1,650 research outputs found
Spatio-temporal control of network activity through gain modulation in cortical circuit models
Get PDFAnimals perform an extraordinary variety of movements over many different time scales. To support this diversity, the motor cortex (M1) exhibits a similarly rich repertoire of activities. Although recent neuronal-network models capture many qualitative aspects of M1 dynamics, they can generate only a few distinct movements all with the same duration. Therefore, these models can still not explain how M1 efficiently controls movements over a wide range of shapes and speeds. In this thesis, we demonstrate that simple modulation of neuronal inputâoutput gains in recurrent neuronal-network models with fixed connectivity can dramatically reorganise neuronal activity and thus downstream muscle outputs. Consistent with the observation of diffuse neuromodulatory projections to M1, our results suggest that a relatively small number of modulatory control units provide sufficient flexibility to adjust high-dimensional network activity on behaviourally relevant time scales. Such modulatory gain patterns can be obtained through a simple reward-based learning rule. Novel movements can also be assembled from previously learned primitives, thereby facilitating fast acquisition of hitherto untrained muscle outputs. Moreover, we show that it is possible to separately change movement speed while preserving movement shape, thus enabling efficient and independent movement control in space and time. Our results provide a new perspective on the role of neuromodulatory systems in controlling cortical activity and suggest that modulation of single-neuron responsiveness is an important aspect of learning.</p
Evaluating Citebase, an open access Web-based citation-ranked search and impact discovery service
No full textCitebase is a new citation-ranked search and impact discovery service that measures citations of scholarly research papers which are openly accessible on the Web, i.e. papers that are assessable continuously online. Other services, such as ResearchIndex, have emerged in recent years to offer citation indexing of Web research papers. In the first detailed user evaluation of an open access Web citation indexing service, Citebase has been evaluated by nearly 200 users from different backgrounds. The paper details the procedures used in the evaluation, and analyses the results of this study, which took place between June and October 2002. It was found that within the scope of its primary components, the search interface and services available from its rich bibliographic records, Citebase can be used simply and reliably for the purpose intended, and that it compares favourably with other bibliographic services. It is shown tasks can be accomplished efficiently with Citebase regardless of the background of the user. More data need to be collected and the process refined before it is as reliable for measuring citation impact of indexed papers. Better explanations and guidance are required for first-time users. Coverage is seen as a limiting factor, even though Citebase indexes over 200,000 papers from arXiv. Non-physicists were frustrated at the lack of papers from other sciences. The principle of citation searching of open access archives has thus been demonstrated and need not be restricted to current users. Since the evaluation, Citebase has become a featured service of the ArXiv physics eprint archives
Author Talk
No full textUniversity president, Jim Schmotter, introduces Tim O'Brien at the author talk in Ives Auditorium, October 26, 2010.</p
Who Belongs? Immigrants, Refugees, Migrants, and Actions Towards Justice: A Conversation With Tim Wise
Get PDFTim Wise is an antiracist activist, essayist and author of seven books on racism, inequality and white privilege. He is among the most prominent anti-racist writers and educators in the United States. Over the past 25 years he has engaged audiences in all 50 states, at over 1000 college and high school campuses, at hundreds of professional and academic conferences, and to community groups across the country. While visiting Iowa State University Tim Wise interviewed with us to discuss Who Belongs? by providing a brief historical perspective of immigration, the current political climate, and the role of activism.</p
Channels and circuits: biophysical and network models of neuronal function
Get PDFNeuroscience research studies the brain at various different levels of detail. Experimental work explores everything from the molecular machinery within each neuron, to the behavioral output of an organism. Similarly, computational models are designed to operate at many scales, and can address different questions depending upon the complexity of the description.
Detailed biophysical modelling incorporates findings about neuronal physiology and structure in order to test hypotheses and generate predictions. However, due to the complexity and number of modelling studies, it is difficult to compare models and to assess biological fidelity. In this work we present a curated database of nearly 3000 voltage-gated ion channel models used in published neuronal simulations, called ICGenealogy. Furthermore, we present a standardized formulation for ion channel dynamics which we fit to all models on this database. Through these two endeavors, we facilitate better experimentally-constrained modelling, while also providing insight into the diversity and complexity of ion channel dynamics seen in single neurons.
At a higher level, neuronal network models integrate findings about neuronal activity and cell types in order to explain representations and computations. Here, we present a model of context-dependent associative memory, which incorporates known principles of memory function from psychology research and proposes concrete functional roles for different components of neural circuits. Through analytics and simulations, we show that a contextual memory system not only provides benefits for memory capacity and robustness, but also enables control of memory expression. This work provides new conceptual ideas for memory research, suggests functional roles for different inhibitory cell types, and may help us to understand the interaction of different memory systems in the brain.
