44,320 research outputs found
A computational study on altered theta-gamma coupling during learning and phase coding
There is considerable interest in the role of coupling between theta and gamma oscillations in the brain in the context of learning and memory. Here we have used a neural network model which is capable of producing coupling of theta phase to gamma amplitude firstly to explore its ability to reproduce reported learning changes and secondly to memory-span and phase coding effects. The spiking neural network incorporates two kinetically different GABAA receptor-mediated currents to generate both theta and gamma rhythms and we have found that by selective alteration of both NMDA receptors and GABAA,slow receptors it can reproduce learning-related changes in the strength of coupling between theta and gamma either with or without coincident changes in theta amplitude. When the model was used to explore the relationship between theta and gamma oscillations, working memory capacity and phase coding it showed that the potential storage capacity of short term memories, in terms of nested gamma-subcycles, coincides with the maximal theta power. Increasing theta power is also related to the precision of theta phase which functions as a potential timing clock for neuronal firing in the cortex or hippocampus
A Computational Predictor of Human Episodic Memory Based on a Theta Phase Precession Network
In the rodent hippocampus, a phase precession phenomena of place cell firing with the local field potential (LFP) theta is called “theta phase precession” and is considered to contribute to memory formation with spike time dependent plasticity (STDP). On the other hand, in the primate hippocampus, the existence of theta phase precession is unclear. Our computational studies have demonstrated that theta phase precession dynamics could contribute to primate–hippocampal dependent memory formation, such as object–place association memory. In this paper, we evaluate human theta phase precession by using a theory–experiment combined analysis. Human memory recall of object–place associations was analyzed by an individual hippocampal network simulated by theta phase precession dynamics of human eye movement and EEG data during memory encoding. It was found that the computational recall of the resultant network is significantly correlated with human memory recall performance, while other computational predictors without theta phase precession are not significantly correlated with subsequent memory recall. Moreover the correlation is larger than the correlation between human recall and traditional experimental predictors. These results indicate that theta phase precession dynamics are necessary for the better prediction of human recall performance with eye movement and EEG data. In this analysis, theta phase precession dynamics appear useful for the extraction of memory-dependent components from the spatio–temporal pattern of eye movement and EEG data as an associative network. Theta phase precession may be a common neural dynamic between rodents and humans for the formation of environmental memories
3D Object Recognition Based On Constrained 2D Views
The aim of the present work was to build a novel 3D object recognition system capable of classifying
man-made and natural objects based on single 2D views. The approach to this problem
has been one motivated by recent theories on biological vision and multiresolution analysis. The
project's objectives were the implementation of a system that is able to deal with simple 3D
scenes and constitutes an engineering solution to the problem of 3D object recognition, allowing
the proposed recognition system to operate in a practically acceptable time frame.
The developed system takes further the work on automatic classification of marine phytoplank-
(ons, carried out at the Centre for Intelligent Systems, University of Plymouth. The thesis discusses
the main theoretical issues that prompted the fundamental system design options. The
principles and the implementation of the coarse data channels used in the system are described.
A new multiresolution representation of 2D views is presented, which provides the classifier
module of the system with coarse-coded descriptions of the scale-space distribution of potentially
interesting features. A multiresolution analysis-based mechanism is proposed, which directs
the system's attention towards potentially salient features. Unsupervised similarity-based
feature grouping is introduced, which is used in coarse data channels to yield feature signatures
that are not spatially coherent and provide the classifier module with salient descriptions of object
views. A simple texture descriptor is described, which is based on properties of a special wavelet
transform.
The system has been tested on computer-generated and natural image data sets, in conditions
where the inter-object similarity was monitored and quantitatively assessed by human subjects,
or the analysed objects were very similar and their discrimination constituted a difficult task even
for human experts. The validity of the above described approaches has been proven. The studies
conducted with various statistical and artificial neural network-based classifiers have shown that
the system is able to perform well in all of the above mentioned situations. These investigations
also made possible to take further and generalise a number of important conclusions drawn during
previous work carried out in the field of 2D shape (plankton) recognition, regarding the behaviour
of multiple coarse data channels-based pattern recognition systems and various classifier
architectures.
The system possesses the ability of dealing with difficult field-collected images of objects and
the techniques employed by its component modules make possible its extension to the domain
of complex multiple-object 3D scene recognition. The system is expected to find immediate applicability
in the field of marine biota classification
A Bayesian approach to the estimation of maps between riemannian manifolds
Let \Theta be a smooth compact oriented manifold without boundary, embedded
in a euclidean space and let \gamma be a smooth map \Theta into a riemannian
manifold \Lambda. An unknown state \theta \in \Theta is observed via
X=\theta+\epsilon \xi where \epsilon>0 is a small parameter and \xi is a white
Gaussian noise. For a given smooth prior on \Theta and smooth estimator g of
the map \gamma we derive a second-order asymptotic expansion for the related
Bayesian risk. The calculation involves the geometry of the underlying spaces
\Theta and \Lambda, in particular, the integration-by-parts formula. Using this
result, a second-order minimax estimator of \gamma is found based on the modern
theory of harmonic maps and hypo-elliptic differential operators.Comment: 20 pages, no figures published version includes correction to eq.s
31, 41, 4
ABJM -Bremsstrahlung at four loops and beyond
In ABJ(M) theory a generalized cusp can be constructed out of the 1/6 BPS
Wilson line by introducing an angle in the spacial contour and/or an
angle in the internal R-symmetry space. The small angles limits of its
anomalous dimension are controlled by corresponding Bremsstrahlung functions.
In this note we compute the internal space -Bremsstrahlung function to
four loops at weak coupling in the planar limit. Based on this result, we
propose an all order conjecture for the -Bremsstrahlung function.Comment: 40 pages; v2: references added, JHEP published extended versio
The Noncommutative Doplicher-Fredenhagen-Roberts-Amorim Space
This work is an effort in order to compose a pedestrian review of the
recently elaborated Doplicher, Fredenhagen, Roberts and Amorim (DFRA)
noncommutative (NC) space which is a minimal extension of the DFR space. In
this DRFA space, the object of noncommutativity () is a
variable of the NC system and has a canonical conjugate momentum. The DFRA
formalism is constructed in an extended space-time with independent degrees of
freedom associated with the object of noncommutativity . A
consistent algebra involving the enlarged set of canonical operators is
described, which permits one to construct theories that are dynamically
invariant under the action of the rotation group. A consistent classical
mechanics formulation is analyzed in such a way that, under quantization, it
furnishes a NC quantum theory with interesting results. The Dirac formalism for
constrained Hamiltonian systems is considered and the object of
noncommutativity plays a fundamental role as an independent
quantity. It is also explained about the generalized Dirac equation issue, that
the fermionic field depends not only on the ordinary coordinates but on
as well. The dynamical symmetry content of such fermionic
theory is discussed, and we show that its action is invariant under . In the last part of this work we analyze the complex scalar fields using
this new framework. As said above, in a first quantized formalism,
and its canonical momentum are seen as
operators living in some Hilbert space. In a second quantized formalism
perspective, we show an explicit form for the extended Poincar\'e generators
and the same algebra is generated via generalized Heisenberg relations. We also
consider a source term and construct the general solution for the complex
scalar fields using the Green function technique
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