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EXPERIMENTALISTS AND MODELERS - CAN WE ALL JUST GET ALONG

TRENDS IN NEUROSCIENCES 1992年第11期15卷 458-461页

作者： BOWER, JM KOCH, C Computation and Neural Systems Program California Institute of Technology Pasadena 91125.

How can the interaction between theoretical neuro-scientists and their experimental counterparts be improved? This article discusses a number of suggestions relating to the presentation of data in experimental studies. In particular, published data should account for the diversity of response properties encountered, rather than concentrating on the 'representative' response, as well as emphasizing the stochastic nature of neurons by routinely including raw, unprocessed data from individual trials, which show the degree of variability prior to averaging.

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Channel noise in excitable neuronal membranes

Channel noise in excitable neuronal membranes

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13th Annual neural Information Processing systems Conference, NIPS 1999

作者： Manwani, Amit Steinmetz, Peter N. Koch, Christof Computation and Neural Systems Program M-S 139-74 California Institute of Technology Pasadena CA 91125 United States

ISBN: (纸本)0262194503

Stochastic fluctuations of voltage-gated ion channels generate current and voltage noise in neuronal membranes. This noise may be a critical determinant of the efficacy of information processing within neural systems. Using Monte-Carlo simulations, we carry out a systematic investigation of the relationship between channel kinetics and the resulting membrane voltage noise using a stochastic Markov version of the Mainen-Sejnowski model of dendritic excitability in cortical neurons. Our simulations show that kinetic parameters which lead to an increase in membrane excitability (increasing channel densities, decreasing temperature) also lead to an increase in the magnitude of the sub-threshold voltage noise. Noise also increases as the membrane is depolarized from rest towards threshold. This suggests that channel fluctuations may interfere with a neuron's ability to function as an integrator of its synaptic inputs and may limit the reliability and precision of neural information processing.

关键词： Membranes

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TOWARD COLOR IMAGE SEGMENTATION IN ANALOG VLSI - ALGORITHM AND HARDWARE

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INTERNATIONAL JOURNAL OF COMPUTER VISION 1994年第1期12卷 17-42页

作者： PEREZ, F KOCH, C 1. Computation and Neural Systems Program 216-76 California Institute of Technology 91125 Pasadena CA

Standard techniques for segmenting color images are based on finding normalized RGB discontinuities, color histogramming, or clustering techniques in RGB or CIE color spaces. The use of the psychophysical variable hue in HSI space has not been popular due to its numerical instability at low saturations. In this article, we propose the use of a simplified hue description suitable for implementation in analog VLSI. We demonstrate that if the integrated white condition holds, hue is invariant to certain types of highlights, shading, and shadows. This is due to the additive/shift invariance property, a property that other color variables lack. The more restrictive uniformly varying lighting model associated with the multiplicative/scale invariance property shared by both hue and normalized RGB allows invariance to transparencies, and to simple models of shading and shadows. Using binary hue discontinuities in conjunction with first-order type of surface interpolation, we demonstrate these invariant properties and compare them against the performance of RGB, normalized RGB, and CIE color spaces. We argue that working in HSI space offers an effective method for segmenting scenes in the presence of confounding cues due to shading, transparency, highlights, and shadows. Based on this work, we designed and fabricated for the first time an analog CMOS VLSI circuit with on-board phototransistor input that computes normalized color and hue.

