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作者： Itoga, Christy A University of Michigan

学位级别：doctor

The overall goal of this thesis was to investigate how the ventral pallidum tracks experimentally-induced changes in the hedonic value of tastes. Taste reactions allows us to measure how 'liked' or 'disliked' a taste is by a rat. These reactions are not purely reflexive as they are altered when circumstances change: hunger can increase and satiety can decrease the tastiness of foods (Berridge 1996) and a salt appetite can make a normally 'disliked' salt solution 'liked' (Berridge et al. 1984, Schulkin 1991). Therefore taste reactions reflect the palatability of tastes. Understanding how the reward pathway tracks changes in the hedonic value of tastes may elucidate how neural coding is affected in disorders such as drug addiction and obesity. The first project investigated how neurons in the ventral pallidum (VP) track changes in hedonic value of a sweet taste by a conditioned taste aversion. When a taste changed from 'liked' to 'disliked', the predominant VP response also changed: taste responsive VP cells tastes typically increase firing rate in response to 'liked' tastes whereas the hedonically devalued taste typically triggered a decrease in firing rate. The second project compared the effects of dopamine and opioid modulation of 'liked', relatively neutral, and 'disliked' taste stimuli. We found that opioid modulation enhanced the hedonic value of quinine (which is normally 'disliked'), but that only morphine resulted in a VP population response that mirrored the hedonic value of the tastes. The third project tested the effects of dopamine and opioid modulation on the hedonic value of a pair of cues (water infusions) and reward (a sucrose infusion). Overall, the cues did increase in hedonic value via association with reward, and the VP reflected the similarity in hedonic value between the cues and reward by responding similarly to cues and reward, under most drug conditions. Amphetamine decreased the proportion of units that responded to the first cue with an in

关键词： Ventral Pallidum neural Responses neural coding Hedonic Value Hedonia Taste Neurosciences Health Sciences

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Suggestive Evidence for a Forward Model of the Arm in the Monkey Motor Cortex

Suggestive Evidence for a Forward Model of the Arm in the Mo...

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13th IEEE International Workshop on Advanced Motion Control (AMC)

作者： Miyashita, Eizo Sakaguchi, Yutaka Tokyo Inst Technol Dept Computat Intelligence & Syst Sci Yokohama Kanagawa 227 Japan Univ Electrocommun Dept Human Media Syst Chofu Tokyo 182 Japan

ISBN: (纸本)9781479923243

To test an idea that neurons in the motor cortex encodes a future state of the arm, we constructed a plausible model using arm state-related variables to explain neuronal activity, and applied a multiple linear regression analysis. We found that the model fit was fairly good with a mean determination coefficient of 0.57 for analyzed 231 neurons and that neuronal activity preceded the actual movement of the arm with 66 ms on average. Presuming that the brain follows optimal feed back control theory, these findings suggest that the motor cortex may contain a forward model of the arm.

关键词： brain control of motion optimal feedback control theory reaching movements neural coding neural information processing

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Seeing sound: A new way to illustrate auditory objects and their neural correlates

Seeing sound: A new way to illustrate auditory objects and t...

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作者： Lim, Yoon Seob Boston University

学位级别：Ph.D.

This thesis develops a new method for time-frequency signal processing and examines the relevance of the new representation in studies of neural coding in songbirds. The method groups together associated regions of the time-frequency plane into objects defined by time-frequency contours. By combining information about structurally stable contour shapes over multiple time-scales and angles, a signal decomposition is produced that distributes resolution adaptively. As a result, distinct signal components are represented in their own most parsimonious forms. Next, through neural recordings in singing birds, it was found that activity in song premotor cortex is significantly correlated with the objects defined by this new representation of sound. In this process, an automated way of finding sub-syllable acoustic transitions in birdsongs was first developed, and then increased spiking probability was found at the boundaries of these acoustic transitions. Finally, a new approach to study auditory cortical sequence processing more generally is proposed. In this approach, songbirds were trained to discriminate Morse-code-like sequences of clicks, and the neural correlates of this behavior were examined in primary and secondary auditory cortex. It was found that a distinct transformation of auditory responses to the sequences of clicks exists as information transferred from primary to secondary auditory areas. Neurons in secondary auditory areas respond asynchronously and selectively — in a manner that depends on the temporal context of the click. This transformation from a temporal to a spatial representation of sound provides a possible basis for the songbird's natural ability to discriminate complex temporal sequences.

