Odor representations in olfactory cortex: distributed rate coding and decorrelated population activity

How information encoded in neuronal spike trains is used to guide sensory decisions is a fundamental question. In olfaction, a single sniff is sufficient for fine odor discrimination but the neural representations on which olfactory decisions are based are unclear. Here, we recorded neural ensemble activity in the anterior piriform cortex (aPC) of rats performing an odor mixture categorization task. We show that odors evoke transient bursts locked to sniff onset and that odor identity can be better decoded using burst spike counts than by spike latencies or temporal patterns. Surprisingly, aPC ensembles also exhibited near-zero noise correlations during odor stimulation. Consequently, fewer than 100 aPC neurons provided sufficient information to account for behavioral speed and accuracy, suggesting that behavioral performance limits arise downstream of aPC. These findings demonstrate profound transformations in the dynamics of odor representations from the olfactory bulb to cortex and reveal likely substrates for odor-guided decisions. VIDEO ABSTRACT:     

Dynamic clamp analysis of synaptic integration in sympathetic ganglia

Advances in modern neuroscience require the identification of principles that connect different levels of experimental analysis, from molecular mechanisms to explanations of cellular functions, then to circuits, and, ultimately, to systems and behavior. Here, we examine how synaptic organization of the sympathetic ganglia may enable them to function as use-dependent amplifiers of preganglionic activity and how the gain of this amplification may be modulated by metabotropic signaling mechanisms. The approach combines a general computational model of ganglionic integration together with experimental tests of the model using the dynamic clamp method. In these experiments, we recorded intracellularly from dissociated bullfrog sympathetic neurons and then mimicked physiological synapses with virtual computer-generated synapses. It, thus, became possible to analyze the synaptic gain by recording cellular responses to complex patterns of synaptic activity that normally arise in vivo from convergent nicotinic and muscarinic synapses. The results of these studies are significant because they illustrate how gain generated through ganglionic integration may contribute to the feedback control of important autonomic behaviors, in particular to the control of the blood pressure. We dedicate this paper to the memory of Professor Vladimir Skok, whose rich legacy in synaptic physiology helped to establish the modern paradigm for connecting multiple levels of analysis in studies of the nervous system. Neirofiziologiya/Neurophysiology, Vol. 39, No. 6, pp. 486–492, November–December, 2007.     

The art of seeing and painting

The human urge to represent the three-dimensional world using two-dimensional pictorial representations dates back at least to Paleolithic times. Artists from ancient to modern times have struggled to understand how a few contours or color patches on a flat surface can induce mental representations of a three-dimensional scene. This article summarizes some of the recent breakthroughs in scientifically understanding how the brain sees that shed light on these struggles. These breakthroughs illustrate how various artists have intuitively understood paradoxical properties about how the brain sees, and have used that understanding to create great art. These paradoxical properties arise from how the brain forms the units of conscious visual perception; namely, representations of three-dimensional boundaries and surfaces. Boundaries and surfaces are computed in parallel cortical processing streams that obey computationally complementary properties. These streams interact at multiple levels to overcome their complementary weaknesses and to transform their complementary properties into consistent percepts. The article describes how properties of complementary consistency have guided the creation of many great works of art.     

Arab sounds in a contested space: life quality,cultural hierarchies and national silencing

Sounds and sonic norms and regimes characterize both spaces/territories and individual bodies. This article explores the meanings of and reactions to Arab sounds in Israel – political struggles over muezzins, stereotypical representations of Israeli Palestinians as loud, and so on – in order to offer general insights into the role of the sonic (both actual sounds and their discursive representations) in the new ‘cultural’ racism, in the everyday ethnicized experience of one's body, and in shaping relations between ethnic and national groups.     

From shared to distinct self–other representations in empathy: evidence from neurotypical function and socio-cognitive disorders

Neuroscientific research has identified two fundamental components of empathy: shared emotional representations between self and other, and self–other distinction. The concept of shared representations suggests that during empathy, we co-represent another person''s affect by engaging brain and bodily functions underpinning the first-hand experience of the emotion we are empathizing with. This possible grounding of empathy in our own emotional experiences explains the necessity for self–other distinction, which is the capacity to correctly distinguish between our own affective representations and those related to the other. In spite of the importance of these two components in empathy, several aspects still remain controversial. This paper addresses some of them and focuses on (i) the distinction between shared activations versus representations, raising the question what shared representations entail in terms of the underlying neural mechanisms, (ii) the possible mechanisms behind self–other distinction in the cognitive and the affective domains, and whether they have distinct neural underpinnings and (iii) the consequences associated with a selective impairment of one of the two components, thereby addressing their importance in mental disorders such as autism spectrum disorders, psychopathy and alexithymia.     

