A C. elegans stretch receptor neuron revealed by a mechanosensitive TRP channel homologue

The nematode Caenorhabditis elegans is commonly used as a genetic model organism for dissecting integration of the sensory and motor systems. Despite extensive genetic and behavioural analyses that have led to the identification of many genes and neural circuits involved in regulating C. elegans locomotion behaviour, it remains unclear whether and how somatosensory feedback modulates motor output during locomotion. In particular, no stretch receptors have been identified in C. elegans, raising the issue of whether stretch-receptor-mediated proprioception is used by C. elegans to regulate its locomotion behaviour. Here we have characterized TRP-4, the C. elegans homologue of the mechanosensitive TRPN channel. We show that trp-4 mutant worms bend their body abnormally, exhibiting a body posture distinct from that of wild-type worms during locomotion, suggesting that TRP-4 is involved in stretch-receptor-mediated proprioception. We show that TRP-4 acts in a single neuron, DVA, to mediate its function in proprioception, and that the activity of DVA can be stimulated by body stretch. DVA both positively and negatively modulates locomotion, providing a unique mechanism whereby a single neuron can fine-tune motor activity. Thus, DVA represents a stretch receptor neuron that regulates sensory-motor integration during C. elegans locomotion.     

Interruption of a basal ganglia-forebrain circuit prevents plasticity of learned vocalizations

Birdsong, like speech, is a learned vocal behaviour that relies greatly on hearing; in both songbirds and humans the removal of auditory feedback by deafening leads to a gradual deterioration of adult vocal production. Here we investigate the neural mechanisms that contribute to the processing of auditory feedback during the maintenance of song in adult zebra finches. We show that the deleterious effects on song production that normally follow deafening can be prevented by a second insult to the nervous system--the lesion of a basal ganglia-forebrain circuit. The results suggest that the removal of auditory feedback leads to the generation of an instructive signal that actively drives non-adaptive changes in song; they also suggest that this instructive signal is generated within (or conveyed through) the basal ganglia-forebrain pathway. Our findings provide evidence that cortical-basal ganglia circuits may participate in the evaluation of sensory feedback during calibration of motor performance, and demonstrate that damage to such circuits can have little effect on previously learned behaviour while conspicuously disrupting the capacity to adaptively modify that behaviour.     

Overlap of internal models in motor cortex for mechanical loads during reaching

A hallmark of the human motor system is its ability to adapt motor patterns for different environmental conditions, such as when a skilled ice-hockey player accurately shoots a puck with or without protective equipment. Each object (stick, shoulder pad, elbow pad) imparts a distinct load upon the limb, and a key problem in motor neuroscience is to understand how the brain controls movement for different mechanical contexts. We addressed this issue by training non-human primates to make reaching movements with and without viscous loads applied to the shoulder and/or elbow joints, and then examined neural representations in primary motor cortex (MI) for each load condition. Even though the shoulder and elbow loads are mechanically independent, we found that some neurons responded to both of these single-joint loads. Furthermore, changes in activity of individual neurons during multi-joint loads could be predicted from their response to subordinate single-joint loads. These findings suggest that neural representations of different mechanical contexts in MI are organized in a highly structured manner that may provide a neural basis for how complex motor behaviour is learned from simpler motor tasks.     

Spontaneous muscle twitches during sleep guide spinal self-organization

During development, information about the three-dimensional shape and mechanical properties of the body is laid down in the synaptic connectivity of sensorimotor systems through unknown adaptive mechanisms. In spinal reflex systems, this enables the fast transformation of complex sensory information into adequate correction of movements. Here we use a computer simulation to show that an unsupervised correlation-based learning mechanism, using spontaneous muscle twitches, can account for the functional adaptation of the withdrawal reflex system. We also show that tactile feedback resulting from spontaneous muscle twitches during sleep does indeed modify sensorimotor transformation in young rats in a predictable manner. The results indicate that these twitches, corresponding to human fetal movements, are important in spinal self-organization.     

