Functional specificity of local synaptic connections in neocortical networks

Neuronal connectivity is fundamental to information processing in the brain. Therefore, understanding the mechanisms of sensory processing requires uncovering how connection patterns between neurons relate to their function. On a coarse scale, long-range projections can preferentially link cortical regions with similar responses to sensory stimuli. But on the local scale, where dendrites and axons overlap substantially, the functional specificity of connections remains unknown. Here we determine synaptic connectivity between nearby layer 2/3 pyramidal neurons in vitro, the response properties of which were first characterized in mouse visual cortex in vivo. We found that connection probability was related to the similarity of visually driven neuronal activity. Neurons with the same preference for oriented stimuli connected at twice the rate of neurons with orthogonal orientation preferences. Neurons responding similarly to naturalistic stimuli formed connections at much higher rates than those with uncorrelated responses. Bidirectional synaptic connections were found more frequently between neuronal pairs with strongly correlated visual responses. Our results reveal the degree of functional specificity of local synaptic connections in the visual cortex, and point to the existence of fine-scale subnetworks dedicated to processing related sensory information.     

Guarding the gateway to cortex with attention in visual thalamus

The massive visual input from the eye to the brain requires selective processing of some visual information at the expense of other information, a process referred to as visual attention. Increases in the responses of visual neurons with attention have been extensively studied along the visual processing streams in monkey cerebral cortex, from primary visual areas to parietal and frontal cortex. Here we show, by recording neurons in attending macaque monkeys (Macaca mulatta), that attention modulates visual signals before they even reach cortex by increasing responses of both magnocellular and parvocellular neurons in the first relay between retina and cortex, the lateral geniculate nucleus (LGN). At the same time, attention decreases neuronal responses in the adjacent thalamic reticular nucleus (TRN). Crick argued for such modulation of the LGN by observing that it is inhibited by the TRN, and suggested that "if the thalamus is the gateway to the cortex, the reticular complex might be described as the guardian of the gateway", a reciprocal relationship we now show to be more than just hypothesis. The reciprocal modulation in LGN and TRN appears only during the initial visual response, but the modulation of LGN reappears later in the response, suggesting separate early and late sources of attentional modulation in LGN.     

Influence of the thalamus on spatial visual processing in frontal cortex

Each of our movements activates our own sensory receptors, and therefore keeping track of self-movement is a necessary part of analysing sensory input. One way in which the brain keeps track of self-movement is by monitoring an internal copy, or corollary discharge, of motor commands. This concept could explain why we perceive a stable visual world despite our frequent quick, or saccadic, eye movements: corollary discharge about each saccade would permit the visual system to ignore saccade-induced visual changes. The critical missing link has been the connection between corollary discharge and visual processing. Here we show that such a link is formed by a corollary discharge from the thalamus that targets the frontal cortex. In the thalamus, neurons in the mediodorsal nucleus relay a corollary discharge of saccades from the midbrain superior colliculus to the cortical frontal eye field. In the frontal eye field, neurons use corollary discharge to shift their visual receptive fields spatially before saccades. We tested the hypothesis that these two components-a pathway for corollary discharge and neurons with shifting receptive fields-form a circuit in which the corollary discharge drives the shift. First we showed that the known spatial and temporal properties of the corollary discharge predict the dynamic changes in spatial visual processing of cortical neurons when saccades are made. Then we moved from this correlation to causation by isolating single cortical neurons and showing that their spatial visual processing is impaired when corollary discharge from the thalamus is interrupted. Thus the visual processing of frontal neurons is spatiotemporally matched with, and functionally dependent on, corollary discharge input from the thalamus. These experiments establish the first link between corollary discharge and visual processing, delineate a brain circuit that is well suited for mediating visual stability, and provide a framework for studying corollary discharge in other sensory systems.     

Generation of end-inhibition in the visual cortex via interlaminar connections

To understand the mechanisms by which the receptive field properties of visual cortical cells are generated, one must consider both the thalamic input to the cortex and the intrinsic cortical connections. In the cat striate cortex, layer 4 is the main recipient of input from the lateral geniculate nucleus, yet the cells in that layer possess several receptive field properties that are distinct from the geniculate input, including orientation specificity, binocularity, directionality and end-inhibition, the last of which allows cells to respond to edges of a restricted length. These properties could be generated by connections within the layer, by its input from the claustrum or by the massive projection that layer 4 receives from layer 6. In the present study, we attempted to determine the functional role of the layer 6 to layer 4 projection by reversible inactivation of layer 6 using the inhibitory transmitter gamma-aminobutyric acid (GABA). After inactivating layer 6, cells in layer 4 lost end-inhibition. Cells in layer 2 + 3, which receive their principal input from layer 4, were similarly affected. The elimination of end-inhibition was specific, other receptive field properties, such as direction selectivity or orientation specificity, remaining intact.     

