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Seeing via miniature eye movements: a dynamic hypothesis for vision

FRONTIERS IN COMPUTATIONAL NEUROSCIENCE 2012年第2012期6卷 89-89页

作者： Ahissar, Ehud Arieli, Amos Weizmann Inst Sci Dept Neurobiol IL-76100 Rehovot Israel

During natural viewing, the eyes are never still. Even during fixation, miniature movements of the eyes move the retinal image across tens of foveal photoreceptors. Most theories of vision implicitly assume that the visual system ignores these movements and somehow overcomes the resulting smearing. However, evidence has accumulated to indicate that fixational eye movements cannot be ignored by the visual system if fine spatial details are to be resolved. We argue that the only way the visual system can achieve its high resolution given its fixational movements is by seeing via these movements. Seeing via eye movements also eliminates the instability of the image, which would be induced by them otherwise. Here we present a hypothesis for vision, in which coarse details are spatially encoded in gaze-related coordinates, and fine spatial details are temporally encoded in relative retinal coordinates. The temporal encoding presented here achieves its highest resolution by encoding along the elongated axes of simple-cell receptive fields and not across these axes as suggested by spatial models of vision. According to our hypothesis, fine details of shape are encoded by interreceptor temporal phases, texture by instantaneous intra-burst rates of individual receptors, and motion by inter-burst temporal frequencies. We further describe the ability of the visual system to readout the encoded information and recode it internally. We show how readingout of retinal signals can be facilitated by neuronalp haselocked loops( NPLLs), which lock to the retinal jitter;this locking enables recoding of motion information and temporal framing of shape and texture processing. A possible implementation of this locking-and-recoding process by specific thalamocortical loops is suggested. Overall it is suggested that high-acuity vision is based primarily on temporal mechanisms of the sort presented here and low-acuity vision is based primarily on spatial mechanisms.

关键词： active vision fixational eye movements neuronal phase-locked loop temporal coding neural coding simple cells thalamocortical loop feedback

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Synergistic coding by Cortical neural Ensembles

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IEEE TRANSACTIONS ON INFORMATION THEORY 2010年第2期56卷 875-889页

作者： Aghagolzadeh, Mehdi Eldawlatly, Seif Oweiss, Karim Michigan State Univ Dept Elect & Comp Engn E Lansing MI 48824 USA Michigan State Univ Neurosci Program E Lansing MI 48824 USA

An essential step towards understanding how the brain orchestrates information processing at the cellular and population levels is to simultaneously observe the spiking activity of cortical neurons that mediate perception, learning, and motor processing. In this paper, we formulate an information theoretic approach to determine whether cooperation among neurons may constitute a governing mechanism of information processing when encoding external covariates. Specifically, we show that conditional independence between neuronal outputs may not provide an optimal encoding strategy when the firing probability of a neuron depends on the history of firing of other neurons connected to it. Rather, cooperation among neurons can provide a "message-passing" mechanism that preserves most of the information in the covariates under specific constraints governing their connectivity structure. Using a biologically plausible statistical learning model, we demonstrate the performance of the proposed approach in synergistically encoding a motor task using a subset of neurons drawn randomly from a large population. We demonstrate its superiority in approximating the joint density of the population from limited data compared to a statistically independent model and a pairwise maximum entropy (MaxEnt) model.

关键词： Cortical networks graph theory maximum entropy (MaxEnt) minimum entropy distance (MinED) neural coding spike trains

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Toward in vivo nanoscale communication networks: utilizing an active network architecture

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中国计算机科学前沿 2011年第3期5卷 316-326页

作者： Stephen F. BUSH GE Global Research One Research Circle Niskayuna NY 12309 USA

A safe and reliable in vivo nanoscale communication network will be of great benefit for medical diagnosis and monitoring as well as medical implant *** review article provides a brief introduction to nanoscale and molecular networking in general and provides opinions on the role of active networking for in vivo nanoscale information *** there are many in vivo communication mechanisms that can be leveraged,for example,forms of cell signaling,gap junctions,calcium and ion signaling,and circulatory borne communication,this review examines two in particular:molecular motor transport and neuronal information *** motors transport molecules representing information and neural coding operates by means of the action potential; these mechanisms are reviewed within the theoretical framework of an active *** review suggests that an active networking paradigm is necessary at the nanoscale along with a new communication constraint,namely,minimizing the communication impact upon the living *** goal is to assemble efficient nanoscale and molecular communication channels while minimizing disruption to the host organism.

