Neuronal rebound spiking,resonance frequency and theta cycle skipping may contribute to grid cell firing in medial entorhinal cortex

Data show a relationship of cellular resonance and network oscillations in the entorhinal cortex to the spatial periodicity of grid cells. This paper presents a model that simulates the resonance and rebound spiking properties of entorhinal neurons to generate spatial periodicity dependent upon phasic input from medial septum. The model shows that a difference in spatial periodicity can result from a difference in neuronal resonance frequency that replicates data from several experiments. The model also demonstrates a functional role for the phenomenon of theta cycle skipping in the medial entorhinal cortex.     

Place cells, neocortex and spatial navigation: a short review

Hippocampal place cells are characterized by location-specific firing, that is each cell fires in a restricted region of the environment explored by the rat. In this review, we briefly examine the sensory information used by place cells to anchor their firing fields in space and show that, among the various sensory cues that can influence place cell activity, visual and motion-related cues are the most relevant. We then explore the contribution of several cortical areas to the generation of the place cell signal with an emphasis on the role of the visual cortex and parietal cortex. Finally, we address the functional significance of place cell activity and demonstrate the existence of a clear relationship between place cell positional activity and spatial navigation performance. We conclude that place cells, together with head direction cells, provide information useful for spatially guided movements, and thus provide a unique model of how spatial information is encoded in the brain.     

Independence of landmark and self-motion-guided navigation: a different role for grid cells

Recent interest in the neural bases of spatial navigation stems from the discovery of neuronal populations with strong, specific spatial signals. The regular firing field arrays of medial entorhinal grid cells suggest that they may provide place cells with distance information extracted from the animal''s self-motion, a notion we critically review by citing new contrary evidence. Next, we question the idea that grid cells provide a rigid distance metric. We also discuss evidence that normal navigation is possible using only landmarks, without self-motion signals. We then propose a model that supposes that information flow in the navigational system changes between light and dark conditions. We assume that the true map-like representation is hippocampal and argue that grid cells have a crucial navigational role only in the dark. In this view, their activity in the light is predominantly shaped by landmarks rather than self-motion information, and so follows place cell activity; in the dark, their activity is determined by self-motion cues and controls place cell activity. A corollary is that place cell activity in the light depends on non-grid cells in ventral medial entorhinal cortex. We conclude that analysing navigational system changes between landmark and no-landmark conditions will reveal key functional properties.     

A survey of some tensor analysis techniques for biological systems

Background: Since biological systems are complex and often involve multiple types of genomic relationships, tensor analysis methods can be utilized to elucidate these hidden complex relationships. There is a pressing need for this, as the interpretation of the results of high-throughput experiments has advanced at a much slower pace than the accumulation of data.Results: In this review we provide an overview of some tensor analysis methods for biological systems.Conclusions: Tensors are natural and powerful generalizations of vectors and matrices to higher dimensions and play a fundamental role in physics, mathematics and many other areas. Tensor analysis methods can be used to provide the foundations of systematic approaches to distinguish significant higher order correlations among the elements of a complex systems via finding ensembles of a small number of reduced systems that provide a concise and representative summary of these correlations.     

Time-courses of memory decay in vector-based and landmark-based systems of navigation in desert ants, Cataglyphis fortis

In foraging and homing, desert ants of the genus Cataglyphis employ two different systems of navigation: a vector-based or dead-reckoning mechanism, depending on angles steered and distances travelled, and a landmark-based piloting mechanism. In these systems the ants use either celestial or terrestrial visual information, respectively. In behavioural experiments we investigated how long these types of information are preserved in the ant's memory, i.e. how long the ants are able to orient properly in either way. To answer this question, ants were tested in specific dead-reckoning and piloting situations, whereby the two vector components, direction and distance, were examined separately. The ability to follow a particular vector course vanishes rapidly. Information about a given homing direction is lost from the 6th day on (the time constant of the exponential memory decay function is τ = 4.5 days). The homing distances show a significantly higher dispersion from the 4th day on (τ = 2.5 days). Having learned a constellation of landmarks positioned at the corners of an equidistant triangle all ants were oriented properly after 10 days in captivity, and 64% of the ants exhibited extremely precise orientation performances even when tested after 20 days. Thus, the memory decay functions have about the same short time-course for information on distance and direction, i.e. information used for dead-reckoning. In contrast, landmark-based information used in pinpointing the nest entrance is stored over the entire lifetime of a Cataglyphis forager. Accepted: 18 January 1997     

Managing electromagnetic fields from residential electrode grounding systems: A predecision analysis