Stereotypes of autism

In their landmark papers, both Kanner and Asperger employed a series of case histories to shape clinical insight into autistic disorders. This way of introducing, assessing and representing disorders has disappeared from today''s psychiatric practice, yet it offers a convincing model of the way stereotypes may build up as a result of representations of autism. Considering that much of what society at large learns on disorders on the autism spectrum is produced by representations of autism in novels, TV-series, movies or autobiographies, it will be of vital importance to scrutinize these representations and to check whether or not they are, in fact, misrepresenting autism. In quite a few cases, media representations of talent and special abilities can be said to have contributed to a harmful divergence between the general image of autism and the clinical reality of the autistic condition.     

Methods for improving the visualization and deconvolution of isotopic signals

Stable isotopes and their associated mechanistic frameworks have provided the means to model biological transformations from inorganic sources to organic sinks, and their impact on long-term terrestrial carbon reservoirs. However, stable isotopes have also the potential to diagnose the mechanisms by which biological systems operate, when using 'multidimensional' analyses of the isotopic outputs. For this purpose, we suggest that isotopic signals may be treated as mathematical vectors to reveal their interrelationships. These visualizations may be achieved, thanks to multidimensional representations (the 'isotopology' method), or by appreciating the colinearity of isotopic vectors to develop a clustering analysis (the 'isotopomic' method) similar to that used in molecular biology. Both methods converge to the same mathematical form, i.e. both lead to a covariation approach. Using simple practical examples, we argue that such procedures allow the deconvolution of plant biological systems by revealing the hierarchy of contributory physiological processes.     

Transnational politics and the politics of the Russian diaspora

This article sketches out a conceptual framework for exploring the diasporic politics of the Russians in the post-Soviet borderlands. Specific consideration is given to the Russians within Estonia and Latvia, the only two postSoviet states not to grant automatic citizenship to all those resident within their sovereign spaces in 1991. The essay not only examines the Russians in relation to the homeland regimes or nationalizing states in which they are located but also looks at the role of transnational political actors- specifically, the state patron (Russia) and Western transnational political institutions (notably the OSCE)- in shaping diasporic politics. It is argued that by examining the relationships among 'the ethnic patron', 'the West' and 'nationalizing state', we are better placed to understand the ways in which the differing representations of homeland by the Russian minorities themselves are being reconstituted as part of a diverse and unravelling community of identity politics, limited political opportunities and survival strategies.     

Extent of enthalpy-entropy compensation in protein-ligand interactions

The extent of enthalpy-entropy compensation in protein-ligand interactions has long been disputed because negatively correlated enthalpy (ΔH) and entropy (TΔS) changes can arise from constraints imposed by experimental and analytical procedures as well as through a physical compensation mechanism. To distinguish these possibilities, we have created quantitative models of the effects of experimental constraints on isothermal titration calorimetry (ITC) measurements. These constraints are found to obscure any compensation that may be present in common data representations and regression analyses (e.g., in ΔH vs. -TΔS plots). However, transforming the thermodynamic data into ΔΔ-plots of the differences between all pairs of ligands that bind each protein diminishes the influence of experimental constraints and representational bias. Statistical analysis of data from 32 diverse proteins shows a significant and widespread tendency to compensation. ΔΔH versus ΔΔG plots reveal a wide variation in the extent of compensation for different ligand modifications. While strong compensation (ΔΔH and -TΔΔS opposed and differing by < 20% in magnitude) is observed for 22% of modifications (twice that expected without compensation), 15% of modifications result in reinforcement (ΔΔH and -TΔΔS of the same sign). Because both enthalpy and entropy changes arise from changes to the distribution of energy states on binding, there is a general theoretical expectation of compensated behavior. However, prior theoretical studies have focussed on explaining a stronger tendency to compensation than actually found here. These results, showing strong but imperfect compensation, will act as a benchmark for future theoretical models of the thermodynamic consequences of ligand modification.     

