Population- wide distributions of neural activity during perceptual decision-making. Cortical activity involves large populations of neurons, even when it is limited to functionally coherent areas. Electrophysiological recordings, on the other hand, involve comparatively small neural ensembles, even when modern-day techniques are used. Here we review results which have started to fill the gap between these two scales of inquiry, by shedding light on the statistical distributions of activity in large populations of cells.
We put our main focus on data recorded in awake animals that perform simple decision-making tasks and consider statistical distributions of activity throughout cortex, across sensory, associative, and motor areas. We transversally review the complexity of these distributionsfrom distributions of firing rates and metrics of spike-train structure, through distributions of tuning to stimuli or Ristea cristian asexual definition and of choice signals, and finally the dynamical evolution of neural population activity and the distributions of pairwise neural interactions.
This approach reveals shared patterns of statistical organization across cortex, including: We discuss how these insights are leading us away from the notion of discrete classes of cells, and are acting as powerful Ristea cristian asexual definition on theories and models of cortical organization and population coding.
Widely distributed SEP events and pseudostreamers. Our analysis of the pseudostreamer magnetic topology reveals new interesting implications for understanding SEP acceleration in CMEs. The possible reasons for the wide distribution Ristea cristian asexual definition some SEP events can be the presence of pseudostreamers in the vicinity of the SEP source region which creates conditions for the existence of strong longitudinal spread of energetic particles as well as an anomalous longitudinal solar wind magnetic field component.
We reconstructed the 3D magnetic configurations of pseudostreamers with a potential field source surface PFSS model, which uses as a lower boundary condition the magnetic field derived from an evolving surface-flux transport model. We found that in cases of the wide SEP distributions a specific configuration of magnetic field appears to exist at low solar latitudes all the way around the sun, we named this phenomenon a Ristea cristian asexual definition belt.
It appears that the presence of the well developed pseudostreamer or, rather multiple pseudostreamers, organized into the pseudostreamer belt can be considered as a very favorable condition for wide SEP events.
Combustion Mechanisms of Wide Distribution Propellants.
This paper describes the application of four evolutionary algorithms to the pruning of neural networks used in classification problems. Besides of a simple genetic algorithm GAthe paper considers three distribution estimation algorithms DEAs: The objective is to determine if the DEAs present advantages over the simple GA in terms of accuracy or speed in this problem. The experiments used a feed forward neural network trained with standard back propagation and public-domain and artificial data sets.
Only in a few cases, pruning resulted in less accurate networks. We found few differences in the accuracy of the networks pruned by the four EAs, but found important differences in the execution time.
The results suggest that a simple GA with a small population might be the best algorithm for pruning Ristea cristian asexual definition on the data sets we tested. Distributed memory approaches for robotic neural controllers.
The suitability is explored of two varieties of distributed memory neutral networks as trainable controllers for a Ristea cristian asexual definition robotics task. The task requires that two cameras observe an arbitrary target point in space.
Coordinates of the target on the camera image planes are passed to a neural controller which must learn to solve the inverse kinematics of a manipulator with one revolute and two prismatic joints.
Two new network designs are evaluated. The first, radial basis sparse distributed memory RBSDMapproximates functional mappings as sums of multivariate gaussians centered around previously learned patterns. In these networks, random N dimensional points are given local connectivities.
They are then exposed to training patterns and readjust their locations based on a nearest neighbor rule. Both approaches are tested based on their ability to interpolate manipulator joint coordinates for simulated arm movement while simultaneously performing stereo fusion of the camera data.
Comparisons are made with classical k-nearest neighbor pattern recognition techniques. The Internet is a unique medium for the distribution of information, and it provides a tremendous opportunity to take advantage of peoples innate interest in transportation issues as they relate to their own lives. In particular, the World Wide Web Periodic bidirectional associative memory neural networks with distributed delays.
Some sufficient conditions are obtained for the existence and global exponential stability of a periodic solution to the general bidirectional associative memory BAM Ristea cristian asexual definition networks with distributed delays by using the continuation theorem of Mawhin's coincidence degree theory and the Lyapunov functional method and the Young's inequality technique.
These results helpful for designing a globally exponentially stable and periodic oscillatory BAM neural network, and the conditions can be easily verified and be applied in practice. An example is also given to illustrate our results. Wide -field optical mapping of neural activity and brain haemodynamics: Ma, Ying; Shaik, Mohammed A.
Although modern techniques such as two-photon microscopy can now provide cellular-level three-dimensional imaging of the intact living brain, the speed and fields of view of these techniques remain limited.
Conversely, two-dimensional wide -field optical mapping WFOMa simpler technique that uses a camera to observe large areas of the exposed cortex under visible light, can detect changes in both neural activity and haemodynamics at very high speeds. Although WFOM may not provide single-neuron or capillary-level resolution, it is an attractive and accessible approach to imaging large areas of the brain in awake, behaving mammals at speeds fast enough to observe widespread neural firing events, as well as their dynamic coupling to haemodynamics.
Although such wide -field optical imaging techniques have a long history, the advent of genetically encoded fluorophores that can report neural activity with high sensitivity, as well as Ristea cristian asexual definition technologies such as light emitting diodes and sensitive and high-speed digital cameras have driven Ristea cristian asexual definition interest in WFOM.
To facilitate the wider adoption and standardization of WFOM approaches for neuroscience and neurovascular coupling research, we provide here an overview of the basic principles of WFOM, considerations for implementation of wide -field fluorescence imaging of neural activity, spectroscopic analysis and interpretation of results.
Hadoop neural network for parallel and distributed feature selection. In this paper, we introduce a theoretical for a Hadoop-based neural network for parallel and distributed feature selection in Big Data sets.
It is underpinned by an associative memory binary neural network which is highly amenable to parallel and distributed processing and fits with the Hadoop paradigm. There are many feature selectors described in the literature which all have various strengths and weaknesses. We present the implementation details of five feature selection algorithms constructed using our artificial neural network framework embedded in Hadoop YARN.
Hadoop allows parallel and distributed processing. Each feature selector can be divided into subtasks and the subtasks can then be processed in parallel. Multiple feature selectors can also be processed simultaneously in parallel allowing multiple feature selectors to be compared. We identify commonalities among the five features selectors. All can be processed in the framework using a single representation and the overall processing can also be "Ristea cristian asexual definition" reduced by only processing the common aspects of the feature selectors once and propagating these aspects across all five feature selectors as necessary.
This allows the best feature selector and the actual features to select to be identified for and high dimensional data sets through exploiting the efficiency and flexibility of embedding the binary associative-memory neural network in Hadoop.
Published by Elsevier Ltd. Distributed neural control of a hexapod walking vehicle. There has been a long standing interest in the design of controllers for multilegged vehicles. The approach is to apply distributed control to this problem, rather than using parallel computing of a centralized algorithm.
Researchers describe a distributed neural network controller for hexapod locomotion is based on the neural control of locomotion in insects. The model considers the simplified kinematics with two degrees of freedom per leg, but the model includes the static stability constraint.