共查询到20条相似文献,搜索用时 15 毫秒
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The response of a cortical neuron to a stimulus can show a very large variability when repeatedly stimulated by exactly the same stimulus. This has been quantified in terms of inter-spike-interval (ISI) statistics by several researchers (e.g., [Softky, W., Koch, C., 1993. The highly irregular firing of cortical cells is inconsistent with temporal integration of random EPSPs. J. Neurosci. 13(1), 334-350.]). The common view is that this variability reflects noisy information processing based on redundant representation in large neuron populations. This view has been challenged by the idea that the apparent noise inherent in brain activity that is not strictly related or temporally coupled to the experiment could be functionally significant. In this work we examine the ISI statistics and discuss these views in a recently published model of interacting cortical areas [Knoblauch, A., Palm, G., 2002. Scene segmentation by spike synchronization in reciprocally connected visual areas. I. Local effects of cortical feedback. Biol. Cybernet. 87(3), 151-167.]. From the results of further single neuron simulations we can isolate temporally modulated synaptic input as a main contributor for high ISI variability in our model and possibly in real neurons. In contrast to alternative mechanisms, our model suggests a function of the temporal modulations for short-term binding and segmentation of figures from background. Moreover, we show that temporally modulated inputs lead to ISI statistics which fit better to the neurophysiological data than alternative mechanisms. 相似文献
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Gay JM 《Theriogenology》2006,66(3):526-533
The concepts and methods of the different branches of epidemiology, particularly clinical epidemiology, have much to offer the discipline of theriogenology. As with theriogenology, epidemiologic methods evolve when technological innovation enables new approaches to old problems. The recent emergence, from clinical epidemiology, of the evidence-based medicine paradigm in human medicine, and the associated developments of systematic reviews and meta-analysis, present new opportunities for collaboration and synergy between the two disciplines. 相似文献
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OBJECTIVE--To monitor nutritional status and food security in order to identify nutritionally vulnerable groups. DESIGN--Members of five different household groups (urban and rural residents, displaced people in collective centres and private accommodation, elderly people living without younger family) and all residents of two old people''s homes were prospectively followed. Households were selected from 20 local communities and nine collective centres. SETTING--Monitoring carried out in three besieged areas of Bosnia-Hercegovina (Sarajevo, Tuzla, and Zenica). SUBJECTS--1739 individuals sampled. INTERVENTIONS--Data collected every month from December 1993 to May 1994. Information on household food security was collected through structured questionnaires. All subjects were weighed and their heights measured. Weight for age Z scores were calculated for children; body mass index was calculated for adults and elderly people. RESULTS--From December 1993 to February 1994, before a temporary cease fire, access to food was reduced. In February 1994 no significant signs of undernutrition were detected among children or adults, but elderly people had higher than expected levels of undernutrition (15.5% with body mass index < 18.5), a higher rate of weight loss than adults (1.2 kg over two months), and a higher prevalence of self reported illness. CONCLUSIONS--Elderly people in Bosnia-Hercegovina are at greater risk of undernutrition than other age groups. Undernutrition may be precipitated in elderly people by sickness, cold, stress, and problems related to food preparation. The health and welfare of elderly people during the emergency in Bosnia-Hercegovina require special attention, and integrated age care programmes are needed. 相似文献
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Andrew V.Z. Brower 《Cladistics : the international journal of the Willi Hennig Society》2016,32(5):573-576
The origins and meanings of “cladogram” are reviewed. Traditionally, “cladogram” has been defined as a graphical representation of an empirical hypothesis of relationships among taxa, based on evidence from synapomorphies alone. Disturbingly, numerous recent authors treat “cladogram” as synonymous with “dendrogram” and do not appreciate the particular methodological connotations of the former term. This is lamented. 相似文献
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PURPOSE OF REVIEW: Randomized trials have shown that statins may reduce the risk of primary stroke. There is no evidence however that statins can reduce recurrent stroke incidence. RECENT FINDINGS: In the SPARCL trial, patients with a recent stroke or transient ischemic attack randomized to atorvastatin 80 mg/day had a significant 16% relative risk reduction of stroke, and a 35% reduction in major coronary events compared with placebo. This was obtained despite 25% of the placebo arm patients receiving a commercially-available statin outside of the trial. Post-hoc analysis used blinded LDL-cholesterol measurements as a marker of adherence to lipid-lowering therapy. Compared with the group with no change or an increase in LDL-cholesterol (the group adherent to placebo or not taking a statin), the group with over 50% reduction in LDL-cholesterol had a significant 31% reduction in stroke. The next step is to define whether achieving LDL-cholesterol below 70 mg/dl is better than a standard dose of statin (LDL around 100-110 mg/dl) in the secondary prevention of stroke. SUMMARY: Statins are effective in reducing both first-ever and recurrent stroke, and this effect seems driven by the extent of LDL-cholesterol lowering. 相似文献
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Vanina A. Fernández Martín Kowalewski Gabriel E. Zunino 《Primates; journal of primatology》2013,54(2):191-199
Decisions about when and where to travel are likely to have a strong influence on the feeding, ecology, and foraging strategies of individual primates living in a cohesive social group. Specifically, given differences in age, sex, reproductive status, or social dominance, particular group members may benefit from remaining at their present location while others may benefit from traveling to another area of their range to feed or rest. In this study, we present data on movement coordination in two groups of wild black and gold howler monkeys inhabiting Isla Brasilera (27º 20′S and 58º 40′W) in northern Argentina. We examine how factors such as sex, age, reproductive status, and dominance affect patterns of group movement coordination at feeding or resting sites, and in the context of intergroup encounters. Two groups were followed five days a month from sunrise to sunset during June to November 2004. Using focal and scan sampling techniques, we recorded 262 group displacements, the identity of the individual initiating and leading displacement, and the identity of the first individual to arrive at feeding, resting, or intergroup encounter sites. We found that overall age was the only factor that influenced group coordination: adults led more often (94.5 %) than immature individuals (5.5 %) in both groups. We did not find differences among adults. However, we found that males lead more often than females at intergroup encounters, consistent with the male-mate defense hypothesis. The distributed leadership pattern among adults observed in this study may suggest that adult individuals make equally shared consensus decisions. This pattern should be further examined using this individual-level approach in other populations of black and gold howlers, other species of howlers, and in other atelines in which within-group social tolerance is the rule rather than the exception. 相似文献
