This paper provides new insights regarding the transfer of information between input signal and the output of neurons. Simulations of the Hodgkin-Huxley (HH) model combined with computational techniques are used to es...
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This paper provides new insights regarding the transfer of information between input signal and the output of neurons. Simulations of the Hodgkin-Huxley (HH) model combined with computational techniques are used to estimate this transfer of information. Our analysis shows that comparatively, mutual information (MI) between input signal and sodium flux is about two times that between input signal and output spikes during each spike within a millisecond-level time domain. This higher transfer of information provided by ionic fluxes extends the working frequency domain of neural cells beyond those accessible to information transfer within spikes alone.
Stimulus selectivity of sensory systems is often characterized by analyzing response-conditioned stimulus ensembles. However, in many cases these response-triggered stimulus sets have structure that is more complex th...
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Stimulus selectivity of sensory systems is often characterized by analyzing response-conditioned stimulus ensembles. However, in many cases these response-triggered stimulus sets have structure that is more complex than assumed. If not taken into account, when present it will bias the estimates of many simple statistics, and distort the estimated stimulus selectivity of a neural sensory system. We present an approach that mitigates these problems by modeling some of the response-conditioned stimulus structure as being generated by a set of transformations acting on a simple stimulus distribution. This approach corrects the estimates of key statistics and counters biases introduced by the transformations. In cases involving temporal spike jitter or spatial jitter of images, the main observed effects of transformations are blurring of the conditional mean and introduction of artefacts in the spectral decomposition of the conditional covariance matrix. We illustrate this approach by analyzing and correcting a set of model stimuli perturbed by temporal and spatial jitter. We apply the approach to neurophysiological data from the cricket cercal sensory system to correct the effects of temporal jitter.
We examine the optimal threshold distribution in populations of noisy threshold devices. When the noise on each threshold is independent, and sufficiently large. the optimal thresholds are realized by the suprathresho...
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We examine the optimal threshold distribution in populations of noisy threshold devices. When the noise on each threshold is independent, and sufficiently large. the optimal thresholds are realized by the suprathreshold stochastic resonance effect, in which case all threshold devices are identical. This result has relevance for neural population coding, as such noisy threshold devices model the key dynamics of nerve fibres. It is also relevant to quantization and lossy source coding theory, since the model provides a form of stochastic signal quantization. Furthermore, it is shown that a bifurcation pattern appears in the optimal threshold distribution as the noise intensity increases. Fisher information is used to demonstrate that the optimal threshold distribution remains in the suprathreshold stochastic resonance configuration as the population size approaches infinity. (c) 2005 Elsevier B.V. All rights reserved.
Neuroscientists are increasingly embracing mice as a means to address central nervous system questions at a molecular level. Examples abound from sensory systems like olfaction and vision. The use of mice to study cen...
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Neuroscientists are increasingly embracing mice as a means to address central nervous system questions at a molecular level. Examples abound from sensory systems like olfaction and vision. The use of mice to study central auditory processing, however, has remained relatively limited. In this commentary, I draw on some of the successes from other fields to highlight directions in which mouse models may contribute valuable and other-wise unattainable insights into the neural circuitry and plasticity within central auditory stations. Efforts towards this are beginning and would benefit from increased collaboration to generate useful transgenic mouse models for such studies. (c) 2006 Elsevier B.V. All rights reserved.
Episodic memory organizes experience in time, so that we can review past events and anticipate the future. in a hippocampus-dependent memory task, spike timing in pairs of simultaneously active CA1 neurons with overla...
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Episodic memory organizes experience in time, so that we can review past events and anticipate the future. in a hippocampus-dependent memory task, spike timing in pairs of simultaneously active CA1 neurons with overlapping place fields distinguished the start and end of trials. At the common starting point of different journeys, the relative spike timing of the neurons was highly correlated. As the rat approached a common goal from different starting points, however, temporal firing patterns were strongly modulated across journeys even if the cells fired in the same spatial locations within fields, implying that different processes influenced when and where cells fire. Spike timing within hippocampal ensembles may thereby help parse the beginning from the end of episodes in memory.
This modeling study examines the short-term synaptic plasticity properties of the electrosensory lateral lobe (ELL) afferent pathway in the weakly electric fish, Apteronotus leptorhynchus. We studied the possible func...
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This modeling study examines the short-term synaptic plasticity properties of the electrosensory lateral lobe (ELL) afferent pathway in the weakly electric fish, Apteronotus leptorhynchus. We studied the possible functional consequences of a simple phenomenological model of synaptic depression by taking into consideration the available in vivo and in vitro results [N. Berman, L. Maler, Inhibition evoked from primary afferents in the electrosensory lateral line lobe of the weakly electric fish (Apteronotus leptorhynchus), J. Neurophysiol. 80(6) (1998) 3173-3196;M.J. Chacron, B. Doiron, L. Maler, A. Longtin, J. Bastian, Non-classical receptive field mediates switch in a sensory neuron's frequency tuning, Nature 26(424) (2003) 1018-1022]. Filtering and coding properties were examined. We find that simple short-term phenomenological synaptic depression can change steady-state filtering properties and explain how the known physiological constraints influence the coding capabilities of the ELL pyramidal cells via dynamic synaptic transmission. (c) 2006 Elsevier B.V. All rights reserved.