基于自适应滤波算法的FIR MIMO系统均衡

为了实现对多输入多输出(MIMO)系统的均衡,提出了一种基于自适应滤波算法的自适应均衡方法。应用判决反馈式均衡器(DFE)的结构,把MIMO信道均衡问题的模型建模成一个简化的滤波模型。这个滤波模型使MIMO系统均衡问题中均衡器的设计问题转化为自适应滤波中最优滤波器的设计问题。两种典型自适应滤波器设计算法——LMS算法和RLS算法被应用于该模型中进行仿真,仿真结果显示了算法的收敛性和均衡方法的可行性。这种自适应均衡方法不需要对信道进行辨识,具有较小的运算量,并且可以适应信道变化。     

基于AFO 的感应电机无速度传感器控制

针对传统的基于模型参考自适应理论MRAS(Model Reference Adaptive System)的感应电机无速度传感器控制系统存在的参考模型不准确的缺点, 提出了一种以电机本身为参考模型, Luenberger 全阶状态观测器为可调模型的自适应无速度传感器AFO(Adaptive Full-Order Observer)控制策略。整个系统包含产生电机所需转子 磁链的全阶观测器和一个使用自适应率估计转速的转速估算机构。以李雅普诺夫稳定性理论为基础, 使用电机的估算定子电流误差和观测出的转子磁链推导出转速自适应率。以观测器极点配置的方法, 设计了一种快速收敛的反馈矩阵, 保证了在大范围内电机的稳定运行。针对转速估计在低速再生制动时的不稳定现象, 利用劳斯稳定判据, 设计了一种新的反馈矩阵保证转速估算的全局稳定性。通过Matlab/ Simulink 仿真验证了结论的有效性。     

Telemetered in vivo strain analysis of locomotor mechanics of brachiating gibbons

The slender elongated form that is characteristic of the forelimb long bones of gibbons (Hylobates) has long been attributed to their functional adaptation to habitual armswinging locomotion, although potential selective advantages of this morphology for brachiation have yet to be demonstrated. If the forces exerted on the limb skeleton during brachiation indeed differ greatly from those of other locomotor modes, then the changes in skeletal loading accompanying a shift in locomotor behaviour could favour alterations in skeletal morphology in brachiating lineages. In vivo skeletal strain patterns recorded by using radiotelemetry during brachiation indicate that the forelimb bones of the gibbon are loaded in substantial tension and show reduced bending and compression in comparison with those of other mammals. We suggest that this unique loading regime could have contributed to the evolution of the distinctive morphology of hylobatid limbs.     

Motor antagonism exposed by spatial segregation and timing of neurogenesis

Walking is a key motor behaviour of limbed animals, executed by contraction of functionally antagonistic muscle groups during swing and stance phases. Nevertheless, neuronal circuits regulating the activation of antagonistic extensor-flexor muscles remain poorly understood. Here we use monosynaptically restricted trans-synaptic viruses to elucidate premotor anatomical substrates for extensor-flexor control in mice. We observe a medio-lateral spatial segregation between extensor and flexor premotor interneurons in the dorsal spinal cord. These premotor interneuron populations are derived from common progenitor domains, but segregate by timing of neurogenesis. We find that proprioceptive sensory feedback from the periphery is targeted to medial extensor premotor populations and is required for extensor-specific connectivity profiles during development. Our findings provide evidence for a discriminating anatomical basis of antagonistic circuits at the level of premotor interneurons, and point to synaptic input and developmental ontogeny as key factors in the establishment of circuits regulating motor behavioural dichotomy.     

Inactivation of the sarcoplasmic reticulum calcium channel by protein kinase.

The ryanodine receptor protein of skeletal muscle sarcoplasmic reticulum (SR) membranes is a calcium ion channel which allows movement of calcium from the SR lumen into the cytoplasm during muscle activation. Gating of this channel is modulated by a number of physiologically important substances including calcium. Interestingly, calcium has both activating and inactivating effects which are concentration- and tissue-specific. In skeletal muscle, calcium-dependent inactivation of calcium release occurs at concentrations reached physiologically, suggesting that calcium may modulate the release process by a negative feedback mechanism. To determine the cellular mechanism responsible for calcium-dependent inactivation, we have investigated the ability of protein phosphorylation to affect single channel gating behaviour using the patch clamp technique. Here we demonstrate that the ryanodine receptor protein/calcium release channel of skeletal muscle SR is inactivated under conditions permissive for protein phosphorylation. This inactivation is reversed by the application of phosphatase and prevented by a peptide inhibitor specific for calcium/calmodulin-dependent protein kinase II. The results provide evidence for an endogenous protein kinase which is closely associated with the ryanodine receptor protein and regulates channel gating.     

