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Results for “functional network connectivity”

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PubMed2001

Functional genomics and the study of development, variation and evolution.

It has rarely been possible to connect the developmental and evolutionary branches of genetics, particularly with regard to the precise changes in the molecular control of development that are responsible for phenotypic variation and evolution. Making such connections will require a high-resolution molecular description of the genetic networks that underlie development and an understanding of their responses to genetic and environmental variation. Functional genomics approaches to development and evolution promise to accelerate the research necessary to accomplish these goals.

Animals↗

PubMed2000

[Aphasia research and speech localization in the brain].

Aphasia research has become an acknowledged branch of modern cognitive neuropsychology research whose aim is to explore more fully the structures of knowledge and of cerebral processes which might both be affected in patients with aphasia. Up to the second half of this century, a model based on a specific cerebral localisation of language processes had emerged based on brain localisation research by Broca and Wernicke (among others). New modern neuroimaging techniques, however, such as computed tomography and magnetic resonance imaging (MRI), but also functional imaging modalities such as positron emission tomography or functional MRI, have modified these concepts. It emerges that in comprehension as well as in production of language, not only a few well defined centres are responsible for the activity, but there is a synchronised activity in large neuronal networks connecting various regions located both in the cortex and in the deep subcortical structures; today, this activity can be demonstrated best in a non-invasive and reproducible way with functional MRI.

Aphasia↗

PubMed1989

Structure of the starburst amacrine network in the cat retina and its association with alpha ganglion cells.

To investigate indirect pathways to ganglion cells we studied the starburst amacrine cell network and its relationship to the alpha ganglion cell. Starburst cells were identified by an antiserum to choline acetyltransferase and alpha cells by injection of Lucifer yellow. The density of on and off starburst cells peaks at the area centralis and decreases with eccentricity by a factor of seven. The fine amacrine processes, interrupted by distinct varicosities, arborize in a planar fashion in the inner plexiform layer. The on network, at the junction of strata 3 and 4, and the off network, in stratum 2, have a similar appearance. Neighboring starburst processes run in intimate association to form a network of bundles. As bundles cross each other, loops of irregular size and shape are formed. The loops are smallest in the area centralis and increase by a factor of three towards the periphery; correspondingly, bundle length per unit area decreases with eccentricity. However, the number of varicosities/bundle length stays constant with eccentricity as does the number of processes per bundle. Segments of the starburst network associate over fairly long distances with dendrites of alpha ganglion cells. About 26% of the alpha ganglion dendritic tree shows such association, and this is significantly greater than would be expected if the alpha and starburst processes were independent. We conclude that the functional unit of the starburst cell is a linear bundle of processes and that the starburst network may connect synaptically to the alpha cell.

Animals↗

PubMed2005

Functional connectivity with the hippocampus during successful memory formation.

Although it is well established that the hippocampus is critical for episodic memory, little is known about how the hippocampus interacts with cortical regions during successful memory formation. Here, we used event-related functional magnetic resonance imaging (fMRI) to identify areas that exhibited differential functional connectivity with the hippocampus during processing of novel objects that were subsequently remembered or forgotten on a postscan test. Functional connectivity with the hippocampus was enhanced during successful, as compared with unsuccessful, memory formation, in a distributed network of limbic cortical areas-including perirhinal, orbitofrontal, and retrosplenial/posterior cingulate cortex-that are anatomically connected with the hippocampal formation. Increased connectivity was also observed in lateral temporal, medial parietal, and medial occipital cortex. These findings demonstrate that successful memory formation is associated with transient increases in cortico-hippocampal interaction.

Adult↗

PubMed2004

Ensemble dynamics of hippocampal regions CA3 and CA1.

Computational models based on hippocampal connectivity have proposed that CA3 is uniquely positioned as an autoassociative memory network, capable of performing the competing functions of pattern completion and pattern separation. Recently, three independent studies, two using parallel neurophysiological recording methods and one using immediate-early gene imaging, have examined the responses of CA3 and CA1 ensembles to alterations of environmental context in rats. The results provide converging evidence that CA3 is capable of performing nonlinear transformations of sensory input patterns, whereas CA1 may represent changes in input in a more linear fashion.

Animals↗

PubMed2006

Principles of diffusion tensor imaging and its applications to basic neuroscience research.

The brain contains more than 100 billion neurons that communicate with each other via axons for the formation of complex neural networks. The structural mapping of such networks during health and disease states is essential for understanding brain function. However, our understanding of brain structural connectivity is surprisingly limited, due in part to the lack of noninvasive methodologies to study axonal anatomy. Diffusion tensor imaging (DTI) is a recently developed MRI technique that can measure macroscopic axonal organization in nervous system tissues. In this article, the principles of DTI methodologies are explained, and several applications introduced, including visualization of axonal tracts in myelin and axonal injuries as well as human brain and mouse embryonic development. The strengths and limitations of DTI and key areas for future research and development are also discussed.

