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Search Results: 1 - 10 of 328136 matches for " Craig S. Henriquez "
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Emergent bursting and synchrony in computer simulations of neuronal cultures
Niru Maheswaranathan,Silvia Ferrari,Craig S. Henriquez
Frontiers in Computational Neuroscience , 2012, DOI: 10.3389/fncom.2012.00015
Abstract: Experimental studies of neuronal cultures have revealed a wide variety of spiking network activity ranging from sparse, asynchronous firing to distinct, network-wide synchronous bursting. However, the functional mechanisms driving these observed firing patterns are not well understood. In this work, we develop an in silico network of cortical neurons based on known features of similar in vitro networks. The activity from these simulations is found to closely mimic experimental data. Furthermore, the strength or degree of network bursting is found to depend on a few parameters: the density of the culture, the type of synaptic connections, and the ratio of excitatory to inhibitory connections. Network bursting gradually becomes more prominent as either the density, the fraction of long range connections, or the fraction of excitatory neurons is increased. Interestingly, biologically prevalent values of parameters result in networks that are at the transition between strong bursting and sparse firing. Using principal components analysis, we show that a large fraction of the variance in firing rates is captured by the first component for bursting networks. These results have implications for understanding how information is encoded at the population level as well as for why certain network parameters are ubiquitous in cortical tissue.
An Explicit Space-time Adaptive Method for Simulating Complex Cardiac Dynamics
Elizabeth M. Cherry,Henry S. Greenside,Craig S. Henriquez
Physics , 1999, DOI: 10.1103/PhysRevLett.84.1343
Abstract: For plane-wave and many-spiral states of the experimentally based Luo-Rudy 1 model of heart tissue in large (8 cm square) domains, we show that an explicit space-time-adaptive time-integration algorithm can achieve an order of magnitude reduction in computational effort and memory - but without a reduction in accuracy - when compared to an algorithm using a uniform space-time mesh at the finest resolution. Our results indicate that such an explicit algorithm can be extended straightforwardly to simulate quantitatively large-scale three-dimensional electrical dynamics over the whole human heart.
Unscented Kalman Filter for Brain-Machine Interfaces
Zheng Li, Joseph E. O'Doherty, Timothy L. Hanson, Mikhail A. Lebedev, Craig S. Henriquez, Miguel A. L. Nicolelis
PLOS ONE , 2009, DOI: 10.1371/journal.pone.0006243
Abstract: Brain machine interfaces (BMIs) are devices that convert neural signals into commands to directly control artificial actuators, such as limb prostheses. Previous real-time methods applied to decoding behavioral commands from the activity of populations of neurons have generally relied upon linear models of neural tuning and were limited in the way they used the abundant statistical information contained in the movement profiles of motor tasks. Here, we propose an n-th order unscented Kalman filter which implements two key features: (1) use of a non-linear (quadratic) model of neural tuning which describes neural activity significantly better than commonly-used linear tuning models, and (2) augmentation of the movement state variables with a history of n-1 recent states, which improves prediction of the desired command even before incorporating neural activity information and allows the tuning model to capture relationships between neural activity and movement at multiple time offsets simultaneously. This new filter was tested in BMI experiments in which rhesus monkeys used their cortical activity, recorded through chronically implanted multielectrode arrays, to directly control computer cursors. The 10th order unscented Kalman filter outperformed the standard Kalman filter and the Wiener filter in both off-line reconstruction of movement trajectories and real-time, closed-loop BMI operation.
