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Temporal dynamics of 2D and 3D shape representation in macaque visual area V4

VISUAL NEUROSCIENCE 2006年第5期23卷 749-763页

作者： Hegde, Jay Van Essen, David C. Washington Univ Sch Med Dept Anat & Neurobiol St Louis MO 63110 USA

We studied the temporal dynamics of shape representation in area V4 of the alert macaque monkey. Analyses were based on two large stimulus sets, one equivalent to the 2D shape stimuli used in a previous study of V2, and the other a set of stereoscopic 3D shape stimuli. As in V2, we found that information conveyed by individual V4 neurons about the stimuli tended to be maximal during the initial transient response and generally lower, albeit statistically significant, afterwards. The population response was substantially correlated from one stimulus to the next during the transients, and decorrelated as responses decayed. V4 responses showed significantly longer latencies than in V2, especially for the 3D stimulus set. Recordings from area VI in a single animal revealed temporal dynamic patterns in response to the 2D shape stimuli that were largely similar to those in V2 and V4. Together with earlier results, these findings provide evidence for a distributed process of coarse-to-fine representation of shape stimuli in the visual cortex.

关键词： decorrelation dimensionality reduction metric multidimensional scaling onset transients rate coding signal-to-noise ratio

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Factors influencing the relation between corticospinal output and muscle force during voluntary contractions

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EUROPEAN JOURNAL OF NEUROSCIENCE 2007年第11期25卷 3469-3475页

作者： Gelli, F. Del Santo, F. Popa, T. Mazzocchio, R. Rossi, A. Univ Siena Sect Clin Neurophysiol Dept Neurol & Behav Sci I-53100 Siena Italy

The mechanisms by which voluntary forces of different strengths are produced in human muscles are not clear. We studied the relation between force and surface electromyography (sEMG) variables over a wide range of voluntary contraction strengths of biceps brachii (BIC) and abductor digiti minimi (ADM). The relation between force and motor evoked potentials (MEPs) to transcranial magnetic stimulation of motor cortex was also assessed. The root mean square of sEMG and median frequency (Mf) of the sEMG power spectrum as well as the MEP area of ADM and BIC were calculated up to the maximum voluntary contraction (MVC). The root mean square of ADM and BIC increased with increasing force levels up to the MVC. The Mf of BIC increased with force levels up to 70% MVC after which it rapidly declined. The Mf of ADM peaked at 40% MVC to slowly decline thereafter. The MEP changes with force were similar to Mf changes. Thus, corticospinal output, as tested by the Mf and MEPs, does not parallel force increments across the contraction range. This decline, which is contingent on the relative contribution of motor unit recruitment and rate coding to force production in each muscle, may depend on reduced motoneurone responsiveness at high firing rates. We suggest that, under controlled conditions, the frequency content of the sEMG signal may be taken to indicate motor unit recruitment range. This information may improve the utility of the Mf to enable evaluation of voluntary activation under different conditions.

关键词： corticospinal excitability human median frequency motor evoked potentials rate coding surface electromyography

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Modulation of motor unit firing rates during a complex sinusoidal force task in young and older adults

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JOURNAL OF APPLIED PHYSIOLOGY 2007年第1期102卷 122-129页

作者： Knight, Christopher A. Kamen, Gary Univ Delaware Coll Hlth Sci Dept Hlth Nutr & Exercise Sci Newark DE 19716 USA Univ Massachusetts Dept Exercise Sci Amherst MA 01003 USA

This study compared motor unit rate coding and muscular force control in the first dorsal interosseous muscle of older ( n = 11, mean 72.3 yr) and young ( n = 12, mean 18.7 yr) adults. rate coding during a sinusoidal isometric force-matching task was evaluated using spectral analysis of the time- varying changes in firing rate. The task required force modulations to match a trajectory comprising the sum of 0.15- and 0.45- Hz sine waves. Based on the amplitude of spectral peaks at 0.15 and 0.45 Hz, the amplitude of force modulation was similar in young and older adults at both frequencies ( F = 1.9, P = 0.17). Force modulation gain ( FMG) was computed as the ratio of the amplitude of force modulation to the amplitude of firing rate modulation. To account for rate coding differences related to the properties of the motoneuron, recruitment threshold force was used as a covariate in age- group comparisons. At both task frequencies, firing rate was modulated with less amplitude ( F = 0 14, P < 0.001) and FMG was greater ( F = 0 27, P < 0.001) in the older adults. In its transformation of neural input to mechanical output, muscle is known to act as a low- pass filter. Compared with modulation at 0.15 Hz, less change in force per change in firing rate at 0.45 Hz ( lower FMG;F = 0 67, P < 0.001), independent of age group, is consistent with this filtering effect. Our conclusion is that there is a reduced amplitude of firing rate modulation in older adults.