Several epidemiological studies have linked exposure to electromagnetic fields (EMFs) with health effects, including leukemia and brain cancer, but the research is still inconclusive. In particular, no clear causal mechanism has been identified by which EMFs may promote cancers. Nevertheless, the concerns raised by the positive epidemiological studies have led to increasing efforts to reduce EMFs from a number of sources. One source of EMFs are home grounding systems that are connected through water pipes in homes to water mains. This paper analyzes whether home owners who are concerned about electromagnetic fields exposure from home grounding systems should take any action to reduce fields. Assuming that the grounding system produces elevated magnetic fields (e.g., 2–3 mG or higher), this study investigates several readily available alternatives and evaluates them with respect to five criteria: risk reduction, cost, fire risk increase, worker risk, and electrical shock risk. Because of the lack of conclusive evidence about an EMF-cancer relationship, this study uses a parameterized approach that makes conditional estimates of health risk depending on future research outcomes and on the nature of the EMF/health effects relationship. This type of analysis, which is called predecision analysis because of its preliminary nature, is therefore highly dependent on a set of assumptions. Nevertheless, this predecision analysis had some fairly clear results. First, waiting for more research or taking a fairly inexpensive corrective action (insulating the water pipe to reduce ground current flow) seem to be the main contenders for the best decision for many different assumptions and parameters. Second, the choice between these two actions is very sensitive to variations in assumptions and parameters. Homeowners who accept the base-case assumptions and parameters of this study should prefer to wait. If any of the base-case parameters are changed to more pessimistic estimates or if psychological concerns (like worry and regret) are considered, then the best action is to insulate the pipe to reduce the current flow through the water pipes. © 1996 Wiley-Liss, Inc.     

Relaxation spectra of interactive neural systems

A nonlinear model of spatially localized interactive neural systems is analyzed in the neighborhood of steady state solutions by computing relaxation spectra which govern the long time approach to steady state activity levels.     

Observational learning promotes hippocampal remote awake replay toward future reward locations

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A Continuous Attractor Network Model Without Recurrent Excitation: Maintenance and Integration in the Head Direction Cell System

Motivated by experimental observations of the head direction system, we study a three population network model that operates as a continuous attractor network. This network is able to store in a short-term memory an angular variable (the head direction) as a spatial profile of activity across neurons in the absence of selective external inputs, and to accurately update this variable on the basis of angular velocity inputs. The network is composed of one excitatory population and two inhibitory populations, with inter-connections between populations but no connections within the neurons of a same population. In particular, there are no excitatory-to-excitatory connections. Angular velocity signals are represented as inputs in one inhibitory population (clockwise turns) or the other (counterclockwise turns). The system is studied using a combination of analytical and numerical methods. Analysis of a simplified model composed of threshold-linear neurons gives the conditions on the connectivity for (i) the emergence of the spatially selective profile, (ii) reliable integration of angular velocity inputs, and (iii) the range of angular velocities that can be accurately integrated by the model. Numerical simulations allow us to study the proposed scenario in a large network of spiking neurons and compare their dynamics with that of head direction cells recorded in the rat limbic system. In particular, we show that the directional representation encoded by the attractor network can be rapidly updated by external cues, consistent with the very short update latencies observed experimentally by Zugaro et al. (2003) in thalamic head direction cells.     

Use of water flow direction to provide spatial information in a small-scale orientation task

Experiments were designed to investigate whether three-spined sticklebacks Gasterosteus aculeatus can use direction of water flow as an orientation cue. The fish had to learn the location of a food patch in a channel where water flow direction was the only reliable indicator of the food patch position. Fish from two ponds and two rivers were trained and tested in the spatial task to determine whether river three-spined sticklebacks are more adept at using water flow as a spatial cue than fish from ponds. All fish were able to use water flow to locate the food patch but one of the two river groups was significantly faster at learning the patch location. When the task was reversed so that fish that had formerly been trained to swim downstream now had to learn to swim upstream and vice versa both river groups learned the reversed task faster than the two pond groups. In a second experiment, to investigate whether fish from ponds or rivers vary in the type of spatial cue that they prefer to use, fish from one pond and one river were given a choice between two different types of spatial cue: flow direction or visual landmarks. A test trial in which these two cues were put into conflict revealed that the river population showed a strong preference for flow direction whilst the pond population preferred to use visual landmarks.     

Whole genome-based phylogenetic analysis of bacterial two-component systems

To adapt to their environment, bacterial strains have developed various environmental signal sensing systems or twocomponent systems. To evaluate the evolutionary relationship of two-component systems, 246 two-component system genes from KEGG were analyzed. Phylogenetic tree structure indicated that most two-component systems are strain specific. Most of two-component system genes have co-evolved, and some two-component system pairs have evolved via recruitment model. By two-component system gene content analysis, new aspect of cellular metabolism evolution was provided.     