Lack of association between intrachromosomal gene conversion and reciprocal exchange

The association of reciprocal exchange with intrachromosomal gene conversion has been examined using an inverted repeat at the HIS3 locus of Saccharomyces cerevisiae. Intrachromosomal gene conversions between the duplicated inverted sequences are frequent. In contrast to gene conversion events between homologous chromosomes, intrachromosomal gene conversion is not associated with reciprocal exchange in flanking sequences. This observation has important consequences for the role of gene conversion in the maintenance of multigene families.     

Retrospective and prospective coding for predicted reward in the sensory thalamus

Reward is important for shaping goal-directed behaviour. After stimulus-reward associative learning, an organism can assess the motivational value of the incoming stimuli on the basis of past experience (retrospective processing), and predict forthcoming rewarding events (prospective processing). The traditional role of the sensory thalamus is to relay current sensory information to cortex. Here we find that non-primary thalamic neurons respond to reward-related events in two ways. The early, phasic responses occurred shortly after the onset of the stimuli and depended on the sensory modality. Their magnitudes resisted extinction and correlated with the learning experience. The late responses gradually increased during the cue and delay periods, and peaked just before delivery of the reward. These responses were independent of sensory modality and were modulated by the value and timing of the reward. These observations provide new evidence that single thalamic neurons can code for the acquired significance of sensory stimuli in the early responses (retrospective coding) and predict upcoming reward value in the late responses (prospective coding).     

N-LDMOSFET的掺杂分布与热载流子效应

文章从MOSFET热载流子效应角度研究了N-LDMOSFET在不同的区域掺杂浓度条件下器件的最坏热载流子应力条件;在确定的器件工作条件下结合器件仿真结果,分析了在不同掺杂浓度下器件电特性退化的趋势;详细分析了导致器件退化趋势不同的原因,重点讨论了沟道掺杂和漂移区掺杂与器件热载流子效应关系,提出了N-LDNMOS中区域掺杂的优化策略。     

Correlations between T-cell specificity and the structure of the antigen receptor

The derived amino-acid sequences of the heterodimeric antigen receptors expressed by a series of murine T-cell clones are presented. A comparison of the receptor sequences indicates that several mechanisms for generating receptor diversity can influence T-cell specificity, including junctional diversity, combinatorial joining, and combinatorial chain associations.     

Prostaglandins and the synergism between VIP and noradrenaline in the cerebral cortex

We have previously shown that vasoactive intestinal peptide (VIP) and noradrenaline (NA) interact synergistically to increase cyclic AMP levels in mouse cerebral cortical slices. The pharmacological mechanism of this synergism is the potentiation by NA, through alpha 1 adrenergic receptors, of the stimulatory effect of VIP on cAMP formation. A similar interaction has been confirmed in guinea pig cerebral cortex and in discrete nuclei of the rat hypothalamus. Furthermore VIP and NA interact synergistically to depress the spontaneous activity of identified neurons in rat neocortex. At the cellular level, this synergistic interaction suggests that VIP- and NA-containing neuronal systems may converge, at least in part, on the same target cells to increase cAMP levels in the cerebral cortex. At the molecular level, the interaction may occur at various steps in signal transduction, between receptors, intramembrane transduction processes or intracellular effector mechanisms. Here we report that the alpha 1-adrenergic potentiation of the increases in cAMP elicited by VIP involves the formation of arachidonic acid metabolites and is mimicked by prostglandins F2 alpha and E2.     

H型钢梁与矩形钢管柱平齐端板单向螺栓节点承载力性能

对H型钢梁与矩形钢管柱平齐式端板单向螺栓连接节点承载性能进行试验和理论分析研究.通过对3种不同形式的平齐式端板单向螺栓连接节点进行单调静力加载试验,获得了各试件的破坏模式和弯矩-转角曲线,讨论了螺栓破坏、端板破坏、柱壁破坏等3种破坏模式.基于试验现象提出了节点螺栓力理论分布模式,并给出了螺栓强度控制的节点抗弯承载力计算公式.通过将端板和钢梁腹板等效为T形件,得出了端板屈服控制的节点抗弯承载力计算公式.基于试验现象并利用屈服线理论提出了钢管柱壁的屈服线模型,运用虚功原理得出由柱壁强度控制的节点抗弯承载力计算公式.研究表明螺栓、端板、柱壁间的相对强弱关系直接影响节点的破坏模式,理论计算值与试验相比结果偏安全.给出了H型钢梁与矩形钢管柱平齐式端板单向螺栓连接节点的设计准则和建议.     

