Browsing by Subject "plasticity"

Now showing 1 - 6 of 6
  • Thumbnail Image
    Item
    Berkovich nanoindentation and FTIR data describing the effect of water on olivine plasticity
    (2023-08-28) Kumamoto, Kathryn, M; Breithaupt, Thomas, P; Hansen, Lars, N; Wallis, David; Li, Bo-Shiuan; Armstrong, David, EJ; Goldsby, David, L; Li, Yang; Warren, Jessica, M; Wilkinson, Angus, J; lnhansen@umn.edu; Hansen, Lars, N; Rock and Mineral Physics Lab
    This data set contains data collected as part of a study to determine the influence of dissolved hydrogen on the mechanical properties of olivine. Nanoindentation experiments were conducted to measure the hardness of both pristine olivine crystals and olivine crystals predoped with hydrogen. The hydrogen content of samples was assessed with Fourier-transform infrared spectroscopy (FTIR). This data set includes mechanical data from indentation experiments as well as spectra from FTIR measurements.
  • Thumbnail Image
    Item
    Beyond Simple Tests of Value: A neuroeconomic, translational, disease-relevant, and circuit-based approach to resolve the computational complexity of decision making
    (2018-07) Sweis, Brian
    How the brain processes information when making decisions depends on how that information is stored. Distinct neural circuits are capable of storing information in many different ways that are better suited for different situations. The decision-making processes that access those different bits of stored information are not singular and occupy separable neural circuits, each of which can operate in parallel with one another, and each of which can confer different information processing properties based on the neural constraints within which a given computation resides. Such is the framework of recent theories in neuroeconomics, which suggest that decisions are multi-faceted and action-selection processes can arise from fundamentally distinct circuit-specific neural computations. In this thesis, I present a body of work that takes a neuroeconomics approach through a series of experiments that reveal the complexities of multiple, parallel decision-making systems through complex behaviors by moving beyond simple tests of value. In the first half of this thesis, I demonstrate how complex behavioral computations can resolve fundamentally distinct valuation algorithms thought to reside in separable neural circuits. I then translate this approach between human and non-human rodent animal models in order to reveal how multiple, parallel decision-making systems are conserved across species over evolution. In the second half of this thesis, I demonstrate the utility of behavioral economics in disease-relevant and circuit-based studies. If multiple, parallel decision-making processes are thought to be intimately related to the heterogeneous ways in which information can be stored in separable neural circuits, I examine how addiction – a disease which is thought to be a disorder of the neurobiological mechanisms of learning and memory – might alter how stored information is processed in separable decision-making systems uniquely using a mouse model of two different forms of addiction. In doing so, I demonstrate how different forms of addiction give rise to unique, lasting vulnerabilities in fundamentally distinct decision-making computations. These discoveries can aid in resolving neuropsychiatric disease heterogeneity by moving beyond simple tests of value where complex behaviors that are measured can more accurately reflect the neurally distinct computations that underlie those behaviors. Finally, I take a neuromodulation approach and directly alter the strength of synaptic transmission in a circuit-specific manner using optogenetics in mice tested in this neuroeconomic framework. I demonstrate how plasticity alterations in projections between the infralimbic cortex and the nucleus accumbens are capable of giving rise to long-lasting disruptions of self-control related decision processes in a foraging valuation algorithm independent of and separate from a deliberative valuation algorithm measured within the same trial. Furthermore, I developed a novel plasticity measurement tool that is assayed at the neuronal population ensemble level and reveals individual differences in separable decision processes. The second half of the thesis demonstrates a potential biomarker to target as a circuit-computation-specific therapeutic intervention tailored to those types of decision-making dysfunctions. Taken together, I present a body of work in this thesis that demonstrates the utility of moving beyond simple tests of value in order to resolve the computational complexity of decision making.