A binary method for simple and accurate two-dimensional cursor control from EEG with minimal subject training
Turan A Kayagil, Ou Bai, Craig S Henriquez, Peter Lin, Stephen J Furlani, Sherry Vorbach, Mark Hallett
Journal of NeuroEngineering and Rehabilitation , 2009, DOI: 10.1186/1743-0003-6-14
Abstract: We tested the paradigm with four healthy subjects, none of whom had prior BCI experience. Each subject played a game wherein he or she attempted to move a cursor to a target within a grid while avoiding a trap. We also present supplementary results including one healthy subject using motor imagery, one primary lateral sclerosis (PLS) patient, and one healthy subject using a single EEG channel without Laplacian derivation.For the four healthy subjects using real hand movement, the system provided accurate cursor control with little or no required user training. The average accuracy of the cursor movement was 86.1% (SD 9.8%), which is significantly better than chance (p = 0.0015). The best subject achieved a control accuracy of 96%, with only one incorrect bit classification out of 47. The supplementary results showed that control can be achieved under the respective experimental conditions, but with reduced accuracy.The binary method provides na?ve subjects with real-time control of a cursor in 2-D using dichotomous classification of synchronous EEG band power readings from a small number of channels during hand movement. The primary strengths of our method are simplicity of hardware and software, and high accuracy when used by untrained subjects.Interfaces which interpret user brain activity to effect some output have potential applications to many fields, including aiding individuals with disabilities to control devices and communicate. There are several different approaches to creating brain-computer interfaces (BCIs). The most invasive method involves single-unit recording, where arrays of implanted electrodes are used to record trains of action potentials from individual neurons. Single-unit recordings have been used successfully to provide fairly sophisticated control [1]. Implantation of the electrodes, however, requires surgery, and a practical clinical implementation of single-unit recordings will require methods that can telemeter the data without transcuta
Learning to Control a Brain–Machine Interface for Reaching and Grasping by Primates
Jose M. Carmena,Mikhail A. Lebedev,Roy E. Crist,Joseph E. O'Doherty,David M. Santucci,Dragan F. Dimitrov,Parag G. Patil,Craig S. Henriquez,Miguel A. L. Nicolelis
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.0000042
Abstract: Reaching and grasping in primates depend on the coordination of neural activity in large frontoparietal ensembles. Here we demonstrate that primates can learn to reach and grasp virtual objects by controlling a robot arm through a closed-loop brain–machine interface (BMIc) that uses multiple mathematical models to extract several motor parameters (i.e., hand position, velocity, gripping force, and the EMGs of multiple arm muscles) from the electrical activity of frontoparietal neuronal ensembles. As single neurons typically contribute to the encoding of several motor parameters, we observed that high BMIc accuracy required recording from large neuronal ensembles. Continuous BMIc operation by monkeys led to significant improvements in both model predictions and behavioral performance. Using visual feedback, monkeys succeeded in producing robot reach-and-grasp movements even when their arms did not move. Learning to operate the BMIc was paralleled by functional reorganization in multiple cortical areas, suggesting that the dynamic properties of the BMIc were incorporated into motor and sensory cortical representations.
Learning to Control a Brain–Machine Interface for Reaching and Grasping by Primates
Jose M Carmena,Mikhail A Lebedev,Roy E Crist,Joseph E O'Doherty,David M Santucci,Dragan F Dimitrov,Parag G Patil,Craig S Henriquez,Miguel A. L Nicolelis
PLOS Biology , 2003, DOI: 10.1371/journal.pbio.0000042
Abstract: Reaching and grasping in primates depend on the coordination of neural activity in large frontoparietal ensembles. Here we demonstrate that primates can learn to reach and grasp virtual objects by controlling a robot arm through a closed-loop brain–machine interface (BMIc) that uses multiple mathematical models to extract several motor parameters (i.e., hand position, velocity, gripping force, and the EMGs of multiple arm muscles) from the electrical activity of frontoparietal neuronal ensembles. As single neurons typically contribute to the encoding of several motor parameters, we observed that high BMIc accuracy required recording from large neuronal ensembles. Continuous BMIc operation by monkeys led to significant improvements in both model predictions and behavioral performance. Using visual feedback, monkeys succeeded in producing robot reach-and-grasp movements even when their arms did not move. Learning to operate the BMIc was paralleled by functional reorganization in multiple cortical areas, suggesting that the dynamic properties of the BMIc were incorporated into motor and sensory cortical representations.
Terrorist Attacks on Non-Governmental Organizations  [PDF]
Craig S. Stapley
Open Journal of Political Science (OJPS) , 2014, DOI: 10.4236/ojps.2014.44029
Abstract: Understanding the process by which terrorist groups decide on whom to target would seem to be a process that might lend itself to study and generalization that would be helpful in predicting later attacks. This study hopes to look at the attacks on non-governmental organizations and determine if there is a systematic set of measures that would allow us to determine if terrorist groups do rationally approach target selection in such a way to derive a pattern that would inform future attack avoidance.
