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Results for “brain network connectivity”

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At least 217 records · Page 12Linked to original sources
PubMed2003

Cell-cell signaling during synapse formation in the CNS.

Synapses join individual nerve cells into a functional network. Specific cell-cell signaling events regulate synapse formation during development and thereby generate a highly reproducible connectivity pattern. The accuracy of this process is fundamental for normal brain function, and aberrant connectivity leads to nervous system disorders. However, despite the overall precision with which neuronal circuits are formed, individual synapses and synaptic networks are also plastic and can readily adapt to external stimuli or perturbations. In recent studies, several trans-synaptic signaling systems have been identified that can mediate various aspects of synaptic differentiation in the central nervous system. It appears that these individual pathways functionally cooperate, thereby generating robustness and flexibility, which ensure normal nervous system function.

Animals↗
PubMed2003

Resonant synchronization in heterogeneous networks of inhibitory neurons.

Brain rhythms arise through the synchronization of neurons and their entrainment in a regular firing pattern. In this process, networks of reciprocally connected inhibitory neurons are often involved, but what mechanism determines the oscillation frequency is not completely understood. Analytical studies predict that the emerging frequency band is primarily constrained by the decay rate of the unitary IPSC. We observed a new phenomenon of resonant synchronization in computer-simulated networks of inhibitory neurons in which the synaptic current has a delayed onset, reflecting finite spike propagation and synaptic transmission times. At the resonant level of network excitation, all neurons fire synchronously and rhythmically with a period approximately four times the mean delay of the onset of the inhibitory synaptic current. The amplitude and decay time constant of the synaptic current have relatively minor effects on the emerging frequency band. By varying the axonal delay of the inhibitory connections, networks with a realistic synaptic kinetics can be tuned to frequencies from 40 to >200 Hz. This resonance phenomenon arises in heterogeneous networks with, on average, as few as five connections per neuron. We conclude that the delay of the synaptic current is the primary parameter controlling the oscillation frequency of inhibitory networks and propose that delay-induced synchronization is a mechanism for fast brain rhythms that depend on intact inhibitory synaptic transmission.

Action Potentials↗
PubMed2006

Comparison of forecasting methodologies using egg price as a test case.

Egg price forecasting of shelled eggs is a complex problem. Traditionally, future egg price has been predicted using a combination of regression analysis and experienced-based intuition to build a model, which is then fine-tuned to prevalent market conditions. Even after collecting reliable and expensive data, the subsequent analysis, in many cases, does not produce a high confidence to explain the variations in egg price. In the current project, a different approach using neural networks was used to forecast egg price. A neural network is a mathematical model of an information-processing structure that is loosely based on our present understanding of the working of human brain. An artificial neural network consists of a large number of simple processing elements connected to each other in a network. Urner Barry egg quotes from 1991 to 2002 as well as number of hens, egg storage capacity, and number of eggs placed for hatching from the USDA databases (1993 to 2000) were used to forecast egg price. Regression analysis explained only 37% of the variation in egg price due to the above-mentioned 3 factors. Neural networks, on the other hand, recognize the pattern in previous years' egg prices and then predict the future price more efficiently. The 3 networks used in this research (Ward, back-propagation, and general regression neural networks) fit the forecast line more tightly to the previous year's egg price line than did regression analysis. In the case of general regression neural networks, the R2 value was as high as 60%. Results suggest that neural networks may be a more reliable method of egg price forecasting than simple regression analysis if reliable data are collected and manipulated for such models.

Agriculture↗
PubMed1987

The psyche and the skin.

The concept of psychosomatic disorders has been undergoing great evolutionary changes during the past 20 to 30 years. There is no longer any significant or reasonable disagreement that the brain and body mutually interact, and the pathways of those interactions are being explored and explained. Enormous amounts of work are being done to unravel the workings of the brain, which is more complex than any other organ because of neural connections and networking of astronomic proportions.

Factitious Disorders↗
PubMed2004

Keeping sensory cells and evolving neurons to connect them to the brain: molecular conservation and novelties in vertebrate ear development.

