节律性听觉刺激下的神经振荡同步化及其应用

大脑的感觉、情绪、认知等功能与其神经振荡模式有密切的联系。通过施加节律性刺激可以调控大脑的神经振荡模式,进而影响个体感受、情绪状态和认知功能等。与近年来常见的非侵入性电刺激和磁刺激相比,同样依赖于外部刺激输入的节律性感觉刺激具有成本低、易操作等优点,被认为是一种极具潜力的神经调控手段。本文以节律性听觉刺激为例,系统综述了不同类型的节律性听觉刺激如何影响大脑的神经振荡模式,进而影响相关状态和功能;并通过总结外部节律性听觉刺激对个体感知觉、情绪与认知功能的影响,讨论其生理机制和应用前景。     

具有节点偏置的高阶神经网络模型

在汪涛文献基础上提出了一个具有节点偏置的高阶神经网络模型、给出了模型的哈密顿量和学习算法,证明了学习算法的收敛性,该模型能对每一神经元自动引入一个节点偏置使得网络能够存储所有学习图样包括相关图样,其存储容量远高于Hebb—rule—like学习算法下的高阶神经网络模型.对由30个神经元组成的二阶神经网络进行了计算机仿真,结果证实了上述结论.此外,对初始突触强度对学习效果的影响和不同存储图样数目下的平均吸引半径进行了仿真计算并分析了所得结果.新模型的特点使其具有良好的应用前景     

采用Reichardt运动检测器和Boltzmann Machine神经网络的运动计算

建立了一个探讨灵长类视皮层从Ｖ１区到ＭＴ区的运动信息加工原理的计算模型,这个过程的突出特征是视觉运动信息经过了从局部检测进步到整体感知。模型的第一层由用于抽提运动模式的局部速度以及结构性质的Ｒｅｉｃｈａｒｄｔ运动检测器组成,进一步的加工是通过Ｂｏｌｔｚｍａｎｎ Ｍａｃｈｉｎｅ神经网络来实现的。这种网络的学习算法具有局部更新的显著性质,在学习阶段,网络不断地修改联结权重以形成对于记录在网络的显单元上     

国家公园类型划分与空间识别——以云南省为例

国家公园是我国推进生态文明建设的重大制度创新,如何科学地对国家公园进行类型划分及空间识别,是国家公园布局和建设中的基础性工作,既有必要性也有紧迫性。本研究以中国国情为基础,参考国际经验,将国家公园划分为荒野导向型、生态优先型、游憩导向型与遗产导向型,构建了一个比较完整的国家公园分类体系。并以自然和人文多样化程度较高的云南为案例,以“双评价”为基础建立了一套指标体系和区划规则,利用人工神经网络建立土地利用演化学习算法,利用融入自适应惯性机制的元胞自动机展开时空模拟,对云南全域进行高分辨率不同类型国家公园的空间辨识,并通过收缩-膨胀原理对识别区域进行比较、修正和优化,进而提出未来云南国家公园布局的综合方案。结果表明: 云南省国家公园主要集中在三江地区与横断山区、滇西以及西南部地区,这3类地区可作为未来国家公园区划与分类保护的重点。本研究所建立的国家公园类型划分和空间识别的一般性可推广的研究范式和工作流程可作为全国应用的参考。     

Changing synaptic specificities in the nervous system of Caenorhabditis elegans: Differentiation of the DD motoneurons

During postembryonic development, the DD motoneurons in the nematode Caenorhabditis elegans completely reorganize their pattern of synapses. Ablation of a pair of embryonic precursors results in the absence of this entire class of motoneurons. In their absence animals exhibit two developmentally distinct locomotory defects. The transition period from one defect to the other is correlated with the synaptic reorganization of the DD mns. Mutations in a gene (unc-123) have been isolated that exhibit locomotory defects similar to those of the ablated adult animals. Genetic and cellular analyses of one of these alleles suggest that the unc-123 gene product may be involved in the reestablishment of functional synapses in these neurons. © 1993 John Wiley & Sons, Inc.     

Neuronal specificity and its development in the Drosophila wing disc and its derivatives

The imaginal wing disc of flies gives rise to the adult wing blade and dorsal thorax (notum). A great deal has been learned in recent years about the process of neurogenesis in this disc; a number of genes that play crucial roles in the formation of sensory mother cells and in the differentiation of the sensory organs have been identified and their roles defined. Given this extensive background of developmental genetics, it has seemed profitable to summarize what is known about the end-products of neural development, the adult sensory organs. Discussed are their physiological function and role in behavior, the pathways followed by their axons in the CNS, and both genes and epigenetic processes that might play some role in the later stages of neural development and in adult function. The highly individual characteristics of certain of the sensory organs is emphasized, both in the context of their adult roles and as a challenge for future studies in developmental genetics. © 1993 John Wiley & Sons, Inc.     