Influencia del empaque y envasado sobre las propiedades fisicoquímicas del hongo comestible Pleurotus ostreatus
Misael Cortés R.,Marilza Ruiz R.,Luís Henriquez,Luís Henriquez
Revista MVZ Córdoba , 2011,
Abstract: Objetivo. Evaluar la influencia de diferentes empaques y atmósferas sobre las propiedades fisicoquímicas del hongo comestible Pleurotus ostreatus. Materiales y métodos. Los hongos fueron almacenados durante 15 días a 4oC, utilizando tres empaques: 1) espuma de poliestireno con película de recubrimiento de polivinil cloruro (empaque comercial), 2) Polietilentereftalato con películas de recubrimiento de polipropileno biorientado y 3) polietileno de baja densidad y tres atmósferas de envasado: 1) Aire, 2) 100% N2 y 3) 10% O2, 10% CO2 y 80% N2. Después de almacenados se derminaron los posibles cambios de las variables fisicoquímicas (pH, acidez, °Brix, humedad, cloruros, color y textura) Resultados. Las muestras presentaron diferencias estadísticas en los parámetros fisicoquímicos del hongo fresco por efecto de los factores tiempo, empaque y atmósfera. Los rangos de variación se consideraron aceptables debido a las características propias del producto, como ente biológico que continua con sus procesos metabólicos. Los cambios de color en las condiciones de control (Grupo 1: Empacado Comercial y Grupo 1: Atmósfera Aire) no fueron muy acentuados, siendo instrumentalmente más apreciable, sin llegar a serlo para el observador. La textura en todos los casos presentó una disminución en la resistencia mecánica, debido a los posibles procesos fermentativos y al deterioro por la alta tasa metabólica. Conclusiones. Los resultados permiten identificar que no hubo un efecto apreciable del empaque y de las atmósferas modificadas en las propiedades fisicoquímicas del hongo Pleurotus ostreatus, lo que hace que el empaque comercial sea más práctico por efecto de costos de producción.
Influencia del empaque y envasado sobre las propiedades fisicoquímicas del hongo comestible Pleurotus ostreatus
Cortés R,Misael; Ruiz R,Marilza; Henriquez,Luís;
Revista MVZ Córdoba , 2011,
Abstract: objective. to determine the effect of different packings and modified atmospheres on the physiochemical properties of a comestible mushroom (pleurotus ostreatus) in fresh state. materials and methods. mushrooms were stored at 4°c during 15 days, using three different forms of packings: 1) polyestiren foam with polyvinyl chloride film cover (commercial packing), 2) polyethylene terephthalate with polypropylene bioriented film cover and 3) polyethylene of low density film cover and three different atmospheres: 1) air, 2) 100% n2 and 3) 10% o2, 10% co2, and 80% n2. after stored possible changes in the physicochemical variables (ph, acidity, °brix, moisture, chlorides, color and texture were determined. results. there was an effect of time, packing and atmosphere on the physiochemical properties of fresh mushrooms. the range of variations was considered acceptable due to the characteristics of the mushrooms, such as biological entity that continuous with their metabolic processes. the changes in color (group1: commercial packing and group 1: air stored) were not very appreciable, for the observer in all groups. the texture presented a decrease in the mechanical resistance, these may be due to the possible fermentative processes and deterioration for the high metabolic rate. conclusions. there was not an appreciable effect of packing and environmental atmospheric conditions on the physiochemical properties of the mushroom pleurotus ostreatus. it was also found that the commercial packing is more practical by issues of production costs.
Secado de Cajuil (anacardium occidentale l. ): Estudio Experimental y Modelado de la Cinética de Secado
Michalewicz,Jacek S; Henriquez,Jorge R; Charamba,José C;
Información tecnológica , 2011, DOI: 10.4067/S0718-07642011000600007
Abstract: the drying kinetics of sliced cashew ( anacardium occidentale l.) has been experimentally studied. samples of 4, 7 and 10 x 10-3 m thick were used. a laboratory tray type dryer was employed and air at temperatures in the range 60 to 80 ° c and velocity from 3 to 5 m/s were imposed. the moisture content profile in the sample with respect to drying time was measured. eleven mathematical models available in the literature were applied to determine which of the model is the best one in correlating the experimental data. the results indicate that the model of page is the most adequate due to its simplicity for relating the moisture content and the variables temperature and drying air velocity.
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