关键词： Neurosciences Auditory objects neural coding Songbird Time-frequency analysis

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neural coding and contextual influences in the whisker system

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BIOLOGICAL CYBERNETICS 2009年第6期100卷 427-446页

作者： Petersen, Rasmus S. Panzeri, Stefano Maravall, Miguel Univ Manchester Fac Life Sci Manchester Lancs England Italian Inst Technol Robot Brain & Cognit Sci Dept I-16163 Genoa Italy UHM CSIC Inst Neurociencias Alicante Sant Joan dAlacant Spain

A fundamental problem in neuroscience, to which Prof. Segundo has made seminal contributions, is to understand how action potentials represent events in the external world. The aim of this paper is to review the issue of neural coding in the context of the rodent whiskers, an increasingly popular model system. Key issues we consider are: the role of spike timing;mechanisms of spike timing;decoding and context-dependence. Significant insight has come from the development of rigorous, information theoretic frameworks for tackling these questions, in conjunction with suitably designed experiments. We review both the theory and experimental studies. In contrast to the classical view that neurons are noisy and unreliable, it is becoming clear that many neurons in the subcortical whisker pathway are remarkably reliable and, by virtue of spike timing with millisecond-precision, have high bandwidth for conveying sensory information. In this way, even small (similar to 200 neuron) subcortical modules are able to support the sensory processing underlying sophisticated whisker-dependent behaviours. Future work on neural coding in cortex will need to consider new findings that responses are highly dependent on context, including behavioural and internal states.

关键词： neural coding Barrel cortex Information theory Vibrissa

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Speech Enhancement for Listeners With Hearing Loss Based on a Model for Vowel coding in the Auditory Midbrain

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IEEE TRANSACTIONS ON BIOMEDICAL ENGINEERING 2014年第7期61卷 2081-2091页

作者： Rao, Akshay Carney, Laurel H. Univ Rochester Dept Elect & Comp Engn Rochester NY 14627 USA

A novel signal-processing strategy is proposed to enhance speech for listeners with hearing loss. The strategy focuses on improving vowel perception based on a recent hypothesis for vowel coding in the auditory system. Traditionally, studies of neural vowel encoding have focused on the representation of formants (peaks in vowel spectra) in the discharge patterns of the population of auditory-nerve (AN) fibers. A recent hypothesis focuses instead on vowel encoding in the auditory midbrain, and suggests a robust representation of formants. AN fiber discharge rates are characterized by pitch-related fluctuations having frequency-dependent modulation depths. Fibers tuned to frequencies near formants exhibit weaker pitch-related fluctuations than those tuned to frequencies between formants. Many auditory midbrain neurons show tuning to amplitude modulation frequency in addition to audio frequency. According to the auditory midbrain vowel encoding hypothesis, the response map of a population of midbrain neurons tuned to modulations near voice pitch exhibits minima near formant frequencies, due to the lack of strong pitch-related fluctuations at their inputs. This representation is robust over the range of noise conditions in which speech intelligibility is also robust for normal-hearing listeners. Based on this hypothesis, a vowel-enhancement strategy has been proposed that aims to restore vowel encoding at the level of the auditory midbrain. The signal processing consists of pitch tracking, formant tracking, and formant enhancement. The novel formant-tracking method proposed here estimates the first two formant frequencies by modeling characteristics of the auditory periphery, such as saturated discharge rates of AN fibers and modulation tuning properties of auditory midbrain neurons. The formant enhancement stage aims to restore the representation of formants at the level of the midbrain by increasing the dominance of a single harmonic near each formant and saturating t

关键词： Auditory models formant detection formant estimation formant tracking hearing aids neural coding speech analysis