Induction and axial patterning of the neural plate: Planar and vertical signals

In this review I summarize recent findings on the contributions of different cell groups to the formation of the basic plan of the nervous system of vertebrate embryos. Midline cells of the mesoderm—the organizer, notochord, and prechordal plate—and midline cells of the neural ectoderm—the notoplate and floor plate—appear to have a fundamental role in the induction and patterning of the neural plate. Vertical signals acting across tissue layers and planar signals acting through the neural epithelium have distinct roles and cooperate in induction and pattern formation. Whereas the prechordal plate and notochord have distinct vertical signaling properties, the initial anteroposterior (A-P) pattern of the neural plate may be induced by planar signals originating from the organizer region. Planar signals from the notoplate may also contribute to the mediolateral (M-L) patterning of the neural plate. These and other findings suggest a general view of neural induction and axial patterning. © 1993 John Wiley & Sons, Inc.     

Modeling of the H-reflex facilitation during ramp and hold contractions

Healthy subjects were asked to make a voluntary ramp and hold contraction. The duration of the ramp stage was 500 ms, and the torque increment in this period was set to 15 Nm. The contraction was made from a relaxed and from a 5 Nm background torque situation. Hoffmann (H-) reflexes were elicited during the voluntary contraction, mostly with 100 ms intervals. These experiments showed an increase (facilitation) in the H-reflex before the torque or the EMG started to increase. This facilitation of the H-reflex remained during all the stages of the voluntary movement and declined to normal levels again only at the very end of the hold phase, which lasted for one second. This specific pattern of facilitation during a voluntary contraction was modeled using a modeling language, that is specifically designed to calculate neuronal systems with a high degree of reality (Ekeberg et al., 1991). Our model consisted of a motoneuron pool with 200 neurons connected to an EMG-model of the human soleus muscle and an extra group of higher-level neurons for controlling the amount of decrease of presynaptic inhibition. The model was used to simulate the observed modulation of the H-reflex with both a presynaptic and a postsynaptic mechanism. Simulations showed that a continuous change in the descending control signals is needed to make the model based on postsynaptic mechanism fit with the experimental data, whereas no extra control from the CNS over the excitatory drive to the motoneuron pool is needed when the decrease of presynaptic inhibition mechanism is applied.     

Astroglial Cells Express Large Amounts of GABAA Receptor Proteins in Mature Brain

Abstract: GABA_A receptors were characterized in cellular fractions isolated from adult bovine brain. The fraction enriched in cortical astrocytes is very rich in high-affinity binding sites for [³H]flunitrazepam and other "central-type" benzodiazepine ligands. The amount of specific [³H]flunitrazepam binding was more than five times higher in the glial fraction than in synaptosomal and perikaryal fractions. [³H]Flunitrazepam was displaced by low concentrations of clonazepam and other specific ligands for central GABA_A receptors. Specific binding sites for GABA, flunitrazepam, barbiturates, and picrotoxin-like convulsants were characterized. Allosteric interactions between the different sites were typical of central-type GABA_A receptors. The presence of α-subunit(s), as revealed by [³H]flunitrazepam photoaffinity labeling, was demonstrated in all brain fractions at molecular mass 51–53 kDa. Photoaffinity labeling was highest in the glial fraction. However, in primary cultured astrocytes from neonate rat cortex, no photoaffinity labeling was detected. Information obtained from astrocytes in culture should thus be taken with caution when extrapolated to differentiated astroglial cells. Our results actually show that, in mature brain, most of the fully pharmacologically active GABA_A receptors are extrasynaptic and expressed in astroglia.     

Elimination of heparan sulfate by heparitinases induces abnormal mesodermal and neural formation in Xenopus embryos

The expression of heparan sulfate glycosaminoglycan (HS-GAG) was examined in Xenopus embryos during the developmental stages. Chemical analysis showed the existence of HS-GAG in the ³⁵S-labeled embryos. By western blot analysis using a specific anti-HS monoclonal antibody, HS-GAG related epitope was found after the neurulation on two protein bands, whose molecular weights were approximately 90 kDa and 100 kDa, respectively. Immunohistochemistry revealed that HS-GAG occurred exclusively in the animal hemisphere in early gastrulae, and then appeared predominantly on the sheath of the neural tube, the notochord and epithelium. To address whether HS-GAG chains contribute to Xenopus embryonic development, we eliminated the embryonic HS-GAG by injecting purified Flavobacterium heparitinases (HSase) into their blastocoels. Most of the injected embryos were aberrant in mesodermal and neural formation, and became acephalic. Histological examination showed that these embryos were completely devoid of the central nervous system and the mesodermal tissues. Neither heat-inactivated heparitinase nor chondroitinase showed such abnormality. The HS-GAG-eliminated embryos showed decreased expression of both muscular and neural-specific markers. These results suggest that HS-GAG plays an indispensable role in establishing the fundamental body plan during early Xenopus development.