The evolution of the mechanosensory cellular module and the molecular details that regulate its development has included morphological modifications of these cells as well as the formation of larger assemblies of mechanosensory cell aggregates among metazoans. This has resulted in a wide diversity of mechanosensory organs. The wide morphological diversity of organs, including the associated morphological modifications of the mechanosensory cells, suggests parallel evolution of these modules and their associated organs. This morphological diversity is in stark contrast to the molecular conservation of developmental modules across phyla. These molecular data suggest that the evolution of mechanosensory transduction might have preceded that of distinct cellular differentiation. However, once a molecular network governing development of specialized cells involved in mechanosensory transduction evolved, that molecular network was preserved across phyla. Present data suggest that at least the common ancestor of triploblastic organisms, perhaps even the common diploblastic ancestor of bilaterian metazoans, had molecular and cellular specializations for mechanosensation. It is argued that the evolution of multicellular organs dedicated to specific aspects of mechanosensation, such as gravity and sound perception, are evolutionary transformations that build on this conserved molecular network for cellular specialization, but reflect distinct morphological solutions. We propose that the sensory neurons, connecting the craniate ear with the brain, are a derived feature of craniates, and possibly chordates, that came about through diversification of the lineage forming mechanosensory cells during development. This evolutionarily late event suggests a heterochronic shift, so that sensory neurons develop in mammals prior to mechanosensory hair cells. However, sensory neuron development is connected to hair cell development, likely in a clonal relationship. The theme of cellular conservation is reiterated in two examples of chordate otic diversification: the evolution of the horizontal canal system and the evolution of the basilar papilla/cochlea. It is suggested that here again, cellular multiplication and formation of a special epithelium predates the functional transformation to an 'organ' system for horizontal angular acceleration and sound pressure reception, respectively. Overall, evolution of the vertebrate ear needs to be understood as an interplay between and utilization of two gene networks or modules. One is at the level of the molecularly and developmentally conserved mechanosensory cellular module. The other is an increased complexity in the morphology of both adult mechanosensory cells and organs by the addition of end-stage and novel features and associated gene networks to detect specific aspects of mechanosensory stimuli.

Animals↗
PubMed2002

Using replicator dynamics for analyzing fMRI data of the human brain.

The understanding of brain networks becomes increasingly the focus of current research. In the context of functional magnetic resonance imagery (fMRI) data of the human brain, networks have been mostly detected using standard clustering approaches. In this work, we present a new method of detecting functional networks using fMRI data. The novelty of this method is that these networks have the property that every network member is closely connected with every other member. This definition might to be better suited to model important aspects of brain activity than standard cluster definitions. The algorithm that we present here is based on a concept from theoretical biology called "replicator dynamics."

Algorithms↗
PubMed2006

Partial correlation for functional brain interactivity investigation in functional MRI.

Examination of functional interactions through effective connectivity requires the determination of three distinct levels of information: (1) the regions involved in the process and forming the spatial support of the network, (2) the presence or absence of interactions between each pair of regions, and (3) the directionality of the existing interactions. While many methods exist to select regions (Step 1), very little is available to complete Step 2. The two main methods developed so far, structural equation modeling (SEM) and dynamical causal modeling (DCM), usually require precise prior information to be used, while such information is sometimes lacking. Assuming that Step 1 was successfully completed, we here propose a data-driven method to deal with Step 2 and extract functional interactions from fMRI datasets through partial correlations. Partial correlation is more closely related to effective connectivity than marginal correlation and provides a convenient graphical representation for functional interactions. As an instance of brain interactivity investigation, we consider how simple hand movements are processed by the bihemispheric cortical motor network. In the proposed framework, Bayesian analysis makes it possible to estimate and test the partial statistical dependencies between regions without any prior model on the underlying functional interactions. We demonstrate the interest of this approach on real data.

Cerebral Cortex↗
PubMed1992

Physiological function of granule cells: a hypothesis.

