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At least 1,693 records · Page 94

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NASA NTRS1983

What does the eye see best?

The quantum efficiency of the human eye is measured for detecting a wide variety of spatiotemporal patterns using foveal vision in bright light. The performance of an ideal visual detector whose weighting function is matched to the signal is analyzed in the abstract, and the conditions of a two-interval forced-choice experiment are described. The best stimulus found is a small, briefly exposed circular patch of sinusoidal grating having a spatial frequency of about 7 c/deg, drifting at about 4 Hz. It is proposed that this is the weighting function of the most efficient human contrast detector. This function resembles the receptive field sensitivity profiles of many cortical neurons. The detectors resemble those derived from other recent experiments on both detection and discrimination and may account for a broad range of previous psychophysical results.

Watson, A. B.↗

NASA NTRS1984

Presynaptic elements involved in the maintenance of the neuromuscular junction

Alterations in the neuromuscular junction were observed in rats preceding loss of muscle mass. In view of the possibility that these alterations involve changes in the secretion of myotrophic agents by presynaptic motor neurons, an investigation was undertaken to characterize a neuronall factor which is thought to be involved in the initiation and maintenance of cholinergic synapses. This factor, which is secreted into the incubation medium by NG108-15 neuroblastoma x glioma hybrid cells, induces the aggregation of nicotinic acetylcholine receptors on primary cultures of rat hindlimb myotubes. Previous attempts to purify this factor failed. Extensive washing of the NG108-15 cells with hepes-buffered salt solution followed by short (4 hour) collection times resulted in the collection of incubation medium containing maximal aggregation activity with as little as 5 ug secreted protein per ml of fresh medium. A three-fold increase in specific activity was obtained after anion exchange chromatography.

Burrows, G. H.↗

NASA NTRS1984

Bioassay, isolation and studies on the mechanism of action of neurite extension factor

The identification and purification of molecules active in promoting neurite outgrowth requires a sensitive reproducible bioassay. A quantitative bioassay was utilized to purify a neurite extension factor (NEF) based on counting the number of phase bright neurons with processes at least equal to one cell body diameter after 20 hrs. in culture is defined, serum free medium. Using a combination of heat treatment DEAE cellulose chromatography and gel filtration, an acidic protein of M sub r = 75,000 was highly purified. Upon reduction, it yields subunits of M sub r = 37,000. Purified fractions are active half maximally at 100 ng/ml in inducing neurite outgrowth in this bioassay. Currently, monoclonal antibodies to NEF are being produced. Female Balb C mice were immunized with the antigen and fusions with mouse myeloma cells will be performed to yield hybridoma cells.

Kligman, D.↗

NASA NTRS1984

ERPS to Monitor Non-conscious Mentation

Event Related Brain Potentials (or ERPs) are extracted from the EEG that can be recorded between a pair of electrodes placed on a person's scalp. The EEG is recorded as a continual fluctuation in voltage. It is the results of the integration of the potential fields generated by a multitude of neuronal ensembles that are active as the brain goes about its business. Within this ongoing signal it is possible to distinguish voltage fluctuations that are triggered in neural structures by the occurrence of specific events. This activity, evoked as it is by an external event, is known as the Evoked, or Event Related, Potential. The ERPs provide a unique opportunity to monitor non-conscious mentation. The inferences that can be based on ERP data are described and the limits of these inferences are emphasized. This, however, will not be an exhaustive review of the use of ERPs in Engineering Psychology. The application, its scope, and its limitations will be illustrated by means of one example. This example is preceded by a brief technical introduction to the methodology used in the study of ERPs. The manner in which ERPs are used to study cognition is described.

Donchin, E.↗

NASA NTRS1985

Neural Mechanism by which Gravitational Stimuli and Stress Affect the Secretion of Renin and Other Hormones

The serotonin-releasing drug p-chloroamphetamine (PCA), as well as L-propranolol and chloriasondamine were used in a study which established that the pathway from the hypothalamus to the kidneys is sympathetic. Which hypothalamic nuclei mediate the response to PCA is being investigated experiments are being conducted to determine a readily reproducible psychological stimulus to renin secretion that can be used in rats. The effects of equithesin, urethane, and inactin on plasma renin activity were examined in preparation for tilting experiments. The relation of vasopressin-secreting neurons in the brain sem to PCA response was explored in Brattleboro rats that are congenitally unable to produce vasopressin in their hypothalami.

Ganong, W. F.↗

NASA NTRS1985

Coupling functions for lead and lead-free neutron monitors from the latitudinal measurements performed in 1982 in the research station Academician Kurchatov

The latitudinal behavior of intensities and multiplicities was registered by the neutron monitor 2 NM and the lead-free neutron monitor 3 SND (slow-neuron detector) in the equator-Kaliningrad line in the Atlantic Ocean. Coupling coefficients for 3 SND show the sensitivity of this detector to primary particles of cosmic rays of energies on the average lower than for 2 NM. As multiplicities increase, the coupling coefficients shift towards higher energies.

