Coupling between neuronal firing, field potentials, and FMRI in human auditory cortex

Functional magnetic resonance imaging (fMRI) is an important tool for investigating human brain function, but the relationship between the hemodynamically based fMRI signals in the human brain and the underlying neuronal activity is unclear. We recorded single unit activity and local field potentials in auditory cortex of two neurosurgical patients and compared them with the fMRI signals of 11 healthy subjects during presentation of an identical movie segment. The predicted fMRI signals derived from single units and the measured fMRI signals from auditory cortex showed a highly significant correlation (r = 0.75, P < 10(-47)). Thus, fMRI signals can provide a reliable measure of the firing rate of human cortical neurons.     

Excitation and inhibition of neuronal firing in visual cortex by reticular stimulation

The frequency of action potentials of about one-third of the neurons sampled in the striate cortex of awake rabbits was clearly modified by mild stimulation of the reticular core of the brain stem. Reticular stimulation often brought about enhancement of firing in units activated by light, while it usually had the contrary effect upon light-inhibited units.     

Clonally related cortical cells show several migration patterns

The mammalian cerebral cortex is organized into columns of cells with common functional properties. During embryogenesis, cortical neurons are formed deep, near the lateral ventricles, and migrate radially to their final position. This observation led to the suggestion that the cortex consists of radial, ontogenetic units of clonally related neurons. In the experiments reported here, this hypothesis was tested by studying cell lineage in the rat cortex with a retroviral vector carrying the Escherichia coli beta-galactosidase gene, which can be easily visualized. Labeled, clonally related cortical neurons did not occur in simple columnar arrays. Instead, clonally related neurons entered several different radial columns, apparently by migrating along different radial glial fibers.     

Human fetal cerebellar cortex: organization and maturation of cells in vitro

Human fetal cerebellar cortex was maintained up to 5 months in vitro. Important features included early migration of granule neurons followed by maturation of Purkinje and granule neurons. Unique areas of organization developed in which a rim of leptomeningeal cells surrounded an explant and its outgrowth zone; these areas subsequently grew as well-defined units.     

Somatosensory cortex: structural alterations following early injury to sense organs

In mouse somatosensory cortex there are discrete cytoarchitectonic units, called "barrels." Each barrel is related to one sensory vibrissa on the muzzle. Individual vibrissae were carefully injured at birth; 12 to 43 days later, the corresponding barrels proved to be absent. Evidently the sensory periphery has an important influence on the structure of the somatosensory cortex.     

新形势下农业科研单位与所办企业关系的变革与创新

新形势下,如何处理农业科研单位与所办企业之间的关系是科技体制改革面临的重要问题。文章指出当前两者之间的关系与国家科技创新体系要求不符合,指明了农业科研单位与所办企业关系的改革方向,即农业科研单位剥离非公益职能、所办企业建立现代企业制度等,并提出了建立直接收益激励机制、创新农业科研单位的存在模式、建立人才激励机制等促进农业科研单位和所办企业共同发展的建议。     

Superior colliculus: single unit responses to stimulation of visual cortex in the cat

Electrical stimulation of area 18 of the cat visual cortex produces intense excitation of neurons in the superior colliculus. Excitation is followed by a period of decreased collicular responsiveness to light stimulation. These effects are seen in both directionally selective and nonselective units. The corticocollicular projection is retinotopically organized.     

CORTICO-SUBCORTICAL HOMEOSTASIS IN THE CAT'S BRAIN

Transcortical polarization of one cerebral hemisphere, while producing the well-known changes in the amplitude of the evoked potentials in the ipsilateral cortex, induced opposite behavior of these indicators in the contralateral cortex. With the corpus callosum sectioned, the reciprocal relationship was enhanced. Anesthetic doses of barbiturates not only eliminated reciprocity but made the potentials on both sides react in unison to unilateral polarization. These findings suggest the existence of a negative feedback system between the cerebral cortex and the subcortex and the existence of a "left-right equalizing" mechanism carried by pathways in the corpus callosum.     

The prefrontal cortex: response selection or maintenance within working memory?

It is controversial whether the dorsolateral prefrontal cortex is involved in the maintenance of items in working memory or in the selection of responses. We used event-related functional magnetic resonance imaging to study the performance of a spatial working memory task by humans. We distinguished the maintenance of spatial items from the selection of an item from memory to guide a response. Selection, but not maintenance, was associated with activation of prefrontal area 46 of the dorsal lateral prefrontal cortex. In contrast, maintenance was associated with activation of prefrontal area 8 and the intraparietal cortex. The results support a role for the dorsal prefrontal cortex in the selection of representations. This accounts for the fact that this area is activated both when subjects select between items on working memory tasks and when they freely select between movements on tasks of willed action.     

Effect of pyramidal tract activity on dorsal column nuclei

The response of single units in cuneate and gracile nuclei to cutaneous stimulation can be modified by prior stimulation of the motor cortex of the cat. Both excitation and inhibition of these neurons can be effected via the pyramidal tract.     

Rhesus monkey vestibular cortex: a bimodal primary projection field

Single units in the rhesus monkey (Macaca mulata) cortex responded to both vestibular and proprioceptive somatosensory stimuli. This bimodal response characteristic is unlike the modality specificity noted for other primary sensory fields. The vestibular field is located, contrary to previous opinion, within a distinct cytoarchitectonic area outside of area 2.     