Palpatory movements ('active' touch) are an integral part of tactile sensing. It is known that tactile signals can be modulated in certain behavioral contexts, but it is still unresolved to what degree this mo...
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Palpatory movements ('active' touch) are an integral part of tactile sensing. It is known that tactile signals can be modulated in certain behavioral contexts, but it is still unresolved to what degree this modulation is related to movement kinematics and whether it stems from tactile receptors or from central sources. Using awake, head-fixed rats, trained to contact an object, we measured trajectories of muscle-propelled whisker movement precisely and compared tactile responses to contacts thus accomplished with 'passive' contacts (motionless whisker contacted by object). Multielectrode extracellular recordings in deep layers of barrel cortex revealed that when the animals moved their whiskers actively, tactile processing switched from high response amplitudes, wide cortical representation and low background firing, to low response amplitudes, narrow spatial representation and elevated background firing. Switching was fast (< 100 ms) and unrelated to the degree of alertness as assessed by spectral analysis of pre-contact field potentials. Switching persisted when information about whisker kinematics was interrupted by transection of the infraorbital nerve and contacts were mimicked by peripheral electrical stimulation. Taken together, these characteristics render central signals derived from the motor system a likely contributor to the processing of active touch.
Hallock, R.M. and Di Lorenzo, P.M. [2006. Temporal coding in the gustatory system. Neurosci. Biobehav. Rev. XX(X) XXX-XXX]. Early investigations of temporal coding in the gustatory system showed that the time course o...
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Hallock, R.M. and Di Lorenzo, P.M. [2006. Temporal coding in the gustatory system. Neurosci. Biobehav. Rev. XX(X) XXX-XXX]. Early investigations of temporal coding in the gustatory system showed that the time course of responses in some neurons showed systematic differences across the various classes of taste stimuli, implying that the temporal characterisics of a response can convey information about a taste stimulus. Studies of temporal coding in the gustatory system have grappled with several unique methodological challenges, including the quantitative description and comparison of temporal patterns as well as the assessment of the relative contributions of spatial and temporal coding to the information contained in a response to a tastant. Other investigations have suggested that the cooperative activity among synchronously firing ensembles of taste-responsive neurons at all levels of processing in the brain can convey information about taste quality (sweet, sour, salty, bitter and umami). Behavioral studies using patterned electrical stimulation of the brain in awake animals have supported the idea that temporal coding of taste stimuli may have functional significance. (c) 2006 Elsevier Ltd. All rights reserved.
Recent experimental and theoretical results have suggested the possibility that cortical neurons may produce only a small number of distinct spiking patterns when stimulated repeatedly by the same signal. Such firing ...
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Recent experimental and theoretical results have suggested the possibility that cortical neurons may produce only a small number of distinct spiking patterns when stimulated repeatedly by the same signal. Such firing patterns invalidate the assumption that cortical responses are Poisson and suggest the possibility of novel cortical information processing strategies. Unfortunately, methods for extracting and quantifying spike patterns from experimental data are still immature. We present a quantitative definition of spike patterns, a principled procedure for their extraction, and methods for validating and quantifying the presence of spike patterns in neuronal data. (c) 2006 Published by Elsevier B.V.
Working memory has often been modeled and conceptualized as a kind of binary (bistable) memory switch, where stimuli turn on plateau-like persistent activity in subsets of cells, in line with many in vivo electrophysi...
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Working memory has often been modeled and conceptualized as a kind of binary (bistable) memory switch, where stimuli turn on plateau-like persistent activity in subsets of cells, in line with many in vivo electrophysiological reports. A potentially related form of bistability, termed up- and down-states, has been studied with regard to its synaptic and ionic basis in vivo and in reduced cortical preparations. Also single cell mechanisms for producing bistability have been proposed and investigated in brain slices and computationally. Recently, however, it has been emphasized that clear plateau-like bistable activity is rather rare during working memory tasks, and that neurons exhibit a multitude of different temporally unfolding activity profiles and temporal structure within their spiking dynamics. Hence, working memory seems to be a highly dynamical neural process with yet unknown mappings from dynamical to computational properties. Empirical findings on ramping activity profiles and temporal structure will be reviewed, as well as neural models that attempt to account for it and its computational significance. Furthermore, recent in vivo, neural culture, and in vitro preparations will be discussed that offer new possibilities for studying the biophysical mechanisms underlying computational processes during working memory. These preparations have revealed additional evidence for temporal structure and spatio-temporally organized attractor states in cortical networks, as well as for specific computational properties that may characterize synaptic processing during high-activity states as during working memory. Together such findings may lay the foundations for highly dynamical theories of working memory based on biophysical principles. (C) 2005 IBRO. Published by Elsevier Ltd. All rights reserved.
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