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Phosphorothioate oligodeoxynucleotides: what is their origin and what is unique about them? 总被引:4,自引:0,他引:4
Eckstein F 《Antisense & nucleic acid drug development》2000,10(2):117-121
The development of nucleoside phosphorothioates is described in its historical context. Examples of the interaction of phosphorothioate groups, present either in oligodeoxynucleotides or in DNA, with nucleases are presented. The structural features responsible for the resistance of the phosphorothioates toward degradation by nucleases are discussed, as are the possible reasons for the high-affinity interaction of phosphorothioate oligodeoxynucleotides with certain proteins. 相似文献
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Noise is a major problem in analyzing tracking data of cargos moved by molecular motors. We use Bayesian statistics to incorporate what is known about the noise in parsing the trajectory of a cargo into a series of constant velocity segments. Tracks with just noise and no underlying motion are fit with constant velocity segments to produce a calibration curve of fit quality versus average segment duration. Fits to tracks of moving cargos are compared to the calibration curves with similar noise. The fit with the optimum number of constant velocity states has the least number of segments needed to match the fit quality of the calibration curve. We have tested this approach using tracks with known underlying motion generated by computer simulations and with a specially designed in vitro experiment. We present the results of using this parsing approach to analyze transport of lipid droplets in Drosophila embryos. 相似文献
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Maria Arias‐Andres 《Molecular ecology resources》2020,20(3):617-619
To fully understand how plastic is affecting the ocean, we need to understand how marine life interacts directly with it. Besides their ecological relevance, microbes can affect the distribution, degradation and transfer of plastics to the rest of the marine food web. From amplicon sequencing and scanning electron microscopy, we know that a diverse array of microorganisms rapidly associate with plastic marine debris in the form of biofouling and biofilms, also known as the “Plastisphere.” However, observation of multiple microbial interactions in situ, at small spatial scales in the Plastisphere, has been a challenge. In this issue of Molecular Ecology Resources, Schlundt et al. apply the combination labelling and spectral imaging – fluorescence in situ hybridization to study microbial communities on plastic marine debris. The images demonstrate the colocalization of abundant bacterial groups on plastic marine debris at a relatively high taxonomic and spatial resolution while also visualizing biofouling of eukaryotes, such as diatoms and bryozoans. This modern imaging technology provides new possibilities to address questions regarding the ecology of marine microbes on plastic marine debris and describe more specific impacts of plastic pollution in the marine food webs. 相似文献
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Linden M 《World psychiatry》2012,11(2):104-105
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Many sources of fluctuation contribute to the functional magnetic resonance imaging (fMRI) signal, complicating attempts to infer those changes that are truly related to brain activation. Unlike methods of analysis of fMRI data that test the time course of each voxel against a hypothesized waveform, data-driven methods, such as independent component analysis and clustering, attempt to find common features within the data. This exploratory approach can be revealing when the brain activation is difficult to predict beforehand, such as with complex stimuli and internal shifts of activation that are not time-locked to an easily specified sensory or motor event. These methods can be further improved by incorporating prior knowledge regarding the temporal and spatial extent of brain activation. 相似文献
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Episodic memory is defined as the recollection of specific events in one's past, accompanied by the experience of having been there personally. This definition presents high hurdles to the investigation of episodic memory in nonhumans. Recent studies operationalize episodic memory as memory for when and where an event occurred, for the order in which events occurred, or for an animal's own behavior. None of these approaches has yet generalized across species, and each fails to capture features of human episodic memory. Nonetheless, the study of episodic memory in nonhumans seems less daunting than it did five years ago. To demonstrate a correspondence between human episodic memory and nonhuman memory, progress is needed in three areas. Putative episodic memories in nonhumans should be shown to be; first, represented in long-term memory, rather than short-term or working memory; second, explicit, or accessible to introspection; and third, distinct from semantic memory, or general knowledge about the world. 相似文献
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《中国科学:生命科学英文版》2017,(7)
Characterized by their low prevalence, rare diseases are often chronically debilitating or life threatening. Despite their low prevalence, the aggregate number of individuals suffering from a rare disease is estimated to be nearly 400 million worldwide.Over the past decades, efforts from researchers, clinicians, and pharmaceutical industries have been focused on both the diagnosis and therapy of rare diseases. However, because of the lack of data and medical records for individual rare diseases and the high cost of orphan drug development, only limited progress has been achieved. In recent years, the rapid development of next-generation sequencing(NGS)-based technologies, as well as the popularity of precision medicine has facilitated a better understanding of rare diseases and their molecular etiology. As a result, molecular subclassification can be identified within each disease more clearly, significantly improving diagnostic accuracy. However, providing appropriate care for patients with rare diseases is still an enormous challenge. In this review, we provide a brief introduction to the challenges of rare disease research and make suggestions on where and how our efforts should be focused. 相似文献
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