Flexible retinotopy: motion-dependent position coding in the visual cortex

Although the visual cortex is organized retinotopically, it is not clear whether the cortical representation of position necessarily reflects perceived position. Using functional magnetic resonance imaging (fMRI), we show that the retinotopic representation of a stationary object in the cortex was systematically shifted when visual motion was present in the scene. Whereas the object could appear shifted in the direction of the visual motion, the representation of the object in the visual cortex was always shifted in the opposite direction. The results show that the representation of position in the primary visual cortex, as revealed by fMRI, can be dissociated from perceived location.     

规模化玉米机械化茬耕整地技术选择与机组性能试验

文章提出适宜规模化种植条件下3种玉米后茬耕整地工艺方案;选择5种典型玉米后茬耕整地机组,采用定距多点同步跟踪试验方法,测试各机组耕整地季节发生时间项目及其数值;建立耕整地机组时间利用率随地块条件变化数学模型,分析规模化生产典型耕整地机组时间利用率随地块条件变化规律。提供玉米茬机械化耕整地工艺方案,明确当地块长度不变时,耕整地机组时间利用率随地块面积增加而增加,当地块面积不变时,耕整地机组时间利用率随地块长度增加而增加,不同机组增加幅度不同。研究旨在完善农业机械运用理论,填补规模生产条件下耕整地机组无定量选型依据空白。     

不同耐旱性玉米根系解剖结构比较研究

以不同耐旱性玉米品种为试验材料,采用徒手切片法和常规石蜡制片法对玉米的初生根和各层次生根的基部、中部和根尖成熟区显微结构进行了系统研究和比较.结果表明:与不耐旱品种玉米的根系相比,耐旱玉米的初生主根的皮层细胞层数较少,木质部导管数量较多、导管直径较小;各层次生根的皮层细胞层数相对较少,木质部导管数量相对较多,导管直径相对较小.     

杜仲叶中绿原酸稳定性研究及沉降试验

研究了绿原酸的稳定性并进行了沉降试验,结果表明,绿原酸在温度小于60℃保持4 h以下及酸性、室内闭光的条件下比较稳定,而在碱性、强光照射下不稳定;同时,沉降剂(cjh∶cjj=1∶3)使用不利于杜仲叶中有效成分绿原酸的提取,造成绿原酸1%的损失。     

Motor cortex reflexes associated with learned movement

In primates, sensory input can generate reflex motor cortex output in association with learned movement when the sensory input has a strong and direct connection to the motor cortex-for example, when a stimulus calling for repositioning of the hand consists of a perturbation of hand position. This finding supports the proposal that neurons of primate motor cortex may function in a transcortical servo-loop.     

Interaction of critical periods in the visual cortex of kittens

The critical period for modifying the preferred direction in cat cortical units occurs earlier than that for monocular deprivation. The independence of the effects of these two types of deprivation from each other was tested by rearing six kittens with both reverse suture and reversed directional deprivation. The kittens were placed in a drum rotating in one direction with one eye open at ages 2 1/2 to 5 weeks; the drum rotation was reversed and the other eye opened when they were 5 to 12 weeks old. Recordings were then made in the visual cortex. The results were the sum of the effects of reverse suture and reversal of directional deprivation: most cells were driven by the eye that was open second, and most unidirectional cells preferred the direction to which the animals were exposed first. Consequently, many unidirectional cells preferred the first direction but were driven by the eye open second--a combination that the animal never saw during rearing. There was also an effect of ocular deprivation on directional properties and vice versa: reverse suture reduced the overall percentage of unidirectional cells, just as directional deprivation has been shown to affect the ocular dominance histogram. This result suggests that the same cells may be affected by both forms of deprivation.     

Visual experience modifies distribution of horizontally and vertically oriented receptive fields in cats

Cats were raised from birth with one eye viewing horizontal lines and one eye viewing vertical lines. Elongated receptive fields of cells in the visual cortex were horizontally or vertically oriented-no oblique fields were found. Units with horizontal fields were activated only by the eye exposed to horizontal lines; units with vertical fields only by the eye exposed to vertical lines.     

杨树苗木蛋白质与内源激素的动态变化研究

[目的]研究杨树苗木蛋白质与内源激素的动态变化。[方法]以1年生杨树无性系797杨（P．deltoides×Peuramericana）苗木为材料，研究其叶片和苗木主干皮层中总蛋白质含量的年动态变化。并用酶联免疫法测定同时期叶片和苗木主干皮层中内源激素的含量变化，分析内源激素与蛋白质含量变化的相关性。[结果]1年生杨树苗木叶片和主干皮层中总蛋白质含量变化趋势相反。春季展叶期间叶片总蛋白质含量较高，皮层含量较低；进入秋冬季节，叶片含量降低，皮层开始逐渐积累蛋白质。内源激素季节性变化起伏波动较大，与蛋白质变化密切相关，并间接地调控杨树营养贮藏蛋白质的降解与合成。[结论]探索植物激素在杨树氮素代谢过程中的调控作用，为杨树丰产栽培提供科学依据。     

狼毒根原料特点及其中柱制备糠醛研究

瑞香狼毒是我国北方草原上典型的多年生草本毒植物,资源化利用是新的治理思想和方式。以青海湖南岸的狼毒为研究对象,对其根部原料特征、化学成分和中柱部分制备糠醛进行了测定分析。结果表明:狼毒根皮层厚度与其最大直径呈直线关系;含水量为4.5%时,狼毒根中柱密度(0.72 g/cm~3)略高于皮层密度(0.69 g/cm~3);狼毒根中柱与皮层的化学成分有较大差异。由于狼毒根中柱部分聚戊糖含量较高,适合作为制备糠醛的原料,本研究中糠醛的得率为8.2%,与目前工业常用的原料蔗渣相仿。研究结果可为狼毒资源化提供参考依据。