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Optimal attentional modulation of a neural population

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FRONTIERS IN COMPUTATIONAL NEUROSCIENCE 2014年第MAR期8卷 34页

作者： Borji, Ali Itti, Laurent Univ So Calif Dept Comp Sci Los Angeles CA 90089 USA Univ So Calif Grad Program Neurosci Los Angeles CA 90089 USA Univ So Calif Dept Psychol Los Angeles CA 90089 USA

Top-down attention has often been separately studied in the contexts of either optimal population coding or biasing of visual search. Yet, both are intimately linked, as they entail optimally modulating sensory variables in neural populations according to top-down goals. Designing experiments to probe top-down attentional modulation is difficult because non-linear population dynamics are hard to predict in the absence of a concise theoretical framework. Here, we describe a unified framework that encompasses both contexts. Our work sheds light onto the ongoing debate on whether attention modulates neural response gain, tuning width, and/or preferred feature. We evaluate the framework by conducting simulations for two tasks: (1) classification (discrimination) of two stimuli s(a) and s(b) and (2) searching for a target T among distractors D. Results demonstrate that all of gain, tuning, and preferred feature modulation happen to different extents, depending on stimulus conditions and task demands. The theoretical analysis shows that task difficulty (linked to difference Lambda between s(a) and s(b), or T, and D) is a crucial factor in optimal modulation, with different effects in discrimination vs. search. Further, our framework allows us to quantify the relative utility of neural parameters. In easy tasks (when Delta is large compared to the density of the neural population), modulating gains and preferred features is sufficient to yield nearly optimal performance;however, in difficult tasks (smaller Delta), modulating tuning width becomes necessary to improve performance. This suggests that the conflicting reports from different experimental studies may be due to differences in tasks and in their difficulties. We further propose future electrophysiology experiments to observe different types of attentional modulation in a same neuron.

关键词： top-down attention neural modulation neural coding gain tuning width feature selectivity

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Theta phase precession and phase selectivity: a cognitive device description of neural coding

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JOURNAL OF neural ENGINEERING 2009年第3期6卷 036002 (18-036002 (18页

作者： Zalay, Osbert C. Bardakjian, Berj L. Univ Toronto Inst Biomat & Biomed Engn Toronto ON M5S 3G9 Canada

Information in neural systems is carried by way of phase and rate codes. Neuronal signals are processed through transformative biophysical mechanisms at the cellular and network levels. neural coding transformations can be represented mathematically in a device called the cognitive rhythm generator (CRG). Incoming signals to the CRG are parsed through a bank of neuronal modes that orchestrate proportional, integrative and derivative transformations associated with neural coding. Mode outputs are then mixed through static nonlinearities to encode (spatio) temporal phase relationships. The static nonlinear outputs feed and modulate a ring device (limit cycle) encoding Output dynamics. Small coupled CRG networks were created to investigate coding functionality associated with neuronal phase preference and theta precession in the hippocampus. Phase selectivity was found to be dependent on mode shape and polarity, while phase precession was a product of modal mixing (i.e. changes in the relative contribution or amplitude of mode outputs resulted in shifting phase preference). Nonlinear system identification was implemented to help validate the model and explain response characteristics associated with modal mixing;in particular, principal dynamic modes experimentally derived from a hippocampal neuron were inserted into a CRG and the neuron's dynamic response was successfully cloned. From our results, small CRG networks possessing disynaptic feedforward inhibition in combination with feedforward excitation exhibited frequency-dependent inhibitory-to-excitatory and excitatory-to-inhibitory transitions that were similar to transitions seen in a single CRG with quadratic modal mixing. This suggests nonlinear modal mixing to be a coding manifestation of the effect of network connectivity in shaping system dynamic behavior. We hypothesize that circuits containing disynaptic feedforward inhibition in the nervous system may be candidates for interpreting upstream rate codes to g

关键词： CRG limit cycle neural coding Blending limit cycles precession Phase

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Suggestive Evidence for a Forward Model of the Arm in the Monkey Motor Cortex

Suggestive Evidence for a Forward Model of the Arm in the Mo...