关键词： nanoscale network molecular communication in vivo network active network molecular motor neural coding

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An introductory review of information theory in the context of computational neuroscience

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BIOLOGICAL CYBERNETICS 2011年第1期105卷 55-70页

作者： McDonnell, Mark D. Ikeda, Shiro Manton, Jonathan H. Inst Stat Math Tokyo 1908562 Japan Univ S Australia Inst Telecommun Res Mawson Lakes SA 5095 Australia Univ Melbourne Melbourne Vic 3010 Australia

This article introduces several fundamental concepts in information theory from the perspective of their origins in engineering. Understanding such concepts is important in neuroscience for two reasons. Simply applying formulae from information theory without understanding the assumptions behind their definitions can lead to erroneous results and conclusions. Furthermore, this century will see a convergence of information theory and neuroscience;information theory will expand its foundations to incorporate more comprehensively biological processes thereby helping reveal how neuronal networks achieve their remarkable information processing abilities.

关键词： Information theory Neuroscience neural coding Channel capacity

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neural HETEROGENEITIES AND STIMULUS PROPERTIES AFFECT BURST coding IN VIVO

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NEUROSCIENCE 2010年第1期168卷 300-313页

作者： Avila-Akerberg, O. Krahe, R. Chacron, M. J. McGill Univ Dept Physiol Montreal PQ H3G 1Y6 Canada McGill Univ Dept Phys Montreal PQ H3G 1Y6 Canada McGill Univ Dept Biol Montreal PQ H3G 1Y6 Canada

Many neurons tend to fire clusters of action potentials called bursts followed by quiescence in response to sensory input. While the mechanisms that underlie burst firing are generally well understood in vitro, the functional role of these bursts in generating behavioral responses to sensory input in vivo are less clear. Pyramidal cells within the electrosensory lateral line lobe (ELL) of weakly electric fish offer an attractive model system for studying the coding properties of burst firing, because the anatomy and physiology of the electrosensory circuitry are well understood, and the burst mechanism of ELL pyramidal cells has been thoroughly characterized in vitro. We investigated the coding properties of bursts generated by these cells in vivo in response to mimics of behaviorally relevant sensory input. We found that heterogeneities within the pyramidal cell population had quantitative but not qualitative effects on burst coding for the low frequency components of broadband time varying input. Moreover, spatially localized stimuli mimicking, for example, prey tended to elicit more bursts than spatially global stimuli mimicking conspecific-related stimuli. We also found small but significant correlations between burst attributes such as the number of spikes per burst or the interspike interval during the burst and stimulus attributes such as stimulus amplitude or slope. These correlations were much weaker in magnitude than those observed in vitro. More surprisingly, our results show that correlations between burst and stimulus attributes actually decreased in magnitude when we used low frequency stimuli that are expected to promote burst firing. We propose that this discrepancy is attributable to differences between ELL pyramidal cell burst firing under in vivo and in vitro conditions. (C) 2010 IBRO. Published by Elsevier Ltd. All rights reserved.

关键词： weakly electric fish neural coding information theory burst firing

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Auditory information coding by modeled cochlear nucleus neurons

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JOURNAL OF COMPUTATIONAL NEUROSCIENCE 2011年第3期30卷 529-542页

作者： Wang, Huan Isik, Michael Borst, Alexander Hemmert, Werner Tech Univ Munich Inst Med Engn D-85748 Garching Germany Infineon Technol AG Neubiberg Germany Max Plank Inst Neurobiol Munich Germany Bernstein Ctr Computat Neurosci Munich Germany