Cultural Identity and Internationally Adopted Children: Qualitative Approach to Parental Representations

Approximately 30 000 children are adopted across national borders each year. A review of the literature on the cultural belonging of these internationally adopted children shows substantial differences between the literature from English-speaking countries and that from France and Europe in general. The objective of this study is to start from the discourse of French adoptive parents to explore their representations of their child''s cultural belonging and their positions (their thoughts and representations) concerning connections with the child''s country of birth and its culture. The study includes 51 French parents who adopted one or more children internationally. Each parent participated in a semi-structured interview, focused on the adoption procedure and their current associations with the child''s birth country. The interviews were analyzed according to a qualitative phenomenological method, Interpretative Phenomenological Analysis. The principal themes that emerged from our analysis of the interviews made it possible to classify the parents into three different groups. The first group maintained no association with the child''s country of birth and refused any multiplicity of cultural identities. The second group actively maintained regular associations with the child''s country of birth and culture and affirmed that their family was multicultural. Finally, the third group adapted their associations with the child''s birth country and its culture according to the child''s questions and interests. Exploring parental representations of the adopted child enables professionals involved in adoption to provide better support to these families and to do preventive work at the level of family interactions.     

Knowledge-based vision and simple visual machines.

The vast majority of work in machine vision emphasizes the representation of perceived objects and events: it is these internal representations that incorporate the ''knowledge'' in knowledge-based vision or form the ''models'' in model-based vision. In this paper, we discuss simple machine vision systems developed by artificial evolution rather than traditional engineering design techniques, and note that the task of identifying internal representations within such systems is made difficult by the lack of an operational definition of representation at the causal mechanistic level. Consequently, we question the nature and indeed the existence of representations posited to be used within natural vision systems (i.e. animals). We conclude that representations argued for on a priori grounds by external observers of a particular vision system may well be illusory, and are at best place-holders for yet-to-be-identified causal mechanistic interactions. That is, applying the knowledge-based vision approach in the understanding of evolved systems (machines or animals) may well lead to theories and models that are internally consistent, computationally plausible, and entirely wrong.     

Conformational analysis of the glycosaminoglycans. II. Bond-angle studies, torsional potential, and steric map for the beta-D-(1leads to 3) linkage.

The geometry of the glycosidic valence-bond angle for both the beta-D-(1linked to4) and beta-D-(1linked to 3) linkages has been investigated by using CNDO and PCILO molecularorbital techniques on model compounds. In each case, the glycosidic valence-bond angle of minimum energy was about 111 degrees, corresponding to the value observed in ether analogs. A secondary energy-minimum was found near 116 degrees, which is the value experimentally observed for saccharides. It was concluded that long-range intra-and/or inter-molecular interactions are responsible for overall preference for the 116 degrees value of the valence-bond angle. The force constants predicted from the shapes of the 116 degrees bond-angle minima gave poor agreement with the experimental values found for ethers and employed in normal coordinate analyses of saccharides. The results did suggest that the beta-D-(1linked to3) bond angle should be 115.6 degrees, which is smaller than the corresponding beta-D-(1linked to4) bond angle. An intrinsic torsional potential-function and general steric map were also determined for the torsion-angle rotations of the beta-D-(1linked to3) linkage.     

以生态景观构建乡村审美空间

乡村审美空间表层是非功利的,实质深层映射出人地关系本质的取向价值,是人地关系永久可持续发展问题。目前乡村研究多注重经济和土地利用,而以现实生态景观构建乡村审美空间还是有待于探讨的重要课题。近年来快速城市化发展,区域中的自然地理性质破坏对于乡村景观是致命的。立足地理生态环境架构乡村审美空间,分析乡村生态景观和审美空间对应的元素,以多尺度景观层面探寻表现在与之相映的景观空间形态结构、格局演化进程与机理响应,进而构建审美空间,组合形成现实的美丽景观体系。将生态文明和社会发展要求安排在景观空间格局配置的中,形成保持整体环境的景观网络。使得风景美的概念渗透在于城镇、乡村以至农田等更广阔的领域,从而建设具有风景画境界的"美丽乡村"。     

The Alliance Hypothesis for Human Friendship

Background

Exploration of the cognitive systems underlying human friendship will be advanced by identifying the evolved functions these systems perform. Here we propose that human friendship is caused, in part, by cognitive mechanisms designed to assemble support groups for potential conflicts. We use game theory to identify computations about friends that can increase performance in multi-agent conflicts. This analysis suggests that people would benefit from: 1) ranking friends, 2) hiding friend-ranking, and 3) ranking friends according to their own position in partners'' rankings. These possible tactics motivate the hypotheses that people possess egocentric and allocentric representations of the social world, that people are motivated to conceal this information, and that egocentric friend-ranking is determined by allocentric representations of partners'' friend-rankings (more than others'' traits).

