Mathematical Logic in the Human Brain: Syntax

Theory predicts a close structural relation of formal languages with natural languages. Both share the aspect of an underlying grammar which either generates (hierarchically) structured expressions or allows us to decide whether a sentence is syntactically correct or not. The advantage of rule-based communication is commonly believed to be its efficiency and effectiveness. A particularly important class of formal languages are those underlying the mathematical syntax. Here we provide brain-imaging evidence that the syntactic processing of abstract mathematical formulae, written in a first order language, is, indeed efficient and effective as a rule-based generation and decision process. However, it is remarkable, that the neural network involved, consisting of intraparietal and prefrontal regions, only involves Broca''s area in a surprisingly selective way. This seems to imply that despite structural analogies of common and current formal languages, at the neural level, mathematics and natural language are processed differently, in principal.     

Ethical Research Issues: Going Beyond the Declaration of Helsinki

La Vaque and Rossiter made a strong, supported argument that it is unethical to use a no treatment control group in a research study if a known, effective treatment is available. Their argument is based on the supposition that the Declaration of Helsinki is the ethical world standard for research with humans. Their argument appears to be straightforward, but is not simple to apply. The issues are very complex, include issues not discussed in their argument, and can lead to a different conclusion as pointed out in this paper. The World Medical Association developed the Declaration of Helsinki as one of their official policies. The Declaration of Helsinki, however, is not accepted as the world ethical standard, as demonstrated by its lack of adoption by many professional associations or even by the United States Federal Government. Perhaps it is not mentioned because its ethical provisions are aspirational rather than mandatory as implied by La Vaque and Rossiter. Researchers and clinicians should also be aware of other ethical issues not directly discussed in the La Vaque and Rossiter paper. The Belmont Report is the basis for the ethical protection of human research subjects for at least 17 federal agencies and does not mention the Declaration of Helsinki. The Belmont Report mentions several ethical principles that form the basis for informed consent, risk/benefit assessment, confidentiality of data, subject selection, Institutional Review Boards, and other protections needed when doing research with human subjects. At least 2 of these core principles have direct implications to the discussion related to the use of placebo controls. The ethical principle of fidelity is also important in guiding research activities with human subjects. Researchers should be familiar with the La Vaque and Rossiter argument, the Belmont Report, and the federal policies developed to implement the provisions of that report, for example, Regulation 45 CFR 46.     

Land Transitions in the Tropics: Going Beyond the Case Studies

Estimates of the percent of Earth's land surface that has either been transformed or degraded by human activity range between 39 and 50 percent, with agriculture accounting for the vast majority of these changes. Although much of the focus of research on land use and cover change in the tropics has been on deforestation, ongoing socioeconomic changes both locally and globally have made land transitions in the tropics extremely fluid. In addition, feedbacks between land cover change and human behavior constrain the extent and trajectories of land transitions. The sustainability of land use systems in the tropics depends on an understanding of coupled human–natural systems that can lead to general frameworks for management and prediction. The unprecedented availability of land use/cover data together with ecological data collected at large spatial scales offer exciting opportunities for advancing our understanding of socioecological systems. We rely on six studies of land transitions in the tropics to illustrate some promising approaches and pose critical questions to guide this body of research.     

Going Beyond a Mean-field Model for the Learning Cortex: Second-Order Statistics

Mean-field models of the cortex have been used successfully to interpret the origin of features on the electroencephalogram under situations such as sleep, anesthesia, and seizures. In a mean-field scheme, dynamic changes in synaptic weights can be considered through fluctuation-based Hebbian learning rules. However, because such implementations deal with population-averaged properties, they are not well suited to memory and learning applications where individual synaptic weights can be important. We demonstrate that, through an extended system of equations, the mean-field models can be developed further to look at higher-order statistics, in particular, the distribution of synaptic weights within a cortical column. This allows us to make some general conclusions on memory through a mean-field scheme. Specifically, we expect large changes in the standard deviation of the distribution of synaptic weights when fluctuation in the mean soma potentials are large, such as during the transitions between the “up” and “down” states of slow-wave sleep. Moreover, a cortex that has low structure in its neuronal connections is most likely to decrease its standard deviation in the weights of excitatory to excitatory synapses, relative to the square of the mean, whereas a cortex with strongly patterned connections is most likely to increase this measure. This suggests that fluctuations are used to condense the coding of strong (presumably useful) memories into fewer, but dynamic, neuron connections, while at the same time removing weaker (less useful) memories.     

Posterior Probability Matching and Human Perceptual Decision Making

Probability matching is a classic theory of decision making that was first developed in models of cognition. Posterior probability matching, a variant in which observers match their response probabilities to the posterior probability of each response being correct, is being used increasingly often in models of perception. However, little is known about whether posterior probability matching is consistent with the vast literature on vision and hearing that has developed within signal detection theory. Here we test posterior probability matching models using two tools from detection theory. First, we examine the models’ performance in a two-pass experiment, where each block of trials is presented twice, and we measure the proportion of times that the model gives the same response twice to repeated stimuli. We show that at low performance levels, posterior probability matching models give highly inconsistent responses across repeated presentations of identical trials. We find that practised human observers are more consistent across repeated trials than these models predict, and we find some evidence that less practised observers more consistent as well. Second, we compare the performance of posterior probability matching models on a discrimination task to the performance of a theoretical ideal observer that achieves the best possible performance. We find that posterior probability matching is very inefficient at low-to-moderate performance levels, and that human observers can be more efficient than is ever possible according to posterior probability matching models. These findings support classic signal detection models, and rule out a broad class of posterior probability matching models for expert performance on perceptual tasks that range in complexity from contrast discrimination to symmetry detection. However, our findings leave open the possibility that inexperienced observers may show posterior probability matching behaviour, and our methods provide new tools for testing for such a strategy.     

