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1.
Hippocampal place cells (PCs) are believed to represent environmental structure. However, it is unclear how and which brain
regions represent goals and guide movements. Recently, another type of cells that fire around a goal was found in rat hippocampus
(we designate these cells as goal place cells, GPCs). This suggests that the hippocampus is also involved in goal representation.
Assuming that the activities of GPCs depend on the distance to a goal, we propose an adaptive navigation model. By monitoring
the population activity of GPCs, the model navigates to shorten the distance to the goal. To achieve the distance-dependent
activities of GPCs, plastic connections are assumed between PCs and GPCs, which are modified depending on two reward-triggered
activities: activity propagation through PC–PC network representing the topological environmental structure, and the activity
of GPCs with different durations. The former activity propagation is regarded as a computational interpretation of “reverse
replay” phenomenon found in rat hippocampus. Simulation results confirm that after reaching a goal only once, the model can
navigate to the goal along almost the shortest path from arbitrary places in the environment. This indicates that the hippocampus
might play a primary role in the representation of not only the environmental structure but also the goal, in addition to
guiding the movement. This navigation strategy using the population activity of GPCs is equivalent to the taxis strategy,
the simplest and most basic for biological systems. Our model is unique because this simple strategy allows the model to follow
the shortest path in the topological map of the environment. 相似文献
2.
The goal of this paper is to propose a model of the hippocampal system that reconciles the presence of neurons that look
like “place cells” with the implication of the hippocampus (Hs) in other cognitive tasks (e.g., complex conditioning acquisition
and memory tasks). In the proposed model, “place cells” or “view cells” are learned in the perirhinal and entorhinal cortex.
The role of the Hs is not fundamentally dedicated to navigation or map building, the Hs is used to learn, store, and predict
transitions between multimodal states. This transition prediction mechanism could be important for novelty detection but,
above all, it is crucial to merge planning and sensory–motor functions in a single and coherent system. A neural architecture
embedding this model has been successfully tested on an autonomous robot, during navigation and planning in an open environment.
Received: 28 June 1999 / Accepted in revised form: 26 April 2001 相似文献
3.
Spatial cognition and neuro-mimetic navigation: a model of hippocampal place cell activity 总被引:10,自引:2,他引:8
A computational model of hippocampal activity during spatial cognition and navigation tasks is presented. The spatial representation
in our model of the rat hippocampus is built on-line during exploration via two processing streams. An allothetic vision-based
representation is built by unsupervised Hebbian learning extracting spatio-temporal properties of the environment from visual
input. An idiothetic representation is learned based on internal movement-related information provided by path integration.
On the level of the hippocampus, allothetic and idiothetic representations are integrated to yield a stable representation
of the environment by a population of localized overlapping CA3-CA1 place fields. The hippocampal spatial representation is
used as a basis for goal-oriented spatial behavior. We focus on the neural pathway connecting the hippocampus to the nucleus
accumbens. Place cells drive a population of locomotor action neurons in the nucleus accumbens. Reward-based learning is applied
to map place cell activity into action cell activity. The ensemble action cell activity provides navigational maps to support
spatial behavior. We present experimental results obtained with a mobile Khepera robot.
Received: 02 July 1999 / Accepted in revised form: 20 March 2000 相似文献
4.
A computational model of the lesion and single unit data from navigation in rats is reviewed. The model uses external (visual)
and internal (odometric) information from the environment to drive the firing of simulated hippocampal place cells. Constraints
on the functional form of these inputs are drawn from experiments using an environment of modifiable shape. The place cell
representation is used to guide navigation via the creation of a representation of goal location via Hebbian modification
of synaptic strengths. The model includes consideration of the phase of firing of place cells with respect to the theta rhythm
of hippocampal EEG. A series of predictions for behavioural and single-unit data in rats are derived from the input and output
representations of the model.
Received: 15 July 1999 / Accepted in revised form: 20 March 2000 相似文献
5.