Methodology/Principal Findings

We report results from three studies that confirm predictions derived from the alliance hypothesis. Our main empirical finding, replicated in three studies, was that people''s rankings of their ten closest friends were predicted by their own perceived rank among their partners'' other friends. This relationship remained strong after controlling for a variety of factors such as perceived similarity, familiarity, and benefits.

Conclusions/Significance

Our results suggest that the alliance hypothesis merits further attention as a candidate explanation for human friendship.     

On the dynamics of operant conditioning

Simple psychological postulates are presented which are used to derive possible anatomical and physiological substrates of operant conditioning. These substrates are compatible with much psychological data about operants. A main theme is that aspects of operant and respondent conditioning share a single learning process. Among the phenomena which arise are the following: UCS-activated arousal; formation of conditioned, or secondary, reinforcers; a non-specific arousal system distinct from sensory and motor representations whose activation is required for sensory processing; polyvalent cells responsive to the sum of CS and UCS inputs and anodal d.c. potential shifts; neural loci responsive to the combined effect of sensory events and drive deprivation; “go”-like or “now print”-like mechanisms which, for example, influence incentive-motivational increases in general activity; a mechanism for learning repetitively to press a bar which electrically stimulates suitable arousal loci in the absence of drive reduction; uniformly distributed potentials, driven by the CS, in the “cerebral cortex” of a trained network; the distinction between short-term and long-term memory, and the possibility of eliminating transfer from short-term to long-term memory in the absence of suitable arousal; networks that can learn and perform arbitrarily complex sequences of acts or sensory memories, without continuous control by sensory feedback, whose rate of performance can be regulated by the level of internal arousal; networks with idetic memory; network analogs of “therapeutic resistance” and “repression”; the possibility of conditioning the sensory feedback created by a motor act to the neural controls of this act, with consequences for sensory-motor adaptation and child development. This paper introduces explicit minimal anatomies and physiological rules that formally give rise to analogous phenomena. These networks consider only aspects of positive conditioning. They are derived from simple psychological facts.     

Challenging the classical notion of time in cognition: a quantum perspective

All mental representations change with time. A baseline intuition is that mental representations have specific values at different time points, which may be more or less accessible, depending on noise, forgetting processes, etc. We present a radical alternative, motivated by recent research using the mathematics from quantum theory for cognitive modelling. Such cognitive models raise the possibility that certain possibilities or events may be incompatible, so that perfect knowledge of one necessitates uncertainty for the others. In the context of time-dependence, in physics, this issue is explored with the so-called temporal Bell (TB) or Leggett–Garg inequalities. We consider in detail the theoretical and empirical challenges involved in exploring the TB inequalities in the context of cognitive systems. One interesting conclusion is that we believe the study of the TB inequalities to be empirically more constrained in psychology than in physics. Specifically, we show how the TB inequalities, as applied to cognitive systems, can be derived from two simple assumptions: cognitive realism and cognitive completeness. We discuss possible implications of putative violations of the TB inequalities for cognitive models and our understanding of time in cognition in general. Overall, this paper provides a surprising, novel direction in relation to how time should be conceptualized in cognition.     

