1,720,957 research outputs found
Spike-timing dependent plasticity and connectivity in primate sensorimotor cortex
No full textThesis (Ph.D.)--University of Washington, 2016-06Specific connectivity between populations of neurons gives rise to network function. The plasticity of these connections allows for network learning and adaptation. While much work has explored plasticity and underlying connectivity, there is still much to learn about why particular connections are susceptible to manipulation. Hebbian plasticity has been shown in a variety of neural circuits, yet there are subtle differences in the mechanisms driving these effects at each synapse. Similarly, functional connectivity has been described utilizing varying methods. Ultimately, these bodies of work tile a broad spatiotemporal view of cortical function. Here, we explore plasticity between sensorimotor populations and the underlying connections which serve targeted changes. The variability we observed in our results further highlights that one size does not fit all, and perhaps only by looking at the collective may we begin to understand the complexities of cortical processing. I. Paired-stimulation for spike-timing dependent plasticity in primate sensorimotor cortex Classic studies in vitro have described spike-timing dependent plasticity (STDP) at a synapse: the connection from neuron A to neuron B is strengthened (or weakened) when A fires before (or after) B within an optimal time window. Accordingly, more recent in vivo works have demonstrated behavioral effects consistent with an STDP mechanism; however, many relied on invasive single-unit recordings. The ability to modify cortical connections becomes useful in the context of injury when connectivity, and associated behavior, is compromised. To avoid the need for long-term, stable isolation of single units, one could control timed activation of two cortical sites with paired, electrical stimulation. We tested the hypothesis that STDP could be induced via prolonged paired-stimulation as quantified by cortical evoked potentials (EPs) in sensorimotor cortex of awake, behaving monkeys. Paired-stimulation between two interconnected sites produced robust effects in EPs consistent with STDP; however, only at a subset of tested pairs (2/15). This protocol otherwise produced increases in global network excitability or depression of the conditioned pair. Taken together, these results suggest that paired-stimulation in vivo is a viable method to induce STDP between cortical populations, but that factors beyond activation timing must be kept in mind to produce a site-independent effect. II. Intrinsic functional connectivity of neural populations in forelimb sensorimotor cortex The structure of neocortex is defined by its anatomical and functional connections, from which processing and cognition arise. Functional connectivity exists and may be investigated along a wide spatiotemporal range utilizing a variety of electrophysiological techniques and analyses. Single- and multi-unit recordings can show connectivity of local micro-circuits whereas electrocorticography (ECoG) or functional imaging highlights macro-scale connections across the whole brain. Further, recordings of action potentials compared to local field potentials (LFPs) in ECoG are based in fundamentally different mechanisms generating neural activity and connectivity. We explored meso-scale connectivity in hand area of primate sensorimotor cortex via EPs and band-limited coherence in spontaneous LFP between cortical sites. The strength of both EPs and coherence showed an inverse relationship with inter-site distance as well as regionality between primary motor (M1) and somatosensory (S1) cortex. Despite these similarities, EP and coherence connectivity maps were not well correlated likely due to different underlying mechanisms driving the two signals. Taken together, these results show connectivity structure at a meso-scale, population level similar to that at other scales. Further exploration utilizing different recording techniques or functional connectivity metrics may elucidate additional network structure
Cortical Stimulation Induces White Matter Plasticity Following Spinal Cord Injury
No full textThesis (Ph.D.)--University of Washington, 2019This thesis describes experiments conducted to elucidate the potential for neuromodulation to induce white matter plasticity in the spinal cord injured rat. In addition, it highlights experiments designed to address the effect of neuromodulation on additional sequalae of spinal cord injury. Potential experiments are proposed to address the mechanisms by which the injured spinal cord responds to neuromodulation and the contribution of white matter plasticity to other facets of spinal cord injury and recovery
Examination of targeted, activity-dependent spinal stimulation in a rat model of spinal cord injury
Full text linkThesis (Master's)--University of Washington, 2023Spinal cord injuries (SCIs) cause debilitating motor and sensory impairments that can significantly impact patients’ quality of life. Although an estimated 300,000 people in the United States are living with a spinal cord injury, there are few available treatments for chronic injuries beyond physical and occupational therapy. Even after injury, the spinal cord has an innate ability for plasticity that can promote spontaneous recovery and be harnessed with therapeutic interventions to improve functional outcomes for patients. Previous work has shown that targeted, activity-dependent electrical stimulation of the spine in an animal model improves functional outcomes greater than open-loop electrical stimulation or physical retraining alone. However, the mechanism by which this targeted stimulation works and whether it is promoting plasticity in particular descending pathways remains unclear. We hypothesized that this therapy paradigm targets descending cortical projections to the spinal cord and that electrophysiological recordings of the motor cortex and anatomical tracing of this corticospinal tract would reveal changes after injury and with therapy. Unfortunately, we were unable to answer these questions, but new knowledge of technical limitations will hopefully provide a baseline for future pursuance of this research
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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