The human cognitive map is known to be hierarchically organized consisting of a set of perceptually clustered landmarks. Patient
studies have demonstrated that these cognitive maps are maintained by the hippocampus, while the neural dynamics are still
poorly understood. The authors have shown that the neural dynamic “theta phase precession” observed in the rodent hippocampus
may be capable of forming hierarchical cognitive maps in humans. In the model, a visual input sequence consisting of object
and scene features in the central and peripheral visual fields, respectively, results in the formation of a hierarchical cognitive
map for object–place associations. Surprisingly, it is possible for such a complex memory structure to be formed in a few
seconds. In this paper, we evaluate the memory retrieval of object–place associations in the hierarchical network formed by
theta phase precession. The results show that multiple object–place associations can be retrieved with the initial cue of
a scene input. Importantly, according to the wide-to-narrow unidirectional connections among scene units, the spatial area
for object–place retrieval can be controlled by the spatial area of the initial cue input. These results indicate that the
hierarchical cognitive maps have computational advantages on a spatial-area selective retrieval of multiple object–place associations.
Theta phase precession dynamics is suggested as a fundamental neural mechanism of the human cognitive map. 相似文献
6.
Multiple sensory-motor maps located in the brainstem and the cortex are involved in spatial orientation. Guiding movements
of eyes, head, neck and arms they provide an approximately linear relation between target distance and motor response. This
involves especially the superior colliculus in the brainstem and the parietal cortex. There, the natural frame of reference
follows from the retinal representation of the environment. A model of navigation is presented that is based on the modulation
of activity in those sensory-motor maps. The actual mechanism chosen was gain-field modulation, a process of multimodal integration
that has been demonstrated in the parietal cortex and superior colliculus, and was implemented as attraction to visual cues
(colour). Dependent on the metric of the sensory-motor map, the relative attraction to these cues implemented as gain field
modulation and their position define a fixed point attractor on the plane for locomotive behaviour. The actual implementation
used Kohonen-networks in a variant of reinforcement learning that are well suited to generate such topographically organized
sensory-motor maps with roughly linear visuo-motor response characteristics. In the following, it was investigated how such
an implicit coding of target positions by gain-field parameters might be represented in the hippocampus formation and under
what conditions a direction-invariant space representation can arise from such retinotopic representations of multiple cues.
Information about the orientation in the plane—as could be provided by head direction cells—appeared to be necessary for unambiguous
space representation in our model in agreement with physiological experiments. With this information, Gauss-shaped “place-cells”
could be generated, however, the representation of the spatial environment was repetitive and clustered and single cells were
always tuned to the gain-field parameters as well 相似文献
7.
Hippocampal population codes play an important role in representation of spatial environment and spatial navigation. Uncovering the internal representation of hippocampal population codes will help understand neural mechanisms of the hippocampus. For instance, uncovering the patterns represented by rat hippocampus (CA1) pyramidal cells during periods of either navigation or sleep has been an active research topic over the past decades. However, previous approaches to analyze or decode firing patterns of population neurons all assume the knowledge of the place fields, which are estimated from training data a priori. The question still remains unclear how can we extract information from population neuronal responses either without a priori knowledge or in the presence of finite sampling constraint. Finding the answer to this question would leverage our ability to examine the population neuronal codes under different experimental conditions. Using rat hippocampus as a model system, we attempt to uncover the hidden "spatial topology" represented by the hippocampal population codes. We develop a hidden Markov model (HMM) and a variational Bayesian (VB) inference algorithm to achieve this computational goal, and we apply the analysis to extensive simulation and experimental data. Our empirical results show promising direction for discovering structural patterns of ensemble spike activity during periods of active navigation. This study would also provide useful insights for future exploratory data analysis of population neuronal codes during periods of sleep. 相似文献
8.
The mechanisms that regulate neuronal function are a sum of genetically determined programs and experience. The effect of
experience on neuronal function is particularly important during development, because early-life positive and adverse experience
(stress) may influence the still “plastic” nervous system long-term. Specifically, for hippocampal-mediated learning and memory
processes, acute stress may enhance synaptic efficacy and overall learning ability, and conversely, chronic or severe stress
has been shown to be detrimental. The mechanisms that enable stress to act as this “double-edged sword” are unclear. Here,
we discuss the molecular mediators of the stress response in the hippocampus with an emphasis on novel findings regarding
the role of the neuropeptide known as corticotropin-releasing hormone (CRH). We highlight the physiological and pathological
roles of this peptide in the developing hippocampus, and their relevance to the long-term effects of early-life experience
on cognitive function during adulthood. 相似文献
9.