人胚胎干细胞膜的特异多肽受体研究

目的:通过多肽筛选和比较分析,找到针对人胚胎干细胞(hESC)特异结合的多肽的膜受体蛋白,为相关通路或特异膜表面蛋白下游的研究奠定基础。方法:首先,在前期运用噬菌体展示技术的基础上进行ELISA重筛选,通过对比结合强度的大小,挑选出特异性结合人胚胎干细胞的噬菌体多肽并且进行测序和合成有poly-his标签的多肽;然后运用His Pull-Down系统获得特异结合人胚胎干细胞的某一特殊噬菌体12肽的膜上靶分子受体蛋白;最后质谱测序后通过Mascot数据库和NCBI进行序列信息分析。结果:1通过ELISA重筛选,得到了高特异性结合人胚胎干细胞的两个噬菌体序列,其序列分别为HGAAWGTRTGHV(HGA)和VPATETAQAGHA(VPA)。2通过His Pull-Down实验得到了一个针对多肽VPA的特异性膜蛋白受体。3通过MALD质谱分析以及NCBI的数据库搜索分析,进一步确认这一VPA多肽特异性结合的潜在受体蛋白可能属于HECT超级家族。结论:寻找到一个潜在未知的人胚胎干细胞的特异表面标志物,此膜受体可与VPA多肽特异性结合,为人胚胎干细胞的筛选和鉴定提供了重要指标。     

Human Perceptual and Phobic Biases for Snakes: A Review of the Experimental Evidence

In this paper I review the literature on the evolutionary origins of phobias and describe the current state of research on the neurobiology and developmental origins of ophidiophobia—fear of snakes. In doing so I compare experimental evidence related to evolutionary explanations for snake fears and phobias which are outlined in Seligman’s Preparedness Theory and Isbell’s Snake Detection Theory. These theories have been tested extensively using a variety of experimental paradigms aimed at determining the “innateness” of snake fears, the neural pathways involved in fear responses to snakes, and the perceptual biases associated with snake stimuli. However, in the vast majority of these experiments, the stimuli presented are photographs of snakes rather than the real thing. I argue that this point of methodology, while ironically supportive of the findings, is based on some assumptions about cognition and consciousness which run counter to neuroscience. In understanding human responses to snakes, we need to understand better the interplay between cognition and consciousness and how these represent a pluralism of mind in which perception is much more than we think.     

Human social organization during the Late Pleistocene: Beyond the nomadic-egalitarian model

Many researchers assume that until 10–12,000 years ago, humans lived in small, mobile, relatively egalitarian bands. This “nomadic-egalitarian model” suffuses the social sciences. It informs evolutionary explanations of behavior and our understanding of how contemporary societies differ from those of our evolutionary past. Here, we synthesize research challenging this model and articulate an alternative, the diverse histories model, to replace it. We review the limitations of using recent foragers as models of Late Pleistocene societies and the considerable social variation among foragers commonly considered small-scale, mobile, and egalitarian. We review ethnographic and archaeological findings covering 34 world regions showing that non-agricultural peoples often live in groups that are more sedentary, unequal, large, politically stratified, and capable of large-scale cooperation and resource management than is normally assumed. These characteristics are not restricted to extant Holocene hunter-gatherers but, as suggested by archaeological findings from 27 Middle Stone Age sites, likely characterized societies throughout the Late Pleistocene (until c. 130 ka), if not earlier. These findings have implications for how we understand human psychological adaptations and the broad trajectory of human history.     

Beyond the Rat Models of Human Neurodegenerative Disorders

The rat is a model of choice in biomedical research for over a century. Currently, the rat presents the best “functionally” characterized mammalian model system. Despite this fact, the transgenic rats have lagged behind the transgenic mice as an experimental model of human neurodegenerative disorders. The number of transgenic rat models recapitulating key pathological hallmarks of Alzheimer’s disease, Huntington’s disease, amyotrophic lateral sclerosis, or human tauopathies is still limited. The reason is that the transgenic rats remain more difficult to produce than transgenic mice. The gene targeting technology is not yet established in rats due to the lack of truly totipotent embryonic stem cells and cloning technology. This extremely powerful technique has given the mouse a clear advantage over the rat in generation of new transgenic models. Despite these limitations, transgenic rats have greatly expanded the range of potential experimental approaches. The large size of rats permits intrathecal administration of drugs, stem cell transplantation, serial sampling of the cerebrospinal fluid, microsurgical techniques, in vivo nerve recordings, and neuroimaging procedures. Moreover, the rat is routinely employed to demonstrate therapeutic efficacy and to assess toxicity of novel therapeutic compounds in drug development. Here we suggest that the rat constitutes a slightly underestimated but perspective animal model well-suited for understanding the mechanisms and pathways underlying the human neurodegenerative disorders.     

Human Language and Our Reptilian Brain: The Subcortical Bases of Speech, Syntax, and Thought

Human Language and Our Reptilian Brain: The Subcortical Bases of Speech, Syntax, and Thought. Philip Lieberman. Cambridge, MA: Harvard University Press, 2000. 221 pp.