In this chapter we review the physiological properties of granule cells in vivo and in vitro. We conclude from the literature that in intact rats granule cells fire rhythmic bursts of action potentials concurrent with exploration-associated theta waves. The population discharge of granule cells coincides with the maximum probability of firing of CA3 pyramidal cells on the positive phase of focally recorded theta waves. During consummatory behaviors, immobility and anesthesia the firing rate of granule cells substantially decreases. We propose that the conjoint activity of the discharging CA3 cells and tetanization of these same cells by mossy fibers during exploratory (theta) behavior will temporarily increase synaptic efficacy among the active CA3 neurons even after the termination of exploration. As a result, the very same CA3 cells that carried information during exploration now become the burst-initiator cells of the sharp-wave associated population bursts during consummatory behaviors and sleep. The creation of new burst-initiator neurons is hypothesized to be essential for memory trace formation. From this perspective the main physiological function of granule cells is to 'tetanize' CA3 pyramidal neurons during exploratory behaviors and induce a meaningful reorganization of the functional connectivity of the CA3 network.

Animals↗
PubMed2004

Fine modulation in network activation during motor execution and motor imagery.

Motor imagery, the 'mental rehearsal of motor acts without overt movements', involves either a visual representation (visual imagery, VI) or mental simulation of movement, associated with a kinesthetic feeling (kinetic imagery, KI). Previous brain imaging work suggests that patterns of brain activation differ when comparing execution (E) with either type of imagery but the functional connectivity of the participating networks has not been studied. Using functional magnetic resonance imaging (fMRI) and structural equation modeling, this study elucidates the inter-relationships among the relevant areas for each of the three motor behaviors. Our results suggest that networks underlying these behaviors are not identical, despite the extensive overlap between E and KI. Inputs to M1, which are facilitatory during E, have the opposite effect during KI, suggesting a physiological mechanism whereby the system prevents overt movements. Finally, this study highlights the role of the connection of superior parietal lobule to the supplementary motor area in both types of motor imagery.

Adult↗
PubMed2004

The three-dimensional structure and the relationship between external and internal vascularizations in the brain of rat embryos.

BACKGROUND: There have been no detailed reports of the three-dimensional structure and the relationship between the external and internal vascularizations observed successively for a long duration in the rat fetus, although many authors have studied the vascular morphology of the developing brain. This study examined the three-dimensional structure of both the external and internal vascularizations of the prenatal rat telencephalon from embryonic days 12 (E12) to 20 (E20). METHOD: A microvascular casting method for scanning electron microscopy (SEM) was used in this study, along with vascular staining using gold-gelatin solution-autometallography (GGS-AMG) after intravascular injection of colloidal gold, as well as hematoxylin-eosin (HE) staining for paraffin embedded specimens. RESULTS: In GGS-AMG stains, E16 fetuses had a few short perforating cortical blood vessels (SPCVs); E17 fetuses had long perforating cortico-medullary vessels (LPCVs). Older fetuses had specific patterns of vascular networks in the cortex and the deeper subcortical part of the telencephalon. In the cortex, fine longitudinal blood vessels were connected by transverse channels. The deep telencephalon had fine blood vessels running in all directions. Using SEM, the external vascularization was already visible in E12 fetuses as arborizations of arterial branches, forming a mesh of fine vascular networks covering the telencephalon. A coralliform fine venous plexus was observed in the external vascularization of E16 fetuses. There were ring-like anastomoses and bud-like protrusions in the network of small blood vessels, most likely the angiogenesis of fetal vessels. From E12 to E16, an immature and incomplete internal vascularization began to appear. There were short blood vessels with ballooned terminals branching from the external vascularization. They penetrated the brain tissue to form networks in the superficial layer, comparable to SPCVs. In E17 to E20 fetuses, tortuous venous branches, straight arterial blood vessels, and a fine network of small blood vessels formed the external vascularization. There were fewer arterial than venous branches connecting to the fine networks of small blood vessels. LPCVs were noted at E17, at the time the white matter emerged. They branched from the external vascularization, and perpendicularly penetrated the brain surface, traversing the cortical plate, and entering into the deep brain. At E17, arterial and venous blood vessels could be clearly distinguished in the external vascularization. At E20, the cortex and white matter contained specific arrangements of networks of fine blood vessels, as seen by GGS-AMG staining. CONCLUSION: These findings show that the development of both the external and internal vascularization follows the development of the telencephalon. In particular, the emergence of the cortical plate and white matter on E16 and E17 influence the development of both the internal and the external vascularization. The laminal arrangement of blood vessels was not observed corresponding to the respective laminal neuronal layers.