10.
This article proposes an abstract mathematical frame for describing some features of cognitive and biological time. We focus
here on the so called “extended present” as a result of protentional and retentional activities (memory and anticipation).
Memory, as retention, is treated in some physical theories (relaxation phenomena, which will inspire our approach), while
protention (or anticipation) seems outside the scope of physics. We then suggest a simple functional representation of biological
protention. This allows us to introduce the abstract notion of “biological inertia”. 相似文献
11.
J. Scott Turner 《Swarm Intelligence》2011,5(1):19-43
Eusociality has evolved independently at least twice among the insects: among the Hymenoptera (ants and bees), and earlier
among the Isoptera (termites). Studies of swarm intelligence, and by inference, swarm cognition, have focused largely on the
bees and ants, while the termites have been relatively neglected. Yet, termites are among the world’s premier animal architects,
and this betokens a sophisticated swarm intelligence capability. In this article, I review new findings on the workings of
the mound of Macrotermes which clarify how these remarkable structures work, and how they come to be built. Swarm cognition in these termites is in
the form of “extended” cognition, whereby the swarm’s cognitive abilities arise both from interaction amongst the individual
agents within a swarm, and from the interaction of the swarm with the environment, mediated by the mound’s dynamic architecture.
The latter provides large scale “cognitive maps” which enable termite swarms to assess the functional state of their structure
and to guide repair efforts where necessary. The crucial role of the built environment in termite swarm cognition also points
to certain “swarm cognitive disorders”, where swarms can be pushed into anomalous activities by manipulating crucial structural
and functional attributes of the termite system of “extended cognition.” 相似文献
12.
Mittelstaedt H 《Biological cybernetics》2000,83(3):261-270
Arthropods as well as mammals are able to return straight home after a random search excursion under conditions that are
designed to exclude all external cues. After a brief clarification of the terminology, two principal systems of information
processing that can achieve this performance are introduced and analysed: Polar versus Cartesian path integration. The different
demands and achievements of the two systems are confronted with neurophysiological findings on the functioning of the hippocampus,
and with a recent comprehensive model of how the hippocampal place cells perform path integration. To connect the neurophysiological
findings with the behavior of the animal, a new model is developed. It achieves three functionally diverse performances: maintenance
and control of a compass direction, navigation by path integration, and formation of goals by connecting non-spatial features
with their location. This is done by three interconnected feedback loops, set by a common reference variable. Their information-processing
structure enables the animal not only to home but also to go straight from any stored goal to any other, without explicit
representation of the distance between them, and without a topological arrangement of the store. The model explains behaviors
not yet understood and predicts still undiscovered performances. Because it allows the isolation of orienting from storing
functions yet also shows how they can be connected, the model may help to reconcile conflicting views on the function of the
hippocampus.
Received: 17 June 1999 / Accepted in revised form: 20 March 2000 相似文献
13.
In vitro liberation of charged gold atoms: autometallographic tracing of gold ions released by macrophages grown on metallic gold surfaces 总被引:2,自引:2,他引:0
The present study demonstrates that cultured macrophages are able to liberate gold ions from metallic gold surfaces, a process
suggested to be called “dissolucytosis”, in a way analogous to the release taking place when metallic implants are placed
in a body. Using the ultra-sensitive autometallographic (AMG) technique, we demonstrate that murine macrophages grown on a
surface of metallic gold liberate gold ions. Ultra-structural AMG reveals that the gold ions are located in an ultra-thin
membrane-like structure, “the dissolution membrane”, intervened between the macrophages and the metal surface. The presence
of AMG silver enhanced gold nanoparticles in the dissolution membrane proves that the release of charged gold atoms takes
place extracellularly. The dissolution membrane is most likely secreted and chemically controlled by the “dissolucytes”, here
macrophages, and the membrane is essential for the dissolution of metal implants and particles, which cannot be phagocytosed.