Animals↗

PubMed2006

Visual activity and cortical rewiring: activity-dependent plasticity of cortical networks.

The mammalian cortex is organized anatomically into discrete areas, which receive, process, and transmit neural signals along functional pathways. These pathways form a system of complex networks that wire up through development and refine their connections into adulthood. Understanding the processes of cortical-pathway formation, maintenance, and experience-dependent plasticity has been among the major goals of contemporary neurobiology. In this chapter, we will discuss an experimental model used to investigate the role of activity in the patterning of cortical networks during development. This model involves the "rewiring" of visual inputs into the auditory thalamus and subsequent remodeling of the auditory cortex to process visual information. We review the molecular, cellular, and physiological mechanisms of visual "rewiring" and activity-dependent shaping of cortical networks.

Animals↗

PubMed2003

Ultrastructural study of gap junctions between dendrites of parvalbumin-containing GABAergic neurons in various neocortical areas of the adult rat.

Parvalbumin (PV)-containing GABAergic neurons in the hippocampus form dual networks linked by both dendrodendritic gap junctions and mutual inhibitory synapses. Recent physiological studies have demonstrated similar functional connectivity among cortical GABAergic neurons, but the corresponding structures have not been fully analyzed at the electron microscopic level. In this study we examined detailed ultrastructural features of gap junctions between PV neurons in the mature neocortex. Light microscopic observations and confocal laser scanning microscopy revealed frequent dendrodendritic contacts between PV neurons. Electron microscopic analysis provided direct morphological evidence for the existence of gap junctions between 22 pairs of PV-immunoreactive dendrites in the visual, auditory, and somatosensory cortices. Their ultrastructural features that were characteristic of immunolabeled profiles were consistent with the general structure of gap junctions. In one case a gap junction coexisted with a dendrodendritic chemical synapse, making a mixed synapse. Importantly, we also encountered a gap junction between PV positive and negative, presumptive non-principal cell-derived, dendrites. Quantitative analysis was made in 16 pairs of PV positive dendrites forming gap junctions in the infragranular layers of the somatosensory cortex. Diameters of these dendrites ranged from 0.3 to 2.7 microm, suggesting diverse locations of gap junctions along the proximal-distal axis of dendritic trees, but the majority (81%) were less than 1 microm. The mean size of gap junctions along apposing membranes was 0.22+/-0.09 microm. By using this size, the theoretical value of a junctional conductance was estimated to be 2.1-5.3 nS. Dendrites of PV neurons in the infragranular layers of the somatosensory cortex were reconstructed light microscopically and the sites of contacts with other PV neurons were mapped. Although these contacts do not necessarily imply gap junctional coupling, their number (5.3+/-2.3 per cell, n=11) suggested the degree of connectivity of less than 10 coupling from single PV neurons with others. Sholl analysis revealed that only 38% of their dendrites occurred within 200 microm from the soma. The present study demonstrated detailed ultrastructural features of gap junctions between mature cortical PV neurons. These features will facilitate not only identification of gap junctions in variously labeled neurons but also analysis of their functional aspects by enabling theoretical estimate of their junctional conductances.

Animals↗

PubMed2004

Antiviral protein Ski8 is a direct partner of Spo11 in meiotic DNA break formation, independent of its cytoplasmic role in RNA metabolism.

Meiotic recombination initiates with double-strand breaks (DSBs) catalyzed by Spo11 in conjunction with accessory proteins whose roles are not understood. Two-hybrid analysis reveals a network of interactions connecting the yeast DSB proteins to one another. Of these proteins, Ski8 was known to function in cytoplasmic RNA metabolism, suggesting that its role in recombination might be indirect. However, obligate partners of Ski8 in RNA metabolism are dispensable for recombination and Ski8 relocalizes to the nucleus and associates with chromosomes specifically during meiosis. Interaction of Ski8 with Spo11 is essential for DSB formation and Ski8 relocalization. Thus, Ski8 plays distinct roles in RNA metabolism and, as a direct partner of Spo11, in DSB formation. Ski8 works with Spo11 to recruit other DSB proteins to meiotic chromosomes, implicating Ski8 as a scaffold protein mediating assembly of a multiprotein complex essential for DSB formation.

Chromatin↗

PubMed2003

Inhibitory feedback required for network oscillatory responses to communication but not prey stimuli.