Animals↗
PubMed1999

Post-lesional plasticity in the central nervous system of the guinea-pig: a "top-down" adaptation process?

Vestibular compensation for the postural and oculomotor deficits following unilateral labyrinthectomy is a model of functional plasticity in the brain of adult vertebrates. The mechanisms involved in this recovery are still controversial. The post-lesional lack of vestibular input might be compensated by changes in the efficacy of the remaining sensory inputs involved in gaze and posture stabilization. However, the compensation process could also rapidly become independent of these external cues, and thus be detectable in vitro in preparations obtained from lesioned animals. In agreement with this hypothesis, we have shown recently that prominent traces of the compensation process appeared three days after the lesion on in vitro isolated brains taken from labyrinthectomized guinea-pigs, where the connectivity of the central vestibular-related networks is preserved. We report here that, one week after the lesion, a slight increase in the intrinsic, spontaneous activity of the deafferented, central vestibular neurons was found in brainstem slices. This increase became stronger in slices taken after one month of compensation, and was associated at this stage with a significant decrease in the intrinsic activity of the vestibular neurons on the contralesional side. Vestibular compensation could thus follow a "top-down" strategy: it would first rely on the external cues given by the intact sensory systems, then on an internal reorganization of the vestibular-related networks, and finally on changes in the intrinsic properties of the vestibular neurons themselves. Similar strategies may be used by the mammalian brain to compensate for other types of deafferentations or environmental changes.

Adaptation, Physiological↗
PubMed2003

From gene networks to brain networks.

The brain's structural organization is so complex that 2,500 years of analysis leaves pervasive uncertainty about (i) the identity of its basic parts (regions with their neuronal cell types and pathways interconnecting them), (ii) nomenclature, (iii) systematic classification of the parts with respect to topographic relationships and functional systems and (iv) the reliability of the connectional data itself. Here we present a prototype knowledge management system (http://brancusi.usc.edu/bkms/) for analyzing the architecture of brain networks in a systematic, interactive and extendable way. It supports alternative interpretations and models, is based on fully referenced and annotated data and can interact with genomic and functional knowledge management systems through web services protocols.

Animals↗
PubMed2005

The meaning of mammalian adult neurogenesis and the function of newly added neurons: the "small-world" network.

Adult neurogenesis has been observed in mammalian brain including human but a question remains: how do new neurons become functional in the adult brain? We propose that the random addition of only a few new neurons functions as a maintenance system for the brain's "small-world" networks. In popular parlance, the small-world network phenomenon is described by the concept of "six degrees of separation", which postulates that everyone in the world is connected to everyone else through a chain of at most six mutual acquaintances. Randomly added to an orderly network, new links enhance signal propagation speed and synchronizability. Newly generated neurons are ideally suited to become such links: they are immature, form more new connections compared to mature ones, and their number but not their precise location may be maintained by continuous proliferation and dying off. Similarly, we envisage that the treatment of brain pathologies by cell transplantation would also create new random links in small-world networks and that even a small number of successfully incorporated new neurons may be functionally important.

Adult↗
PubMed2005

Developmental expression of MNAR mRNA in the mouse brain.