Our findings support the notion that whenever a metallic gold surface is attacked by dissolucytes, gold ions are liberated
and taken up by surrounding cells. As gold ions can suppress the inflammatory process, it is reasonable to expect that when
dissolucytosis takes place in the living organism the liberated gold ions will cause local immunosuppression. 相似文献
14.
Evolutionary biology owes much to Charles Darwin, whose discussions of common descent and natural selection provide the foundations
of the discipline. But evolutionary biology has expanded well beyond its foundations to encompass many theories and concepts
unknown in the 19th century. The term “Darwinism” is, therefore, ambiguous and misleading. Compounding the problem of “Darwinism”
is the hijacking of the term by creationists to portray evolution as a dangerous ideology—an “ism”—that has no place in the
science classroom. When scientists and teachers use “Darwinism” as synonymous with evolutionary biology, it reinforces such
a misleading portrayal and hinders efforts to present the scientific standing of evolution accurately. Accordingly, the term
“Darwinism” should be abandoned as a synonym for evolutionary biology. 相似文献
15.
Kubík S Stuchlík A Fenton AA 《Physiological research / Academia Scientiarum Bohemoslovaca》2006,55(4):445-452
Spatial navigation is used as a popular animal model of higher cognitive functions in people. The data suggest that the hippocampus is important for both storing spatial memories and for performing spatial computations necessary for navigation. Animals use multiple behavioral strategies to solve spatial tasks often using multiple memory systems. We investigated how inactivation of the rat hippocampus affects performance in a place avoidance task to determine if the role of the hippocampus in this task could be attributed to memory storage/retrieval or to the computations needed for navigation. Injecting tetrodotoxin (TTX) into both hippocampi impaired conditioned place avoidance, but after injecting only one hippocampus, the rats learned the place avoidance as well as without any injections. Retention of the place avoidance learned with one hippocampus was not impaired when the injection was switched to the hippocampus that had not been injected during learning. The result suggests that during learning, the hippocampus did not store the place avoidance memory. 相似文献
16.
Electrical transmission in the mammalian brain is now well established. A new study by Thomson and colleagues elegantly demonstrates
coupling between CA1 hippocampal pyramidal cells, which is far more common than previously supposed. Although the history
of coupling is extensive, doubt, predjudice, and technical issues long kept it from wide acceptance. Here “spikelets” or “fast
prepotentials” are found when two cells are coupled and in this situation result from electrical transmission of impulses
from one coupled cell to the other. Interesting questions remain as to whether connexin or pannexin gap junctions serve as
the molecular substrate of transmission, and the role of electrical transmission in hippocampal physiology is uncertain. Increased
coupling could well contribute to the known tendency of the hippocampus to exhibit seizure activity. 相似文献
17.
Tumor cells act upon, and react to both their proximate and more distant environment, the mechanisms by which this is achieved
being both autocrine and paracrine in nature. This interaction, however, takes place not only between adjacent malignant cells,
but also non-malignant cells such as those of the immune system, the latter also partaking in the modeling of the tumor environment.
Although tumor cells descend from normal tissue cells and thus bear in classical immunological terms ‘self signals’, it is
evident that the immune system is able to recognize tumor cells as a harassment for the body and in consequence tries to eliminate
these cells. On the counterpart, tumor cells acquire various characteristics which allow them to evade this immunological
surveillance, and have been collectively coined with the term “tumor escape mechanisms”. This review will describe and summarize
current understanding of tumor escape strategies, and also more closely elaborate on the modulatory role of the neuroendocrine
system in the immune system–tumor cell interaction. 相似文献
18.
Summary Explants of rat adrenal medulla were grown in tissue culture. The effects of various doses of dbcAMP ranging from 0.001 mM
up to 1 mM and equimolar amounts of theophylline were recorded by phase contrast optics and catecholamine histochemistry (glyoxylic
acid method) over six days. There was a dose-dependent inhibition of the normally occurring outgrowth of Schwann cells, “chromaffin”
cells and axons from the explants. Maintenance of glyoxylic acid-induced fluorescence in “chromaffin” cells was dose-dependent,
too. Since theophylline is known to enhance intracellular levels of cAMP only, these effects are probably due to the action
of cAMP. cAMP obviously maintains the degree of differentiation of chromaffin cells. Thus it could be argued that a certain
degree of dedifferentiation is a prerequisite for the formation of axons from these cells. 相似文献
19.