Stimulus-induced oscillations occur in visual, olfactory and somatosensory systems. Several experimental and theoretical studies have shown how such oscillations can be generated by inhibitory connections between neurons. But the effects of realistic spatiotemporal sensory input on oscillatory network dynamics and the overall functional roles of such oscillations in sensory processing are poorly understood. Weakly electric fish must detect electric field modulations produced by both prey (spatially localized) and communication (spatially diffuse) signals. Here we show, through in vivo recordings, that sensory pyramidal neurons in these animals produce an oscillatory response to communication-like stimuli, but not to prey-like stimuli. On the basis of well-characterized circuitry, we construct a network model of pyramidal neurons that predicts that diffuse delayed inhibitory feedback is required to achieve oscillatory behaviour only in response to communication-like stimuli. This prediction is experimentally verified by reversible blockade of feedback inhibition that removes oscillatory behaviour in the presence of communication-like stimuli. Our results show that a sensory system can use inhibitory feedback as a mechanism to 'toggle' between oscillatory and non-oscillatory firing states, each associated with a naturalistic stimulus.

Acoustic Stimulation↗

PubMed2000

The organization of networks within the orbital and medial prefrontal cortex of rats, monkeys and humans.

This paper reviews architectonic subdivisions and connections of the orbital and medial prefrontal cortex (OMPFC) in rats, monkeys and humans. Cortico-cortical connections provide the basis for recognition of 'medial' and 'orbital' networks within the OMPFC. These networks also have distinct connections with structures in other parts of the brain. The orbital network receives sensory inputs from several modalities, including olfaction, taste, visceral afferents, somatic sensation and vision, which appear to be especially related to food or eating. In contrast, the medial network provides the major cortical output to visceromotor structures in the hypothalamus and brainstem. The two networks have distinct connections with areas of the striatum and mediodorsal thalamus. In particular, projections to the nucleus accumbens and the adjacent ventromedial caudate and putamen arise predominantly from the medial network. Both networks also have extensive connections with limbic structures. Based on these and other observations, the OMPFC appears to function as a sensory-visceromotor link, especially for eating. This linkage appears to be critical for the guidance of reward-related behavior and for setting of mood. Imaging and histological observations on human brains indicate that clinical depressive disorders are associated with specific functional and cellular changes in the OMPFC, including activity and volume changes, and specific changes in the number of glial cells.

Animals↗

PubMed1990

Overall functioning and criteria of progress in rehabilitation of alcohol abusers: longitudinal analyses of changes.

The aim was to compare alcohol consumption and vocational adjustment as criteria of rehabilitation progress of alcoholics, with regard to links to concomitant changes in functioning in other life areas. Thirty-four advanced alcohol abusers in rehabilitation were examined twice with an interval of 2 years between each examination. Change scores in alcohol consumption and work capacity were correlated with change scores in social network, activities, life-satisfaction, psychological well-being, psychiatric symptoms, and biomedical functioning. Improved drinking habits were connected with some changes in overall functioning, however not solely in a favorable direction. Negative mood changes were especially noteworthy. Improvements in vocational adjustment, on the other hand, appeared to be somewhat more unequivocally and encompassingly associated with amelioration in the wider range of functioning. The results indicate that drinking measures alone are not sufficient indicators of progress in rehabilitation and underscores the need of more global criteria of general adjustment.

Activities of Daily Living↗

PubMed2006

Gene regulatory networks in the evolution and development of the heart.

The heart, an ancient organ and the first to form and function during embryogenesis, evolved by the addition of new structures and functions to a primitive pump. Heart development is controlled by an evolutionarily conserved network of transcription factors that connect signaling pathways with genes for muscle growth, patterning, and contractility. During evolution, this ancestral gene network was expanded through gene duplication and co-option of additional networks. Mutations in components of the cardiac gene network cause congenital heart disease, the most common human birth defect. The consequences of such mutations reveal the logic of organogenesis and the evolutionary origins of morphological complexity.

Animals↗

PubMed1992

Connectivity and condensation in dreaming.

Converging developments in the cognitive- and neurosciences have brought Freud's hope of a bridge between psychoanalysis and psychophysiology nearer to hand. This paper concerns the relation between dream construction and memory in terms of these new developments. The neural network architecture of memory structures in the brain is described and illustrated with simple examples. We see how a network is connected and how connection weights vary with experience. The distributed representation stored by the network and its crucial properties for mental functioning are discussed. These concepts are used to explain how particular memories of past events are selected for inclusion in the dream. The properties of the neural network suggest that images of distinct past events are conflated at times during the selection process. The appearance of these conflated images may complicate the matching of day residues with representations of past events in the dream itself. Some likely implications for psychoanalytic theory are explored.

Dreams↗

PubMed1996

Structure/function studies on the pH-dependent actin-binding protein hisactophilin in Dictyostelium mutants.