In this paper we use information theory to quantify the information in the output spike trains of modeled cochlear nucleus globular bushy cells (GBCs). GBCs are part of the sound localization pathway. They are known for their precise temporal processing, and they code amplitude modulations with high fidelity. Here we investigated the information transmission for a natural sound, a recorded vowel. We conclude that the maximum information transmission rate for a single neuron was close to 1,050 bits/s, which corresponds to a value of approximately 5.8 bits per spike. For quasi-periodic signals like voiced speech, the transmitted information saturated as word duration increased. In general, approximately 80% of the available information from the spike trains was transmitted within about 20 ms. Transmitted information for speech signals concentrated around formant frequency regions. The efficiency of neural coding was above 60% up to the highest temporal resolution we investigated (20 mu s). The increase in transmitted information to that precision indicates that these neurons are able to code information with extremely high fidelity, which is required for sound localization. On the other hand, only 20% of the information was captured when the temporal resolution was reduced to 4 ms. As the temporal resolution of most speech recognition systems is limited to less than 10 ms, this massive information loss might be one of the reasons which are responsible for the lack of noise robustness of these systems.

关键词： Onset neuron Information theory neural coding Automatic speech recognition Temporal resolution

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Information transmission and detection thresholds in the vestibular nuclei: single neurons vs. population encoding

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JOURNAL OF NEUROPHYSIOLOGY 2011年第4期105卷 1798-1814页

作者： Massot, Corentin Chacron, Maurice J. Cullen, Kathleen E. McGill Univ Dept Physiol Aerosp Med Res Unit Montreal PQ Canada McGill Univ Dept Phys Montreal PQ Canada

Massot C, Chacron MJ, Cullen KE. Information transmission and detection thresholds in the vestibular nuclei: single neurons vs. population encoding. J Neurophysiol 105: 1798-1814, 2011. First published February 9, 2011;doi:10.1152/jn.00910.2010.-Understanding how sensory neurons transmit information about relevant stimuli remains a major goal in neuroscience. Of particular relevance are the roles of neural variability and spike timing in neural coding. Peripheral vestibular afferents display differential variability that is correlated with the importance of spike timing;regular afferents display little variability and use a timing code to transmit information about sensory input. Irregular afferents, conversely, display greater variability and instead use a rate code. We studied how central neurons within the vestibular nuclei integrate information from both afferent classes by recording from a group of neurons termed vestibular only (VO) that are known to make contributions to vestibulospinal reflexes and project to higher-order centers. We found that, although individual central neurons had sensitivities that were greater than or equal to those of individual afferents, they transmitted less information. In addition, their velocity detection thresholds were significantly greater than those of individual afferents. This is because VO neurons display greater variability, which is detrimental to information transmission and signal detection. Combining activities from multiple VO neurons increased information transmission. However, the information rates were still much lower than those of equivalent afferent populations. Furthermore, combining responses from multiple VO neurons led to lower velocity detection threshold values approaching those measured from behavior (degrees 2.5 vs. 0.5-1 degrees/s). Our results suggest that the detailed time course of vestibular stimuli encoded by afferents is not transmitted by VO neurons. Instead, they suggest that higher vestibular

关键词： vestibular neurons neural variability information processing neural coding population coding

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coding movement direction by burst firing in electrosensory neurons

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JOURNAL OF NEUROPHYSIOLOGY 2011年第4期106卷 1954-1968页

作者： Khosravi-Hashemi, Navid Fortune, Eric S. Chacron, Maurice J. McGill Univ Dept Physiol Montreal PQ Canada McGill Univ Ctr Appl Math Biol & Med Montreal PQ Canada Johns Hopkins Univ Dept Psychol & Brain Sci Baltimore MD USA Johns Hopkins Univ Dept Neurosci Baltimore MD USA

Khosravi-Hashemi N, Fortune ES, Chacron MJ. coding movement direction by burst firing in electrosensory neurons. J Neurophysiol 106: 1954-1968, 2011. First published July 20, 2011;doi: 10.1152/jn. 00116.2011.-Directional selectivity, in which neurons respond strongly to an object moving in a given direction ("preferred") but respond weakly or not at all to an object moving in the opposite direction ("null"), is a critical computation achieved in brain circuits. Previous measures of direction selectivity have compared the numbers of action potentials elicited by each direction of movement, but most sensory neurons display patterning, such as bursting, in their spike trains. To examine the contribution of patterned responses to direction selectivity, we recorded from midbrain neurons in weakly electric fish and found that most neurons responded with a combination of both bursts and isolated spikes to moving object stimuli. In these neurons, we separated bursts and isolated spikes using an interspike interval (ISI) threshold. The directional bias of bursts was significantly higher than that of either the full spike train or the isolated spike train. To examine the encoding and decoding of bursts, we built biologically plausible models that examine 1) the upstream mechanisms that generate these spiking patterns and 2) downstream decoders of bursts. Our model of upstream mechanisms uses an interaction between afferent input and subthreshold calcium channels to give rise to burst firing that occurs preferentially for one direction of movement. We tested this model in vivo by application of calcium antagonists, which reduced burst firing and eliminated the differences in direction selectivity between bursts, isolated spikes, and the full spike train. Our model of downstream decoders used strong synaptic facilitation to achieve qualitatively similar results to those obtained using the ISI threshold criterion. This model shows that direction selective information carried by