A detailed analysis is presented of the main contributions, both local and international, to the fields of oceanography and
fishery sciences resulting from exploratory cruises carried out on the continental shelf off Argentina over the last 100 years.
The end of the 19th century is chosen as a starting point for this analysis as it marks the beginning of active marine research
by Argentinian scientists and an accumulation of information on Antarctic and Subantarctic organisms in foreign journals.
Mention is also made of previous contributions derived from the classic expeditions and global circumnavigational voyages
during the 18th and 19th centuries. Although the aims of those were not always strictly oceanographic, they rendered significant
information to this field of knowledge. In the early years, references arose mainly from the particular geographic situation
of the Argentinian shelf, a necessary passage in the navigation routes to the Pacific Ocean, and later on the way to Antarctica.
Sources of information are divided into four categories: (a) foreign scientific projects in the area; (b) investigation by
Argentinian scientists and research vessels; (c) joint projects between Argentinian and foreign institutions; and (d) contributions
from sources other than oceanographic cruises (commercial navigation, maritime weather reports, satellite images, etc.). The
analysis includes an updated and classified bibliographical list of the main contributions to the fields of oceanography and
fishery sciences derived from those sources, published either in international or local journals or appearing as technical
and internal reports. The motivations, objectives and main achievements of foreign surveys and programmes in the area and
their impact on local scientific progress are discussed. The early sixties mark a turning point in the evolution of international
research in the area. The creation of biological stations along the Argentinian coast, and the support given to the pooling
of human resources set the basis for the development of bilateral programmes. Similar progress in Brazil and Uruguay led to
the outgrowth of regional activities. Joint scientific efforts described in this analysis include the programmes carried out
by the research vessels of Germany (“Walther Herwig”, “Meteor”), Japan (“Kaiyo Maru”, “Orient Maru”, “Shinkai Maru”), Poland
(“Professor Siedlecki”), Russia (“Evrika”, “Dimitry Stefanov”) and the USA (“Vema”, “Atlantis II”), the achievements of which
are a landmark in the evolution of marine science in the aea. 相似文献
20.
Pedersen PL 《Journal of bioenergetics and biomembranes》2007,39(1):1-12
This introductory article to the review series entitled “The Cancer Cell’s Power Plants as Promising Therapeutic Targets”
is written while more than 20 million people suffer from cancer. It summarizes strategies to destroy or prevent cancers by
targeting their energy production factories, i.e., “power plants.” All nucleated animal/human cells have two types of power
plants, i.e., systems that make the “high energy” compound ATP from ADP and P
i
. One type is “glycolysis,” the other the “mitochondria.” In contrast to most normal cells where the mitochondria are the
major ATP producers (>90%) in fueling growth, human cancers detected via Positron Emission Tomography (PET) rely on both types
of power plants. In such cancers, glycolysis may contribute nearly half the ATP even in the presence of oxygen (“Warburg effect”).
Based solely on cell energetics, this presents a challenge to identify curative agents that destroy only cancer cells as they
must destroy both of their power plants causing “necrotic cell death” and leave normal cells alone. One such agent, 3-bromopyruvate
(3-BrPA), a lactic acid analog, has been shown to inhibit both glycolytic and mitochondrial ATP production in rapidly growing
cancers (Ko et al., Cancer Letts., 173, 83–91, 2001), leave normal cells alone, and eradicate advanced cancers (19 of 19)
in a rodent model (Ko et al., Biochem. Biophys. Res. Commun., 324, 269–275, 2004). A second approach is to induce only cancer
cells to undergo “apoptotic cell death.” Here, mitochondria release cell death inducing factors (e.g., cytochrome c). In a
third approach, cancer cells are induced to die by both apoptotic and necrotic events. In summary, much effort is being focused
on identifying agents that induce “necrotic,” “apoptotic” or apoptotic plus necrotic cell death only in cancer cells. Regardless
how death is inflicted, every cancer cell must die, be it fast or slow. 相似文献