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Search Results: 1 - 10 of 341482 matches for " William S. Anderson "
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Predicting single-neuron activity in locally connected networks
Feraz Azhar,William S. Anderson
Quantitative Biology , 2015, DOI: 10.1162/NECO_a_00343
Abstract: The characterization of coordinated activity in neuronal populations has received renewed interest in the light of advancing experimental techniques which allow recordings from multiple units simultaneously. Across both in vitro and in vivo preparations, nearby neurons show coordinated responses when spontaneously active, and when subject to external stimuli. Recent work (Truccolo, Hochberg, & Donoghue, 2010) has connected these coordinated responses to behavior, showing that small ensembles of neurons in arm related areas of sensorimotor cortex can reliably predict single-neuron spikes in behaving monkeys and humans. We investigate this phenomenon utilizing an analogous point process model, showing that in the case of a computational model of cortex responding to random background inputs, one is similarly able to predict the future state of a single neuron by considering its own spiking history, together with the spiking histories of randomly sampled ensembles of nearby neurons. This model exhibits realistic cortical architecture and displays bursting episodes in the two distinct connectivity schemes studied. We conjecture that the baseline predictability we find in these instances is characteristic of locally connected networks more broadly considered.
Electrical neurostimulation for chronic pain: on selective relay of sensory neural activities in myelinated nerve fibers
Pierre Sacré,Sridevi V. Sarma,Yun Guan,William S. Anderson
Quantitative Biology , 2015,
Abstract: Chronic pain affects about 100 million adults in the US. Despite their great need, neuropharmacology and neurostimulation therapies for chronic pain have been associated with suboptimal efficacy and limited long-term success, as their mechanisms of action are unclear. Yet current computational models of pain transmission suffer from several limitations. In particular, dorsal column models do not include the fundamental underlying sensory activity traveling in these nerve fibers. We developed a (simple) simulation test bed of electrical neurostimulation of myelinated nerve fibers with underlying sensory activity. This paper reports our findings so far. Interactions between stimulation-evoked and underlying activities are mainly due to collisions of action potentials and losses of excitability due to the refractory period following an action potential. In addition, intuitively, the reliability of sensory activity decreases as the stimulation frequency increases. This first step opens the door to a better understanding of pain transmission and its modulation by neurostimulation therapies.
15N Chemical Shifts in Energetic Materials: CP/MAS and ab Initio Studies of Aminonitropyridines, Aminonitropyrimidines, and Their N-Oxides
Karen L. Anderson,Lawrence H. Merwin,William S. Wilson,Julio C. Facelli
International Journal of Molecular Sciences , 2002, DOI: 10.3390/i3080858
Abstract: Solid state 15N NMR chemical shift measurements have been performed on a series of nitro- and amino-substituted nitrogen-containing heterocycles that are of interest as potential new insensitive explosives. Due to low solubilities, many of these compounds are not amenable to study by solution state methods. Theoretical calculations of 15N chemical shift parameters have been performed on the structures of interest and are reported herein. The calculated and experimental values are in good agreement. The use of a model that includes intermolecular effects and allows the proton positions of the nearest neighbors to be optimized leads to the best agreement between calculated and experimental values. The theoretical models accurately predict the effects of nitro and amino substituents on ringnitrogen chemical shifts, explaining a seeming reversal in trend that is noted in the pyridine and pyridine-1-oxide chemical shifts of the highly substituted compounds.
Decrease in gamma-band activity tracks sequence learning
Radhika Madhavan,Hanlin Tang,Nathan E. Crone,Frederick Lenz,Joseph Madsen,William S. Anderson
Frontiers in Systems Neuroscience , 2014, DOI: 10.3389/fnsys.2014.00222
Abstract: Learning novel sequences constitutes an important example of declarative memory formation. Performance in sequence learning tasks improves with repetition and involves forming temporal associations over scales of seconds to minutes. To further understand the neural circuits underlying declarative sequence learning over trials, we tracked changes in intracranial field potentials from 1142 electrodes in fourteen human subjects while they learned the temporal-order of multiple sequences over trials through repeated recall. We observed a decrease in power in the gamma frequency band (30-100Hz) in the recall phase during the course of learning over trials, particularly in areas within the temporal lobe. Gamma power was directly correlated with the improvement in recall performance and was reset when learning new sequences. The decrease in gamma frequency band amplitudes over trials may reflect the need for plasticity early in the learning process combined with relatively reduced levels of plasticity required to maintain learned memory traces.
Design Differences between the Pan-STARRS PS1 and PS2 Telescopes
Jeffrey S. Morgan,Nicholas Kaiser,Vincent Moreau,David Anderson,William Burgett
Physics , 2012, DOI: 10.1117/12.926646
Abstract: The PS2 telescope is the second in an array of wide-field telescopes that is being built for the Panoramic-Survey Telescope and Rapid Response System (Pan-STARRS) on Haleakala. The PS2 design has evolved incrementally based on lessons learned from PS1, but these changes should result in significant improvements in image quality, tracking performance in windy conditions, and reductions in scattered light. The optics for this telescope are finished save for their coatings and the fabrication for the telescope structure itself is well on the way towards completion and installation on-site late this year (2012). The most significant differences between the two telescopes include the following: secondary mirror support changes, improvements in the optical polishing, changes in the optical coatings to improve throughput and decrease ghosting, removal of heat sources inside the mirror cell, expansion of the primary mirror figure control system, changes in the baffle designs, and an improved cable wrap design. This paper gives a description of each of these design changes and discusses the motivations for making them.
