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Search Results: 1 - 10 of 215 matches for " Mriganka Sur "
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The Emerging Role of microRNAs in Schizophrenia and Autism Spectrum Disorders
Nikolaos Mellios,Mriganka Sur
Frontiers in Psychiatry , 2012, DOI: 10.3389/fpsyt.2012.00039
Abstract: MicroRNAs (miRNAs) are small non-coding RNAs conserved throughout evolution whose perceived importance for brain development and maturation is increasingly being understood. Although a plethora of new discoveries have provided novel insights into miRNA-mediated molecular mechanisms that influence brain plasticity, their relevance for neuropsychiatric diseases with known deficits in synaptic plasticity, such as schizophrenia and autism, has not been adequately explored. In this review we discuss the intersection between current and old knowledge on the role of miRNAs in brain plasticity and function with a focus in the potential involvement of brain expressed miRNAs in the pathophysiology of neuropsychiatric disorders.
Sensory Adaptation and Short Term Plasticity as Bayesian Correction for a Changing Brain
Ian H. Stevenson,Beau Cronin,Mriganka Sur,Konrad P. Kording
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0012436
Abstract: Neurons in the sensory system exhibit changes in excitability that unfold over many time scales. These fluctuations produce noise and could potentially lead to perceptual errors. However, to prevent such errors, postsynaptic neurons and synapses can adapt and counteract changes in the excitability of presynaptic neurons. Here we ask how neurons could optimally adapt to minimize the influence of changing presynaptic neural properties on their outputs. The resulting model, based on Bayesian inference, explains a range of physiological results from experiments which have measured the overall properties and detailed time-course of sensory tuning curve adaptation in the early visual cortex. We show how several experimentally measured short term plasticity phenomena can be understood as near-optimal solutions to this adaptation problem. This framework provides a link between high level computational problems, the properties of cortical neurons, and synaptic physiology.
Denoising Two-Photon Calcium Imaging Data
Wasim Q. Malik,James Schummers,Mriganka Sur,Emery N. Brown
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0020490
Abstract: Two-photon calcium imaging is now an important tool for in vivo imaging of biological systems. By enabling neuronal population imaging with subcellular resolution, this modality offers an approach for gaining a fundamental understanding of brain anatomy and physiology. Proper analysis of calcium imaging data requires denoising, that is separating the signal from complex physiological noise. To analyze two-photon brain imaging data, we present a signal plus colored noise model in which the signal is represented as harmonic regression and the correlated noise is represented as an order autoregressive process. We provide an efficient cyclic descent algorithm to compute approximate maximum likelihood parameter estimates by combing a weighted least-squares procedure with the Burg algorithm. We use Akaike information criterion to guide selection of the harmonic regression and the autoregressive model orders. Our flexible yet parsimonious modeling approach reliably separates stimulus-evoked fluorescence response from background activity and noise, assesses goodness of fit, and estimates confidence intervals and signal-to-noise ratio. This refined separation leads to appreciably enhanced image contrast for individual cells including clear delineation of subcellular details and network activity. The application of our approach to in vivo imaging data recorded in the ferret primary visual cortex demonstrates that our method yields substantially denoised signal estimates. We also provide a general Volterra series framework for deriving this and other signal plus correlated noise models for imaging. This approach to analyzing two-photon calcium imaging data may be readily adapted to other computational biology problems which apply correlated noise models.
