Historically, taste research has often been guided by the concept that there are only four (or possibly five) basic taste qualities (sweet, sour, salty, and bitter, and possibly "umami"). All other tastes ha...
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Historically, taste research has often been guided by the concept that there are only four (or possibly five) basic taste qualities (sweet, sour, salty, and bitter, and possibly "umami"). All other tastes have been presumed to be combinations of these basic tastes. This psychophysical concept has been extended to electrophysiological data. That is, the neural code for each basic taste is hypothesized to be coded by a dedicated channel of neurons (the "Labeled-Line'' theory);i.e., one group of neurons signals "salty" and another separate group signals ''sweet." Numerous psychophysical and electrophysiological findings, however, cannot be accomodated by this quadripartite theory, which limits taste to four basic qualities and four basic neuron types. Rather, the data described in this article suggest that the range of taste is more extensive than four or five basic tastes, and that this breadth of taste quality results initially from the activation of a broad array of ion channels, receptors, and second messengers associated with taste cell membranes. These findings have implications for neural organization and provide support for the "Across-Fiber Pattern" theory in which the neural code for taste is represented by the pattern of activity across all of the neurons, i.e., neurons are not exclusively labeled for a particular sensation but cooperate with the others in the ensemble to encode taste quality. (C) 2000 Elsevier Science Inc. All rights reserved.
During normal vision, when subjects attempt to fix their gaze on a small stimulus feature, small fixational eye movements persist. We have recorded the impulse activity of single neurons in primary visual cortex (V1) ...
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During normal vision, when subjects attempt to fix their gaze on a small stimulus feature, small fixational eye movements persist. We have recorded the impulse activity of single neurons in primary visual cortex (V1) of macaque monkeys while their fixational eye movements moved the receptive-field activating region (AR) over and around a stationary stimulus. Three types of eye movement activation were found. (1) Saccade cells discharged when a Fixation:ll saccade moved the AR onto the stimulus, off the stimulus, or across the stimulus. (2) Position/drift calls discharged during the intersaccadic (drift) intervals and were not activated by saccades that swept the AR across the stimulus without remaining on it. To activate these neurons, it was essential that the AR be placed on the stimulus and many of these cells were selective for the sign of contrast. They had smaller ARs than the other cell types. (3) Mixed cells fired bursts of activity immediately following saccades and continued to fire at a lower rate during intersaccadic intervals. The tendency of each neuron to fire transient bursts or sustained trains of impulses following saccades was strongly correlated with the transiency of its response to stationary flashed stimuli. For one monkey, an extraretinal influence accompanying fixational saccades was identified. During natural viewing, the different eye movement classes probably make different contributions to visual processing. Position/drift neurons are well suited for coding spatial details of the visual scene because of their small AR size and their selectivity for sign of contrast and retinal position. However, saccade neurons transmit information that is ambiguous with respect to the spatial details of the retinal image because they are activated whether the AR lands on a stimulus contour, or the AR leaves or crosses the contour and lands in another location. Saccade neurons may be involved in constructing a stable world in spite of incessant retinal i
A brief review of the evolution of hypotheses about neural coding in the chemical senses provides some perspective on the current status of these fields, and implications for further development. (C) 2000 Elsevier Sci...
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A brief review of the evolution of hypotheses about neural coding in the chemical senses provides some perspective on the current status of these fields, and implications for further development. (C) 2000 Elsevier Science Inc. All rights reserved.
The history of viewing spike trains as point processes along time is that of the inference that spike trains participate in neural codings. A characteristic thought process, the "Conceptual Framework", prese...
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The history of viewing spike trains as point processes along time is that of the inference that spike trains participate in neural codings. A characteristic thought process, the "Conceptual Framework", present always and with sequential components, upholds the logic of this view. Early research in the 1920's introduced the view: experiments, though largely primitive, were designed and interpreted adequately and thus demonstrated convincingly this role. Modern research, starting around 1950, has contributed impressively. Essential was the mathematical Theory of Point Processes that permitted rigorous studies;computer implementation, though no substitute for clear thinking, was enormously helpful. Contributions, besides confirming the key inference, include wide-range train participation in neural codings, with many courses of action and formal implications involving neuronal performances individually and in networks, discharge forms, dynamic behaviors, critical Information and Communication issues, etc. (C) 2009 Elsevier Ltd. All rights reserved.
The broad responsiveness of single taste fibers to different classes of chemical stimuli has provided strong evidence against interpretations according to the classical doctrine of quality-specific fiber types. An alt...
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The broad responsiveness of single taste fibers to different classes of chemical stimuli has provided strong evidence against interpretations according to the classical doctrine of quality-specific fiber types. An alternative suggested by Pfaffmann was later developed as an "across-fiber patterning'' model by Erickson. Rats were found able to behaviorally discriminate among taste stimuli in accord with predictions based on comparing the responses of many single fibers to several different stimuli;with many fibers responding to a particular stimulus, the differential responsiveness of each fiber to a number of stimuli thus appeared to be the basis for encoding stimulus quality. The replicability and generality of Erickson''s finding was tested using the Virginia opossum as an experimental subject;a behavioral measure suitable to this species was developed for the purpose. The results are in aggrement with those obtained from rats and offer evidence for the generality of across-fiber pattern coding in mammalian gustation. Although certain differences appear in comparing single fiber data from rat and opossum, results of a "neural response function" analysis do not suggest any fundamental differences in the gustatory coding mechanisms of the 2 species.