关键词： direction selectivity neural coding weakly electric fish action potential patterning

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Basolateral amygdala responds robustly to social calls: spiking characteristics of single unit activity

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JOURNAL OF NEUROPHYSIOLOGY 2011年第5期105卷 2389-2404页

作者： Naumann, Robert T. Kanwal, Jagmeet S. Georgetown Univ Dept Physiol & Biophys Washington DC 20057 USA

Naumann RT, Kanwal JS. Basolateral amygdala responds robustly to social calls: spiking characteristics of single unit activity. J Neurophysiol 105: 2389-2404, 2011. First published March 2, 2011;doi:10.1152/jn.00580.2010.-Vocalizations emitted within a social context can trigger call-specific changes in the emotional and physiological/autonomic state of the receiver. The amygdala is implicated in mediating these changes, but its role in call perception remains relatively unexplored. We examined call and pitch selectivity of single neurons within the basolateral amygdala (BLA) by recording spiking activity in response to 5 pitch variants of each of 14 species-specific calls presented to awake, head-restrained mustached bats, Pteronotus parnellii. A response-wise analysis across neurons revealed seven types of temporal response patterns based on the timing and duration of spiking. Roughly half of the responses to different call types were significantly affected by changes in call pitch. A neuron-wise analysis revealed that similar to 12% (8/69) of the neurons preferred the same pitch across all call types. Ninety-three percent (93/100) of neurons were excited by at least one call type and 76% exhibited either complete or transient suppression to one or more call types. The majority of neurons preferred fewer than half of the 14 different simple-syllabic calls. A call-wise analysis of spiking activity revealed that call types signaling either threat or fear most consistently evoked increases in the spike rate. In contrast, calls emitted during appeasement tended to evoke spike suppression. Our data suggest that BLA neurons participate in the processing of multiple call types and exhibit a rich variety of temporal response patterns that are neither neuron nor call specific.

关键词： auditory system affect communication pitch perception valence neural coding

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Object decoding with attention in inferior temporal cortex

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PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA 2011年第21期108卷 8850-8855页

作者： Zhang, Ying Meyers, Ethan M. Bichot, Narcisse P. Serre, Thomas Poggio, Tomaso A. Desimone, Robert MIT Dept Brain & Cognit Sci McGovern Inst Cambridge MA 02139 USA Brown Univ Dept Cognit Linguist & Psychol Sci Providence RI 02912 USA

Recognizing objects in cluttered scenes requires attentional mechanisms to filter out distracting information. Previous studies have found several physiological correlates of attention in visual cortex, including larger responses for attended objects. However, it has been unclear whether these attention-related changes have a large impact on information about objects at the neural population level. To address this question, we trained monkeys to covertly deploy their visual attention from a central fixation point to one of three objects displayed in the periphery, and we decoded information about the identity and position of the objects from populations of similar to 200 neurons from the inferior temporal cortex using a pattern classifier. The results show that before attention was deployed, information about the identity and position of each object was greatly reduced relative to when these objects were shown in isolation. However, when a monkey attended to an object, the pattern of neural activity, represented as a vector with dimensionality equal to the size of the neural population, was restored toward the vector representing the isolated object. Despite this nearly exclusive representation of the attended object, an increase in the salience of nonattended objects caused "bottom-up" mechanisms to override these "top-down" attentional enhancements. The method described here can be used to assess which attention-related physiological changes are directly related to object recognition, and should be helpful in assessing the role of additional physiological changes in the future.

关键词： macaque vision readout population coding neural coding

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