关键词： motor control muscle rate coding motoneuron

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Facilitation of mossy fibre-driven spiking in the cerebellar nuclei by the synchrony of inhibition

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JOURNAL OF PHYSIOLOGY-LONDON 2017年第15期595卷 5245-5264页

作者： Wu, Yeechan Raman, Indira M. Northwestern Univ Interdept Neurosci Program Evanston IL 60208 USA Northwestern Univ Dept Neurobiol 2205 Tech Dr Evanston IL 60208 USA

Large projection neurons of the cerebellar nuclei (CbN cells), whose activity generates movement, are inhibited by Purkinje cells and excited by mossy fibres. The high convergence, firing rates and strength of Purkinje inputs predict powerful suppression of CbN cell spiking, raising the question of what activity patterns favour excitation over inhibition. Recording from CbN cells at near-physiological temperatures in cerebellar slices from weanling mice, we measured the amplitude, kinetics, voltage dependence and short-term plasticity of mossy fibre-mediated EPSCs. Unitary EPSCs were small and brief (AMPA receptor, approximate to 1nS, approximate to 1ms;NMDA receptor, approximate to 0.6nS, approximate to 7ms) and depressed moderately. Using these experimentally measured parameters, we applied combinations of excitation and inhibition to CbN cells with dynamic clamp. Because Purkinje cells can fire coincident simple spikes during cerebellar behaviours, we varied the proportion (0-20 of 40) and precision (0-4ms jitter) of synchrony of inhibitory inputs, along with the rates (0-100spikess(-1)) and number (0-800) of excitatory inputs. Even with inhibition constant, when inhibitory synchrony was higher, excitation increased CbN cell firing rates more effectively. Partial inhibitory synchrony also dictated CbN cell spike timing, even with physiological rates of excitation. These effects were present with 10 inhibitory inputs active within 2-4ms of each other. Conversely, spiking was most effectively suppressed when inhibition was maximally asynchronous. Thus, the rate and relative timing of Purkinje-mediated inhibition set the rate and timing of cerebellar output. The results suggest that increased coherence of Purkinje cell activity can facilitate mossy fibre-driven spiking by CbN cells, in turn driving movements.

关键词： cerebellum deep cerebellar nuclei dynamic clamp purkinje cell rate coding temporal coding

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Biomechanical conditioning of the motor unit transitory force decrease following a reduction in stimulation rate

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BMC SPORTS SCIENCE MEDICINE AND REHABILITATION 2020年第1期12卷 1页

作者： Rakoczy, Joanna Krysciak, Katarzyna Drzymala-Celichowska, Hanna Raikova, Rositsa Celichowski, Jan Poznan Univ Phys Educ Dept Neurobiol 27-39 Krolowej Jadwigi St PL-61871 Poznan Poland Bulgarian Acad Sci Inst Biophys & Biomed Engn Sofia Bulgaria

Background The biomechanical background of the transitory force decrease following a sudden reduction in the stimulation frequency under selected experimental conditions was studied on fast resistant motor units (MUs) of rat medial gastrocnemius in order to better understand the mechanisms of changes in force transmission. Methods Firstly, MUs were stimulated with three-phase trains of stimuli (low-high-low frequency pattern) to identify patterns when the strongest force decrease (3-36.5%) following the middle high frequency stimulation was observed. Then, in the second part of experiments, the MUs which presented the largest force decrease in the last low-frequency phase were alternatively tested under one of five conditions to analyse the influence of biomechanical factors of the force decrease: (1) determine the influence of muscle stretch on amplitude of the force decrease, (2) determine the numbers of interpulse intervals necessary to evoke the studied phenomenon, (3) study the influence of coactivation of other MUs on the studied force decrease, (4) test the presence of the transitory force decrease at progressive changes in stimulation frequency, (5) and perform mathematical analysis of changes in twitch-shape responses to individual stimuli within a tetanus phase with the studied force decrease. Results Results indicated that (1) the force decrease was highest when the muscle passive stretch was optimal for the MU twitch (100 mN);(2) the middle high-frequency burst of stimuli composed of at least several pulses was able to evoke the force decrease;(3) the force decrease was eliminated by a coactivation of 10% or more MUs in the examined muscle;(4) the transitory force decrease occured also at the progressive decrease in stimulation frequency;and (5) a mathematical decomposition of contractions with the transitory force decrease into twitch-shape responses to individual stimuli revealed that the force decrease in question results from the decrease of twitch f