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International Workshop on Advanced Motion Control

作者： Eizo Miyashita Yutaka Sakaguchi Dept. of Computational Intelligence & Systems Science Tokyo Institute of Technology Yokohama Japan Dept. of Human Media Systems University of Electro-Communications Chofu Japan

ISBN: (纸本)9781479957637

关键词： brain control of motion optimal feedback control theory reaching movements neural coding neural information processing

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Motion processing across multiple topographic maps in the electrosensory system

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PHYSIOLOGICAL REPORTS 2014年第3期2卷 e00253-e00253页

作者： Khosravi-Hashemi, Navid Chacron, Maurice J. McGill Univ Dept Physiol 3655 Sir William OslerRoom 1137 Montreal PQ Canada McGill Univ Dept Phys Montreal PQ Canada

Animals can efficiently process sensory stimuli whose attributes vary over orders of magnitude by devoting specific neural pathways to process specific features in parallel. Weakly electric fish offer an attractive model system as electrosensory pyramidal neurons responding to amplitude modulations of their self-generated electric field are organized into three parallel maps of the body surface. While previous studies have shown that these fish use parallel pathways to process stationary stimuli, whether a similar strategy is used to process motion stimuli remains unknown to this day. We recorded from electrosensory pyramidal neurons in the weakly electric fish Apteronotus leptorhynchus across parallel maps of the body surface (centromedial, centrolateral, and lateral) in response to objects moving at velocities spanning the natural range. Contrary to previous observations made with stationary stimuli, we found that all cells responded in a similar fashion to moving objects. Indeed, all cells showed a stronger directionally nonselective response when the object moved at a larger velocity. In order to explain these results, we built a mathematical model incorporating the known antagonistic center-surround receptive field organization of these neurons. We found that this simple model could quantitatively account for our experimentally observed differences seen across E and I-type cells across all three maps. Our results thus provide strong evidence against the hypothesis that weakly electric fish use parallel neural pathways to process motion stimuli and we discuss their implications for sensory processing in general.

关键词： neural coding pyramidal neuron velocity tuning weakly electric fish

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Small-world networks in neuronal populations: A computational perspective

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neural NETWORKS 2013年 44卷 143-156页

作者： Zippo, Antonio G. Gelsomino, Giuliana Van Duin, Pieter Nencini, Sara Caramenti, Gian Carlo Valente, Maurizio Biella, Gabriele E. M. CNR Inst Mol Bioimaging & Physiol Milan Italy Univ Milan Dept Comp Sci Milan Italy CNR Inst Biomed Technol Milan Italy

The analysis of the brain in terms of integrated neural networks may offer insights on the reciprocal relation between structure and information processing. Even with inherent technical limits, many studies acknowledge neuron spatial arrangements and communication modes as key factors. In this perspective, we investigated the functional organization of neuronal networks by explicitly assuming a specific functional topology, the small-world network. We developed two different computational approaches. Firstly, we asked whether neuronal populations actually express small-world properties during a definite task, such as a learning task. For this purpose we developed the Inductive Conceptual Network (ICN), which is a hierarchical bio-inspired spiking network, capable of learning invariant patterns by using variable-order Markov models implemented in its nodes. As a result, we actually observed small-world topologies during learning in the ICN. Speculating that the expression of small-world networks is not solely related to learning tasks, we then built a de facto network assuming that the information processing in the brain may occur through functional small-world topologies. In this de facto network, synchronous spikes reflected functional small-world network dependencies. In order to verify the consistency of the assumption, we tested the null-hypothesis by replacing the small-world networks with random networks. As a result, only small world networks exhibited functional biomimetic characteristics such as timing and rate codes, conventional coding strategies and neuronal avalanches, which are cascades of bursting activities with a power-law distribution. Our results suggest that small-world functional configurations are liable to underpin brain information processing at neuronal level. (C) 2013 Elsevier Ltd. All rights reserved.

关键词： Neuronal assemblies Information abstraction Machine learning Small-world networks Neuronal avalanches neural coding

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