Output Neurons (output + neuron)

Distribution by Scientific Domains


Selected Abstracts


Inversion of time-dependent nuclear well-logging data using neural networks

GEOPHYSICAL PROSPECTING, Issue 1 2008
Laura Carmine
ABSTRACT The purpose of this work was to investigate a new and fast inversion methodology for the prediction of subsurface formation properties such as porosity, salinity and oil saturation, using time-dependent nuclear well logging data. Although the ultimate aim is to apply the technique to real-field data, an initial investigation as described in this paper, was first required; this has been carried out using simulation results from the time-dependent radiation transport problem within a borehole. Simulated neutron and ,-ray fluxes at two sodium iodide (NaI) detectors, one near and one far from a pulsed neutron source emitting at ,14 MeV, were used for the investigation. A total of 67 energy groups from the BUGLE96 cross section library together with 567 property combinations were employed for the original flux response generation, achieved by solving numerically the time-dependent Boltzmann radiation transport equation in its even parity form. Material property combinations (scenarios) and their correspondent teaching outputs (flux response at detectors) are used to train the Artificial Neural Networks (ANNs) and test data is used to assess the accuracy of the ANNs. The trained networks are then used to produce a surrogate model of the expensive, in terms of computational time and resources, forward model with which a simple inversion method is applied to calculate material properties from the time evolution of flux responses at the two detectors. The inversion technique uses a fast surrogate model comprising 8026 artificial neural networks, which consist of an input layer with three input units (neurons) for porosity, salinity and oil saturation; and two hidden layers and one output neuron representing the scalar photon or neutron flux prediction at the detector. This is the first time this technique has been applied to invert pulsed neutron logging tool information and the results produced are very promising. The next step in the procedure is to apply the methodology to real data. [source]


Multiple functions of GABAA and GABAB receptors during pattern processing in the zebrafish olfactory bulb

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2008
Rico Tabor
Abstract ,-Aminobutyric acid (GABA)ergic synapses are thought to play pivotal roles in the processing of activity patterns in the olfactory bulb (OB), but their functions have been difficult to study during odor responses in the intact system. We pharmacologically manipulated GABAA and GABAB receptors in the OB of zebrafish and analysed the effects on odor responses of the output neurons, the mitral cells (MCs), by electrophysiological recordings and temporally deconvolved two-photon Ca2+ imaging. The blockade of GABAB receptors enhanced presynaptic Ca2+ influx into afferent axon terminals, and changed the amplitude and time course of a subset of MC responses, indicating that GABAB receptors have a modulatory influence on OB output activity. The blockade of GABAA receptors induced epileptiform firing, enhanced excitatory responses and abolished fast oscillations in the local field potential. Moreover, the topological reorganization and decorrelation of MC activity patterns during the initial phase of the response was perturbed. These results indicate that GABAA receptor-containing circuits participate in the balance of excitation and inhibition, the regulation of total OB output activity, the synchronization of odor-dependent neuronal ensembles, and the reorganization of odor-encoding activity patterns. GABAA and GABAB receptors are therefore differentially involved in multiple functions of neuronal circuits in the OB. [source]


Neuronal representation of odourants in the olfactory bulb of Xenopus laevis tadpoles

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2003
Dirk Czesnik
Abstract When an odourant enters the nose, olfactory receptor neurons (ORNs) convey information about it to the olfactory bulb (OB), where this information is processed and where the first central representations of the odourant are generated. In this paper we show how odourants are represented by ensembles of OB neurons, in particular mitral cells (MCs) which are the output neurons of the OB. We were able to demonstrate for the first time that the intracellular calcium concentrations ([Ca2+]i) in the somata of these neurons undergo specific changes and that different stimuli are represented by different neuronal [Ca2+]i patterns. The similarity of patterns was assessed by cross-correlation analysis. We further show that noradrenaline (NA), which is reported to be involved in olfactory memory formation and to modulate synaptic transmission at dendrodendritic synapses in the OB, profoundly changes the representation of odourants at the level of MCs. [source]


Analysis of the function of GABAB receptors on inhibitory afferent neurons of Purkinje cells in the cerebellar cortex of the rat

EUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2002
Marta Than
Abstract Purkinje cells, the output neurons of the cerebellar cortex, receive inhibitory input from basket, stellate and neighbouring Purkinje cells. The aim of the present study was to clarify the role of GABAB receptors on neurons giving inhibitory input to Purkinje cells. In sagittal slices prepared from the cerebellar vermis of the rat, the GABAB receptor agonist baclofen lowered the frequency and amplitude of spontaneous inhibitory postsynaptic currents (IPSCs) recorded in Purkinje cells. These effects were prevented by the GABAB receptor antagonist CGP 55845. Two mechanisms were involved in the depression of the inhibitory input to Purkinje cells. The first mechanism was suppression of the firing of basket, stellate and Purkinje cells. The second mechanism was presynaptic inhibition of GABA release from terminals of the afferent axons. This was indicated by the finding that baclofen decreased the amplitude of IPSCs occurring in Purkinje cells synchronously with action potentials recorded in basket cells. A further support for the presynaptic inhibition is the observation that baclofen decreased the amplitude of autoreceptor currents which are due to activation of GABAA autoreceptors at axon terminals of basket cells by synaptically released GABA. The presynaptic inhibition was partly due to direct inhibition of the vesicular release mechanism, because baclofen lowered the frequency of miniature IPSCs recorded in Purkinje cells in the presence of cadmium and in the presence of tetrodotoxin plus ionomycin. The results show that activation of GABAB receptors decreased GABAA receptor-mediated synaptic input to cerebellar Purkinje cells both by lowering the firing rate of the inhibitory input neurons and by inhibiting GABA release from their axon terminals with a presynaptic mechanism. [source]


Central control of thermogenesis in mammals

EXPERIMENTAL PHYSIOLOGY, Issue 7 2008
Shaun F. Morrison
Thermogenesis, the production of heat energy, is an essential component of the homeostatic repertoire to maintain body temperature in mammals and birds during the challenge of low environmental temperature and plays a key role in elevating body temperature during the febrile response to infection. The primary sources of neurally regulated metabolic heat production are mitochondrial oxidation in brown adipose tissue, increases in heart rate and shivering in skeletal muscle. Thermogenesis is regulated in each of these tissues by parallel networks in the central nervous system, which respond to feedforward afferent signals from cutaneous and core body thermoreceptors and to feedback signals from brain thermosensitive neurons to activate the appropriate sympathetic and somatic efferents. This review summarizes the research leading to a model of the feedforward reflex pathway through which environmental cold stimulates thermogenesis and discusses the influence on this thermoregulatory network of the pyrogenic mediator, prostaglandin E2, to increase body temperature. The cold thermal afferent circuit from cutaneous thermal receptors ascends via second-order thermosensory neurons in the dorsal horn of the spinal cord to activate neurons in the lateral parabrachial nucleus, which drive GABAergic interneurons in the preoptic area to inhibit warm-sensitive, inhibitory output neurons of the preoptic area. The resulting disinhibition of thermogenesis-promoting neurons in the dorsomedial hypothalamus and possibly of sympathetic and somatic premotor neurons in the rostral ventromedial medulla, including the raphe pallidus, activates excitatory inputs to spinal sympathetic and somatic motor circuits to drive thermogenesis. [source]


On estimation of the number of image principal colors and color reduction through self-organized neural networks

INTERNATIONAL JOURNAL OF IMAGING SYSTEMS AND TECHNOLOGY, Issue 3 2002
A. Atsalakis
A new technique suitable for reduction of the number of colors in a color image is presented in this article. It is based on the use of the image Principal Color Components (PCC), which consist of the image color components and additional image components extracted with the use of proper spatial features. The additional spatial features are used to enhance the quality of the final image. First, the principal colors of the image and the principal colors of each PCC are extracted. Three algorithms were developed and tested for this purpose. Using Kohonen self-organizing feature maps (SOFM) as classifiers, the principal color components of each PCC are obtained and a look-up table, containing the principal colors of the PCC, is constructed. The final colors are extracted from the look-up table entries through a SOFM by setting the number of output neurons equal to the number of the principal colors obtained for the original image. To speed up the entire algorithm and reduce memory requirements, a fractal scanning subsampling technique is employed. The method is independent of the color scheme; it is applicable to any type of color images and can be easily modified to accommodate any type of spatial features. Several experimental and comparative results exhibiting the performance of the proposed technique are presented. © 2002 Wiley Periodicals, Inc. Int J Imaging Syst Technol 12, 117,127, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.10019 [source]


Memory effects description by neural networks with delayed feedback connections

INTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 4 2004
Petia D. Koprinkova
For the purpose of dynamic systems modeling, it was proposed to include feedback connections or delay elements in the classical feed-forward neural network structure so that the present output of the neural network depends on its previous values. These delay elements can be connected to the hidden and/or output neurons of the main neural network. Each delay element gets a value of a state variable at a past time instant and keeps this value during a single sampling period. The groups of delay elements record the values of the state variables for a given time period in the past. Changing the number of the delay elements, which belongs to one group, a shorter or a longer time period in the past can be accounted for. Thus, the connection weights determine the influence of the past process states on the present state in a similar way as it is in the time delay kernel or cause-effect relation membership function (CER-MF) models. Specific feed-forward neural networks with time delay connections are used to solve the problem of neural network chemostat modeling as well as specific kinetic rates modeling. The weights of the feedback connections obtained during model training are discussed as the points of a time delay kernel or as the strength levels in a CER model (the points in the CER-MF). The corresponding changes in these weights with the changing time period in the past are shown. © 2004 Wiley Periodicals, Inc. [source]