关键词： Motor unit Unfused tetanus rate coding Force regulation Stimulation frequency

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Sound coding in the Auditory Nerve: From Single Fiber Activity to Cochlear Mass Potentials in Gerbils

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NEUROSCIENCE 2019年第0期407卷 83-92页

作者： Huet, A. Batrel, C. Wang, J. Desmadryl, G. Nouvian, R. Puel, J. L. Bourien, J. Univ Montpellier INSERM INM Montpellier France

Auditory nerve fibers (ANFs) convey acoustic information from the sensory cells to the brainstem using an elaborated neural code based on both spike timing and rate. As the stimulus tone frequency increases, time coding fades and ceases, resulting in high-frequency tone encoding that relies mostly on the spike discharge rate. Here, we recapitulated our recent single-unit data from gerbil's auditory nerve to highlight the most relevant mode of coding (spike timing versus spike rate) in tone-in-noise. We report that high-spontaneous rate (SR) fibers driven by low-frequency tones in noise are able to phase lock similar to 30 dB below the level that evoked a significant elevation of the discharge rate, whereas medium-and low-SR fibers switch their preferential mode of coding from rate coding in quiet, to time coding in noise. For high-frequency tone, the low-threshold/high-SR fibers reach their maximum discharge rate in noise and do not respond to tones, whereas medium- and low-SR fibers are still able to respond to tones making them more resistant to background noise. Based on these findings, we first discuss the ecological function of the ANF distribution according to their spontaneous discharge rate. Then, we point out the poor synchronization of the low-SR ANFs, accounting for the discrepancy between ANF number and the amplitude of the compound action potential of the of the auditory nerve. Finally, we proposed a new diagnostic tool to assess low-SR fibers, which does not rely on the onset response of the ANFs. This article is part of a Special Issue entitled: Hearing Loss, Tinnitus, Hyperacusis, Central Gain. (C) 2018 IBRO. Published by Elsevier Ltd. All rights reserved.

关键词： temporal coding rate coding auditory nerve background noise hidden hearing loss

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FORCE REGULATION AND ELECTRICAL PROPERTIES OF MOTOR UNITS IN OVERLOADED MUSCLE

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MUSCLE & NERVE 2016年第1期53卷 96-106页

作者： Krysciak, Katarzyna Celichowski, Jan Drzymala-Celichowska, Hanna Gardiner, Phillip F. Krutki, Piotr Univ Sch Phys Educ Poznan Dept Neurobiol PL-61871 Poznan Poland Univ Manitoba Spinal Cord Res Ctr Winnipeg MB Canada Univ Manitoba Fac Kinesiol & Recreat Management Winnipeg MB Canada

Introduction: The influence of long-term muscle overload on force regulation and electrical properties of motor units (MUs) was investigated in rats. Methods: Compensatory overload of the medial gastrocnemius was induced by tenotomy of its synergists. Electrophysiological experiments were performed on functionally isolated MUs 3 months after the surgery. Results: Force-frequency curves for overloaded MUs were shifted rightward compared with control, thus MUs developed the same relative tetanic forces at higher frequencies. Higher force increase was achieved in response to an increase in stimulation frequency in overloaded fast MUs compared with control. The optimal tetanic contraction, characterized by the highest force-time area per pulse, was evoked at higher stimulation frequencies for all overloaded MUs except FF. Only minor adaptive changes in MU action potentials occurred. Conclusions: Compensatory muscle overload leads to substantial modifications in MU force development mechanisms, which are MU-type-specific and influence whole muscle force regulation.