关键词： Color image processing

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THE MODULATION OF LEARNING STATE IN A BIOLOGICAL ASSOCIATIVE MEMORY - AN IN-VITRO, IN-VIVO, AND IN COMPUTO STUDY OF OBJECT RECOGNITION IN MAMMALIAN OLFACTORY CORTEX

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ARTIFICIAL INTELLIGENCE REVIEW 1993年第5期7卷 261-269页

作者： BOWER, JM 1. Division of Biology Computation and Neural Systems Program California Institute of Technology 91125 Pasadena CA

During learning of overlapping input patterns in an associative memory, recall of previously stored patterns can interfere with the learning of new patterns. Most associative memory models avoid this difficulty by ignoring the effect of previously modified connections during learning, by clamping network activity to the patterns to be learned. Through the interaction of experimental and modeling techniques, we now have evidence to suggest that a somewhat analogous approach may have been taken by biology within the olfactory cerebral cortex. Specifically we have recently discovered that the naturally occurring neuromodulator acetylcholine produces a variety of effects on cortical cells and circuits which, when taken together, can prevent memory interference in a biologically realistic memory model. Further, it has been demonstrated that these biological mechanisms can actually improve the memory storage performance of previously published abstract ''neural network'' associative memory models.

关键词： NEUROBIOLOGY OLFACTION ASSOCIATIVE MEMORY SIMULATIONS MODELING

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Adaptive Retina with Center-Surround Receptive Field 8

Adaptive Retina with Center-Surround Receptive Field

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8th International Conference on neural Information Processing systems, NIPS 1995

作者： Liu, Shih-Chii Boahen, Kwabena Computation and Neural Systems 139-74 California Institute of Technology PasadenaCA91125 United States

Both vertebrate and invertebrate retinas are highly efficient in extracting contrast independent of the background intensity over five or more decades. This efficiency has been rendered possible by the adaptation of the DC operating point to the background intensity while maintaining high gain transient responses. The centersurround properties of the retina allows the system to extract information at the edges in the image. This silicon retina models the adaptation properties of the receptors and the antagonistic centersurround properties of the laminar cells of the invertebrate retina and the outer-plexiform layer of the vertebrate retina. We also illustrate the spatio-temporal responses of the silicon retina on moving bars. The chip has 59x64 pixels on a 6.9x6.8mm'2 die and it is fabricated in 2 μm n-well technology. © NIPS 1995: Proceedings of the 8th International Conference on neural Information Processing systems. All rights reserved.

关键词： Transient analysis

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Contribution of somatosensory cortex to responses in the rat cerebellar granule cell layer following peripheral tactile stimulation

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EXPERIMENTAL BRAIN RESEARCH 1996年第2期109卷 240-250页

作者： Morissette, J Bower, JM Computation and Neural Systems Program Caltech 216-76 California Institute of Technology Pasadena USA

The spatial coincidence of somatosensory cerebral cortex (SI) and trigeminal projections to the cerebellar hemisphere has been previously demonstrated. In this paper we describe the temporal relationship between tactilely-evoked responses in SI and in the granule cell layer of the cerebellar hemisphere, in anesthetized rats. We simultaneously recorded field potentials in areas of common receptive fields of SI and of the cerebellar folium crus IIa after peripheral tactile stimulation of the corresponding facial area. Response of the cerebellar granule cell layer to a brief tactile stimulation consisted of two components at different latencies. We found a strong correlation between the latency of the SI response and that of the second (long-latency) cerebellar component following facial stimulation. No such relationship was found between the latency of the SI response and that of the first (short-latency) cerebellar component, originating from a direct trigeminocerebellar pathway. In addition, lidocaine pressure injection in SI, cortical ablation, and decerebration all significantly affected the second cerebellar peak but not the first. Further, when tactile stimuli were presented 75 ms apart, the response in SI failed, as did the second cerebellar peak, while the short-latency cerebellar response still occurred. We found a wide spatial distribution of the upper lip response beyond the upper lip area in crus IIa for the long-latency component of the cerebellar response. Our results demonstrate that SI is the primary contributor to the cerebellar long-latency response to peripheral tactile stimulation. These results are discussed in the context of Purkinje cell responses to tactile input.

关键词： field potential timing lidocaine somatosensory cerebral cortex crus Ila mossy fiber cerebellum rat

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Attentional modulation of human pattern discrimination psychophysics reproduced by a quantitative model

Attentional modulation of human pattern discrimination psych...