Changes in the connections of the main olfactory bulb after mitral cell selective neurodegeneration

JOURNAL OF NEUROSCIENCE RESEARCH, Issue 11 2007
Javier S. Recio
Abstract The connections of the main olfactory bulb (OB) of the mouse were studied with iontophoretic injections of biotinylated dextran amine. To sort efferences from mitral cells and tufted cells, the Purkinje cell degeneration (PCD) mouse was used. This mutant animal undergoes a specific neurodegeneration of mitral cells, whereas tufted cells do not degenerate. The unilateral tracer injections used were small and confined largely to the OB of both PCD and control mice at P120. Seven days after tracer injection, the efferences from the OB and the centrifugal afferences from secondary olfactory structures to it were studied. Although there is a large overlap of their target fields, mitral cell axons innervated more caudal regions of the olfactory cortex than tufted cell axons, thus providing definitive evidence of the differential projections of olfactory output neurons. Additionally, an important increase in retrogradely-labeled neurons was detected in the ipsilateral anterior olfactory nucleus of the mutant animals. This was not observed in any other secondary olfactory structure, suggesting a strengthening of the centrifugal input to the OB from that central area after mitral cell loss. Moreover, we recorded a complete loss of bilaterality in the olfactory connections of the PCD mice due to degeneration of the anterior commissure. These results point to an important reorganization of this essential olfactory circuit between the anterior olfactory nucleus and the OB, and hint at a transsynaptic level of plasticity not considered previously in literature. © 2007 Wiley-Liss, Inc. [source]


Comparative cellular distribution of GABAA and GABAB receptors in the human basal ganglia: Immunohistochemical colocalization of the ,1 subunit of the GABAA receptor, and the GABABR1 and GABABR2 receptor subunits

THE JOURNAL OF COMPARATIVE NEUROLOGY, Issue 4 2004
Henry J. Waldvogel
Abstract The GABAB receptor is a G-protein linked metabotropic receptor that is comprised of two major subunits, GABABR1 and GABABR2. In this study, the cellular distribution of the GABABR1 and GABABR2 subunits was investigated in the normal human basal ganglia using single and double immunohistochemical labeling techniques on fixed human brain tissue. The results showed that the GABAB receptor subunits GABABR1 and GABABR2 were both found on the same neurons and followed the same distribution patterns. In the striatum, these subunits were found on the five major types of interneurons based on morphology and neurochemical labeling (types 1, 2, 3, 5, 6) and showed weak labeling on the projection neurons (type 4). In the globus pallidus, intense GABABR1 and GABABR2 subunit labeling was found in large pallidal neurons, and in the substantia nigra, both pars compacta and pars reticulata neurons were labeled for both receptor subunits. Studies investigating the colocalization of the GABAA ,1 subunit and GABAB receptor subunits showed that the GABAA receptor ,1 subunit and the GABABR1 subunit were found together on GABAergic striatal interneurons (type 1 parvalbumin, type 2 calretinin, and type 3 GAD neurons) and on neurons in the globus pallidus and substantia nigra pars reticulata. GABABR1 and GABABR2 were found on substantia nigra pars compacta neurons but the GABAA receptor ,1 subunit was absent from these neurons. The results of this study provide the morphological basis for GABAergic transmission within the human basal ganglia and provides evidence that GABA acts through both GABAA and GABAB receptors. That is, GABA acts through GABAB receptors, which are located on most of the cell types of the striatum, globus pallidus, and substantia nigra. GABA also acts through GABAA receptors containing the ,1 subunit on specific striatal GABAergic interneurons and on output neurons of the globus pallidus and substantia nigra pars reticulata. J. Comp. Neurol. 470:339,356, 2004. © 2004 Wiley-Liss, Inc. [source]


Comparison of Artificial Neural Networks with Partial Least Squares Regression for Simultaneous Determinations by ICP-AES

CHINESE JOURNAL OF CHEMISTRY, Issue 11 2007
Mohamad KHAYATZADEH MAHANI
Abstract Simultaneous determination of several elements (U, Ta, Mn, Zr and W) with inductively coupled plasma atomic emission spectrometry (ICP-AES) in the presence of spectral interference was performed using chemometrics methods. True comparison between artificial neural network (ANN) and partial least squares regression (PLS) for simultaneous determination in different degrees of overlap was investigated. The emission spectra were recorded at uranium analytical line (263.553 nm) with a 0.06 nm spectral window by ICP-AES. Principal component analysis was applied to data and scores on 5 dominant principal components were subjected to ANN. A 5-5-5 (input, hidden and output neurons) network was used with linear transfer function after both hidden and output layers. The PLS model was trained with five latent variables and 20 samples in calibration set. The relative errors of predictions (REP) in test set were 3.75% and 3.56% for ANN and PLS respectively. [source]