Our previous studies have shown that the actin-binding protein hisactophilin from Dictyostelium discoideum is a candidate for organizing the actin cytoskeleton at the plasma membrane in a pH-dependent manner. To further characterize this interaction we isolated hisactophilin overexpression (hisII+) and hisactophilin minus (his-) mutants. D. discoideum contains two hisactophilin isoforms; both genes are independently transcribed and carry a short intron at the same position of the coding region. The deduced amino acid sequence of hisactophilin II showed a characteristic high content of 35 histidine residues out of a total 118 amino acids. After transformation of Dictyostelium AX2 wild-type cells with a genomic fragment designed to inactivate the hisactophilin I gene we obtained hisactophilin II overexpressing mutants (hisII+). Multiple integration of the vector led to strong overexpression of hisactophilin II which even outnumbered the actin concentration by a factor of two. Hisactophilin II protein showed the same biochemical properties as hisactophilin I during purification and in its pH-dependent binding to F-actin; as shown by mass spectrometry the hisactophilin II fraction was almost completely myristoylated despite of this high overexpression. The inactivation of both hisactophilin genes was achieved by gene replacement with a vector construct encompassing parts of gene I and gene II connected by a geneticin cassette. The properties of the hisII+ and his- cells with regard to growth in shaking culture and on Klebsiella plates, development, chemotaxis and morphology were not affected under normal conditions. However, the hisII+ transformants revealed a significant difference to wild-type cells and his- cells when the cytoplasmic pH was lowered by diethylstilbestrol (DES), a proton pump inhibitor. HisII+ cells were more resistant to the acidification; in contrast to AX2 wild-type cells and his- cells they did not form plasma membrane protrusions, showed an increase in F-actin content, and contained large clusters of F-actin. Lowering the internal pH caused an accumulation of hisactophilin below the plasma membrane. The fact that cells deficient in hisactophilin again lose resistance to acidification is in good agreement with the hypothesis that hisactophilin functions as a pH sensor at the plasma membrane by reversibly connecting the membrane with the actin cortical network upon local changes of the proton concentration.

Actins↗

PubMed1997

A polysynaptic feedback circuit in rat visual cortex.

Feedback connections from extrastriate cortex to primary visual cortex (V1) in the primate may provide "top-down" information that plays a role in visual attention and object recognition. Our work in a rodent model of corticocortical circuitry demonstrates that feedback pathways synapse preferentially with pyramidal cells in V1 () and favor excitation over inhibition in cortical microcircuits (). To investigate the polysynaptic circuits activated by feedback inputs, we studied chains of neurons postsynaptic to feedback connections using a combination of axonal tract tracing and anterograde degeneration. This approach enabled independent labeling of local collaterals of forward-projecting neurons in V1 and feedback connections from extrastriate lateromedial (LM) visual area to V1. Postsynaptic targets were identified in the electron microscope after retrograde transport of biotinylated dextran amine (BDA) to identify dendrites of forward-projecting neurons (i.e., from V1 to LM) and postembedding immunogold labeling to identify GABAergic interneurons. The results show that feedback connections provide strong monosynaptic input to forward-projecting neurons in V1. These neurons in turn make local connections that preferentially form synapses with other pyramidal cells ( approximately 97%), many of which were identified as forward-projecting neurons. This indicates that feedback pathways provide input directly to neurons which make the reciprocal forward connection, and that feedback-recipient forward-projecting neurons are strongly interconnected. The function of these excitatory networks within V1 may be to amplify feedback activity and provide a circuit for modulation of striate cortical activity by top-down influences.

Animals↗

PubMed2002

Mixed-anion complexes with a bipyrazolyl ligand. A new entry to a realm of three-dimensional five-connected coordination topologies.

Cross-linking of corrugated square grid coordination layers by anionic bridging groups generates five-connected coordination networks; the 3D topologies of mixed-anion cobalt(II) and nickel(II) complexes with a tetramethyl-substituted 4,4'-bipyrazolyl ligand are supported by mu-SO4(2-) functions and exist as neutral or cationic five-connected arrays involving additional terminal (NCS-) or non-coordinated (NO3-, ClO4-) groups.

Journal Article↗

PubMed2005

A network of transcriptionally coordinated functional modules in Saccharomyces cerevisiae.

Recent computational and experimental work suggests that functional modules underlie much of cellular physiology and are a useful unit of cellular organization from the perspective of systems biology. Because interactions among modules can give rise to higher-level properties that are essential to cellular function, a complete knowledge of these interactions is necessary for future work in systems biology, including in silico modeling and metabolic engineering. Here we present a computational method for the systematic identification and analysis of functional modules whose activity is coordinated at the level of transcription. We applied this method, Search for Pairwise Interactions (SPIN), to obtain a global view of functional module connectivity in Saccharomyces cerevisiae and to provide insight into the biological mechanisms underlying this coordination. We also examined this global network at higher resolution to obtain detailed information about the interactions of particular module pairs. For instance, our results reveal possible transcriptional coordination of glycolysis and lipid metabolism by the transcription factor Gcr1p, and further suggest that glycolysis and phosphoinositide signaling may regulate each other reciprocally.

Gene Expression Profiling↗