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12th Annual Conference on neural Information Processing systems, NIPS 1998

作者： Itti, Laurent Braun, Jochen Lee, Dale K. Koch, Christof Computation and Neural Systems MSC 139-74 California Institute of Technology Pasadena CA 91125 United States

ISBN: (纸本)0262112450

We previously proposed a quantitative model of early visual processing in primates, based on non-linearly interacting visual filters and statistically efficient decision. We now use this model to interpret the observed modulation of a range of human psychophysical thresholds with and without focal visual attention. Our model-calibrated by an automatic fitting procedure - simultaneously reproduces thresholds for four classical pattern discrimination tasks, performed while attention was engaged by another concurrent task. Our model then predicts that the seemingly complex improvements of certain thresholds, which we observed when attention was fully available for the discrimination tasks, can best be explained by a strengthening of competition among early visual filters.

关键词： Modulation

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A model of early visual processing

A model of early visual processing

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11th Annual Conference on neural Information Processing systems, NIPS 1997

作者： Itti, Laurent Braun, Jocheri Lee, Dale K. Koch, Christof Computation and Neural Systems California Institute of Technology MSG 139-74 Pasadena CA 91125 United States

ISBN: (纸本)0262100762

We propose a model for early visual processing in primates. The model consists of a population of linear spatial filters which interact through non-linear excitatory and inhibitory pooling. Statistical estimation theory is then used to derive human psychophysical thresholds from the responses of the entire population of units. The model is able to reproduce human thresholds for contrast and ori-entation discrimination tasks, and to predict contrast thresholds in the presence of masks of varying orientation and spatial frequency.

关键词： Mammals

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Distinct rhythmic locomotor patterns can be generated by a simple adaptive neural circuit: Biology, simulation, and VLSI implementation

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Journal of computational Neuroscience 1994年第4期1卷 339-358页

作者： Ryckebusch, Sylvie Wehr, Mike Laurent, Gilles California Institute ofTechnology Biology Division Computation and Neural Systems Program Pasadena 91125 CA Mail Code 139-74 United States

Rhythmic motor patterns can be induced in leg motor neurons of isolated locust thoracic ganglia by bath application of pilocarpine. We observed that the relative phases of levators and depressors differed in the three thoracic ganglia. Assuming that the central pattern generating circuits underlying these three segmental rhythms are probably very similar, we developed a simple model circuit that can produce any one of the three activity patterns and characteristic phase relationships by modifying a single synaptic weight. We show results of a computer simulation of this circuit using the neuronal simulator neuralOG/Spike. We built and tested an analog VLSI circuit implementation of this model circuit that exhibits the same range of "behaviors" as the computer simulation. This multidisciplinary strategy will be useful to explore the dynamics of central pattern generating networks coupled to physical actuators, and ultimately should allow the design of biologically realistic walking robots. © 1994 Kluwer Academic Publishers.

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BAYESIAN MODELING AND CLASSIFICATION OF neural SIGNALS

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neural computation 1994年第5期6卷 1005-1030页

作者： LEWICKI, MS Computation Neural Systems Program California Institute of Technology 216-76 Pasadena CA 91125 USA

Identifying and classifying action potential shapes in extracellular neural waveforms have long been the subject of research, and although several algorithms for this purpose have been successfully applied, their use has been limited by some outstanding problems. The first is how to determine shapes of the action potentials in the waveform and, second, how to decide how many shapes are distinct. A harder problem is that action potentials frequently overlap making difficult both the determination of the shapes and the classification of the spikes. In this report, a solution to each of these problems is obtained by applying Bayesian probability theory. By defining a probabilistic model of the waveform, the probability of both the form and number of spike shapes can be quantified. In addition, this framework is used to obtain an efficient algorithm for the decomposition of arbitrarily complex overlap sequences. This algorithm can extract many times more information than previous methods and facilitates the extracellular investigation of neuronal classes and of interactions within neuronal circuits.

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