Cracking the neural code has long been a central issue in neuroscience. However, it has been proved difficult because there logically exist an infinite number of other models and interpretations that could account for...
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Cracking the neural code has long been a central issue in neuroscience. However, it has been proved difficult because there logically exist an infinite number of other models and interpretations that could account for the same data and phenomena (i.e. the problem of underdetermination). Therefore, I suggest that applying biologically realistic multiple constraints from ion-channel level to system level (e.g. cognitive neuroscience and human brain disorders) can only solve the problem of underdetermination. Here I have explored whether the noise shaping/predictive neural coding hypothesis can provide a unified view on following realistic multiple constraints: (1) cortical gain control mechanisms in vivo;(2) the relationships between acetylcholine, nicotine, dopamine, calcium-activated potassium ion-channel, and cognitive functions;(3) oscillations and synchrony;(4) why should spontaneous activity be irregular;(5) whether the cortical neurons in vivo are coincidence detectors or integrators;and (6) the causal relationship between theta oscillation, gamma band fluctuation, and P3 (or P300) ERP responses. Finally, recent experimental results supporting the unified view shall be discussed. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.
This communication introduces the topic. Foundations: Core concepts: codings are relations summarized by rules or 'codes'. Special codings are 'neural', 'natural' (in everyday life), 'exper...
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This communication introduces the topic. Foundations: Core concepts: codings are relations summarized by rules or 'codes'. Special codings are 'neural', 'natural' (in everyday life), 'experimental' (in laboratories), 'conditional' (to partner restrictions), etc. Partial aspects are mechanisms, what partners say about each other, etc. Critical experimental issues: Trains are evaluated by when spikes occur: i.e. as point processes mid timings. Trains and point process representations become synonyms. Any code must: (i) be a 'number (rate) cod' and an 'interval cod';and (ii) include 'referent, train' covariations involving steady states with overall averages and fluctuations with patterns (dispersions, sequences). Seminal findings. Early data proved trains participated in codings;this is accepted unanimously. Inevitably, though accepted less readily, codings included rates, intervals, averages and patterns. Literature highlights. (1) Confirmed the seminal finding (2.2.) over vast domains;(2) Demonstrated both general and synaptic codings (referents, respectively, sensory, states, etc, and trains in directly connected neurons);(3) Revealed overlap between general and synaptic coding features. Overlap allows train participation in network dynamics;(4) Introduced natural formal contexts. (Point Process Mathematics, Communication. Information and Dynamical Systems Theories);(5) Includes confused opinions: (i) Opposition between rates and intervals;(ii) claims that averages are meaningful but patterns irrelevant. Both, overlooking foundations and evidence, are untenable. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.
Visual context plays a significant role in humans' gaze movement for target searching. How to transform the visual context into the internal representation of a brain-like neural network is an interesting issue. P...
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ISBN:
(纸本)9783642158186
Visual context plays a significant role in humans' gaze movement for target searching. How to transform the visual context into the internal representation of a brain-like neural network is an interesting issue. Population cell coding is a neural representation mechanism which was widely discovered in primates' visual neural system. This paper presents a biologically inspired neural network model which uses a population cell coding mechanism for visual context representation and target searching. Experimental results show that the population-cell-coding generally performs better than the single-cell-coding system.
One of the primary challenges facing neuroscientists is understanding how information is represented in neural circuits. These representations provide insight into the computations performed by individual neurons and ...
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One of the primary challenges facing neuroscientists is understanding how information is represented in neural circuits. These representations provide insight into the computations performed by individual neurons and neural circuits. Complicating this endeavor is the variability in neural responses: repeatedly presenting the same stimulus does not elicit identical responses. Although variability is often treated as a nuisance that obscures relevant features of the neural response, the origin and nature of this variability have meaningful implications for how we understand computations in neural circuits, as well as the perceptions and behaviors that rely on these computations. Here, I present multiple approaches to characterizing the role that variability plays in how information is processed in the nervous system. I first examine a widely used class of models, generalized linear models, and evaluate its ability to capture response features observed in biological neurons. I then examine how variability in the responses of retinal ganglion cells changes under different conditions and propose a new model that accounts for responses under both conditions. Finally, I examine how the origin of noise in neural circuits influences optimal coding strategies.
Information theoretic techniques are often used to investigate neural coding. Results - in terms of bits per second or bits per spike - have been used as evidence to support temporal or rate coding, spike timing preci...
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ISBN:
(纸本)0780378989
Information theoretic techniques are often used to investigate neural coding. Results - in terms of bits per second or bits per spike - have been used as evidence to support temporal or rate coding, spike timing precision, etc. Despite its use this way, information theory does not tell one what the neural code (or any code) is. In artificial systems, codes are often purposefully made sub-optimal from a pure information density point of view. This work tests the feasibility of a neural code containing error correction characteristics which uses greater spike timing precision than might be necessary to simply transmit a given amount of information. A model of the recognized prototype of an inhibitory synapse shows that, even compared to small input imprecision and in the: presence of robust dynamical behaviors, high timing precision can enable error correction.
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