Together, the work presented here spans two distinct levels of detail and addresses current challenges both in biophysically detailed models, as well as computation in abstract network models.</p
Synaptic plasticity models in brain development and neurodevelopmental disorders
Get PDFMathematical and computational models are powerful tools that can help us gain a deeper understanding about the world around us. In Neuroscience, however, there is still debate as to what the role of models is in research. In this thesis we build models of synaptic plasticity of varying degrees of complexity, and at different levels of abstraction in order to generate experimentally testable hypotheses and propose new ways of thinking about synaptic plasticity in development and in neurodevelopmental disorders. We applied our models to two datasets.
First, we studied a transient translaminar cortical circuit that connects layer 5b (L5b) interneurons with L4 excitatory spiny stellate neurons (SSN), or the L5b-L4 loop, that is present in the mouse barrel cortex during the first two postnatal weeks (Marques-Smith et al., 2016).. We used spiking neural networks and rate models with plastic connections to explore the mechanisms that drive these large connectivity changes, as well as the possible role these may play in the developing mouse barrel cortex.
Second, we analysed extracellular plasticity data recorded from Ts65Dn animals, a mouse model for Down Syndrome. We used three abstract models to formalise and test the hypothesis that synapses in Ts65Dn animals are more saturated, i.e. the baseline synaptic weights are closer to their maximum. First, we used a theory of synaptic plasticity that explicitly fit the baseline and the maximum synaptic weight, then we fit a descriptive phenomenological model, and finally, we adapted the Moran process, a model from evolutionary biology, to describe extracellular plasticity experiments.
The methodological differences between how experimental and theoretical work is carried out makes it challenging to integrate modelling into an experimental framework, and vice versa. However, through these five modelling examples, we argue that a successful model is not one that can capture all the features of the data, but rather one that can address the questions and hypotheses that cannot be studied with experiments alone. </p
Accepting Optimally in Automated Negotiation with Incomplete Information (abstract)
No full textIntelligent SystemsElectrical Engineering, Mathematics and Computer Scienc
Whose Voice? Tim Crouch’s The Author and Active Listening on the Contemporary Stage
No full textThe essay discusses Tim Crouch’s recent play The Author (2009) in the context of active listening, audience participation, response and responsibility in contemporary theatre. It provides a critical engagement with the spectatorial experience of the piece so as to problematize the multiple uses of the physical medium of voice and speech in a contemporary play that delivers a fresh angle to narrativity and metatheatricality. At the same time, the essay probes the varied range of possibilities but also realistic extent of audience involvement in the play, tracing its deep textual contingencies to produce an overall understanding of the equally rewarding and precarious interrelationship between performance piece and audience.</p
UTSim2 validation
Get PDFThe Center for NDE (CNDE) at Iowa State University has a long history of developing physics models for NDE and packaging these models into simulation tools which make the modeling capabilities accessible to CNDEs industrial sponsors. Recent work at CNDE has led to the development of a new ultrasonic simulation package, UTSim2, which aims to continue this tradition of supporting industrial application of CNDE models. In order to meet this goal, UTSim2 has been designed as an extensible software package which can support previously-developed physics models as well as future models yet to be developed. Initial work has focused on the implementation of a Gauss-Hermite beam model, a paraxial approximation, which is implemented as part of the Thompson-Gray measurement model. This paper will present recent validation results and include comparisons against both previously-validated model output and newly-performed experiments.This proceeding may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This proceeding appeared in Grandin, Robert, and Tim Gray. "UTSim2 validation." AIP Conference Proceedings, 1806, no. 1 (2017): 150007, and may be found at DOI: 10.1063/1.4974731. Posted with permission.</p
Nostalgia: content, triggers, functions
Get PDFSeven methodologically diverse studies addressed 3 fundamental questions about nostalgia. Studies 1 and 2 examined the content of nostalgic experiences. Descriptions of nostalgic experiences typically featured the self as a protagonist in interactions with close others (e.g., friends) or in momentous events (e.g., weddings). Also, the descriptions contained more expressions of positive than negative affect and often depicted the redemption of negative life scenes by subsequent triumphs. Studies 3 and 4 examined triggers of nostalgia and revealed that nostalgia occurs in response to negative mood and the discrete affective state of loneliness. Studies 5, 6, and 7 investigated the functional utility of nostalgia and established that nostalgia bolsters social bonds, increases positive self-regard, and generates positive affect. These findings demarcate key landmarks in the hitherto uncharted research domain of nostalgi
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