Alekanyan, T. M.↗

NASA NTRS1983

Tyrosine administration enhances dopamine synthesis and release in light-activated rat retina

Exposure of dark-adapted albino rats to light (350 lux) significantly elevated retinal levels of the dopamine metabolite dihydroxyphenyl acetic acid during the next hour; their return to a dark environment caused dihydroxyphenyl acetic acid levels to fall. Retinal dopamine levels were increased slightly by light exposure, suggesting that the increase in dihydroxyphenyl acetic acid reflected accelerated dopamine synthesis. Administration of tyrosine (100 mg/kg, i.p.) further elevated retinal dihydroxyphenyl acetic acid among light-exposed animals, but failed to affect dopamine release among animals in the dark. These observations show that a physiological stimulus - light exposure - can cause catecholaminergic neurons to become tyrosine-dependent; they also suggest that food consumption may affect neurotransmitter release within the retina.

Gibson, C. J.↗

NASA NTRS1985

Simulated hypogravity and synaptogenesis in culture

A study on the effects of simulated microgravity on spinal neurons and myocytes cultured from X. laevis, is performed. Horizontal clinorotation at 1-10 rpm lasted from 16-36 hours, a sufficient time for cells to proceed through ontogenetic maturation. Late appearance of striations, retarded consumpton of yolk platelets and fewer and thinner neurites indicate subnormal expression of cell functions. Furthermore, these cells do not respond normally to environmental cues like trophic substances or surface contact. The observed delay in cell maturation is consistent with a hypothesis that cellular graviperception may effect the centriole and cytoskeleton.

Gruener, R.↗

NASA NTRS1986

Vestibular system and neural correlates of motion sickness

Initial studies re-examine the role of certain central nervous system structures in the production of vestibular-induced vomiting and vomiting in general. All experiments were conducted using cats. Since these studies demonstrated that the essential role of various central structures in vestibular-induced vomiting is only poorly understood, efforts were re-directed to study the control of the effector muscles (diaphragm and abdominal muscles) that produce the pressure changes responsible for vomiting, with the goal of determining how this control mechanism is engaged during motion sickness. Experiments were conducted to localize the motoneurons that innervate the individual abdominal muscles and the portion of the diaphragm that surrounds the esophagus. A central question regarding respiratory muscle control during vomiting is whether these muscles are activated via the same brain stem pre-motor neurons that provide descending respiratory drive and/or by other descending input(s). In other experiments, the use of a combination of pitch and roll motions to produce motion sickness in unrestrained cats was evaluated. This stimulus combination can produce vomiting in only the most susceptible cats and is thus not as provacative a stimulus for cats as vertical linear acceleration.

Miller, Alan D.↗

NASA NTRS1986

Axoglial contacts in the area postrema of the cat - An ultrastructural study

Axoglial contacts were observed in an ultrastructural study of the area postrema of the cat. According to the disposition of the electron-dense projections attached to the adjoining membranes these contacts were classified as symmetrical or asymmetrical. The axon profiles contained aggregations of clear vesicles randomly distributed or grouped in clusters adjacent to the electron-dense projections. Dense core vesicles were occasionally seen. The neuroglial profiles were either astrocytic or ependymoglial in nature. The astrocytes showed a clear cytoplasm, polymorphous vesicles, mitochondria, glycogen granules, and bundles of filaments. The ependymal cells, in contrast, had a more electron-dense and granular appearance, tubular structures, irregular vesicular formations, profiles of smooth reticuloendoplasm, and filaments grouped in bundles or isolated in the cytoplasm. The possibility that these contacts might play a role in the chemical transfer from neurons to glial cells is discussed on the basis of existing biochemical data.

Damelio, Fernando E.↗

NASA NTRS1987

Electronic implementation of associative memory based on neural network models

An electronic embodiment of a neural network based associative memory in the form of a binary connection matrix is described. The nature of false memory errors, their effect on the information storage capacity of binary connection matrix memories, and a novel technique to eliminate such errors with the help of asymmetrical extra connections are discussed. The stability of the matrix memory system incorporating a unique local inhibition scheme is analyzed in terms of local minimization of an energy function. The memory's stability, dynamic behavior, and recall capability are investigated using a 32-'neuron' electronic neural network memory with a 1024-programmable binary connection matrix.