The development of spatial behaviour and the hippocampal neural representation of space

The role of the hippocampal formation in spatial cognition is thought to be supported by distinct classes of neurons whose firing is tuned to an organism''s position and orientation in space. In this article, we review recent research focused on how and when this neural representation of space emerges during development: each class of spatially tuned neurons appears at a different age, and matures at a different rate, but all the main spatial responses tested so far are present by three weeks of age in the rat. We also summarize the development of spatial behaviour in the rat, describing how active exploration of space emerges during the third week of life, the first evidence of learning in formal tests of hippocampus-dependent spatial cognition is observed in the fourth week, whereas fully adult-like spatial cognitive abilities require another few weeks to be achieved. We argue that the development of spatially tuned neurons needs to be considered within the context of the development of spatial behaviour in order to achieve an integrated understanding of the emergence of hippocampal function and spatial cognition.     

The connectome of neural crest enhancers reveals regulatory features of signaling systems

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解码大脑的空间方位认知

在过去的几十年间,与大脑空间方位认知功能相关的位置细胞、网格细胞、头朝向细胞和边界细胞陆续被发现,它们共同构成了大脑内部的导航定位系统。O'Keefe教授和Moser夫妇这三位科学家也正是由于发现了位置细胞和网格细胞,而共同获得了2014年的诺贝尔生理学或医学奖。     

基于TM影像的景观空间自相关分析——以北京昌平区为例

格局与尺度之间的关系是景观生态学的核心研究内容。景观格局发生在不同的尺度 ,而尺度又影响格局的研究 ,因而 ,在景观生态学研究中应用多种量化研究方法于一系列尺度来确定和特征化空间格局研究 ,并探求空间格局与生态学功能和生态学过程之间的关系是非常必要的。以北京昌平区为例 ,从 TM影像中选取 5个具有突出自然和社会经济背景差异的景观 ,即林地景观、农田景观、都市边缘景观、卫星城景观和灌丛景观为研究对象 ,基于归一化植被指数 (N DVI) ,采用常用空间自相关指数 ,即 Moran的 I系数和 Geary的 c系数进行一系列的空间自相关分析 ,旨在阐明 :变化的空间粒度如何影响空间分析 ?以及空间分析如何响应划区效应 ?此外 ,基于 N DVI和数字高程模型 (DEM)也探讨了对于不同的数据类型 ,格局的尺度依赖性如何变化。研究结果表明 :空间粒度的变化对于景观分析有着显著的影响 ,随着空间粒度的增加 ,空间自相关均呈下降趋势 ;不同景观类型对于空间粒度的变化有着不同的响应 ,人为干扰较多的景观具有较低的空间自相关 ,但对空间粒度的变化表现出较强的敏感性 ;对于不同的数据类型 ,格局分析对空间粒度变化的响应是不同的     

Large-scale two-photon calcium imaging in freely moving mice

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The evolution of intelligence: adaptive specializations versus general process

Darwin argued that between-species differences in intelligence were differences of degree, not of kind. The contemporary ecological approach to animal cognition argues that animals have evolved species-specific and problem-specific processes to solve problems associated with their particular ecological niches: thus different species use different processes, and within a species, different processes are used to tackle problems involving different inputs. This approach contrasts both with Darwin's view and with the general process view, according to which the same central processes of learning and memory are used across an extensive range of problems involving very different inputs. We review evidence relevant to the claim that the learning and memory performance of non-human animals varies according to the nature of the stimuli involved. We first discuss the resource distribution hypothesis, olfactory learning-set formation, and the 'biological constraints' literature, but find no convincing support from these topics for the ecological account of cognition. We then discuss the claim that the performance of birds in spatial tasks of learning and memory is superior in species that depend heavily upon stored food compared to species that either show less dependence upon stored food or do not store food. If it could be shown that storing species enjoy a superiority specifically in spatial (and not non-spatial) tasks, this would argue that spatial tasks are indeed solved using different processes from those used in non-spatial tasks. Our review of this literature does not find a consistent superiority of storing over non-storing birds in spatial tasks, and, in particular, no evidence of enhanced superiority of storing species when the task demands are increased, by, for example, increasing the number of items to be recalled or the duration of the retention period. We discuss also the observation that the hippocampus of storing birds is larger than that of non-storing birds, and find evidence contrary to the view that hippocampal enlargement is associated with enhanced spatial memory; we are, however, unable to suggest a convincing alternative explanation for hippocampal enlargement. The failure to find solid support for the ecological view supports the view that there are no qualitative differences in cognition between animal species in the processes of learning and memory. We also argue that our review supports our contention that speculation about the phylogenetic development and function of behavioural processes does not provide a solid basis for gaining insight into the nature of those processes. We end by confessing to a belief in one major qualitative difference in cognition in animals: we believe that humans alone are capable of acquiring language, and that it is this capacity that divides our intelligence so sharply from non-human intelligence.