Dynamics of orientation tuning in cat V1 neurons depend on location within layers and orientation maps
James Schummers,Beau Cronin,Klaus Wimmer,Marcel Stimberg,Robert Martin,Klaus Obermayer,Konrad Koerding,Mriganka Sur
Frontiers in Neuroscience , 2007, DOI: 10.3389/neuro.01.1.1.011.2007
Abstract: Analysis of the timecourse of the orientation tuning of responses in primary visual cortex (V1) can provide insight into the circuitry underlying tuning. Several studies have examined the temporal evolution of orientation selectivity in V1 neurons, but there is no consensus regarding the stability of orientation tuning properties over the timecourse of the response. We have used reverse-correlation analysis of the responses to dynamic grating stimuli to re-examine this issue in cat V1 neurons. We find that the preferred orientation and tuning curve shape are stable in the majority of neurons; however, more than forty percent of cells show a significant change in either preferred orientation or tuning width between early and late portions of the response. To examine the influence of the local cortical circuit connectivity, we analyzed the timecourse of responses as a function of receptive field type, laminar position, and orientation map position. Simple cells are more selective, and reach peak selectivity earlier, than complex cells. There are pronounced laminar differences in the timing of responses: middle layer cells respond faster, deep layer cells have prolonged response decay, and superficial cells are intermediate in timing. The average timing of neurons near and far from pinwheel centers is similar, but there is more variability in the timecourse of responses near pinwheel centers. This result was reproduced in an established network model of V1 operating in a regime of balanced excitatory and inhibitory recurrent connections, confirming previous results. Thus, response dynamics of cortical neurons reflect circuitry based on both vertical and horizontal location within cortical networks.
Afferent specificity, feature specific connectivity influence orientation selectivity: A computational study in mouse primary visual cortex
Dipanjan Roy,Yenni Tjandra,Konstantin Mergenthaler,Jeremy Petravicz,Caroline A. Runyan,Nathan R. Wilson,Mriganka Sur,Klaus Obermayer
Quantitative Biology , 2013,
Abstract: Primary visual cortex (V1) provides crucial insights into the selectivity and emergence of specific output features such as orientation tuning. Tuning and selectivity of cortical neurons in mouse visual cortex is not equivocally resolved so far. While many in-vivo experimental studies found inhibitory neurons of all subtypes to be broadly tuned for orientation other studies report inhibitory neurons that are as sharply tuned as excitatory neurons. These diverging findings about the selectivity of excitatory and inhibitory cortical neurons prompted us to ask the following questions: (1) How different or similar is the cortical computation with that in previously described species that relies on map? (2) What is the network mechanism underlying the sharpening of orientation selectivity in the mouse primary visual cortex? Here, we investigate the above questions in a computational framework with a recurrent network composed of Hodgkin-Huxley (HH) point neurons. Our cortical network with random connectivity alone could not account for all the experimental observations, which led us to hypothesize, (a) Orientation dependent connectivity (b) Feedforward afferent specificity to understand orientation selectivity of V1 neurons in mouse. Using population (orientation selectivity index) OSI as a measure of neuronal selectivity to stimulus orientation we test each hypothesis separately and in combination against experimental data. Based on our analysis of orientation selectivity (OS) data we find a good fit of network parameters in a model based on afferent specificity and connectivity that scales with feature similarity. We conclude that this particular model class best supports data sets of orientation selectivity of excitatory and inhibitory neurons in layer 2/3 of primary visual cortex of mouse.
Ten_m3 Regulates Eye-Specific Patterning in the Mammalian Visual Pathway and Is Required for Binocular Vision
Catherine A. Leamey,Sam Merlin,Paul Lattouf,Atomu Sawatari,Xiaohong Zhou,Natasha Demel,Kelly A. Glendining,Toshitaka Oohashi,Mriganka Sur,Reinhard F?ssler
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.0050241
Abstract: Binocular vision requires an exquisite matching of projections from each eye to form a cohesive representation of the visual world. Eye-specific inputs are anatomically segregated, but in register in the visual thalamus, and overlap within the binocular region of primary visual cortex. Here, we show that the transmembrane protein Ten_m3 regulates the alignment of ipsilateral and contralateral projections. It is expressed in a gradient in the developing visual pathway, which is consistently highest in regions that represent dorsal visual field. Mice that lack Ten_m3 show profound abnormalities in mapping of ipsilateral, but not contralateral, projections, and exhibit pronounced deficits when performing visually mediated behavioural tasks. It is likely that the functional deficits arise from the interocular mismatch, because they are reversed by acute monocular inactivation. We conclude that Ten_m3 plays a key regulatory role in the development of aligned binocular maps, which are required for normal vision.