  • Thumbnail Image
    Item
    Female crickets reared in silence exhibit risk-sensitive behavior in response to the preferred song
    (2018-12) Ghalichi, Narmin
    Female choice is influenced by many environmental cues that get experienced during different stages of female development. Cues experienced in juvenile stage may have larger impact on female mate choice than mating decisions in response to cues experienced during adult mate choice. To examine how juvenile acoustic rearing interacts with immediate perception of risk in shaping female mate preference, we used the system of Pacific field cricket (Teleogryllus oceanicus). Females raised in silence were predicted to be more responsive under conditions associated with low risk without discriminating across song models. Females raised in the presence of song were expected to exhibit preference for a song model under conditions associated with low risk. Our results showed no interaction for females raised in the presence of song; females raised in silence exhibited preference for a song model under conditions associated with risk.
  • Thumbnail Image
    Item
    From individuals to species: how natural selection and phenotypic plasticity shape ecomorphological evolution in freshwater mussels
    (2023-05) Keogh, Sean
    Adaptation is the hallmark of evolutionary biology, explaining how species achieve ecological success through natural selection. However, adaptation is challenging to identify leading to frequent ‘just-so stories’ to explain the adaptive features of organisms. At the core of adaptive studies is the motivation to find the fit between morphological and functional diversity. Here I used the freshwater mussels of North America as a study system to investigate the fit between morphological and ecological traits both within and across species. I used comparative and experimental inferences to identify the evolutionary mechanisms driving ecomorphological patterns. My first chapter identified ecomorphological patterns within and across species between shell thickness, shell anterior thickening, and flow rate. Across species, I found widespread convergence in these traits showing that natural selection produces the following adaptations to riverine flow rates: thick and anteriorly thickened shells in high flow rates (likely for stability in the substratum) and thin and uniformly thickened shells in low flow rates (likely for burrowing efficiency). Additionally, within species, I found a creditably positive relationship between shell thickness and flow rate, effectively mirroring interspecific relationships albeit at different scales. Intraspecific processes may therefore be partially responsible for the evolvability and ecological diversification of the clade. Although I identified this intraspecific ecomorphological pattern, I could not identify the mechanism producing this pattern. To address this, in my second chapter I conducted a common garden experiment on a morphologically variable species, Pyganodon grandis. The morphology of this species varies predictably between lake and stream environments and I investigated if this relationship was due to phenotypic plasticity or genetic differentiation. By rearing siblings from a single female’s broodstock, I minimized genetic variation, and released ~6,000 marked individuals into nine sites (four streams, five lakes). Two years after release, I recaptured a total of 70 individuals from both stream and lake sites showing significant shell shape differences between habitats and no shell shape differences between recaptured siblings and wild P. grandis reared at the same site, showing definitively that phenotypic plasticity rather than genetic differentiation is driving ecomorphological patterns. In my third and final chapter I ran a fluvial experiment investigating the function of mussel posterior ‘ribbed’ sculpture. I measured water velocity magnitude, direction, and streambed erosion surrounding mussel models with sculpture and with their sculpture manually removed. In opposition to previous studies, I found more streambed erosion associated with sculptured models. However, mussel orientation to streamflow was the more significant driver to variations in water velocity magnitude, direction, and streambed erosion. This body of work illustrates the complementary nature of phylogenetic comparative methods and experiments to finding the evolutionary mechanisms of phenotypic variation. Lastly, the role of phenotypic plasticity in macroevolutionary outcomes has seldom been investigated but the widespread convergence of ecomorphological traits in chapter 1 and common garden experiment in chapter 2 suggest plasticity may be a key mechanism to macroevolutionary diversification.
