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  • 1
    Electronic Resource
    Electronic Resource
    [s.l.] : Macmillan Magazines Ltd.
    Nature 391 (1998), S. 245-250 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The many distinct cortical areas of the macaque monkey visual system can be arranged hierarchically, but not in a unique way. We suggest that the connections between these cortical areas never form strong, directed loops. For connections between the visual cortex and particular thalamic nuclei, ...
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 385 (1997), S. 207-210 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Over the past few decades, neural networks have provided the dominant framework for understanding how the brain implements the computations necessary for its survival. At the heart of these networks are simplified and static models of nerve cells. But neuroscience is undergoing a revolution, and ...
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computational neuroscience 2 (1995), S. 63-82 
    ISSN: 1573-6873
    Keywords: voltage threshold ; current threshold ; action potential initiation ; integrate-and-fire models ; single cell models
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine , Physics
    Notes: Abstract The majority of neural network models consider the output of single neurons to be a continuous, positive, and saturating firing ratef(t), while a minority treat neuronal output as a series of delta pulses ∑δ (t — t i ). We here argue that the issue of the proper output representation relates to the biophysics of the cells in question and, in particular, to whether initiation of somatic action potentials occurs when a certain thresholdvoltage or a thresholdcurrent is exceeded. We approach this issue using numerical simulations of the electrical behavior of a layer 5 pyramidal cell from cat visual cortex. The dendritic tree is passive while the cell body includes eight voltage- and calcium-dependent membrane conductances. We compute both the steady-state (I ∞ static (V m )) and the instantaneous (I o (Vm)) I–V relationships and argue that the amplitude of the local maximum inI ∞ static (V m ) corresponds to the current thresholdI th for sustained inputs, while the location of the middle zero-crossing ofI o corresponds to a fixed voltage thresholdV th for rapid inputs. We confirm this using numerical simulations: for “rapid” synaptic inputs, spikes are initiated if the somatic potential exceedsV th, while for slowly varying inputI th must be exceeded. Due to the presence of the large dendritic tree, no charge thresholdQ th exists for physiological input. Introducing the temporal average of the somatic membrane potential 〈(V m)〉 while the cell is spiking repetitively, allows us to define a dynamic I-V relationship ∞ dynamic (〈(V m)〉). We find an exponential relationship between 〈(V m)〉 and the net current sunk by the somatic membrane during spiking (diode-like behavior). The slope ofI∞/dynamic(〈(V m))〉 allows us to define a dynamic input conductance and a time constant that characterizes how rapidly the cell changes its output firing frequency in response to a change in its input.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computational neuroscience 6 (1999), S. 169-184 
    ISSN: 1573-6873
    Keywords: extracellular field potential ; volume conduction ; branch point failure ; axon hillock/initial segment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Medicine , Physics
    Notes: Abstract Ephaptic interactions between a neuron and axons or dendrites passing by its cell body can be, in principle, more significant than ephaptic interactions among axons in a fiber tract. Extracellular action potentials outside axons are small in amplitude and spatially spread out, while they are larger in amplitude and much more spatially confined near cell bodies. We estimated the extracellular potentials associated with an action potential in a cortical pyramidal cell using standard one-dimensional cable theory and volume conductor theory. Their spatial and temporal pattern reveal much about the location and timing of currents in the cell, especially in combination with a known morphology, and simple experiments could resolve questions about spike initiation. From the extracellular potential we compute the ephaptically induced polarization in a nearby passive cable. The magnitude of this induced voltage can be several mV, does not spread electrotonically, and depends only weakly on the passive properties of the cable. We discuss their possible functional relevance.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Autonomous robots 7 (1999), S. 211-224 
    ISSN: 1573-7527
    Keywords: optomotor system ; analog VLSI ; optic flow ; motion detector ; insect vision
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Sensing visual motion gives a creature valuable information about its interactions with the environment. Flies in particular use visual motion information to navigate through turbulent air, avoid obstacles, and land safely. Mobile robots are ideal candidates for using this sensory modality to enhance their performance, but so far have been limited by the computational expense of processing video. Also, the complex structure of natural visual scenes poses an algorithmic challenge for extracting useful information in a robust manner. We address both issues by creating a small, low-power visual sensor with integrated analog parallel processing to extract motion in real-time. Because our architecture is based on biological motion detectors, we gain the advantages of this highly evolved system: A design that robustly and continuously extracts relevant information from its visual environment. We show that this sensor is suitable for use in the real world, and demonstrate its ability to compensate for an imperfect motor system in the control of an autonomous robot. The sensor attenuates open-loop rotation by a factor of 31 with less than 1 mW power dissipation.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 377 (1995), S. 294-295 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] CRICK AND KOCH REPLY — An unstated assumption in our thinking1 is that, in terms of neural 'computation', we make a distinction between the computations themselves and their results. A rough analogy would be between all the activity within a computer (the computations) and the results of ...
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 375 (1995), S. 121-123 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] It is usually assumed that people are visually aware of at least some of the neuronal activity in the primary visual area, V1, of the neocortex. But the neuroanatomy of the macaque monkey suggests that, although primates may be aware of neural activity in other visual cortical ...
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 381 (1996), S. 123-124 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE most famous twentieth-century philosophical treatise ends with the enigmatic invocation "Wovon man nicht sprechen kann, daruber mufl man schweigen" ("Whereof one cannot speak, thereof one must be silent"). David Chalmers has obviously considered these words as a challenge and has written a ...
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Analog integrated circuits and signal processing 13 (1997), S. 69-78 
    ISSN: 1573-1979
    Keywords: neuromorphic analog VLSI ; saccadic eye movements ; learning ; floating-gate ; short-term adaptation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: Abstract In this paper we describe an analog VLSI circuit, fabricatedusing a standard 2 µm, n-well, BiCMOS process,which utilizes floating-gate structures for non-volatile, on-chip,analog parameter storage. This circuit is designed to operatein the context of a hardware model of the primate oculomotorsystem and performs visually-guided, saccadic adaptation. Thechip contains a one-dimensional array of photoreceptors and floating-gatecircuits which are used to map retinal positions to motor outputcommands. The system's functionality is demonstrated by trainingthe chip with several different mapping functions using a supervised-learningtechnique.
    Type of Medium: Electronic Resource
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  • 10
    Book
    Book
    Oxford u.a. :Oxford University Pr.,
    Title: Biophysics of computation : information processing in single neurons
    Author: Koch, Christof
    Publisher: Oxford u.a. :Oxford University Pr.,
    Year of publication: 1999
    Pages: 562 S.
    Series Statement: Computational neuroscience
    Type of Medium: Book
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