基于图论算法的脊髓损伤后大脑皮层运动区神经元网络分析

 脊髓损伤(SCI)后大脑皮层运动区神经元的功能重组对机体功能康复的影响仍然不为人知。脊髓损伤前后,对一只在跑步机上直立行走的恒河猴的大脑皮层运动区神经元信号进行记录,利用不同神经元动作电位序列间的相关系数建立神经元网络图。为了研究神经元活动模式的变化与功能康复之间的联系,利用图论算法计算了神经元网络图的全局效能指标和神经元脆弱性指标。结果显示,不同时期神经元活动模式的显著变化意味着运动区神经元的功能重组(神经可塑性)与脊髓损伤后猴子的功能康复状态紧密相关,且这种神经功能重组对于猴子步行功能的康复起了非常重要的积极作用。     

基于MRFAC的感应电机控制器设计

结合感应电机这一非线性控制对象,设计了感应电机的模型参考模糊自适应速度控制器。该控制器具有传统模型参考自适应控制构架,传统模型参考自适应控制系统中的反馈控制器和常规自适应机构分别由主模糊控制器、模糊自适应机构替代,模糊逆模型结合自适应调整算法构成的模糊自适应机构对主控制器参数进行实时调整,以达到快速适应对象参数和状态变化的目的。基于模块化建模工具Matlab/Simulink建立感应电机控制系统模型,仿真结果表明该控制器运行平稳,具有良好的动、静态性能。     

Interdependence of behavioural variability and response to small stimuli in bacteria

The chemotaxis signalling network in Escherichia coli that controls the locomotion of bacteria is a classic model system for signal transduction. This pathway modulates the behaviour of flagellar motors to propel bacteria towards sources of chemical attractants. Although this system relaxes to a steady state in response to environmental changes, the signalling events within the chemotaxis network are noisy and cause large temporal variations of the motor behaviour even in the absence of stimulus. That the same signalling network governs both behavioural variability and cellular response raises the question of whether these two traits are independent. Here, we experimentally establish a fluctuation-response relationship in the chemotaxis system of living bacteria. Using this relationship, we demonstrate the possibility of inferring the cellular response from the behavioural variability measured before stimulus. In monitoring the pre- and post-stimulus switching behaviour of individual bacterial motors, we found that variability scales linearly with the response time for different functioning states of the cell. This study highlights that the fundamental relationship between fluctuation and response is not constrained to physical systems at thermodynamic equilibrium but is extensible to living cells. Such a relationship not only implies that behavioural variability and cellular response can be coupled traits, but it also provides a general framework within which we can examine how the selection of a network design shapes this interdependence.     

Regulation of cell movement is mediated by stretch-activated calcium channels.

Intracellular calcium regulates many of the molecular processes that are essential for cell movement. It is required for the production of actomyosin-based contractile forces, the regulation of the structure and dynamics of the actin cytoskeletons, and the formation and disassembly of cell-substratum adhesions. Calcium also serves as a second messenger in many biochemical signal-transduction pathways. However, despite the pivotal role of calcium in motile processes, it is not clear how calcium regulates overall cell movement. Here we show that transient increases in intracellular calcium, [Ca2+]i, during the locomotion of fish epithelial keratocytes, occur more frequently in cells that become temporarily 'stuck' to the substratum or when subjected to mechanical stretching. We find that calcium transients arise from the activation of stretch-activated calcium channels, which triggers an influx of extracellular calcium. In addition, the subsequent increase in [Ca2+]i is involved in detachment of the rear cell margin. Thus, we have defined a mechanism by which cells can detect and transduce mechanical forces into biochemical signals that can modulate locomotion.     

Separate sodium and calcium spikes in the same axon

Aglantha digitale is a jellyfish (order Hydromedusae) capable of two distinct kinds of locomotion; 'slow' swimming which is generated endogenously and is used in fishing behaviour, and 'fast' swimming which is evoked by predators and serves for escape. Both forms of swimming are produced by contraction of the bell-shaped body wall and expulsion of a jet of water from an opening at the base of the animal. During slow swimming, the contractions are weak and the animal moves about 15 mm, roughly one body length, but during a fast swim there is a more violent contraction which can propel the animal five times as far. Both forms of contraction depend on impulses in the eight giant motor axons that synapse directly with the muscle sheet making up the inner surface of the body wall. We report here that the giant motor axons are able to mediate both kinds of activity because they can conduct two different sorts of impulse. Fast swimming requires a rapidly conducted Na+-dependent action potential whereas slow swimming depends on a low amplitude Ca2+ 'spike'. This is the first report of an axon capable of two kinds of impulse propagation and it provides a physiological function for low potential Ca2+ activation.     