Minimal cross-trial generalization in learning the representation of an odor-guided choice task

There is no single way to represent a task. Indeed, despite experiencing the same task events and contingencies, different subjects may form distinct task representations. As experimenters, we often assume that subjects represent the task as we envision it. However, such a representation cannot be taken for granted, especially in animal experiments where we cannot deliver explicit instruction regarding the structure of the task. Here, we tested how rats represent an odor-guided choice task in which two odor cues indicated which of two responses would lead to reward, whereas a third odor indicated free choice among the two responses. A parsimonious task representation would allow animals to learn from the forced trials what is the better option to choose in the free-choice trials. However, animals may not necessarily generalize across odors in this way. We fit reinforcement-learning models that use different task representations to trial-by-trial choice behavior of individual rats performing this task, and quantified the degree to which each animal used the more parsimonious representation, generalizing across trial types. Model comparison revealed that most rats did not acquire this representation despite extensive experience. Our results demonstrate the importance of formally testing possible task representations that can afford the observed behavior, rather than assuming that animals’ task representations abide by the generative task structure that governs the experimental design.     

Coupling dynamic models of climate and vegetation

Numerous studies have underscored the importance of terrestrial ecosystems as an integral component of the Earth's climate system. This realization has already led to efforts to link simple equilibrium vegetation models with Atmospheric General Circulation Models through iterative coupling procedures. While these linked models have pointed to several possible climate–vegetation feedback mechanisms, they have been limited by two shortcomings: (i) they only consider the equilibrium response of vegetation to shifting climatic conditions and therefore cannot be used to explore transient interactions between climate and vegetation; and (ii) the representations of vegetation processes and land-atmosphere exchange processes are still treated by two separate models and, as a result, may contain physical or ecological inconsistencies. Here we present, as a proof concept, a more tightly integrated framework for simulating global climate and vegetation interactions. The prototype coupled model consists of the GENESIS (version 2) Atmospheric General Circulation Model and the IBIS (version 1) Dynamic Global Vegetation Model. The two models are directly coupled through a common treatment of land surface and ecophysiological processes, which is used to calculate the energy, water, carbon, and momentum fluxes between vegetation, soils, and the atmosphere. On one side of the interface, GENESIS simulates the physics and general circulation of the atmosphere. On the other side, IBIS predicts transient changes in the vegetation structure through changes in the carbon balance and competition among plants within terrestrial ecosystems. As an initial test of this modelling framework, we perform a 30 year simulation in which the coupled model is supplied with modern CO₂ concentrations, observed ocean temperatures, and modern insolation. In this exploratory study, we run the GENESIS atmospheric model at relatively coarse horizontal resolution (4.5° latitude by 7.5° longitude) and IBIS at moderate resolution (2° latitude by 2° longitude). We initialize the models with globally uniform climatic conditions and the modern distribution of potential vegetation cover. While the simulation does not fully reach equilibrium by the end of the run, several general features of the coupled model behaviour emerge. We compare the results of the coupled model against the observed patterns of modern climate. The model correctly simulates the basic zonal distribution of temperature and precipitation, but several important regional biases remain. In particular, there is a significant warm bias in the high northern latitudes, and cooler than observed conditions over the Himalayas, central South America, and north-central Africa. In terms of precipitation, the model simulates drier than observed conditions in much of South America, equatorial Africa and Indonesia, with wetter than observed conditions in northern Africa and China. Comparing the model results against observed patterns of vegetation cover shows that the general placement of forests and grasslands is roughly captured by the model. In addition, the model simulates a roughly correct separation of evergreen and deciduous forests in the tropical, temperate and boreal zones. However, the general patterns of global vegetation cover are only approximately correct: there are still significant regional biases in the simulation. In particular, forest cover is not simulated correctly in large portions of central Canada and southern South America, and grasslands extend too far into northern Africa. These preliminary results demonstrate the feasibility of coupling climate models with fully dynamic representations of the terrestrial biosphere. Continued development of fully coupled climate-vegetation models will facilitate the exploration of a broad range of global change issues, including the potential role of vegetation feedbacks within the climate system, and the impact of climate variability and transient climate change on the terrestrial biosphere.     

VENTILATION BY FLOATING LEAVES IN NUPHAR

The network of internal gas spaces in the yellow waterlily constitutes a pressurized flow-through system which forces oxygen to the rhizome buried in anaerobic sediment. This ventilation has been documented previously in a subspecies of Nuphar luteum with aerial leaves, and appeared to occur only during daylight when the leaves are warmed by the sun's radiation. In this study we have found the ventilation system operating in two different subspecies of N. luteum growing in Alaska and in Massachusetts. These plants have floating leaves so that during certain times of the year the leaves are warmed not only by the sun in daylight but also by lake water at night, allowing the ventilation to continue during darkness.