  • Thumbnail Image
    Item
    Inducing Neural Plasticity and Modulation Using Multisensory Stimulation: Techniques for Sensory Disorder Treatment
    (2017-06) Gloeckner, Cory Dale
    In this dissertation, we characterized the modulatory and plasticity effects of paired multisensory stimulation on neural firing in sensory systems across the brain. In the auditory system, we discovered that electrical somatosensory stimulation can either suppress or facilitate neural firing in the inferior colliculus (IC) and primary auditory cortex (A1) depending stimulation location. We also tested plasticity effects in A1 in response to paired somatosensory and acoustic stimulation with different inter-stimulus delays in anesthetized guinea pigs, and found that plasticity induced by paired acoustic and right mastoid stimulation was consistently suppressive regardless of delay, but paired acoustic and pinna stimulation was timing-dependent, where one inter-stimulus delay was consistently suppressive while other delays induced random changes. These experiments were repeated in awake animals with paired acoustic and pinna stimulation, and two animal groups of different stress levels were used to assess stress effects on plasticity. We found that in low-stress animals, the same inter-stimulus delay was consistently suppressive and a neighboring delay was consistently facilitative across all animals, which matches previous invasive spike-timing dependent plasticity studies (anesthesia may have affected these trends). Meanwhile, high-stress animal results were not consistent with expected time dependence and exhibited no trends across inter-stimulus delays, indicating that stress can have adverse effects on neuromodulation plasticity outcomes. In all other primary sensory cortices, we found that differential effects can be induced with paired sensory stimulation such that the location, amount, type, and timing of plasticity can be controlled by strategically choosing sensory stimulation parameters for modulation of each sensory cortex. We also investigated the ability to target subpopulations of neurons within a brain region and found that by stimulating at levels near activation thresholds, specific subpopulations of IC neurons can be targeted by varying somatosensory stimulation location. Furthermore, acoustic stimulation can excite or modulate specific areas of somatosensory cortex, and we mapped the guinea pig homunculus to characterize this. Overall, these findings illustrate the immense interconnectivity between sensory systems, and multisensory stimulation may provide a noninvasive neuromodulation approach for inducing controlled plasticity to disrupt pathogenic neural activity in neural sensory disorders, such as tinnitus and pain.
  • Thumbnail Image
    Item
    Physiological and fitness consequences of seasonal rainfall variation in neotropical live oak seedlings (Quercus oleoides): implications for global change
    (2015-06) Center, Alyson
    Broadly distributed species often span a large range of environmental conditions, which pose contrasting physiological challenges. Such species are thought to persist across this heterogeneity, either by locally adapting or by evolving wide environmental tolerances via phenotypic plasticity or maintaining high genetic variation. The extent to which populations display local adaptation, phenotypic plasticity, and high within-population genetic variation will have large impacts on species responses to climate change. Large- scale habitat fragmentation impedes migration making plasticity and adaptation important mechanisms for in situ persistence. Using common gardens with reciprocal plantings we investigated the consequences of changes in water availability in the broadly distributed tropical live oak, Quercus oleoides. Chapter 1 examines the relationship among seed production timing, germination and seedling fitness at the local scale in dry forests of NW Costa Rica. In chapter 2, I investigate the extent to which four populations of Q. oleoides from regions with contrasting rainfall patterns exhibit local adaptation and the role of changes in water availability on seedlings fitness. In chapter 3, I examine the extent that populations exhibit differentiation in traits related to carbon and water use. Chapter 3 also investigates the role of trait plasticity in seedling responses to changes in seasonal water availability and the patterns of phenotypic selection on traits. Results from these studies show that local-scale differences in seed production timing have significant consequences for germination and seedling fitness. At a larger spatial scale, results of this work indicate that the broadly distributed Q. oleoides does not consist of a series of locally adapted populations, but rather, of populations with wide environmental tolerances. Seedlings from all populations show similar physiological and morphological responses to changes in water availability and differences among garden sites. Trait plasticity contributes more to phenotypic trait variation than within-population genetic differences. Overall, populations of Q. oleoides lineage represent a lineage well-adapted to drought. Populations are able to maintain fitness with changes in water availability in the short-term through plasticity but may be limited in their long-term adaptive capacity to future changes in rainfall patterns due to low within-population genetic variation for physiological traits.