Ten_m3 Regulates Eye-Specific Patterning in the Mammalian Visual Pathway and Is Required for Binocular Vision
Catherine A Leamey ,Sam Merlin,Paul Lattouf,Atomu Sawatari,Xiaohong Zhou,Natasha Demel,Kelly A Glendining,Toshitaka Oohashi,Mriganka Sur,Reinhard F?ssler
PLOS Biology , 2007, DOI: 10.1371/journal.pbio.0050241
Abstract: Binocular vision requires an exquisite matching of projections from each eye to form a cohesive representation of the visual world. Eye-specific inputs are anatomically segregated, but in register in the visual thalamus, and overlap within the binocular region of primary visual cortex. Here, we show that the transmembrane protein Ten_m3 regulates the alignment of ipsilateral and contralateral projections. It is expressed in a gradient in the developing visual pathway, which is consistently highest in regions that represent dorsal visual field. Mice that lack Ten_m3 show profound abnormalities in mapping of ipsilateral, but not contralateral, projections, and exhibit pronounced deficits when performing visually mediated behavioural tasks. It is likely that the functional deficits arise from the interocular mismatch, because they are reversed by acute monocular inactivation. We conclude that Ten_m3 plays a key regulatory role in the development of aligned binocular maps, which are required for normal vision.
Artificial Neural Network for Performance Modeling and Optimization of CMOS Analog Circuits
Mriganka Chakraborty
Computer Science , 2012, DOI: 10.5120/9380-3731
Abstract: This paper presents an implementation of multilayer feed forward neural networks (NN) to optimize CMOS analog circuits. For modeling and design recently neural network computational modules have got acceptance as an unorthodox and useful tool. To achieve high performance of active or passive circuit component neural network can be trained accordingly. A well trained neural network can produce more accurate outcome depending on its learning capability. Neural network model can replace empirical modeling solutions limited by range and accuracy.[2] Neural network models are easy to obtain for new circuits or devices which can replace analytical methods. Numerical modeling methods can also be replaced by neural network model due to their computationally expansive behavior.[2][10][20]. The pro- posed implementation is aimed at reducing resource requirement, without much compromise on the speed. The NN ensures proper functioning by assigning the appropriate inputs, weights, biases, and excitation function of the layer that is currently being computed. The concept used is shown to be very effective in reducing resource requirements and enhancing speed.
Adult wilms′ tumor
Sharma Mriganka,Ahmed Mufiz
Saudi Journal of Kidney Diseases and Transplantation , 2009,
Abstract: Adult Wilms′ Tumor (AWT) is a rare entity arising from the metanephric blastema. There are only about 200 cases reported in world literature. The staging of AWT is done in the same way as in children according to the National Wilms′ Tumour Stage Group (NWTSG). Defini-tive treatment plans for AWT are undefined but surgical treatment has the highest priority. There is also consensus on the need for multimodality approach. We report a case of AWT who remains disease free, three years after undergoing multimodality treatment.
Measurement of the Transverse Single-Spin Asymmetries for $π^{0}$ and Jet-like Events at Forward Rapidities at STAR in $p+p$ Collisions at $\sqrt{s}$ = 500 GeV
Mriganka Mouli Mondal
Physics , 2014,
Abstract: Large transverse single-spin asymmetries ($A_N$) have been observed for forward inclusive hadron production in $p+p$ collisions at various experiments. In the collinear perturbative scattering picture, twist-3 multi-parton correlations can give rise to such an asymmetry. A transversely polarized quark can also give rise to a spin-dependent distribution of its hadron fragments via the higher twist effects or the Collins fragmentation function. The observed $A_N$ may involve contributions from both processes. These can be disentangled by studying asymmetries for jets, direct photons and jet-fragments. The STAR Forward Meson Spectrometer (FMS), a Pb-glass electromagnetic calorimeter covering the pseudo-rapidity ($\eta$) range 2.6-4.2 and full azimuth, can detect photons, neutral pions and eta mesons. We are measuring $A_N$ for $\pi^{0}$ and jet-like events reconstructed from photons in the FMS in $p+p$ collisions at $\sqrt{s}$ = 500 GeV that were recorded during the 2011 RHIC run. We study $A_N$ as a function of the number of observed photons in the FMS, thereby exploring asymmetries for a range of event classes. We further study $A_N$ for forward jets and its dependency on forward-midrapidity jet correlation. The current status of the analysis will be discussed.
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