings, if they occurred. Our preliminary results suggest stark differences in offspring mortality between generations. When a population is first exposed to Pb reproduction is suppressed by approximately 30% but mortality is not affected. When the developmental exposed offspring of that parent generation reproduce, the 60% suppression of reproduction and increase in mortality is sex dependent. Differences in outcomes were not found when the male (compared with the female) parent was exposed to Pb. These results suggest that the behavioral impact of Pb exposure (specifically an apparent failure to perform normal parenting tasks) during development is more pronounced than the direct physiological impact.BiologyBachelors of Science (BS
“Experimental Philosophy, For Gentlemen and Ladies:” A Foundling Hospital Token History, 1741-1756
No full textFrom 1741-1756, experimental philosopher, Mr. Erasmus King, advertised scientific lectures from his home in Duke’s Court, London for both ladies and gentlemen. Sometime in those same years an anonymous mother won a place for her child through a lottery system at the London Foundling Hospital. When prompted by the orphanage to leave a token with her child, she produced a small piece of metal inscribed with the words “King’s Experimental Philosophy, Duke’s Court.” What that small material object reveals are connections between women, charity, science, and fashion in London’s social history. These connections point to larger eighteenth-century anxieties and acceptance of women’s place in the quickly changing scientific sphere of society. This project addresses the scientific culture of London by reassessing the events of experimental philosophy lectures from the perspective of female audiences, and the project presents new analysis of material culture and letters associated with the home and experiment room of Erasmus King and his wife Elizabeth. This analysis places the material, emotional, and spatial history of women at the forefront of the project. Scientific ideas inundated the eighteenth-century British urban consciousness, and the manifestations of that culture in London were unavoidable, regardless of gender. Therefore, while society did not often offer women a full and authoritative role in this culture, science could weave its way into crucial parts of women’s lives from mundanity to motherhood.HistoryBachelors of Arts (BA
A Cross-National Examination of Adverse Childhood Experiences and Depression in Young Adults: The Mediating Roles of Emotion Regulation, Distress Tolerance, and Rumination
No full textAdverse childhood experiences have been linked to poor mental health outcomes, including depression, yet the underlying mechanisms remain unclear. The present study aimed to investigate how adverse childhood experiences are related to depressive symptoms among college students, focusing on emotion regulation, distress tolerance, and rumination as potential mediating pathways. Our analytic sample consisted of 4,337 participants (67.2% female) from six countries—United States, Canada, Spain, England, Argentina, and South Africa—who completed questionnaires assessing their adverse childhood experiences, depressive symptoms, use of emotion regulation strategies, distress tolerance, and ruminative thinking. We used a comprehensive mediation model in Mplus 8.3 (Muthén & Muthén, 1998–2017) to test for significant pathways. Within our model, greater adverse childhood experiences were significantly associated with greater depressive symptoms through several mediators: greater use of expressive suppression (an emotion regulation strategy), lower distress tolerance, and increased ruminative thinking across three facets (problem-focused, repetitive, and anticipatory thoughts). Model invariance analyses suggested that these findings were consistent across countries and sex at birth. The results highlight the importance of targeting emotion regulation, distress tolerance, and rumination in interventions aimed at reducing depression, particularly among individuals with a history of childhood adversity. Furthermore, the findings suggest that interventions targeting these mechanisms may be broadly applicable across global populations. Future research should employ longitudinal designs to further clarify the directionality of these associations and examine them across more diverse populations, including various age groups and cultural backgrounds. Keywords: adverse childhood experiences, depression, emotion regulation, distress tolerance, ruminationPsychologyBachelors of Science (BS
Methylation Dynamics in Helicobacter pylori: Exploring Acidic Stress Effects on Epigenetic Acclimation.
No full textHelicobacter pylori is the only known bacterium classified as a Class I carcinogen and infects over 50% of the global population. Although most infections are asymptomatic, 10–15% progress to gastric cancer or peptic ulcers, reflecting significant strain-strain variability as well as host variability. H. pylori exhibits an unusually high number of restriction-modification (R-M) systems relative to its small genome, contributing to a dynamic methylome increasingly implicated in bacterial gene regulation. In this study, we analyzed the methylomes of two mutant strains of H. pylori 26695, each under neutral (pH 7) and acidic (pH 5) growth conditions. We identified one hypomethylated region of 21kBp with 21 annotated genes across all four methylomes analyzed. Notably, over 660 protein coding regions and 12 different promoters displayed differential methylation between pH conditions, involved in the expression of several known virulence factors. The vacA gene, encoding the Vacuolating Cytotoxin A, exhibited eight differentially methylated positions between pH 7 and pH 5 within the H. pylori 26695 control mutant methylome, potentially contributing to its previously documented 32-fold down regulation of mRNA in acidic environments. Methylation changes were also enriched among genes encoding cell envelope proteins, specifically within flagellar associated coding regions and within the genes sabA and babA. Together, these results highlight a remarkable plasticity of the H. pylori methylome and suggest that dynamic DNA methylation, responsive to environmental pH both dependent upon and independent of the ArsRS two-component system, serves as an important layer of gene regulation in acclimation to hostile gastric environments.Computational & Applied Mathematics & StatisticsBachelors of Science (BS
Development of Dynamic Nuclear Polarization for Single-sided Nuclear Magnetic Resonance
No full textNuclear magnetic resonance (NMR) is a tool used to determine molecular structure and chemical dynamics within a magnetic field. This magnetic field creates different energy levels that nuclear spins can occupy. The difference in the number of spins at each energy level determines the amount of polarization, which is proportional to the detected signal. Typically, NMR instruments are expensive, require regular upkeep, restrict sample sizes to small tubes, and give low measurement signal. Single-sided NMR combats some limitations by allowing for larger sample sizes, at the expense of a larger magnetic field gradient which lowers measurement resolution. We aim to circumvent limitations by applying dynamic nuclear polarization (DNP) techniques to single-sided NMR. DNP transfers the polarization from unpaired electrons to hydrogen nuclei, increasing the detected signal and sensitivity. DNP is dependent on factors related to microwave power, radical concentration, and inherent molecular characteristics. This work demonstrates successful construction of a DNP system that maintains the open geometry of single-sided NMR using alternative hardware to excite electron spins. Various experiments reveal a large dependency on power to adequately hyperpolarize samples, leading to further developments in probing thin, interfacial regions within a large field gradient. Future work involves optimizing the DNP system in order to investigate material and biological applications using single-sided NMR.ChemistryBachelors of Science (BS