Moopenn, A.↗

NASA NTRS1986

Morphometric studies of heavy ion damage in the brains of rodents

The relative biological effectiveness (RBE) of different heavy ions for the mammalian brain was determined in mice irradiated at 100 days of age with He-4, C-12, Ne-20, Fe-56, Ar-40, or Co-60 gamma photons (with the primary particle LET values ranging from 2 to 650). Brain preparations were examined 16 months later for volume changes in the external plexiform layer (P-zone) of the olfactory bulb and an internal region (G-zone), which consists of the granule cells, the internal plexiform layer, and the mitral cell layer. The result indicate that the volume changes did occur in the olfactory bulb, not only in absolute terms but also when expressed as the ratio of the structures to each other and to the bulb as a whole. While the observed increased neuronal loss in mice receiving 700 cGy of Co-60 support the earlier data from irradiated rabbits, the increases observed in bulbar volumes and in the volume ratios of the P and the G zones measured in the mice given lower doses (320 or 160 cGy of He or C), were not expected.

Kraft, L. M.↗

NASA NTRS1988

Integrated Circuit For Simulation Of Neural Network

Ballast resistors deposited on top of circuit structure. Cascadable, programmable binary connection matrix fabricated in VLSI form as basic building block for assembly of like units into content-addressable electronic memory matrices operating somewhat like networks of neurons. Connections formed during storage of data, and data recalled from memory by prompting matrix with approximate or partly erroneous signals. Redundancy in pattern of connections causes matrix to respond with correct stored data.

Thakoor, Anilkumar P.↗

NASA NTRS1988

Orthogonal patterns in binary neural networks

A binary neural network that stores only mutually orthogonal patterns is shown to converge, when probed by any pattern, to a pattern in the memory space, i.e., the space spanned by the stored patterns. The latter are shown to be the only members of the memory space under a certain coding condition, which allows maximum storage of M=(2N) sup 0.5 patterns, where N is the number of neurons. The stored patterns are shown to have basins of attraction of radius N/(2M), within which errors are corrected with probability 1 in a single update cycle. When the probe falls outside these regions, the error correction capability can still be increased to 1 by repeatedly running the network with the same probe.

Baram, Yoram↗

NASA NTRS1987

The cortex transform - Rapid computation of simulated neural images

With a goal of providing means for accelerating the image processing, machine vision, and testing of human vision models, an image transform was designed, which makes it possible to map an image into a set of images that vary in resolution and orientation. Each pixel in the output may be regarded as the simulated response of a neuron in human visual cortex. The transform is amenable to a number of shortcuts that greatly reduce the amount of computation.

Watson, Andrew B.↗

NASA NTRS1987

Optimization of the computational load of a hypercube supercomputer onboard a mobile robot

A combinatorial optimization methodology is developed, which enables the efficient use of hypercube multiprocessors onboard mobile intelligent robots dedicated to time-critical missions. The methodology is implemented in terms of large-scale concurrent algorithms based either on fast simulated annealing, or on nonlinear asynchronous neural networks. In particular, analytic expressions are given for the effect of single-neuron perturbations on the systems' configuration energy. Compact neuromorphic data structures are used to model effects such as precedence constraints, processor idling times, and task-schedule overlaps. Results for a typical robot-dynamics benchmark are presented.

Barhen, Jacob↗

NASA NTRS1987

A neurocomputer based on an analog-digital hybrid architecture

A novel analog-digital hybrid architecture based on the utilization of high density digital random access memories for the storage of the synaptic weights of a neural network, and high speed analog hardware to perform neural computation is described. An electronic neurocomputer based on such an architecture is ideally suited for investigating the dynamics, associative recall properties, and computational capabilities of neural networks and provides significant speed improvement in comparison to conventional software based neural network simulations. As a demonstration of the feasibility of the hybrid architectural concept, a prototype breadboard hybrid neurocomputer system with 32 neurons has been designed and fabricated with off-the-shelf hardware components. The performance of the breadboard system has been tested for variety of applications including associative memory and combinatorial problem solving such as Graph Coloring, and is discussed in this paper.

Moopenn, A.↗

NASA NTRS1988

On the stability, storage capacity, and design of nonlinear continuous neural networks

The stability, capacity, and design of a nonlinear continuous neural network are analyzed. Sufficient conditions for existence and asymptotic stability of the network's equilibria are reduced to a set of piecewise-linear inequality relations that can be solved by a feedforward binary network, or by methods such as Fourier elimination. The stability and capacity of the network is characterized by the post synaptic firing rate function. An N-neuron network with sigmoidal firing function is shown to have up to 3N equilibrium points. This offers a higher capacity than the (0.1-0.2)N obtained in the binary Hopfield network. Moreover, it is shown that by a proper selection of the postsynaptic firing rate function, one can significantly extend the capacity storage of the network.

Guez, Allon↗