During the development of the central nervous system, estrogen influences cellular differentiation and determines the functional connectivity of distinct neural networks. Estrogens generally act through nuclear estrogen receptors (ERs). Recent research has additionally revealed rapid estrogen effects requiring the binding of estrogen to membrane/cytoplasmic ERs and the activation of intracellular signaling systems such as the Src/MAPK cascade. The scaffold protein MNAR/PELP1 appears to be the designated functional mediator of such non-genomic estrogen effects between non-nuclear ERs and Src/MAPKs. In this study, we demonstrate the expression and differential regulation of MNAR mRNA in the developing male and female mouse brain by quantitative polymerase chain reaction. In the midbrain and hypothalamus, a gradual decline in MNAR mRNA levels has been observed prenatally with the highest values at embryonic day 15 and lowest at postnatal day 15. In the cortex, mRNA levels do not fluctuate until postnatal day 7 but decrease thereafter. No differences in MNAR expression between sexes have been detected. Analysis of neuronal and astroglia-enriched cell cultures has revealed the presence of MNAR in both cell types.

Animals↗
PubMed1989

The brain and the immune system: a psychosomatic network.

The central nervous system (CNS) and the immune system, communicating through the neuroendocrine system, are closely involved in the individual's adaptation to the environment. The data from basic science research and clinical observations are overviewed, and more recent studies are summarized. As changes in immune function may mediate the effects of psychosocial factors in psychosomatic disorders, it is important for all biopsychosocially oriented physicians to understand the network that connects the central nervous and immune systems.

Brain↗
PubMed2004

Anatomy of attentional networks.

Attention is a central theme in psychological science. As with other biological systems, attention has a distinct anatomy that carries out basic psychological functions. Disparate attentional networks correlate with discrete neural circuitry and can be influenced by specific brain injuries, states, and drugs. Accordingly, thinking about attention as an organ system is advantageous for understanding the details of this complex cognitive process. In the context of an influential model of attention, this article introduces the broad notion of attention, then addresses its prominent characteristics, mechanisms, and theories. The presentation emphasizes the role of recent neuroimaging data in outlining the functional neuroanatomy subserving distinct attentional networks. A discussion of pertinent results connects attentional networks with self-regulation, development, and rehabilitation training.

Attention↗
PubMed1996

Imaging motor-to-sensory discharges in the human brain: an experimental tool for the assessment of functional connectivity.

We present a new approach to studying functional connectivity in the human brain. This approach is based on the observation that when we engage in motor activity, a discharge corollary to the motor command is sent from motor to sensory structures. Thus, as long as movement-related sensory input is either prevented or masked, modulation of neuronal activity in sensory structures would indicate the presence of functional connectivity between the motor and the sensory regions. Using positron emission tomography, such a central interaction between motor and sensory regions can be assessed by measuring regional changes in cerebral blood flow (CBF) in sensory regions. In this paper, we describe the experimental design and the results of two studies of corollary discharges, namely those generated during eye movements and speech. In these studies, a graded approach was used to establish the relationship between the number of eye movements or utterances and CBF in visual or auditory regions, respectively. Significant covariations between the number of movements and CBF in sensory regions were found, thus indicating the presence of functional connectivity between motor and sensory regions. In addition, interregional CBF covariations were computed and the effect of removing the intersubject variance on these covariations was evaluated. The corollary-discharge-based approach to studying functional connectivity is discussed in the context of more traditional computational approaches to network analysis in functional brain imaging.

Brain↗
PubMed1995

Inner connections within domain of dementia praecox: role of supervisory mental processes in schizophrenia.

Kraepelin's conclusion that there were underlying common features justifying the amalgamation of catatonia, hebephrenia and paranoia hallucinatoria to form a single illness is confirmed by factor analytic studies delineating the various dimensions of schizophrenic psychopathology. Neuropsychological studies reveal that the three cardinal dimensions reflect disorder of the supervisory mental processes responsible for initiation, selection and monitoring of self-generated mental activity. Brain-imaging studies indicate that the underlying neuropathology entails disordered functional connectivity within the neural networks in multimodal association cortex that are the substrate of the supervisory mental processes, consistent with Kraepelin's own speculation about the essential nature of the condition.

Humans↗