斜拉桥合理墩形及墩梁约束体系抗震研究

过渡墩、辅助墩墩顶设置平衡重是斜拉桥一种常见设计方式,此设计的特点是墩顶所受质量大、但重力小,由此导致过渡墩、辅助墩在地震作用下受到的地震力大、而轴压力小,进而引发过渡墩、辅助墩的动轴拉力、支座动反拉力以及支座剪力过大等抗震问题。以某斜拉桥为背景,针对其过渡墩、辅助墩墩高小的特点,以及纵向+竖向地震作用下,竖向地震作用使辅助墩墩顶支座以及墩底截面产生较大动反拉力和动轴拉力的现象,提出过渡墩以墙式墩取代门式框架墩、辅助墩墩顶支座改为双向滑动支座、过渡墩墩梁之间横向设置速度型动力锁定装置的比选方案。分析表明,此比选方案可有效解决墩中的动轴拉力、支座动反拉力以及支座剪力过大的问题。但是,由于锁定力需求较大,速度型动力锁定装置的选取需根据进一步的经济比选决定。     

Requirement for subplate neurons in the formation of thalamocortical connections

The neurons of layer 4 in the adult cerebral cortex receive their major ascending inputs from the thalamus. In development, however, thalamic axons arrive at the appropriate cortical area long before their target layer 4 neurons have migrated into the cortical plate. The axons accumulate and wait in the zone below the cortical plate, the subplate, for several weeks before invading the cortical plate. The subplate is a transient zone that contains the first postmitotic neurons of the telencephalon. These neurons mature well before other cortical neurons, and disappear by cell death after the thalamic axons have grown into the overlying cortical plate. The close proximity of growing thalamocortical axons and subplate neurons suggests that they might be involved in interactions important for normal thalamocortical development. Here we show that early in development the deletion of subplate neurons located beneath visual cortex prevents axons from the lateral geniculate nucleus of the thalamus from recognizing and innervating visual cortex, their normal target. In the absence of subplate neurons, lateral geniculate nucleus axons continue to grow in the white matter past visual cortex despite the presence of their target layer 4 neurons. Thus the transient subplate neurons are necessary for appropriate cortical target selection by thalamocortical axons.     

浅谈汉语中对陌生年轻女性的称谓语缺环

称谓语使甩的能力,是交际能力的一种体现,然而称谓语造成的尴尬相当普遍。其中一个例子就是人们在面对陌生年轻女性时,不知如何称呼,存在着称谓缺环。“小姐”、“大姐”、“姑娘”、“美女”等几个称谓语都不能弥补这个缺环。汉语中称谓语缺环现象是新旧观念的撞击造成的,解决的途径是要转变人们的伦理观念,建立一种开放的新型的语言交际观。     

管法兰垫片连接系统的可视化设计

鉴于适用于压力管道连接的法兰、垫片标准众多、数据量庞大且连接结构的设计过程十分复杂,本连接系统通过建立法兰和垫片标准尺寸的Access数据库,开发了基于Visual Basic的管法兰垫片连接系统的设计软件,集成了连接系统的紧密性分析、可靠性分析和寿命预测等模块,实现了管法兰垫片连接系统的可视化设计.     

Dissociation between hand motion and population vectors from neural activity in motor cortex

The population vector hypothesis was introduced almost twenty years ago to illustrate that a population vector constructed from neural activity in primary motor cortex (MI) of non-human primates could predict the direction of hand movement during reaching. Alternative explanations for this population signal have been suggested but could not be tested experimentally owing to movement complexity in the standard reaching model. We re-examined this issue by recording the activity of neurons in contralateral MI of monkeys while they made reaching movements with their right arms oriented in the horizontal plane-where the mechanics of limb motion are measurable and anisotropic. Here we found systematic biases between the population vector and the direction of hand movement. These errors were attributed to a non-uniform distribution of preferred directions of neurons and the non-uniformity covaried with peak joint power at the shoulder and elbow. These observations contradict the population vector hypothesis and show that non-human primates are capable of generating reaching movements to spatial targets even though population vectors based on MI activity do not point in the direction of hand motion.