A role for recurrent processing in object completion: neurophysiological, psychophysical and computational"evidence
Hanlin Tang,Calin Buia,Joseph Madsen,William S. Anderson,Gabriel Kreiman
Quantitative Biology , 2014, DOI: 10.1016/j.neuron.2014.06.017.
Abstract: Recognition of objects from partial information presents a significant challenge for theories of vision because it requires spatial integration and extrapolation from prior knowledge. We combined neurophysiological recordings in human cortex with psychophysical measurements and computational modeling to investigate the mechanisms involved in object completion. We recorded intracranial field potentials from 1,699 electrodes in 18 epilepsy patients to measure the timing and selectivity of responses along human visual cortex to whole and partial objects. Responses along the ventral visual stream remained selective despite showing only 9-25% of the object. However, these visually selective signals emerged ~100 ms later for partial versus whole objects. The processing delays were particularly pronounced in higher visual areas within the ventral stream, suggesting the involvement of additional recurrent processing. In separate psychophysics experiments, disrupting this recurrent computation with a backward mask at ~75ms significantly impaired recognition of partial, but not whole, objects. Additionally, computational modeling shows that the performance of a purely bottom-up architecture is impaired by heavy occlusion and that this effect can be partially rescued via the incorporation of top-down connections. These results provide spatiotemporal constraints on theories of object recognition that involve recurrent processing to recognize objects from partial information.
Sensitivity to Timing and Order in Human Visual Cortex
Jedediah M. Singer,Joseph R. Madsen,William S. Anderson,Gabriel Kreiman
Quantitative Biology , 2014,
Abstract: Visual recognition takes a small fraction of a second and relies on the cascade of signals along the ventral visual stream. Given the rapid path through multiple processing steps between photoreceptors and higher visual areas, information must progress from stage to stage very quickly. This rapid progression of information suggests that fine temporal details of the neural response may be important to the how the brain encodes visual signals. We investigated how changes in the relative timing of incoming visual stimulation affect the representation of object information by recording intracranial field potentials along the human ventral visual stream while subjects recognized objects whose parts were presented with varying asynchrony. Visual responses along the ventral stream were sensitive to timing differences between parts as small as 17 ms. In particular, there was a strong dependency on the temporal order of stimulus presentation, even at short asynchronies. This sensitivity to the order of stimulus presentation provides evidence that the brain may use differences in relative timing as a means of representing information.
Targeted treatment in COPD: a multi-system approach for a multi-system disease
David Anderson, William MacNee
International Journal of Chronic Obstructive Pulmonary Disease , 2009, DOI: http://dx.doi.org/10.2147/COPD.S2999
Abstract: rgeted treatment in COPD: a multi-system approach for a multi-system disease Review (6940) Total Article Views Authors: David Anderson, William MacNee Published Date August 2009 Volume 2009:4 Pages 321 - 335 DOI: http://dx.doi.org/10.2147/COPD.S2999 David Anderson1, William MacNee2 1South Glasgow University NHS Trust, Glasgow, UK; 2University of Edinburgh, UK Abstract: Chronic obstructive pulmonary disease is a varied condition when examined from a number of different perspectives including factors which influence disease development, pathological process and clinical features. There may be a complex interaction between the degree by which each of these processes influences the development of COPD and the subsequent clinical phenotype with which the patient presents. The varied host response and subsequent clinical phenotype has generated much interest in recent years. It is possible that failure of treatment to impact on mortality and reverse the disease process is because of the heterogeneous nature of the condition. Identification and targeted treatment of clinical and pathological phenotypes within the broad spectrum of COPD may therefore improve outcome. This article will review previous work which has attempted to phenotype COPD and identify if specific treatment for these phenotypes has been shown to be of benefit. It will examine the work on pathological processes and clinical manifestations, both pulmonary and systemic, and will focus on pharmacological therapies.
A new species of callaeum (malpighiaceae) from Puebla, Mexico
William R. Anderson
Acta botánica mexicana , 2006,
Abstract: Se describe e ilustra a Callaeum johnsonii (Malpighiaceae) como una nueva especie del estado mexicano de Puebla. Morfológicamente, C. johnsonii es similar a C. clavipetalum D. M. Johnson de Oaxaca, pero difiere en caracteres de las estípulas, hojas, brácteas y bractéolas.
Support of a Problem-Based Learning Curriculum by Basic Science Faculty
William L. Anderson
Medical Education Online , 2002,
Abstract: Although published reports describe benefits to students of learning in a problem-based, student-centered environment, questions have persisted about the excessive faculty time commitments associated with the implementation of PBL pedagogy. The argument has been put forward that the excessive faculty costs of such a curriculum cannot be justified based upon the potential benefits to students. However, the magnitude of the faculty time commitment to a PBL curriculum to support the aforementioned argument is not clear to us and we suspect that it is also equally unclear to individuals charged with making resource decisions supporting the educational efforts of the institution. Therefore, to evaluate this cost - benefit question, we analyzed the actual basic science faculty time commitment in a hybrid PBL curriculum during the first phase 18 months of undergraduate medical education. The results of this analysis do demonstrate an increase in faculty time commitments but do not support the argument that PBL pedagogy is excessively costly in terms of faculty time. For the year analyzed in this report, basic science faculty members contributed on average of 27.4 hours to the instruction of medical students. The results of the analysis did show significant contributions (57% of instructional time) by the clinical faculty during the initial 18 months of medical school. In addition, the data revealed a four-fold difference between time commitments of the four basic science departments. We conclude that a PBL curriculum does not place unreasonable demands on the time of basic science faculty. The demands on clinical faculty, in the context of their other commitments, could not be evaluated. Moreover, this type of analysis provides a tool that can be used to make faculty resource allocation decisions fairly.
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