含时滞扰动非线性系统的输出反馈自适应控制

研究了一类含变时滞扰动不确定系统的输出反馈自适应稳定问题.假定不确定性满足所谓的匹配条件且标称系统的传递函数矩阵是严格反馈正实的.基于Lyapunov稳定性理论和Lyapunov-Krasovskii型泛函设计出了一种自适应输出反馈控制器,并证明了此控制器使得闭环系统最终一致有界.最后给出一个仿真例子说明结论的有效性.     

Vestibular evidence for the evolution of aquatic behaviour in early cetaceans

Early cetaceans evolved from terrestrial quadrupeds to obligate swimmers, a change that is traditionally studied by functional analysis of the postcranial skeleton. Here we assess the evolution of cetacean locomotor behaviour from an independent perspective by looking at the semicircular canal system, one of the main sense organs involved in neural control of locomotion. Extant cetaceans are found to be unique in that their canal arc size, corrected for body mass, is approximately three times smaller than in other mammals. This reduces the sensitivity of the canal system, most plausibly to match the fast body rotations that characterize cetacean behaviour. Eocene fossils show that the new sensory regime, incompatible with terrestrial competence, developed quickly and early in cetacean evolution, as soon as the taxa are associated with marine environments. Dedicated agile swimming of cetaceans thus appeared to have originated as a rapid and fundamental shift in locomotion rather than as the gradual transition suggested by postcranial evidence. We hypothesize that the unparalleled modification of the semicircular canal system represented a key 'point of no return' event in early cetacean evolution, leading to full independence from life on land.     

参数扫描应用的网格自适应调度

提出一种自适应调度方法,可使参数扫描应用在运行时保持近似的网格负载平衡,为适应资源性能的动态性,一个参数应用被分成若干作业顺序调度,每个作业运行后反馈的网格负载信息用于调整下一个作业的调度。使之适应资源性能波动,从而使后一个作业在运行时实现网格负载的近似平衡。每个作业被分成若干子作业,分别指派到不同的网格资源。子作业的运行时间构成一个网格负载向量,从中可计算出网格负载失衡因子,失衡因子表示作业运行时网格负载失衡的程度。负载向量用于调整下一个作业的划分方法,失衡因子用于调整下一个作业的规模。较小的失衡因子可使作业的规模有更快的增长,这样可使调度成本的增长速度慢于应用规模的增大速度。实验表明,自适应调度可保持近似的网格负载平衡,与其他资源性能的静态调度相比,可有效缩短参数应用的总运行时间。     

Adaptive coding of visual information in neural populations

Our perception of the environment relies on the capacity of neural networks to adapt rapidly to changes in incoming stimuli. It is increasingly being realized that the neural code is adaptive, that is, sensory neurons change their responses and selectivity in a dynamic manner to match the changes in input stimuli. Understanding how rapid exposure, or adaptation, to a stimulus of fixed structure changes information processing by cortical networks is essential for understanding the relationship between sensory coding and behaviour. Physiological investigations of adaptation have contributed greatly to our understanding of how individual sensory neurons change their responses to influence stimulus coding, yet whether and how adaptation affects information coding in neural populations is unknown. Here we examine how brief adaptation (on the timescale of visual fixation) influences the structure of interneuronal correlations and the accuracy of population coding in the macaque (Macaca mulatta) primary visual cortex (V1). We find that brief adaptation to a stimulus of fixed structure reorganizes the distribution of correlations across the entire network by selectively reducing their mean and variability. The post-adaptation changes in neuronal correlations are associated with specific, stimulus-dependent changes in the efficiency of the population code, and are consistent with changes in perceptual performance after adaptation. Our results have implications beyond the predictions of current theories of sensory coding, suggesting that brief adaptation improves the accuracy of population coding to optimize neuronal performance during natural viewing.     

一类具有时滞的模糊反应扩散神经网络的自适应同步研究

研究了一类具有时滞的模糊反应扩散神经网络的自适应同步,在两种不同的边界条件下,利用泛函微分方程的LaSalle不变原理以及反馈控制的方法,得到了系统同步的充分条件.     

一种基于模糊逻辑优先级的雷达任务自适应调度算法

为适应目标环境变化情况,提出了一种基于模糊逻辑优先级的雷达任务自适应调度算法.该方法基于目标运动状态和属性通过模糊逻辑推理动态确定任务的优先级,并结合时间窗的特点采用一步回溯方法调整发生冲突的任务,保证更多高优先级的任务在其期望的时间内被调度.仿真结果表明,该调度算法在保证调度率的前提下降低了任务的调度代价.