关键词： motor unit MUAP optimal tetanus overload rate coding

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Is there a neural code?

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NEUROSCIENCE AND BIOBEHAVIORAL REVIEWS 1998年第2期22卷 355-370页

作者： Eggermont, JJ Univ Calgary Dept Psychol Behav Neurosci Res Grp Calgary AB T2N 1N4 Canada

rate coding and temporal coding are two extremes of the neural coding process. The concept of a stationary state corresponds to the information processing approach that views the brain as a decision maker, adopts rate coding as its main strategy and endorses the single-or few neuron approach. If information derived from sensory stimulation is used to continuously update the brain's internal representation of the world, then neural codes may change with time through learning. As a consequence, the same spike sequence may be interpreted differently (or evoke a different behavior) later in the day. This non-stationary viewpoint is embodied hi the representational model of brain function that stresses learning and plasticity and employs temporal coding in neural assemblies. We argue that the switching between quasi-stable brain states as a result of learning is more relevant than the neuronal patterns, and the correlations between them, that are found during stationary states. The neural code likely resides in the activity patterns that cause this state-switching. (C) 1998 Elsevier Science Ltd. All rights reserved.

关键词： rate coding temporal coding population coding cardinal cells neural assembly plasticity brain as a dynamical system synchronized EEG brain states state-switching

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Dual coding and effects of global feedback in multilayered neural networks

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NEUROCOMPUTING 2004年 58卷 33-39页

作者： Masuda, N Aihara, K Yokohama Natl Univ Fac Engn Yokohama Kanagawa Japan Univ Tokyo Inst Ind Sci Tokyo Japan

The synchronous firing code mode and the population rate code mode can alternatively appear in a single neural network to be dually used depending upon situations. In this paper, we examine by using multi-layered feedforward networks how the preferred coding mode switches as signals pass through layers. It is also shown that global feedback synchronizes neurons in the upstream layers. (C) 2004 Elsevier B.V. All rights reserved.

关键词： integrate-and-fire neurons rate coding synchrony feedback

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The effects of local forearm muscle cooling on motor unit properties

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EUROPEAN JOURNAL OF APPLIED PHYSIOLOGY 2018年第2期118卷 401-410页

作者： Mallette, Matthew M. Green, Lara A. Gabriel, David A. Cheung, Stephen S. Brock Univ Dept Kinesiol 1812 Sir Isaac Brock Way St Catharines ON L2S 3A1 Canada

Purpose Muscle cooling impairs maximal force. Using needle electromyography (EMG) to assess motor unit properties during muscle cooling, is limited and equivocal. Therefore, we aimed to determine the impact of local muscle cooling on motor unit firing properties using surface EMG decomposition. Methods Twenty participants (12 M, 8 F) completed maximal, evoked, and trapezoidal contractions during thermoneutral and cold muscle conditions. Forearm muscle temperature was manipulated using 10-min neutral (similar to 32 degrees C) or 20-min cold (similar to 3 degrees C) water baths. Twitches and maximal voluntary contractions were performed prior to, and after, forearm immersion in neutral or cold water. Motor unit properties were assessed during trapezoidal contractions to 50% baseline force using surface EMG decomposition. Results Impaired contractile properties from muscle cooling were evident in the twitch amplitude, duration, and rate of force development indicating that the muscle was successfully cooled from the cold water bath (all d >= 0.5, P < 0.05). Surface EMG decomposition showed muscle cooling increased the number of motor units (d = 0.7, P = 0.01) and motor unit action potential (MUAP) duration (d = 0.6, P < 0.001), but decreased MUAP amplitude (d = 0.2, P = 0.012). Individually, neither motor unit firing rates (d = 0.1, P = 0.843) nor recruitment threshold (d = 0.1, P = 0.746) changed;however, the relationship between the recruitment threshold and motor unit firing rate was steeper (d = 1.0, P < 0.001) and had an increased y-intercept (d = 0.9, P = 0.007) with muscle cooling. Conclusions Since muscle contractility is impaired with muscle cooling, these findings suggest a compensatory increase in the number of active motor units, and small but coupled changes in motor unit firing rates and recruitment threshold to produce the same force.

关键词： rate coding Muscle temperature Recruitment threshold Decomposition electromyography Flexor carpi radialis

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